Dissertations / Theses: 'Low temperature physics[Cryogenics]'

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Nichols, Timothy Robert. "Experiments on polarized and unpolarized dilute '3He-'4He solutions." Thesis, Lancaster University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259335.

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Park, Jung Hyun. "Microstructure development and evolution of sputter deposited indium thin films in cryogenics." Auburn, Ala., 2007. http://repo.lib.auburn.edu/07M%20Theses/PARK_JUNG-HYUN_51.pdf.

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Park, Jung Hyun Kim Dong Joo. "Microstructure development and evolution of sputter deposited indium thin films in cryogenics." Auburn, Ala., 2007. http://repo.lib.auburn.edu/07M%20Theses/PARK_JUNG-HYUN_51.pdf.

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Witwicky, Julien. "Heat dissipation due to microvibrations in low temperature experiments." Thesis, KTH, Fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293485.

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Ultra-sensitive photodetectors on-board space missions need very low temperatures to keep a good resolution. Cryo-coolers, such as pulse-tubes, help maintaining these conditions within a cryostat. In return however, they generate micro-vibrations. These micro-vibrations dissipate enough heat to cause temperature fluctuations at the detector's support, thus lowering the detector's resolution. The first objective is to establish a test bench almost from scratch. The test bench includes a dummy representing the detector's support. The next objectives is to verify that we can measure heat dissipation at the dummy, corresponding to very low values of power ; and finally, to find a link between mechanics and heat dissipation. The dummy consists of a mass suspended by Kevlar chords and is mounted on the cold plate of a cryostat. From the cryostat enclosure, we were able to generate micro-vibrations at the suspended mass and to carry out acceleration and temperature measurements. At 4 K, we were able to measure heat dissipation only around the suspended mass resonance modes. As a first quantitative result, we found that an acceleration of thousands µg (g is the gravitational acceleration) on the cold plate dissipates hundreds of nano-watts. However, these are preliminary results and we will need to improve the test bench for future measurement campaigns.
Ultrakänsliga fotodetektorer ombord rymduppdrag behover mycket låga temperaturer för att hålla en rätt upplösning. Kryokylare, såsom pulse-tubes, hjälper att upprätthålla dessa förhållanden i en kryostat. I gengäld genererar de dock mikrovibrationer. Dessa mikrovibrationer släpper ut tillräckligt med värme för att orsaka temperatursvängningar vid detektorns stöd, vilket sänker detektorns upplösning. Det första målet är att upprätta en testbänk från grunden. Testbänken innehåller en dummy som representerar detektorns stöd. Nästa mål är att kontrollera att vi kan mäta värmeavledning vid dummy, vilket motsvarar mycket låga effektvärden. Sista mål är att hitta en länk mellan mekanik och värmeavledning. Dummy består av en massa som är upphängd av Kevlar och är monterad på en kryostats kallplatta. Från kryostathöljet kunde vi generera mikrovibrationer vid den upphängda massan och genomföra accelerations- och temperaturmätningar. Vid 4 K kunde vi bara mäta värmeavledning runt upphängda massans resonanslägen. Som ett första kvantitativt resultat, upptäckte vi att en acceleration på tusentals µg (g är tyngdaccelerationen) på kylplattan försvinner hundratals nanowatt. Detta är dock preliminära resultat och vi kommer att behöva förbättra testbänken för framtida mätkampanjer.

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Piskorski, Julia Hege. "Cooling, Collisions and non-Sticking of Polyatomic Molecules in a Cryogenic Buffer Gas Cell." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13070052.

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We cool and study trans-Stilbene, Nile Red and Benzonitrile in a cryogenic (7K) cell filled with low density helium buffer gas. No molecule-helium cluster formation is observed, indicating limited atom-molecule sticking in this system. We place an upper limit of 5% on the population of clustered He-trans-Stilbene, consistent with a measured He-molecule collisional residence time of less than \(1 \mu s\). With several low energy torsional modes, trans-Stilbene is less rigid than any molecule previously buffer gas cooled into the Kelvin regime. We report cooling and gas phase visible spectroscopy of Nile Red, a much larger molecule. Our data suggest that buffer gas cooling will be feasible for a variety of small biological molecules. The same cell is also ideal for studying collisional relaxation cross sections. Measurements of Benzonitrile vibrational state decay results in determination of the vibrational relaxation cross sections of \(\sigma_{22} = 8x10^{-15} cm^2\) and \(\sigma_{21} = 6x10^{-15} cm^2\) for the 22 (v=1) and 21 (v=1) states. For the first time, we directly observe formation of cold molecular dimers in a cryogenic buffer gas cell and determine the dimer formation cross section to be \(\sim10^{-13} cm^2\).
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Pathak, Mihir Gaurang. "Periodic flow physics in porous media of regenerative cryocoolers." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49056.

