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Superconductivity

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Articles 91 - 110 of 110

Full-Text Articles in Physics

Vortex Physics In Confined Geometries, M. Cristina Marchetti, David R. Nelson Feb 2008

Vortex Physics In Confined Geometries, M. Cristina Marchetti, David R. Nelson

Physics - All Scholarship

Patterned irradiation of cuprate superconductors with columnar defects allows a new generation of experiments which can probe the properties of vortex liquids by forcing them to flow in confined geometries. Such experiments can be used to distinguish experimentally between continuous disorder-driven glass transitions of vortex matter, such as the vortex glass or the Bose glass transition, and nonequilibrium polymer-like glass transitions driven by interaction and entanglement. For continuous glass transitions, an analysis of such experiments that combines an inhomogeneous scaling theory with the hydrodynamic description of viscous flow of vortex liquids can be used to infer the critical behavior. After …

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Superconductivity Close To Magnetic Instability In Fe(Se1−Xtex)0.82, M H. Fang, H M. Pham, B Qian, T J. Liu, E K. Vehstedt, Y Liu, L Spinu, Z Q. Mao Jan 2008

Superconductivity Close To Magnetic Instability In Fe(Se1−Xtex)0.82, M H. Fang, H M. Pham, B Qian, T J. Liu, E K. Vehstedt, Y Liu, L Spinu, Z Q. Mao

Physics Faculty Publications

We report our study of the evolution of superconductivity and the phase diagram of the ternary Fe(Se1−xTex)0.82 (0≤x≤1.0) system. We discovered a superconducting phase with Tc,max=14 K in the 0.30.82, which exhibits an incommensurate antiferromagnetic order. We discuss the relationship between the superconductivity and magnetism of this material system in terms of recent results from neutron-scattering measurements. Our results and analyses suggest that superconductivity in this class of Fe-based compounds is associated with magnetic fluctuations and therefore may be unconventional in nature.

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Picovoltmeter For Probing Vortex Dynamics In A Single Weak-Pinning Corbino Channel, T. W. Heitmann, Kang Yu, C. Song, M P. Defeo, B.L.T. Plourde Jan 2008

Picovoltmeter For Probing Vortex Dynamics In A Single Weak-Pinning Corbino Channel, T. W. Heitmann, Kang Yu, C. Song, M P. Defeo, B.L.T. Plourde

Physics - All Scholarship

We have developed a picovoltmeter using a Nb dc Superconducting QUantum Interference Device (SQUID) for measuring the flux-flow voltage from a small number of vortices moving through a submicron weak-pinning superconducting channel. We have applied this picovoltmeter to measure the vortex response in a single channel arranged in a circle on a Corbino disk geometry. The circular channel allows the vortices to follow closed orbits without encountering any sample edges, thus eliminating the influence of entry barriers.

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Fabrication Of Robust Superconducting Granular Aluminium/Palladium Bilayer Microbolometers With Sub-Nanosecond Response, Thomas E. Wilson Dec 2007

Fabrication Of Robust Superconducting Granular Aluminium/Palladium Bilayer Microbolometers With Sub-Nanosecond Response, Thomas E. Wilson

Physics Faculty Research

We provide a convenient recipe for fabricating reliable superconducting microbolometers as acoustic phonon detectors with sub-nanosecond response, using imagereversal optical lithography and dc-magnetron sputtering, and our recipe requires no chemical or plasma etching. Our approach solves the traditional problem for granular aluminium bolometers of unreliable (i.e., non-Ohmic) electrical contacts by sequentially sputtering the granular aluminium film and then a palladium capping layer. We use dc calibration data, the method of Danilchenko et al. [1], and direct nanosecond-pulsed photoexcitation to obtain the microbolometer’s characteristic current, thermal conductance, characteristic relaxation time, and heat capacity. We also demonstrate the use of the deconvolution …

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Quantum Analysis Of A Linear Dc Squid Mechanical Displacement Detector, M. P. Blencowe, E. Buks Jul 2007

Quantum Analysis Of A Linear Dc Squid Mechanical Displacement Detector, M. P. Blencowe, E. Buks

Dartmouth Scholarship

We provide a quantum analysis of a dc SQUID mechanical displacement detector within the subcritical Josephson current regime. A segment of the SQUID loop forms the mechanical resonator and motion of the latter is transduced inductively through changes in the flux threading the loop. Expressions are derived for the detector signal response and noise, which are used to evaluate the position and force detection sensitivity. We also investigate cooling of the mechanical resonator due to detector back reaction.

