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Superconductivity

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Full-Text Articles in Physics

Loop Currents And Anomalous Hall Effect From Time-Reversal Symmetry-Breaking Superconductivity On The Honeycomb Lattice, P.M.R. Brydon, D.S.L. Abergel, Daniel Agterberg, Victor M. Yakovenko Aug 2019

Loop Currents And Anomalous Hall Effect From Time-Reversal Symmetry-Breaking Superconductivity On The Honeycomb Lattice, P.M.R. Brydon, D.S.L. Abergel, Daniel Agterberg, Victor M. Yakovenko

Physics Faculty Articles

We study a tight-binding model on the honeycomb lattice of chiral d-wave superconductivity that breaks time-reversal symmetry. Because of its nontrivial sublattice structure, we show that it is possible to construct a gauge-invariant time-reversal-odd bilinear of the pairing potential. The existence of this bilinear reflects the sublattice polarization of the pairing state. We show that it generates persistent loop current correlations around each lattice site and opens a topological mass gap at the Dirac points, resembling Haldane’s model of the anomalous quantum Hall effect. In addition to the usual chiral d-wave edge states, there also exist electronlike ...


Ternary Inorganic Electrides With Mixed Bonding, Junjie Wang, Qiang Zhu, Zhenhai Wang, Hideo Hosono Feb 2019

Ternary Inorganic Electrides With Mixed Bonding, Junjie Wang, Qiang Zhu, Zhenhai Wang, Hideo Hosono

Physics & Astronomy Faculty Publications

A high-throughput screening based on first-principles calculations was performed to search for new ternary inorganic electrides. From the available materials database, we identified three new thermodynamically stable materials (Li12Mg3Si4, NaBa2O, and Ca5Ga2N4) as potential electrides made by main group elements, in addition to the well known mayenite based electride (C12A7:e−). Different from those conventional inorganic electrides in which the excess electrons play only the role of anions, the three new materials, resembling the electrides found in simple metals under high pressure, possess mixed ionic and metallic bonding. The interplay between two competing mechanisms, together with the different crystal packing ...


Scanning Tunneling Spectroscopy Investigations Of Superconducting-Doped Topological Insulators: Experimental Pitfalls And Results, Stefan Wilfert, Paolo Sessi, Zhiwei Wang, Henrik Schmidt, M. Carmen Martínez-Velarte, Seng Huat Lee, Yew San Hor, Alexander F. Otte, Yoichi Ando, Weida Wu, Matthias Bode Aug 2018

Scanning Tunneling Spectroscopy Investigations Of Superconducting-Doped Topological Insulators: Experimental Pitfalls And Results, Stefan Wilfert, Paolo Sessi, Zhiwei Wang, Henrik Schmidt, M. Carmen Martínez-Velarte, Seng Huat Lee, Yew San Hor, Alexander F. Otte, Yoichi Ando, Weida Wu, Matthias Bode

Physics Faculty Research & Creative Works

Recently, the doping of topological insulators has attracted significant interest as a potential route towards topological superconductivity. Because many experimental techniques lack sufficient surface sensitivity, however, definite proof of the coexistence of topological surface states and surface superconductivity is still outstanding. Here we report on highly surface sensitive scanning tunneling microscopy and spectroscopy experiments performed on Tl-doped Bi2Te3, a three-dimensional topological insulator which becomes superconducting in the bulk at TC=2.3 K. Landau level spectroscopy as well as quasiparticle interference mapping clearly demonstrated the presence of a topological surface state with a Dirac point energy ...


Universal Doping Evolution Of The Superconducting Gap Anisotropy In Single Crystals Of Electron-Doped Ba(Fe1-Xrhx)(2)As-2 From London Penetration Depth Measurements, Hyunsoo Kim, Makariy A. Tanatar, C. Martin, E. C. Blomberg, Ni Ni, Sergey L. Bud’Ko, Paul C. Canfield, Ruslan Prozorov Jun 2018

Universal Doping Evolution Of The Superconducting Gap Anisotropy In Single Crystals Of Electron-Doped Ba(Fe1-Xrhx)(2)As-2 From London Penetration Depth Measurements, Hyunsoo Kim, Makariy A. Tanatar, C. Martin, E. C. Blomberg, Ni Ni, Sergey L. Bud’Ko, Paul C. Canfield, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