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Pulse tube cryocoolers (PTC) are a class of rugged and high-endurance refrigeration systems that operate without moving parts at their low temperature ends, and are capable of reaching temperatures down to and below 123 K. PTCs are particularly suitable for applications in space, guiding systems, cryosurgery, medicine preservation, superconducting electronics, magnetic resonance imaging, weather observation, and liquefaction of gases. Applications of these cryocoolers span across many industries including defense, aerospace, biomedical, energy, and high tech. Among the challenges facing the PTC research community is the improvement of system efficiency, which is a direct function of the regenerator component performance. A PTC implements the theory of oscillatory compression and expansion of the gas within a closed volume to achieve desired refrigeration. An important deficiency with respect to the state of art models dealing with PTCs is the limited understanding of the hydrodynamic and thermal transport parameters associated with periodic flow of a cryogenic fluid in micro-porous structures. In view of the above, the goals of this investigation include: 1) experimentally measuring and correlating the steady and periodic flow Darcy permeability and Forchheimer’s inertial hydrodynamic parameters for available rare-Earth ErPr regenerator filler; 2) employing a CFD-assisted methodology for the unambiguous quantification of the Darcy permeability and Forchheimer’s inertial hydrodynamic parameters, based on experimentally measured steady and periodic flow pressure drops in porous structures representing recently developed regenerator fillers; and 3) performing a direct numerical pore-level investigation for steady and periodic flows in a generic porous medium in order to elucidate the flow and transport processes, and quantify the solid-fluid hydrodynamic and heat transfer parameters. These hydrodynamic resistances parameters were found to be significantly different for steady and oscillatory flows.

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Roberts, Anthony M. "Implementing a Piezoelectric Transformer for a Ferroelectric Phase Shifter Circuit." Cleveland State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=csu1337025849.

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Luanje, Appolinaire Tifang. "INTEGRATED OPTICAL FIBER RAMAN SENSOR FOR CRYOGENIC APPLICATION." MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04042008-155057/.

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An integrated fiber optical Raman sensor was designed for real-time, non intrusive detection of liquid and gaseous mixtures at high pressure and high flow rates. The integrated sensor employs a high-power solid-state pumped Nd:YAG frequency doubled (532nm) laser (3W), a modified In Photonics Raman probe which has built-in Raman signal filter optics, and two high-resolution spectrometers and photomultiplier tubes (PMT) with selected bandpass filters to collect both N2 and O2 Raman signals. The detection unit was also integrated with Lab View software interfaced PMT modules for fast data acquisition.

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Barraclough, Jack Matthew. "Electrical transport properties of URhGe and BiPd at very low temperature." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6327.

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URhGe has garnered interest recently as one of the few known ferromagnetic superconductors. The superconductivity in this material appears to arise from magnetic fluctuations rather than phonons, and take a triplet form which is remarkably resistant to field. In this thesis, a number of measurements on the material are presented. Some probe the Fermiology, with strong evidence appearing for a model which as both light open sheets and heavy, small, closed pockets. The open sheets, associated with chains of real-space electron density running along the b axis, dominate the conductivity in most circumstances. Evidence for their existence arises from the general large and non-saturating magnetoresistance, and from the unusual observation of negative temperature coefficient of resistance at high fields. The closed pockets have provided a few Shubnikov-de Haas oscillations, but mostly they remain inferred from the high specific heat γ and their role in the magnetism. In order to better probe the superconductivity, a high precision low noise DC resistance measurement bridge was built using a SQUID. Along with conventional measurements, this provides evidence that the two pockets of superconductivity on the phase diagram are the same phase. The re-entrance an be understood simply as a result of magnetic field being a tuning parameter, but also suppressing bulk superconductivity through orbital limiting. The SQUID bridge allowed the detection of domain wall superconductivity linking up these two pockets. The SQUID bridge was also used to study the highly structured superconducting transition in BiPd. This material lacks inversion symmetry in its crystal structure, so is a good candidate for unusual forms of superconductivity. Here again non-bulk superconductivity is considered the most likely cause for the structure. Unusual and distinctive IV curves have been measured, and a simple model of inhomogeneous conductivity channels with different critical currents is proposed as an explanation.

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Posavec, Tony. "An Investigation into the Fluorescence of Polymers." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499353221343727.

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Lynch, Alice A. "A cryogenic scintillation UCN detector for a neutron EDM experiment." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:d154d231-79c2-4e2e-b31e-41aca59fe964.