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Decoherence And Recoherence In A Vibrating Rf Squid, Eyal Buks, M. P. Blencowe Nov 2006

Decoherence And Recoherence In A Vibrating Rf Squid, Eyal Buks, M. P. Blencowe

Dartmouth Scholarship

We study an rf SQUID, in which a section of the loop is a freely suspended beam that is allowed to oscillate mechanically. The coupling between the rf SQUID and the mechanical resonator originates from the dependence of the total magnetic flux threading the loop on the displacement of the resonator. Motion of the latter affects the visibility of Rabi oscillations between the two lowest energy states of the rf SQUID. We address the feasibility of experimental observation of decoherence and recoherence, namely decay and rise of the visibility, in such a system.

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Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour Nov 2005

Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour

Dartmouth Scholarship

We present an analysis of the dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor (SSET) in the vicinity of Josephson quasi-particle (JQP) and double Josephson quasi-particle (DJQP) resonances. For weak coupling and wide separation of dynamical timescales, we find that for either superconducting resonances the dynamics of the resonator are given by a Fokker–Planck equation, i.e. the SSET behaves effectively as an equilibrium heat bath, characterized by an effective temperature, which also damps the resonator and renormalizes its frequency. Depending on the gate and drain–source voltage bias points with respect to the superconducting resonance, the SSET can …

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Investigation Of The Superconducting Properties Of Niobium Radio-Frequency Cavities, Gianluigi Ciovati Jul 2005

Investigation Of The Superconducting Properties Of Niobium Radio-Frequency Cavities, Gianluigi Ciovati

Physics Theses & Dissertations

Radio-frequency (rf) superconducting cavities are widely used to increase the energy of a charged particle beam in particle accelerators. The maximum gradients of cavities made of bulk niobium have constantly improved over the last ten years and they are approaching the theoretical limit of the material. Nevertheless, rf tests of niobium cavities are still showing some "anomalous" losses (so-called "Q-drop"), characterized by a marked increase of the surface resistance at high rf fields, in absence of field emission. A low temperature "in-situ" baking under ultra-high vacuum has been successfully applied by several laboratories to reduce those losses and …

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Weak Point Disorder In Strongly Fluctuating Flux-Line Liquids, Panayotis Benetatos, M. Cristina Marchetti Apr 2005

Weak Point Disorder In Strongly Fluctuating Flux-Line Liquids, Panayotis Benetatos, M. Cristina Marchetti

Physics - All Scholarship

We consider the effect of weak uncorrelated quenched disorder (point defects) on a strongly fluctuating flux-line liquid. We use a hydrodynamic model which is based on mapping the flux-line system onto a quantum liquid of relativistic charged bosons in 2+1 dimensions [P. Benetatos and M. C. Marchetti, Phys. Rev. B 64, 054518, (2001)]. In this model, flux lines are allowed to be arbitrarily curved and can even form closed loops. Point defects can be scalar or polar. In the latter case, the direction of their dipole moments can be random or correlated. Within the Gaussian approximation of our hydrodynamic model, …

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Electrical And Structural Properties Of Ex-Situ Annealed Superconducting Bi_2sr_2cacu_2o_8 Thin Films Obtained By Coevaporation Of Components, Necdet Baştürk Jan 2005

Electrical And Structural Properties Of Ex-Situ Annealed Superconducting Bi_2sr_2cacu_2o_8 Thin Films Obtained By Coevaporation Of Components, Necdet Baştürk

Turkish Journal of Physics

Bi_2Sr_2CaCu_2O_8 system superconducting thin films were obtained by synchronized deposition of Bi, Cu, CaF_2 and SrF_2 components onto cleaved MgO (100) single crystal substrates after annealing in the temperature range 600--840 °C. The films were annealed in H_2O and O_2, then dry O_2 atmosphere for the removal of fluorine from the structure and to attain superconducting properties. X-ray powder diffraction patterns were used to characterize the obtained film structure. The films were observed to grow along c-axis perpendicular to the substrate surface with the identified reflection on the (00l, l = 6, 8, 10...) planes. The films having the critical …