Doping evolution of the superconducting gap anisotropy was studied in single crystals of 4d-electron doped Ba(Fe1-xRhx)(2)As-2 using tunnel diode resonator measurements of the temperature variation of the London penetration depth Delta lambda(T). Single crystals with doping levels representative of an underdoped regime x = 0.039 (T-c = 15.5 K), close to optimal doping x = 0.057 (T-c = 24.4 K) and overdoped x = 0.079 (T-c = 21.5 K) and x = 0.131 (T-c = 4.9 K) were studied. Superconducting energy gap anisotropy was characterized by the exponent, n, by fitting the data to the power-law ...


Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney Nov 2017

Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Low temperature powder inelastic neutron scattering measurements were performed on three different powder samples; parent BaMn2As2,12.5% K-doped Ba0.875K0.125Mn2As2 and 25% K-doped Ba(0.75)K0.25Mn2As2. The Heisenberg Model involving J1‐J2‐Jz coupling constants were compared to the data by a powder integration routine using Monte Carlo integration methods. The best magnetic parameters were selected using a chi-square test where model intensities were compared to the full (q,E) dependence of magnetic scattering. A key step to this analysis is the characterization of the background which is formed mostly by phonon scattering intensities along with ...


Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield Oct 2017

Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report the temperature-pressure phase diagram of CaKFe4As4 established using high-pressure electrical resistivity, magnetization, and high-energy x-ray diffraction measurements up to 6 GPa. With increasing pressure, both resistivity and magnetization data show that the bulk superconducting transition of CaKFe4As4 is suppressed and then disappears at p≳4 GPa. High-pressure x-ray data clearly indicate a phase transition to a collapsed tetragonal phase in CaKFe4As4 under pressure that coincides with the abrupt loss of bulk superconductivity near 4 GPa. The x-ray data, combined with resistivity data, indicate that the collapsed tetragonal transition line is essentially independent of pressure, occurring at 4.0 ...


Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, Aashish Sapkota, B. G. Ueland, V. K. Anand, N. S. Sangeetha, D. L. Abernathy, M. B. Stone, J. L. Niedziela, D. C. Johnston, A. Kreyssig, A. I. Goldman, R. J. Mcqueeney Oct 2017

Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, Aashish Sapkota, B. G. Ueland, V. K. Anand, N. S. Sangeetha, D. L. Abernathy, M. B. Stone, J. L. Niedziela, D. C. Johnston, A. Kreyssig, A. I. Goldman, R. J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Inelastic neutron scattering measurements on the itinerant antiferromagnet CaCo2−yAs2 at a temperature of 8 K reveal two orthogonal planes of scattering perpendicular to the Co square lattice in reciprocal space, demonstrating the presence of effective one-dimensional spin interactions. These results are shown to arise from near-perfect bond frustration within the J1-J2 Heisenberg model on a square lattice with ferromagnetic J1 and hence indicate that the extensive previous experimental and theoretical study of the J1-J2 Heisenberg model on local-moment square spin lattices should be expanded to include itinerant spin systems.


Calorimetric Measurements Of Magnetic-Field-Induced Inhomogeneous Superconductivity Above The Paramagnetic Limit, Charles C. Agosta, Nathanael Alexander Fortune, Scott T. Hannahs, Shuyao Gu, Lucy Liang, Ju-Hyun Park, John A. Schleuter Jun 2017

Calorimetric Measurements Of Magnetic-Field-Induced Inhomogeneous Superconductivity Above The Paramagnetic Limit, Charles C. Agosta, Nathanael Alexander Fortune, Scott T. Hannahs, Shuyao Gu, Lucy Liang, Ju-Hyun Park, John A. Schleuter

Physics: Faculty Publications

We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor κ−(BEDT−TTF)2Cu(NCS)2 as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit Hp is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field ...