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The observed imbalance of matter and anti-matter in the universe is one of physics' most fundamental unresolved questions. The leading theories to explain this imbalance require CP violation, and the neutron electric dipole moment (nEDM) is a sensitive parameter in its determination. Many new theories of physics beyond the standard model can be constrained or ruled-out by setting limits on the nEDM. Many next generation nEDM experiments require Ultra Cold Neutrons (UCN), produced in superfluid helium. One such experiment is cryoEDM. This thesis explores various types of UCN detection technologies applicable to cryoEDM or any high-density high-efficiency cryogenic nEDM experiment. Cryogenic Phonon Scintillation detectors (CPSD) are modified for this application by operating at 500 mK, and by using a titanium transition edge sensor for phonon signal readout. A CPSD is stabilised in the transition using a novel infra-red light feedback system which reduced the response time to O(100 μs). The detector is characterised and calibrated using an ²⁴¹Am α source. It was found to operate reliably at this elevated temperature and measure an alpha spectrum with 11% resolution at 5.5 MeV. Scintillators are identified as a promising technology for UCN detection at low temperature. Suitable materials that are bright with fast decay times and low γ sensitivity are studied in the temperature range 300 - 6 K. Their light yield to alpha excitation, their decay time characteristics and spectroscopic properties under VUV excitation are investigated. This study includes the first comprehensive investigation of the luminescence properties of plastic scintillators and of ⁶LiF/ZnS(Ag) down to 6 K. It is found that there is no degradation of the luminescence or kinetic properties of these materials across the whole temperature range, revealing them as suitable cryogenic detector materials. Using a plastic scintillator, a prototype UCN detector for operation in liquid helium is designed, manufactured and tested. It is read out using WLS optical fibres to a room temperature photomultiplier. The detector is successfully tested with cold neutrons at the ISIS neutron science facility and found to effectively measure neutrons, with a signal that is clear from background. Recommendations are made for its integration into a cryogenic neutron EDM experiment. This low-cost detector offers a promising method for the passive detection of UCN in a challenging cryogenic environment, with minimal electric interference and low background sensitivity. This technology offers the potential for improved UCN detection efficiency and thus improved sensitivity of the measurement of the neutron EDM.

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Hartwig, Jason W. "Liquid Acquisition Devices for Advanced In-Space Cryogenic Propulsion Systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396562473.

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Roberts, Susan Penelope Sara. "Low temperature injuries in Chlamydomonas reinhardtii (CW15+)." Thesis, University of Plymouth, 1988. http://hdl.handle.net/10026.1/1110.

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The responses of Chlamydomonas reinhardtii CW15+ (a wall-less mutant) to freezing stress have been examined: Tests following freezing of bulk (0.5ml) samples reveal the existence of an optimum cooling rate f o r preservation of viability, close to l*C min-1. Direct observation of cells during freezing and thawing on a cryo light microscope have allowed different forms of injury to be classified. At suboptimal cooling rates, reduction in surface area during shrinkage can be achieved by severe distortion or by the formation of layered stacks of membrane. Lethal injury is not evident until thawing takes place. The manifestation of injury depends upon the severity of the freezing treatment. The first symptom of injury is membrane blebbing at the cell surface, leading to swelling of the entire cell, followed by collapse. The membrane involved in the swelling might originate i n the mitochondrion and chloroplast envelope. Regions of fusion between membrane of these organelles and the plasma membrane have been observed during rewarming by electron microscopy. Fluorescent markers of the mitochondrial membrane have been detected i n the membrane involved in blebbing. Further damage during slow cooling contributes to rapid lysis on re-expansion. If the freezing treatment is still more severe, osmotic unresponsiveness will result. At supraoptimal cooling rates loss inviability is associated with intra cellular freezing. These responses have been examined in the light of available data regarding the freeze-thaw responses of higher plant protoplasts . The first symptom of damage seen in 'C reinhardtii ie. that of blebbing and massive swelling, is not common to both systems. Thus general rules concerning the responses of plant cells to freezing stresses cannot be made by using either of these protoplasts as a model system, although each may be useful for study of particular aspects of higher plant and algal cell freezing as separate investigations.

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Reinke, Benjamin T. "Design, Characterization, and Simulation of a Cryogenic Irradiation Facility in the Ohio State University Research Reactor Pool." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437746576.

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Blake, Robert. "The effects of realistic surface properties on low temperature space observatories." Thesis, Open University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262697.

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Ball, Christopher D. "Rotational energy transfer in low temperature molecules /." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487951214940079.

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Lupien, Christian. "Piezoresistive torque magnetometry at low temperature." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ37143.pdf.

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MacLachlan, Craig S. "Numerical modelling of low temperature plasma." Thesis, University of Glasgow, 2009. http://theses.gla.ac.uk/911/.