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Understanding The Origin Of The Recovery Of Superconductivity In Halogenated Ybco Single Crystal : Atomic Structure Study, Lamine Mohamed Kollakoye Dieng May 2004

Understanding The Origin Of The Recovery Of Superconductivity In Halogenated Ybco Single Crystal : Atomic Structure Study, Lamine Mohamed Kollakoye Dieng

Dissertations

The recovery of superconductivity in underdoped YBa2Cu3O6+y (YBCO) by exposure to bromine, iodine, chlorine and fluorine is a long-standing problem which has not been clearly resolved. The key question concerns the role of these halogens in the lattice. In order to shed light to this problem, we have performed multiple-edge x-ray absorption fine structure (XAFS) measurements about the Y K, Ba L3, I L3, Cu K and Br K-edges at room temperature on brominated (non-brominated) and iodinated (non-iodinated) YBCO single crystals. Our XAFS results at the Br K (brominated) and I …

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Coherent Vs Incoherent Interlayer Transport In Layered Metals, Gary L. Gard, J. Wosnitza, J. Hagel, J. S. Qualls, J. S. Brooks, E. Balthes, D. Schweitzer, J. A. Schlueter, U. Geiser, Javid Mohtasham, Rolf Walter Winter Apr 2002

Coherent Vs Incoherent Interlayer Transport In Layered Metals, Gary L. Gard, J. Wosnitza, J. Hagel, J. S. Qualls, J. S. Brooks, E. Balthes, D. Schweitzer, J. A. Schlueter, U. Geiser, Javid Mohtasham, Rolf Walter Winter

Chemistry Faculty Publications and Presentations

The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For k -BEDT-TTF)₂I₃, where BEDTTTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at Q590°(field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃. This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal.

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Depression Of Superconducting Transition Temperature Due To Pr In The (La2.5-X Prxnd0.5) Caba3cu7oz System, Darshan C. Kundaliya, Reeta Vij, R. G. Kulkarni, William B. Yelon, S. K. Malik Mar 2002

Depression Of Superconducting Transition Temperature Due To Pr In The (La2.5-X Prxnd0.5) Caba3cu7oz System, Darshan C. Kundaliya, Reeta Vij, R. G. Kulkarni, William B. Yelon, S. K. Malik

Physics Faculty Research & Creative Works

Structural and superconducting properties of (La2.5-xPrxNd0.5)CaBa3Cu7Oz (0≤x≤0.7) compounds have been investigated. Neutron diffraction studies reveal that these crystallize in the triple-perovskite structure (space group P4/mmm) with an oxygen content of 16.6 per formula unit nearly independent of the Pr content. The superconducting transition temperature, Tc, of x = 0 compound is ∼ 79K and decreases almost linearly with increasing x to ∼ 42K for x = 0.7. In order to see if the depression of Tc due to Pr can be compensated by Ca, we examined the compounds (La …

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Driven Vortices In Confined Geometry: The Corbino Disk, M. Cristina Marchetti Jul 2000

Driven Vortices In Confined Geometry: The Corbino Disk, M. Cristina Marchetti

Physics - All Scholarship

The fabrication of artificial pinning structures allows a new generation of experiments which can probe the properties of vortex arrays by forcing them to flow in confined geometries. We discuss the theoretical analysis of such experiments in both flux liquids and flux solids, focusing on the Corbino disk geometry. In the liquid, these experiments can probe the critical behavior near a continuous liquid-glass transition. In the solid, they probe directly the onset of plasticity.

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Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, M. Cristina Marchetti, Alan Middleton, Thomas Prellberg Dec 1999

Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, M. Cristina Marchetti, Alan Middleton, Thomas Prellberg

Physics - All Scholarship

We have investigated the mean field dynamics of an overdamped viscoelastic medium driven through quenched disorder. The model introduced incorporates coexistence of pinned and sliding degrees of freedom and can exhibit continuous elastic depinning or first order hysteretic depinning. Numerical simulations indicate mean field instabilities that correspond to macroscopic stick-slip events and lead to premature switching. The model is relevant for the dynamics of driven vortex arrays in superconductors and other extended disordered systems.