Rotational Symmetry Breaking In A Trigonal Superconductor Nb-Doped Bi₂Se₃, T. Asaba, B. J. Lawson, C. Tinsman, L. Chen, P. Corbae, G. Li, Y. Qiu, Yew San Hor, L. Fu, L. Li Jan 2017

Rotational Symmetry Breaking In A Trigonal Superconductor Nb-Doped Bi₂Se₃, T. Asaba, B. J. Lawson, C. Tinsman, L. Chen, P. Corbae, G. Li, Y. Qiu, Yew San Hor, L. Fu, L. Li

Physics Faculty Research & Creative Works

The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi2Se3) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi2Se3 ...


Cryogenic Rf Test Of The First Srf Cavity Etched In An Rf Ar/Cl2 Plasma, J. Upadhyay, A. Palczewski, S. Popovic, A.-M. Valente-Feliciano, Do Im, H. L. Phillips, L. Vuskovic Jan 2017

Cryogenic Rf Test Of The First Srf Cavity Etched In An Rf Ar/Cl2 Plasma, J. Upadhyay, A. Palczewski, S. Popovic, A.-M. Valente-Feliciano, Do Im, H. L. Phillips, L. Vuskovic

Physics Faculty Publications

An apparatus and a method for etching of the inner surfaces of superconducting radio frequency (SRF) accelerator cavities are described. The apparatus is based on the reactive ion etching performed in an Ar/Cl2 cylindrical capacitive discharge with reversed asymmetry. To test the effect of the plasma etching on the cavity rf performance, a 1497 MHz single cell SRF cavity was used. The single cell cavity was mechanically polished and buffer chemically etched and then rf tested at cryogenic temperatures to provide a baseline characterization. The cavity's inner wall was then exposed to the capacitive discharge in a ...


Exact Solution Of Quadratic Fermionic Hamiltonians For Arbitrary Boundary Conditions, Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, Lorenza Viola Aug 2016

Exact Solution Of Quadratic Fermionic Hamiltonians For Arbitrary Boundary Conditions, Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, Lorenza Viola

Open Dartmouth: Faculty Open Access Scholarship

We present a procedure for exactly diagonalizing finite-range quadratic fermionic Hamiltonians with arbitrary boundary conditions in one of D dimensions, and periodic in the remaining D−1. The key is a Hamiltonian-dependent separation of the bulk from the boundary. By combining information from the two, we identify a matrix function that fully characterizes the solutions, and may be used to construct an efficiently computable indicator of bulk-boundary correspondence. As an illustration, we show how our approach correctly describes the zero-energy Majorana modes of a time-reversal-invariant s-wave two-band superconductor in a Josephson ring configuration, and predicts that a fractional 4π-periodic Josephson ...


Dynamical Generation Of Floquet Majorana Flat Bands In S-Wave Superconductors, A. Poudel, G. Ortiz, L. Viola Apr 2015

Dynamical Generation Of Floquet Majorana Flat Bands In S-Wave Superconductors, A. Poudel, G. Ortiz, L. Viola

Open Dartmouth: Faculty Open Access Scholarship

We present quantum control techniques to engineer flat bands of symmetry-protected Majorana edge modes in s -wave superconductors. Specifically, we show how periodic control may be employed for designing time-independent effective Hamiltonians, which support Floquet Majorana flat bands, starting from equilibrium conditions that are either topologically trivial or only support individual Majorana pairs. In the first approach, a suitable modulation of the chemical potential simultaneously induces Majorana flat bands and dynamically activates a pre-existing chiral symmetry which is responsible for their protection. In the second approach, the application of effective parity kicks dynamically generates a desired chiral symmetry by suppressing ...


Majorana Flat Bands In S -Wave Gapless Topological Superconductors, Shusa Deng, Gerardo Ortiz, Amrit Poudel, Lorenza Viola Apr 2014

Majorana Flat Bands In S -Wave Gapless Topological Superconductors, Shusa Deng, Gerardo Ortiz, Amrit Poudel, Lorenza Viola

Open Dartmouth: Faculty Open Access Scholarship

We demonstrate how the nontrivial interplay between spin-orbit coupling and nodeless s-wave superconductivity can drive a fully gapped two-band topological insulator into a time-reversal invariant gapless topological superconductor supporting symmetry-protected Majorana flat bands. We characterize topological phase diagrams by a Z2×Z2 partial Berry-phase invariant, and show that, despite the trivial crystal geometry, no unique bulk-boundary correspondence exists. We trace this behavior to the anisotropic quasiparticle bulk gap closing, linear vs quadratic, and argue that this provides a unifying principle for gapless topological superconductivity. Experimental implications for tunneling conductance measurements are addressed, relevant for lead chalcogenide materials.