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The intention of this thesis is to gain a better understanding of basic physical processes occurring in low temperature plasmas. This is achieved by applying both analytic and numerical models. Low temperature plasmas are found in both technological and astrophysical contexts. Three different situations are investigated: an instability in electronegative plasmas; electron avalanches during plasma initiation; and a phenomenon called the Critical Ionisation Velocity interaction. Industrial plasma discharges with electronegative gases are found to be unstable in certain conditions. Fluctuations in light emission, particle number densities and potential are observed. The instability has been reproduced in a variety of experiments. Reports from the experiments are discussed to characterise the key features of the instability. An, as yet un-considered, physical process that could explain the instability is introduced. The instability relies on the plasma's transparency to the electric field. This mechanism is investigated using simple zero-dimensional numerical and analytic models. The results from the models are compared to experimental results. The calculated frequencies are in good agreement with the experimental measurements. This shows that the instability mechanism described here is relevant. For the remaining two problems a three-dimensional particle model is constructed. This model calculates the trajectories of each individual particle. The potential field is solved self-consistently on a computational mesh. Poisson's equation is solved using a Multigrid technique. This iterative solution method uses many grids, of different resolutions, to smooth the error on all spatial scales. The mathematical foundation and details of the components of the Multigrid method are presented. Several test cases where analytic solutions of Poisson's equation exist are used to determine the accuracy of the solver. The implemented solver is found to be both efficient and accurate. Collisions are vitally important to the evolution of plasmas. The chemistry resulting from collisions is the reason why plasmas are so useful in technological applications. Electron collisions are included in the particle model using a Monte-Carlo technique. A basic method is given and several improvements are described. The most efficient combination of improvements is determined through a series of test cases. The error resulting from the collision selection process is characterised. Technological plasmas are formed from the electrical breakdown of a neutral gas. At atmospheric pressure the breakdown occurs as an electron avalanche. The particle model is used to simulate the nanosecond evolution of the avalanche from a single electron-ion pair. Special attention is paid to the inelastic collisions and the creation of metastables. The inelastic losses are used to estimate the photon emission from the electron avalanche. The Critical Ionisation Velocity phenomena is investigated using the particle model. When a neutral gas streams across a magnetised plasma the ionisation rate increases rapidly if the speed of the neutrals exceeds a critical value. Collisions between neutrals and positive ions create pockets of unbalanced negative charge. Electrons in these pockets are accelerated by their potential field and can reach energies capable of ionisation. The evolution of such an electron overdensity is simulated and their energy gain under different density and magnetic field conditions is calculated. The results from the simulation may explain the discrepancy between laboratory and space experiments.

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Durst, Adam Craig 1974. "Low temperature quasiparticle transport in d-wave superconductors." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29305.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2002.
Includes bibliographical references (p. 120-124).
Experiments have now established that the order parameter (gap) in the high-Tc cuprate superconductors exhibits d-wave symmetry, vanishing at four nodal points on the Fermi surface. Near each of these four gap nodes, quasiparticles are easily excited and behave more like massless relativistic particles than electrons in a metal. In this thesis, we study the transport properties of these nodal quasiparticles, providing theoretical interpretations for the results of low temperature thermal and (microwave) electrical transport experiments in the cuprates. We begin by considering the very low temperature regime in which transport is dominated by quasiparticles induced by the very presence of impurities. This is known as the universal limit because prior calculations indicate that the transport coefficients obtain universal (scattering-independent) values. We improve upon prior results by including the contribution of vertex corrections and find that while the electrical conductivity obtains a scattering-dependent correction, the thermal and spin conductivity maintain their universal values.
(cont.) We then focus on the microwave electrical conductivity and consider the slightly higher temperature regime where quasiparticles are excited thermally. Since measurements in detwinned samples yield results that are inconsistent with simple models of impurity scattering, we hypothesize that line defects, remnant from the process of removing twin boundaries, may provide an additional scattering mechanism. We calculate the self-energy and microwave conductivity due to line defect scattering and obtain results that agree well with experiment. Finally, we turn on a magnetic field and consider thermal transport in the mixed (vortex) state. In the weak-field regime, the thermal conductivity tensor can be expressed in terms of the cross section for quasiparticle scattering from a single vortex. We calculate this cross section and thereby obtain both the longitudinal thermal conductivity and the thermal Hall conductivity in surprisingly good qualitative agreement with the measured data. The transparent nature of our calculation allows us to obtain a physical understanding of the features seen in experiments.
by Adam Craig Durst.
Ph.D.

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Smith, David John. "Optical diagnostics of low temperature plasmas." Thesis, University of Strathclyde, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248331.

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Slobinsky, Demian G. "Low temperature magnetisation properties of the spin ice material Dy₂Ti₂O₇." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3102.

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A way to obtain materials that show novel phenomena is to explore the interplay between geometry and interactions. When it is not geometrically possible to satisfy all the interactions by a given configuration, then to find the ground state becomes very complicated. This interplay between geometry and interactions defines geometrical frustration. One of the most popular examples of geometrical frustration in magnetism is spin ice. In this system, nearest neighbour ferromagnetic interactions between Ising spins in a pyrochlore structure emulate water ice by showing the same degree of frustration. This is manifested by the same ground state residual entropy. Although the clearest example of spin ice among magnets is shown by Dy₂Ti₂O₇, the behaviour of this material is richer than that of pure spin ice. The large magnetic moments of the rare earth Dy form a spin ice that also interacts via dipolar interactions. These long range interactions give rise to monopolar excitations which dramatically affect the dynamics of the system with respect to the pure spin ice case. In this thesis magnetisation experiments and numerical methods are used to explore the properties of the magnetic insulator Dy₂Ti₂O₇. We study its excitations at low temperature and describe the out-of-equilibrium characteristics of the magnetisation processes, below a temperature where the system freezes out. For temperatures above the freezing temperature, we describe and measure a 3D Kasteleyn transition and the concomitant Dirac strings associated to it, for the field in the [100] crystallographic direction. For temperatures below the freezing temperature, we find new out-of-equilibrium phenomena. Magnetic jumps are measured and their sweep rate dependence analysed. A deflagration theory is proposed and supported by simultaneous magnetisation and sample temperature measurements obtained by a new design of a Faraday magnetometer.

