Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J36: Superconductivity: Properties and Phenomena |
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Sponsoring Units: DCMP Chair: Zhigang Wu, Colorado School of Mines Room: 344 |
Tuesday, March 19, 2013 2:30PM - 2:42PM |
J36.00001: Copper Substitution in Iron Telluride: A Phase Diagram Patrick Valdivia, Thomas Forrest, Costel Rotundu, Jinsheng Wen, Edith Bourret-Courchesne, Robert Birgeneau Investigations of superconductivity in the FeCh family (Ch$=$S,Se,Te) have produced rich physics and notable materials challenges despite the ostensible simplicity of the system. We have studied the effects of copper substitution in iron-telluride. Our interests in this system are two-fold: to compare the properties of copper substitution in iron-telluride with those in the selenium-substituted compounds, and to study if there are additional controllable factors in this system such as the total excess metal content, and the distribution of iron and copper atoms over the two sites. Our initial investigations into this phase diagram involve both diffraction and transport measurements which may be used address these research goals. [Preview Abstract] |
Tuesday, March 19, 2013 2:42PM - 2:54PM |
J36.00002: Kerr effect as evidence of gyrotropic order in the cuprates Srinivas Raghu, Pavan Hosur, Steven Kivelson, Aharon Kapitulnik, Joseph Orenstein The Kerr effect can arise in a time-reversal invariant dissipative medium that is ``gyrotropic", {\it i.e.} one that breaks spatial inversion and all mirror symmetries. Examples of such systems include electron analogs of cholesteric liquid crystals, and their descendants, such as systems with chiral charge ordering. We present arguments that the striking Kerr onset, {\it which is not invertible by application of a magnetic field}, in the pseudogap phase of a large number of cuprate high temperature superconductors is evidence of chiral charge ordering. We discuss additional experimental consequences of a phase transition to a gyrotropic system. [Preview Abstract] |
Tuesday, March 19, 2013 2:54PM - 3:06PM |
J36.00003: Anomalous Hall effect in current-carrying states of matter: topology, commensuration effects, and application to Kerr measurements in the underdoped cuprates Catherine Kallin, Edward Taylor We calculate the anomalous Hall conductivity for states characterized by patterns of spontaneous currents. Using an exact Ward identity, we find that the DC Hall conductivity is topological provided the current pattern is commensurate and the Fermi surface is fully gapped. For incommensurate patterns, the DC Hall conductivity can be infinite, analogous to the infinite conductivity of a sliding charge density wave. We also discuss the optical Hall conductivity at high frequencies, in connection with Kerr rotation experiments performed on the underdoped cuprates. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:18PM |
J36.00004: ABSTRACT HAS BEEN MOVED TO B29.00015 |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J36.00005: Thermodynamic studies of Cu$_{0.10}$TiSe$_2$ via ac-calorimetry and Hall-probe magnetometry Zuzana Pribulova, Jozef Kacmarcik, Peter Samuely, Zuzana Medvecka, Viktoria Solteszova, Petra Barancekova Husanikova, Vladimir Cambel, Goran Karapetrov TiSe$_{2}$ is a compound with the charge density wave (CDW) transition at 200 K, the CDW state is gradually suppressed when intercalated by copper and for certain amount of Cu superconductivity occurs. We report the studies of the critical fields of an optimally doped sample with a superconducting transition at $T_{\mathrm{c}}$ $\sim$ 3.9 K. Upper critical field $H_{\mathrm{c2}}$ has been derived from the specific heat measurements while the lower critical field $H_{\mathrm{c1}}$ has been extracted from local magnetization measurements using miniature Hall-probes. The temperature dependence of $H_{\mathrm{c2}}$ and $H_{\mathrm{c1}}$ and its anisotropy will be presented. Moreover, local magnetometry using array of 8 Hall-probes shows that vortices after penetration into the sample move towards the centre resulting into a dome-shape induction profile suggesting relatively low pinning. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J36.00006: Study of Inhomogeneous Organic Superconductors Charles C. Agosta, Christopher Conroy, Daniel Ellowitz, William Von Noppen In many anisotropic superconductors, we have found evidence that they are inhomogeneous superconductors, such as those predicted by Fulde and Ferrell and Larkin and Ovchinnikov (FFLO), at the extremes of low temperature and high magnetic field. A FFLO superconductor has an order parameter with nonzero pair momentum that oscillates periodically as a function of distance, unlike traditional superconductors where the order parameter is uniform. During the last several years, our research group at Clark University has made careful and systematic measurements of quasi-2D organic superconductors that suggest an FFLO state can be stabilized in three different organic conductors if a magnetic field is applied precisely parallel to the conducting layers. We will compare our results with theoretical expressions that we have modified from the current literature, with the goal of extracting quantitative results from the phase diagram data such as the Maki parameter and scattering times. We will also describe improvements to our pulsed magnetic field - tunnel diode oscillator penetration depth apparatus. [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J36.00007: Superconductivity in the misfit compound of (LaSe)$_{1.14}$(NbSe$_2)$: STM/S, calorimetric and magnetization studies P. Samuely, P. Szabo, J. Kacmarcik, Z. Pribulova, T. Samuely, J.G. Rodrigo, C. Marcenat, T. Klein, L. Cario (LaSe)$_1.14$(NbSe$_2)$ is a low temperature superconductor with $T_{c}$ around 1.2 K belonging to the family of the lamellar chalcogenides. Electron transfer from the LaSe to the NbSe$_2$ slab results in a natural layered system of the insulating LaSe and (super) conducting NbSe$_2$ sheets. In our previous investigations of the anisotropic transport [P. Szab\'{o} et al., Phys. Rev. Lett. 86, 5990 (2001)] indications have been found that this system behaves as a stack of Josephson-coupled superconducting NbSe$_2$ sheets separated by insulating LaSe