Higher Order Mode Damping In Superconducting Spoke Cavities, C. S. Hopper, J. R. Delayen Jan 2014

Higher Order Mode Damping In Superconducting Spoke Cavities, C. S. Hopper, J. R. Delayen

Physics Faculty Publications

Parasitic higher order modes (HOMs) can be severely detrimental to the performance of superconducting cavities. For this reason, the mode spectrum and beam coupling strength must be examined in detail to determine which modes must be damped. One advantage of the spoke cavity geometry is that couplers can be placed on the outer body of the cavity rather than in the beam line space. We present an overview of the HOM properties of spoke cavities and methods for suppressing the most harmful ones.


Multiband S -Wave Topological Superconductors: Role Of Dimensionality And Magnetic Field Response, Shusa Deng, Gerardo Ortiz, Lorenza Viola May 2013

Multiband S -Wave Topological Superconductors: Role Of Dimensionality And Magnetic Field Response, Shusa Deng, Gerardo Ortiz, Lorenza Viola

Open Dartmouth: Faculty Open Access Scholarship

We further investigate a class of time-reversal-invariant two-band s-wave topological superconductors introduced earlier [Deng, Viola, and Ortiz, Phys. Rev. Lett. 108, 036803 (2012)]. Provided that a sign reversal between the two superconducting pairing gaps is realized, the topological phase diagram can be determined exactly (within mean field) in one and two dimensions as well as in three dimensions upon restricting to the excitation spectrum of time-reversal-invariant momentum modes. We show how, in the presence of time-reversal symmetry, Z2 invariants that distinguish between trivial and nontrivial quantum phases can be constructed by considering only one of the Kramers’ sectors in which ...


Imaging The Anisotropic Nonlinear Meissner Effect In Nodal Yba 2Cu3O7-Δ Thin-Film Superconductors, Alexander P. Zhuravel, Behnood G. Ghamsari, Cihan Kurter, Philipp Jung, Stephen K. Remillard, John A. Abrahams, Alexander V. Lukashenko, Alexey V. Ustinov, Steven Mark Anlage Feb 2013

Imaging The Anisotropic Nonlinear Meissner Effect In Nodal Yba 2Cu3O7-Δ Thin-Film Superconductors, Alexander P. Zhuravel, Behnood G. Ghamsari, Cihan Kurter, Philipp Jung, Stephen K. Remillard, John A. Abrahams, Alexander V. Lukashenko, Alexey V. Ustinov, Steven Mark Anlage

Physics Faculty Research & Creative Works

We have directly imaged the anisotropic nonlinear Meissner effect in an unconventional superconductor through the nonlinear electrodynamic response of both (bulk) gap nodes and (surface) Andreev bound states. A superconducting thin film is patterned into a compact self-resonant spiral structure, excited near resonance in the radio-frequency range, and scanned with a focused laser beam perturbation. At low temperatures, direction-dependent nonlinearities in the reactive and resistive properties of the resonator create photoresponse that maps out the directions of nodes, or of bound states associated with these nodes, on the Fermi surface of the superconductor. The method is demonstrated on the nodal ...


Switching Nonlinearity In A Superconductor-Enhanced Metamaterial, Cihan Kurter, Philippe Tassin, Alexander P. Zhuravel, Lei Zhang, Thomas Koschny, Alexey V. Ustinov, Costas M. Soukoulis, Steven M. Anlage Mar 2012

Switching Nonlinearity In A Superconductor-Enhanced Metamaterial, Cihan Kurter, Philippe Tassin, Alexander P. Zhuravel, Lei Zhang, Thomas Koschny, Alexey V. Ustinov, Costas M. Soukoulis, Steven M. Anlage

Physics Faculty Research & Creative Works

We demonstrate a nonlinear metamaterial that can be switched between low and high transmission by controlling the power level of the incident beam. The origin of this nonlinear response is the superconducting Nb thin film employed in the metamaterial structure. We show that with moderate RF power of about 22 dBm it is possible to quench the superconducting state as a result of extremely strong current densities at the corners of the metamaterial's split-ring resonators. We measure a transmission contrast of 10 dB and a change in group delay of 70 ns between the low and high power states.