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Radmanesh, Seyed Mohammad Ali. "Ultra-low Temperature Properties of Correlated Materials." ScholarWorks@UNO, 2018. https://scholarworks.uno.edu/td/2511.

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Abstract After the discovery of topological insulators (TIs), it has come to be widely recognized that topological states of matter can actually be widespread. In this sense, TIs have established a new paradigm about topological materials. Recent years have seen a surge of interest in topological semimetals, which embody two different ways of generalizing the effectively massless electrons to bulk materials. Dirac and, particularly, Weyl semimetals should support several transport and optical phenomena that are still being sought in experiments. A number of promising experimental results indicate superconductivity in members of half-Hesuler semimetals which realize the mixing singlet and triplet pairing symmetry. We now turn to results we got through the work on topological semimetals. This work presents quantum high field transports on Dirac and Weyl topological semimetals including Sr1-yMn1-zSb2 (y, z < 0.1), YbMnBi2 and TaP. In case of Sr1-yMn1-zSb2 (y, z < 0.1), massless relativistic fermion was reported with m* = 0.04-0.05m0. This material presented a ferromagnetic order for in 304 K < T < 565 K, but a canted antiferromagnetic order with a net ferromagnetic component for T < 304 K. These are considered striking features of Dirac fermions For YbMnBi2, we reported the unusual interlayer quantum transport behavior in magnetoresistivity, resulting from the zeroth LL mode observed in this time reversal symmetry breaking type II Weyl semimetal. Also, for Weyl semimetal TaP the measurements probed multiple Fermi pockets, from which nontrivial π Berry phase and Zeeman splitting were extracted. Our ultra-low penetration depth measurements on half-Heuslers YPdBi and TbPdBi revealed a power- law behavior with n= 2.76 ± 0.04 for YPdBi samples and n=2.6 ± 0.3 for TbPdBi sample. We may conclude the exponent n > 2 implies nodless superconducting gap in our samples. Also, we found that despite the increase in magnetic correlations from YPdBi to TbPdBi, superconductivity remains robust in both systems which indicates that AF fluctuations do not play a major role in superconducting mechanism.

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Richardson-Bullock, J. S. "Low temperature semiconductor-superconductor junctions & their optimisation." Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/66735/.

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The research presented in this thesis focuses on the relatively young field of direct electron cooling via semiconductor-superconductor tunnel junctions. These devices utilise the superconducting energy gap to form a high pass electron filter, capable of lowering the effective electron temperature in the semiconductor electrode. The presented research focuses on optimizing the performance of such junctions i.e. the minimum achieved electron temperature, primarily by modifying the electrical properties of the semiconductor/superconductor and influencing the quality of the semiconductor-superconductor interface. In the semiconducting electrode, the effect of carrier type on the thermal coupling of the system is studied, as is the effect of mechanical strain, induced via lattice mismatch. A study is made of alternative superconductors, modifying their properties through the use of thin films for the superconducting contact. Finally, a comprehensive investigation is presented into the importance of fabrication procedures on device characteristics, leading to the development of the first semiconductor-insulator-superconductor junction.

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Borges, de Araujo M. A. "Hyperfine interactions studied by low temperature nuclear orientation." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355725.

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Upstone, Richard Peter. "Low temperature studies of transport in silicon MOSFETs." Thesis, University of Cambridge, 1986. https://www.repository.cam.ac.uk/handle/1810/265340.

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This dissertation is the outcome of three years work in the semiconductor Physics group at the Cavendish Laboratory, during which time I was financially _supported by the Science and Engineering Research Council. Many thanks are due to my supervisor, Mike Pepper, for his advice and enthusiastic encouragement. I would also like to warmly thank the past and present members of the group who have helped to make the these three years an enjoyable experience. I cannot mention everyone here, but particular thanks are due to Alan Marsh, Colin Dean, Richard Newbury for his efforts to revive the Rutherford fridge, and to Normand Paquin and Donald Pooke for their excellent proof reading of this dissertation. This work would not have been possible without the invaluable technical assistance provided by the members of the Low Temperature Physics workshop, and Dr. s. Read at .the Rutherford Appleton Laboratory. Useful discussions were held during the course of this work with Professors M.Ya. Azbel, K.F. Berggren, and M. Kaveh. This dissertation is the result of my own work and includes nothing which is the outcome of work done in collaboration. It is not the same as any other that I have submitted, or am submitting, for a degree, diploma or any other qualification to any other university.

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Boskovic, Bojan O. "Room and low temperature synthesis of carbon nanofibres." Thesis, University of Surrey, 2002. http://epubs.surrey.ac.uk/843497/.