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Onset Of Superconductivity In Decreasing Fields For General Domains, Andrew J. Bernoff, Peter Sternberg Mar 1998

Onset Of Superconductivity In Decreasing Fields For General Domains, Andrew J. Bernoff, Peter Sternberg

All HMC Faculty Publications and Research

Ginzburg–Landau theory has provided an effective method for understanding the onset of superconductivity in the presence of an external magnetic field. In this paper we examine the instability of the normal state to superconductivity with decreasing magnetic field for a closed smooth cylindrical region of arbitrary cross-section subject to a vertical magnetic field. We examine the problem asymptotically in the boundary layer limit (i.e., when the Ginzburg–Landau parameter, k, is large). We demonstrate that instability first occurs in a region exponentially localized near the point of maximum curvature on the boundary. The transition occurs at a value of the …

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Anyonic Superconductivity In A Modified Large-U Hubbard Model, Asim Gangopadhyaya, Prasanta K. Panigrahi Nov 1991

Anyonic Superconductivity In A Modified Large-U Hubbard Model, Asim Gangopadhyaya, Prasanta K. Panigrahi

Physics: Faculty Publications and Other Works

A modified large-U Hubbard model at half filling is analyzed by a mean-field approach. Preserving a local U(1) symmetry of the action, the fluctuations about half filling are studied in the spirit of the commensurate-flux-phase condition. The fluctuations then contribute a Chern-Simons term to the tree-level Lagrangian with a coefficient appropriate to that of a half fermion. With the Coulomb repulsion term, we study the low-energy excitations of the model and show the existence of superconductivity in the presence of a four-Fermi interaction term.

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Possible Origins Of High-Tc, Superconductivity, John R. Hardy, John W. Flocken May 1988

Possible Origins Of High-Tc, Superconductivity, John R. Hardy, John W. Flocken

Physics Faculty Publications

A new mechanism is proposed to explain high-T, superconductivity in copper-oxide-based, open perovskitelike systems. It is shown that, should the oxygen ions be moving in a double-well potential, an order-of-magnitude enhancement of the electron-lattice coupling follows automatically from a consistent treatment of this motion. Both theoretical and experimental evidence for the presence of such double wells is cited.

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Superconductivity At 155 K, David D. Allred, S. R. Ovshinsky, R. T. Young, G. Demaggio, G. A. Van Der Leeden Jun 1987

Superconductivity At 155 K, David D. Allred, S. R. Ovshinsky, R. T. Young, G. Demaggio, G. A. Van Der Leeden

Faculty Publications

Transition to a superconducting zero-resistance state at 155 K is observed for the first time in bulk material. A new five-element compound has been synthesized with nominal composition Y1Ba2Cu3F2Oy. Fluorine plays a critical role in achieving this effect. X-ray diffraction and electron microprobe analysis indicate that the samples are multiphasic. Evidence is presented that the samples contain superconducting phases with onset temperatures considerably above 155 K. Magnetic measurements suggest a flux-trapping effect below 260 K, and diamagnetic deviations from Curie-Weiss behavior in the range from 250 K≤T≤100 K indicate that Meissner effect in a small superconducting volume fraction.

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Thermal Propagation And Stability In Superconducting Films, Kenneth E. Gray, Robert T. Kampwirth, John F. Zasadzinski, Stephen P. Ducharme Jan 1983

Thermal Propagation And Stability In Superconducting Films, Kenneth E. Gray, Robert T. Kampwirth, John F. Zasadzinski, Stephen P. Ducharme

Stephen Ducharme Publications

Thermal propagation and stable hot spots (normal domains) are studied in various high Tc superconducting films (Nb3Sn, Nb, NbN and Nb3Ge). The prediction of the thermal propagation velocity of the long-standing model of Broom and Rhoderick (1960) is verified quantitatively in the regime of its validity. A new energy balance model is shown to give reasonable quantitative agreement of the dependence of the propagation velocity on the length of short normal domains. The steady state (zero velocity) measurements indicate the existence of two distinct situations for films on high thermal conductivity (sapphire) substrates. For low power per unit area the …

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