Majorana Modes In Time-Reversal Invariant S -Wave Topological Superconductors, Shusa Deng, Lorenza Viola, Gerardo Ortiz Jan 2012

Majorana Modes In Time-Reversal Invariant S -Wave Topological Superconductors, Shusa Deng, Lorenza Viola, Gerardo Ortiz

Open Dartmouth: Faculty Open Access Scholarship

We present a time-reversal invariant s-wave superconductor supporting Majorana edge modes. The multiband character of the model together with spin-orbit coupling are key to realizing such a topological superconductor. We characterize the topological phase diagram by using a partial Chern number sum, and show that the latter is physically related to the parity of the fermion number of the time-reversal invariant modes. By taking the self-consistency constraint on the s-wave pairing gap into account, we also establish the possibility of a direct topological superconductor-to-topological insulator quantum phase transition.


Nonlinear Hydrodynamics Of Disentangled Flux-Line Liquids, Panayotis Benetatos, M. Cristina Marchetti Jul 2011

Nonlinear Hydrodynamics Of Disentangled Flux-Line Liquids, Panayotis Benetatos, M. Cristina Marchetti

Physics

In this paper we use non-Gaussian hydrodynamics to study the magnetic response of a flux-line liquid in the mixed state of a type-II superconductor. Both the derivation of our model, which goes beyond conventional Gaussian flux liquid hydrodynamics, and its relationship to other approaches used in the literature are discussed. We focus on the response to a transverse tilting field which is controlled by the tilt modulus, c44, of the flux array. We show that interaction effects can enhance c44 even in infinitely thick clean materials. This enhancement can be interpreted as the appearance of a disentangled flux-liquid fraction. In ...


Theory Of Double-Sided Flux Decorations, M. Cristina Marchetti, David R. Nelson Jul 2011

Theory Of Double-Sided Flux Decorations, M. Cristina Marchetti, David R. Nelson

Physics

A novel two-sided Bitter decoration technique was recently employed by Yao et al. to study the structure of the magnetic vortex array in high-temperature superconductors. Here we discuss the analysis of such experiments. We show that two-sided decorations can be used to infer {\it quantitative} information about the bulk properties of flux arrays, and discuss how a least squares analysis of the local density differences can be used to bring the two sides into registry. Information about the tilt, compressional and shear moduli of bulk vortex configurations can be extracted from these measurements.


Classical Analogue Of Electromagnetically Induced Transparency With A Metal-Superconductor Hybrid Metamaterial, Cihan Kurter, Philippe Tassin, Lei Zhang, Thomas Koschny, Alexander P. Zhuravel, Alexey V. Ustinov, Steven Mark Anlage, Costas M. Soukoulis Jul 2011

Classical Analogue Of Electromagnetically Induced Transparency With A Metal-Superconductor Hybrid Metamaterial, Cihan Kurter, Philippe Tassin, Lei Zhang, Thomas Koschny, Alexander P. Zhuravel, Alexey V. Ustinov, Steven Mark Anlage, Costas M. Soukoulis

Physics Faculty Research & Creative Works

Metamaterials are engineered materials composed of small electrical circuits producing novel interactions with electromagnetic waves. Recently, a new class of metamaterials has been created to mimic the behavior of media displaying electromagnetically induced transparency (EIT). Here we introduce a planar EIT metamaterial that creates a very large loss contrast between the dark and radiative resonators by employing a superconducting Nb film in the dark element and a normal-metal Au film in the radiative element. Below the critical temperature of Nb, the resistance contrast opens up a transparency window along with a large enhancement in group delay, enabling a significant slowdown ...