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Carbon nanotubes and nanofibres have attracted attention in recent years as new materials with a number of very promising potential applications. Carbon nanotubes are potential candidates for field emitters in flat panel displays. Carbon nanofibres could also be used as a hydrogen storage material and as a filling material in polymer composites. Carbon nanotubes are already used as tips in scanning probe microscopy due to their remarkable mechanical and electrical properties, and could be soon used as nanotweezers. Use of carbon nanotubes in nanoelectronics will open further miniaturisation prospects. Temperatures ranging from 450 to 1000 °C have been a required for catalytic growth of carbon nanotubes and nanofibres. Researchers have been trying to reduce the growth temperatures for decades. Low temperature growth conditions will allow the growth of carbon nanotubes on different substrates, such glass (below 650 °C) and as plastics (below 150 °C) over relatively large areas, which is especially suitable for flat panel display applications. Room temperature growth conditions could open up the possibility of using different organic substrates and bio-substrates for carbon nanotubes synthesis. Carbon nanofibres have been synthesised at room temperature and low temperatures below 250 °C using radio frequency plasma enhanced chemical vapour deposition (r.f PECVD). Previously, the growth of carbon nanofibres has been via catalytic decomposition of hydrocarbons or carbon monoxide at temperatures above 300 °C. To the best of our knowledge, this is the first evidence of the growth of carbon nanofibres at temperatures lower than 300 °C by any method. The use of a transition metal catalyst and r.f. PECVD system is required for the growth of the carbon nanofibre when a hydrocarbon flows above the catalyst. Within the semiconductor industry r.f. PECVD is a well established technique which lends itself for the growth of carbon nanofibres for various electronic and photonic device applications. A new catalytic method for the growth of carbon nanofibres using radio frequency supported microwave plasma-enhanced chemical vapour deposition (PECVD) has been developed. Nickel powder used as a catalyst was placed on a water-cooled sample holder in order to obtain growth at room temperature. Carbon nanofibres grown by our method have shown remarkable characteristics of branching during the growth including the forming of "Y"-shaped junctions and interconnecting networks. A graphite strip heater vacuum system for carbon nanofibres thermal chemical vapour deposition (CVD) has been set up, using methane or acetylene as the carbon containing source gas, and nickel powder as the catalyst. Various carbon nanofibre morphologies have been produced: "whisker-like", helical, branched, bi-directional, and "bead-like". Using this low-pressure thermal CVD synthesis method carbon nanofibres and nanotubes were synthesised at relatively low temperatures from 350 °C. Optimum deposition conditions for the produced fibres with higher graphitic structures at low temperatures have been established by series of experiments varying pressure, temperature, substrate and gas mixture. Optimum growth temperature was found to be around 500 °C. Ropes of roughly aligned carbon nanotubes have been observed after synthesis using nickel catalysed CVD of methane at temperatures of 500 °C, or after radio frequency assisted microwave PECVD. Mixtures of remaining nickel powder and synthesized carbon nanofibres and nanotubes have been treated in 35% nitric acid for periods of 3 to 10 minutes and carbon nanotube ropes have been observed in the dried sediment by scanning electron microscope examination. Rope diameters range from 20?m up to 80?m, and lengths up to few millimeters have been observed. The large size of these ropes means that easy manipulation is possible for their characterisation and applications. A growth model for the room temperature and low temperature produced carbon nanofibres is proposed. Characterisation of produced carbon nanofibres and carbon nanoropes have been performed using scanning electron microscope, Raman spectroscopy and transmission electron microscopy with electron energy loss spectroscopy.

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Woodburn, Charles N. "Development of low-temperature, ultra high vacuum, scanning tunnelling microscope." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264506.

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Xu, Jie. "The low temperature synthesis, characterization and properties of ferroelectrics." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/26239.

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29

Mace, Daniel. "Low temperature electron transport in III-V semiconductor devices." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259629.

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30

Roseman, Mark A. "Low temperature magnetic force microscopy studies of superconducting niobium films." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38266.

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Low temperature magnetic force microscopy studies of superconducting niobium films have been undertaken with the goal of studying the interplay between artificial pinning centers and magnetic vortices.
Measurements were performed using a custom built low temperature magnetic force microscope, capable of operation at temperatures ranging from 4.2 K to room temperature. Special attention has been paid to optimizing the instrumentation through a detailed study of the noise characteristics, with particular emphasis placed on achieving a large signal-to-noise ratio and corresponding high force gradient sensitivity.
Magnetic force spectroscopy data has been used to deduce the critical temperature of the superconducting samples, based upon the repulsive Meissner interaction between the magnetic tip and the sample. Images of vortices as a function of applied magnetic field demonstrate the expected linear relation between vortex density and field strength, and confirms that only single vortices, each carrying one flux quantum, are observed. Two different methods are put forward to determine the magnetic penetration depth; one using magnetic force spectroscopy, the other using constant height imaging of vortices. Images of vortices as a function of temperature demonstrate that as temperatures rise, vortices become more easily depinned during the scanning process through interactions with the magnetic field of the tip. Dissipation images of vortices suggest eddy current damping as well as vortex motion within potential wells as major sources of energy loss. Studies on a patterned niobium film show that only interstitial vortices are easily detectable by MFM, but that a strong tip influence results in significant tip induced motion of these vortices around the antidots.

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Alonzo-Proulx, Olivier. "Low-temperature thermal conductivity of the amorphous superconductor FexNi₁-xZr₂." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97890.

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Thermal conductivity is a powerful tool to probe the phonon and electron exitations in a solid, especially in superconductors were one can basically tune the respective electronic and phononic contributions by applying a magnetic field below Tc.
After a short review on the concepts of superconductivity, thermal conductivity and amorphous matter, we present a study of the thermal conductivity of an exotic material, the amorphous metallic superconductor Fe0.5Ni 0.5Zr2. The results indicate an unexpected dominant electonic contribution to the thermal conductivity across the superconducting transition, in accordance with an inhomogeneous sample composed of a bulk normal phase with inhomogeneous superconducting phases.

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32

Tschanz, Steven J. "Modeling low temperature C-V profiling in blocked impurity band detectors." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FTschanz.pdf.

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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, September 2005.
Thesis Advisor(s): Nancy M. Haegel, Donald L. Walters. Includes bibliographical references (p. 49). Also available online.

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33

Briffa, Amy K. R. "Low temperature magnetic ordering of frustrated rare-earth pyrochlores." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3722/.

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We study the low temperature magnetic ordering of rare-earth pyrochlores. The dominant magnetic interaction: nearest neighbour antiferromagnetic Heisenberg exchange, is frustrated with a macroscopic ground-state degeneracy. This degeneracy is lifted by weaker interactions, stabilising long-range order. First we study the dipolar governed gadolinium stannate with an external magnetic field. Factorising the Hamiltonian in terms of ten quadratics provides exact solutions to the over-constrained model with fields orientated along highly symmetrical directions. Next we study the isostructural gadolinium titanate: the much more complex magnetism is indexed by a different propagation-vector to gadolinium stannate due to further neighbour exchange interactions. This material is controversial: elastic neutron scattering and Mössbauer experiments have been using contradictory interpretations. We propose a new state which appears to resolve this inconsistency. Finally we model erbium titanate, which is approached differently due to the dominant crystal-field. Existing elastic neutron scattering data is reexamined and found inconsistent with the state currently discussed in the literature so we suggest an unusual multiple-q state. The spins are not orientated along the expected crystal-field direction: a consequence of frustration. Energetics are studied phenomenologically. We suggest that experimentally observed gapless spin-waves control transfer of spin density between different q-points of the proposed state.

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34

Churchill, Hugh O. H. "Low-temperature infrared spectroscopy of H2 in solid C60." Oberlin College Honors Theses / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1206292667.

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35

McMenamin, C. S. "Low temperature thermal measurements on cuprate superconductors in high magnetic fields." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260823.

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36

Daine, Robert John. "Temperature Dependence of Current Transport in Metal-SWNT Structures." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1438958818.

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37

Hedberg, James. "Low temperature force microscopy on a deeply embedded two dimensional electron gas." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97016.

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Experimental physics in the low temperature limit has consistently produced major advances for condensed matter research. Likewise, scanning probe microscopy offers a unique view of the nanometer scale features that populate the quantum landscape. This work discusses the merger of the two disciplines via the development of the Ultra Low Temperature Scanning Probe Microscope, the ULT-SPM. We focus on the novel characterization of an exotic condensed matter system: a deeply buried two dimensional electron gas with a cleaved edge overgrowth geometry. By coupling the dynamics of the force sensing probe microscope to the electrostatics of the electron gas, we can remotely and non-invasively measure charge transport features which are normally only observable using physically contacted electrodes. Focusing on the quantum Hall regime, we can exploit the high sensitivity of the local force sensor to study spatially dependent phenomena associated with electronic potential distributions. The instrument shows promise for many exciting experiments in which low temperatures, high magnetic ﬁelds, and local measurements are critical.Designed for operation at 50 mK, in magnetic ﬁelds reaching 16 T, many components of the instrument are not commercially available and were therefore designed and constructed in- house. As such, the intricate details of its design, construction and operation are documented thoroughly. This includes: the microscope assembly, the modular components such as the scan head and coarse motors, the electronics developed for controlling the instrument, and the general integration into the low temperature infrastructure. A quartz tuning fork is used as the force sensor in this instrument, enabling a wide selection between different modes of operation, the most relevant being electrostatic force microscopy. Noise limits are investigated and matched sources of experimental noise are identified. Detailed schematics of the instrument are also included.
La physique expérimentale aux limites des basses températures contribue constamment à des percées majeures dans le domaine de la matière condensée. Pour sa part, la microscopie à balayage de sonde offre la possibilité unique d'observer les éléments nanométriques qui car- actérisent le paysage quantique. Ce projet allie les avantages de ces deux disciplines par le développement d'un microscope à balayage de sonde opérant à très basse température (Ultra Low Temperature Scanning Probe Microscope), le « ULT-SPM. » Nous étudions en particulier un système exotique de la matière condensée : un gaz d'électrons bidimensionnel profondément enfoui, comportant une croissance latérale sur le bord clivé. Le couplage des forces dynamiques de la sonde du microscope et électrostatiques du gaz à électrons, nous permet de mesurer à distance et de façon non invasive, les caractéristiques de transport des charges, qui ne sont normalement observables qu'à l'aide d'électrodes et donc, par un contact physique. Dans le régime de l'effet Hall quantique, nous pouvons exploiter la grande sensibilité du capteur de force local pour étudier des phénomènes spatiodépendants associés aux distribu- tions de potentiel électronique. L'instrument se révèle prometteur pour la poursuite de nom- breuses expériences passionnantes où les conditions de basse température, champ magnétique élevé et mesures locales sont essentielles. Comme il est conçu pour fonctionner à 50 mK et sous un champ magnétique pouvant at- teindre 16 T, plusieurs composantes du microscope ne sont pas disponibles commercialement et ont donc été entièrement conçues et fabriquées sur place. Les détails intrinsèques de la con- ception, de la construction et du fonctionnement sont ainsi documentés à fond. Ceci inclut : l'assemblage du microscope, les composantes modulaires comme la tête de balayage et les mo- teurs, l'électronique des contrôles de l'instrument et l'intégration à l'infrastructure opérant à basse température. Dans cet instrument, un diapason de quartz fait ofﬁce de capteur, ce qui permet une grande ﬂexibilité quant aux différents modes d'opération, le plus utile étant la mi- croscopie de force électrostatique. Les limites de bruit sont étudiées et comparées aux sources de bruit expérimentales. Les schémas détaillés de l'instrument sont également inclus.