Millimeter-Wave Study Of London Penetration Depth Temperature Dependence In Ba(Fe0.926co0.074)2as2 Single Crystal, A. A. Barannik, N. T. Cherpak, Ni Ni, Makariy A. Tanatar, S. A. Vitusevich, V. N. Skresanov, Paul C. Canfield, Ruslan Prozorov, V. V. Glamazdin, K. I. Torokhtii Jan 2011

Millimeter-Wave Study Of London Penetration Depth Temperature Dependence In Ba(Fe0.926co0.074)2as2 Single Crystal, A. A. Barannik, N. T. Cherpak, Ni Ni, Makariy A. Tanatar, S. A. Vitusevich, V. N. Skresanov, Paul C. Canfield, Ruslan Prozorov, V. V. Glamazdin, K. I. Torokhtii

Ames Laboratory Publications

In-plane surface Ka-band microwave impedance of optimally dopedsingle crystals of the Fe-based superconductor Ba(Fe0.926Co0.074)2As2 (Tc  = 22.8 K) was measured. Sensitive sapphire disk quasi-optical resonator with high-Tc cuprate conducting endplates was developed specially for Fe-pnictide superconductors. It allowed finding temperature variation of London penetration depth in a form of power law, namely Δλ(T) ∼ Tn with n = 2.8 from low temperatures up to at least 0.6Tc consisted with radio-frequency measurements. This exponent points towards nodeless state with pairbreaking scattering, which can support one ...


Bandwidth Tuning Triggers Interplay Of Charge Order And Superconductivity In Two-Dimensional Organic Materials, S. Kaiser, M. Dressel, Y. Sun, A. Greco, J. A. Schlueter, Gary L. Gard, N. Drichko Nov 2010

Bandwidth Tuning Triggers Interplay Of Charge Order And Superconductivity In Two-Dimensional Organic Materials, S. Kaiser, M. Dressel, Y. Sun, A. Greco, J. A. Schlueter, Gary L. Gard, N. Drichko

Chemistry Faculty Publications and Presentations

We observe charge-order fluctuations in the quasi-two-dimensional organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃, both by means of vibrational spectroscopy, locally probing the fluctuating charge order, and by investigating the in-plane dynamical response by infrared reflectance spectroscopy. The decrease of the effective electronic interaction in an isostructural metal suppresses both charge-order fluctuations and superconductivity, pointing to their interplay. We compare the results of our experiments with calculations on the extended Hubbard model.


Dynamical Conductivity At The Dirty Superconductor-Metal Quantum Phase Transition, Adrian Del Maestro, Bernd Rosenow, Jose A. Hoyos, Thomas Vojta Oct 2010

Dynamical Conductivity At The Dirty Superconductor-Metal Quantum Phase Transition, Adrian Del Maestro, Bernd Rosenow, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We study the transport properties of ultrathin disordered nanowires in the neighborhood of the superconductor-metal quantum phase transition. To this end we combine numerical calculations with analytical strong-disorder renormalization group results. The quantum critical conductivity at zero temperature diverges logarithmically as a function of frequency. In the metallic phase, it obeys activated scaling associated with an infinite-randomness quantum critical point. We extend the scaling theory to higher dimensions and discuss implications for experiments.


Anomalously Elastic Intermediate Phase In Randomly Layered Superfluids, Superconductors, And Planar Magnets, Priyanka Mohan, Paul M. Goldbart, Rajesh Narayanan, John Toner, Thomas Vojta Aug 2010

Anomalously Elastic Intermediate Phase In Randomly Layered Superfluids, Superconductors, And Planar Magnets, Priyanka Mohan, Paul M. Goldbart, Rajesh Narayanan, John Toner, Thomas Vojta

Physics Faculty Research & Creative Works

We show that layered quenched randomness in planar magnets leads to an unusual intermediate phase between the conventional ferromagnetic low-temperature and paramagnetic high-temperature phases. In this intermediate phase, which is part of the Griffiths region, the spin-wave stiffness perpendicular to the random layers displays anomalous scaling behavior, with a continuously variable anomalous exponent, while the magnetization and the stiffness parallel to the layers both remain finite. Analogous results hold for superfluids and superconductors. We study the two phase transitions into the anomalous elastic phase, and we discuss the universality of these results, and implications of finite sample size as well ...