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38

Chen, Tianjiao. "Low Temperature Surface Reconstruction Study on Wurtzite Gallium Nitride." Ohio University Honors Tutorial College / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1392904494.

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39

Hetel, Iulian Nicolae. "Quantum Critical Behavior In The Superfluid Density Of High-Temperature Superconducting Thin Films." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204918571.

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40

Georgiacodis, D. N. "Low temperature ion-irradiation effects in silicon studied by ion-channelling techniques." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304345.

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41

Weedon, M. A. "Low temperature transport properties of ultra-thin Ag deposits on Ge(100)." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358439.

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42

Christian, Aaron Brandon. "Magnetic and Thermal Properties of Low-Dimensional Single-Crystalline Transition-Metal Antimonates and Tantalates." Thesis, Montana State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10268687.

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This work contributes to the study of magnetic interactions in the low-dimensional antiferromagnets M(Sb,Ta)₂O₆, where M is a transition metal. By virtue of the trirutile structure, M-O-O-M chains propagate along [110] at z = 0 and [110] at z = 1/2 of the unit cell. These chains are separated along [001] by sheets of weakly-interacting diamagnetic ions. The spin-exchange coupling perpendicular to the chains is weak, permitting the low-dimensional classification. Single crystals have been grown using chemical vapor deposition and the floating zone method. Magnetization, in-field heat capacity, and high-resolution thermal expansion measurements have been performed along various axes, revealing significant anisotropy due to the peculiar magnetic structures and low dimensionality.

The Neel temperature, T_N, at which long-range order occurs is found to be unstable against the application of magnetic field above 2 T. Large fields tend to lower T_N of the set of moments with projections along the applied field. Moments which are aligned perpendicular to the field are significantly less affected. This can lead to the formation of a secondary peak in heat capacity when magnetic field is along either [110] or [110]. The change in heat capacity at the location of the newly formed peak means there is a change in entropy, which depends upon the direction of applied field with respect to the magnetic moments. Consequently, an anisotropic magnetocaloric effect arises due to the unique magnetic structure. The anisotropic nature of this effect has potential applications in magnetic refrigeration.

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43

Alhasan, Ahmad Abdulraheem. "Low Temperature Characterization of Foamed Warm Mix Asphalt." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1374676401.

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44

Roseman, Mark A. "Design and characteristics of a low-temperature atomic force microscope." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ44260.pdf.

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45

Carney, John Paul. "Non linear damping by ballistic quasiparticles in superfluid '3HE-#beta#." Thesis, Lancaster University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253496.

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46

Jackson, Douglas Anthony. "Experiments on a dilute '3He-'4He solution in a large magnetic field gradient." Thesis, Lancaster University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384881.

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47

White, Jeremy Philip. "A PrNiâ†5 refrigerator developed for nuclear orientation below 1mK." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302870.

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48

Church, Rosemary Jane. "Properties of '3He-'4He mixtures." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329879.

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49

Mossavati, Ruzbeh. "Use of '1'9F NMR thermometry in the investigation of magnetic textures in superfluid '3He-A." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329594.

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50

Ryder, J. "An experimental investigation into the electrical transport properties of Laâ†2CuOâ†4â†+â†#delta# and Ndâ†2CuOâ†4â†+â†#delta#." Thesis, University of Bristol, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279724.

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Dissertations / Theses on the topic 'Low temperature physics[Cryogenics]'

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