Miniaturized Superconducting Metamaterials For Radio Frequencies, Cihan Kurter, John A. Abrahams, Steven Mark Anlage Jun 2010

Miniaturized Superconducting Metamaterials For Radio Frequencies, Cihan Kurter, John A. Abrahams, Steven Mark Anlage

Physics Faculty Research & Creative Works

We have developed a low-loss, ultrasmall radio frequency (rf) metamaterial operating at ~76 MHz. This miniaturized medium is made up of planar spiral elements with diameter as small as ~λ/658 (λ is the free space wavelength), fashioned from Nb thin films on quartz substrates. The transmission data are examined below and above the superconducting transition temperature of Nb for both a single spiral and a one dimensional array. The validity of the design is tested through numerical simulations and good agreement is found. We discuss how superconductors enable such a compact design in the rf with high loaded-quality factor ...


Upper Limits On A Possible Gluon Mass, Shmuel Nussinov, Robert Shrock Jan 2010

Upper Limits On A Possible Gluon Mass, Shmuel Nussinov, Robert Shrock

Mathematics, Physics, and Computer Science Faculty Articles and Research

We analyze upper limits on a possible gluon mass, mg. We first discuss various ways to modify quantum chromodynamics to include m(g) not equal 0, including a bare mass, a Higgs mechanism, and dynamical breaking of color SU(3)(c). From an examination of experimental data, we infer an upper limit m(g) < O(1) MeV. As part of our analysis, we show that a claim, hitherto unrefuted in the literature, of a much stronger upper limit on m(g), is invalid. We discuss subtleties in interpreting gluon mass limits in view of the fact that at scales below Lambda(QCD), quantum chromodynamics is strongly coupled, perturbation theory is not reliable, and the physics is not accurately described in terms of the Lagrangian degrees of freedom, including gluons. We also point out a fundamental difference in the behavior of quantum chromodynamics with a nonzero gluon mass and a weakly coupled gauge theory with a gauge boson mass.


Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: I. Echo Scheme, A. D. Armour, M. P. Blencowe Sep 2008

Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: I. Echo Scheme, A. D. Armour, M. P. Blencowe

Open Dartmouth: Faculty Open Access Scholarship

We propose a scheme in which the quantum coherence of a nanomechanical resonator can be probed using a superconducting qubit. We consider a mechanical resonator coupled capacitively to a Cooper pair box and assume that the superconducting qubit is tuned to the degeneracy point so that its coherence time is maximized and the electro-mechanical coupling can be approximated by a dispersive Hamiltonian. When the qubit is prepared in a superposition of states, this drives the mechanical resonator progressively into a superposition which in turn leads to apparent decoherence of the qubit. Applying a suitable control pulse to the qubit allows ...


Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: Ii. Implementation, M. P. Blencowe, A. D. Armour Sep 2008

Probing The Quantum Coherence Of A Nanomechanical Resonator Using A Superconducting Qubit: Ii. Implementation, M. P. Blencowe, A. D. Armour

Open Dartmouth: Faculty Open Access Scholarship

We describe a possible implementation of the nanomechanical quantum superposition generation and detection scheme described in the preceding, companion paper (Armour A D and Blencowe M P 2008 New. J. Phys. 10 095004). The implementation is based on the circuit quantum electrodynamics (QED) set-up, with the addition of a mechanical degree of freedom formed out of a suspended, doubly-clamped segment of the superconducting loop of a dc SQUID located directly opposite the centre conductor of a coplanar waveguide (CPW). The relative merits of two SQUID based qubit realizations are addressed, in particular a capacitively coupled charge qubit and inductively coupled ...


Quantum Analysis Of A Nonlinear Microwave Cavity-Embedded Dc Squid Displacement Detector, P. D. Nation, M. P. Blencowe, E. Buks Sep 2008

Quantum Analysis Of A Nonlinear Microwave Cavity-Embedded Dc Squid Displacement Detector, P. D. Nation, M. P. Blencowe, E. Buks

Open Dartmouth: Faculty Open Access Scholarship

We carry out a quantum analysis of a dc superconducting quantum interference device (SQUID) mechanical displacement detector, comprising a SQUID with mechanically compliant loop segment, which is embedded in a microwave transmission line resonator. The SQUID is approximated as a nonlinear current-dependent inductance, inducing an external flux tunable nonlinear Duffing self-interaction term in the microwave resonator mode equation. Motion of the compliant SQUID loop segment is transduced inductively through changes in the external flux threading SQUID loop, giving a ponderomotive radiation pressure-type coupling between the microwave and mechanical resonator modes. Expressions are derived for the detector signal response and noise ...