layers. We test this hypothesis by STM/S measurements at subkelvin temperatures and in magnetic fields. Superconducting energy gap obtained by STM opens at the same temperature and field where the interlayer resistivity starts to increase before drop to zero value. Before any conclusions are made homogeneity of the superconducting parameters is to be tested. STM indicates large areas without any gap but calorimetric measurements have shown the bulk superconductivity and magnetization revealed extremely low pinning. [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J36.00008: Microwave stimulated enhancement of the upper critical field in type-II superconducting films Antonio Lara, Ahmad Awad, Alejandro Silhanek, Victor Moshchalkov, Farkhad Aliev A few decades ago it was theoretically predicted and experimentally observed that moderate power electromagnetic fields in the GHz range could stimulate superconductivity, increasing the superconducting critical temperature and critical current. Here, on the example of Pb films without / with periodic vortex pinning centers in the form of circular Permalloy dots in the magnetic vortex state, we investigate experimentally how the microwave stimulated superconductivity phenomenon behaves in the presence of a superconducting vortex system. Namely, we present the first, to our best knowledge, experimental investigation of influence of microwave induced superconductivity on the upper critical field of type II superconducting films. An enhancement of the critical temperature of the film of up to 0.1{\%} and of the upper critical field of up to 10{\%} have been observed at a drive frequency of 6 GHz. A qualitative explanation for the observed difference in the dependence of the upper critical field on the temperature and microwave power, depending on the nearly parallel or perpendicular alignments of the field to the sample, is provided. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J36.00009: New Evidences for the observation of the Higgs boson in the Superconductor 2H-NbSe$_2$ Marie-aude Measson, Bertrand Clair, Yann Gallais, Maximilien Cazayous, Pierre Rodi\`ere, Laurent Cario, Alain Sacuto We provide here new evidences for the observation of the amplitude mode of the superconducting order parameter, the so-called Higgs Boson, in 2H-NbSe$_2$. We report quantitatively comparative electronic Raman measurements on the dichalcogenides 2H-NbSe$_2$, whose superconductivity (SC) coexists with a charge density wave order (CDW), and 2H-NbS$_2$, which exhibits only the SC. A SC pair breaking peak develops below T$_c$ in 2H-NbS$_2$ whose intensity is much smaller than the peak associated with the SC in 2H-NbSe$_2$. Thus, the peak observed in 2H-NbSe$_2$ below T$_c$ certainly doesn't get its intensity only from the superconducting condensate. Moreover, we measure precisely a spectral weight transfer from the amplitude mode of the CDW to the SC peak in 2H-NbSe$_2$, versus decreasing temperature. The total spectral weight for both peaks is constant within $\pm~3\%$. This result is consistent with the theory of the observation of a Higgs mode thanks to its coupling with an amplitudon developed by Littlewood and Varma. This result complements what was firstly observed by Sooryakumar et Klein under magnetic field. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J36.00010: Imaging the Anisotropic Nonlinear Meissner Effect in Unconventional Superconductors Steven Anlage, A.P. Zhuravel, B.G. Ghamsari, C. Kurter, J. Abrahams, S. Remillard, P. Jung, A.V. Lukashenko, Alexey Ustinov 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 [1]. 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 superconductor YBa\textunderscore 2Cu\textunderscore 3O\textunderscore 7-$\backslash $delta and the results are consistent with theoretical predictions for the bulk and surface contributions. [1] A. P. Zhuravel, \textit{et al}., \underline {arXiv:1208.1511}. ~ [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J36.00011: X-ray edge singularity in resonant inelastic x-ray scattering (RIXS) Robert Markiewicz, John Rehr, Arun Bansil We develop a lattice model based on the theory of Mahan, Nozi{\'e}res, and de Dominicis for x-ray absorption to explore the effect of the core hole on the RIXS cross section. The dominant part of the spectrum can be described in terms of the dynamic structure function $S(q,\omega )$ dressed by matrix element effects, but there is also a weak background associated with multi-electron-hole pair excitations. The model reproduces the decomposition of the RIXS spectrum into well- and poorly-screened components. An edge singularity arises at the threshold of both components. Fairly large lattice sizes are required to describe the continuum limit. [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J36.00012: Using photon to probe spin excitations Chunjing Jia, Cheng-Chien Chen Chen, Brian Moritz, Tom Devereaux Elementary spin excitations have attracted considerable attention in the understanding of strongly correlated materials, especially in high temperature superconductors where a full understanding of spin dynamics might reveal important information where the phase emerges in proximity of magnetic order. Photon spectroscopies, such as resonant inelastic x-ray scattering (RIXS) and optical Raman scattering, are powerful tools for the measurement of spin excitations. In this presentation, I will discuss the simulation of various spectroscopies that can reveal spin excitations, using both single- and multi-orbital models. I will show that transition metal in-direct RIXS provides information about two-magnon excitations at low energies in addition to the usual charge transfer excitations; while direct RIXS measures single spin-flip (single magnon) excitations, making it a complementary technique to inelastic neutron scattering. I also will show that Raman scattering can probe two-magnon spin excitations in correlated materials. We track the evolution of these excitations as functions of momentum and doping. These results highlight the nature of spin excitations in correlated materials and are an important step in our understanding of the corresponding experiments in real materials [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J36.00013: Investigation of 1/f flux noise in SQUIDs and Superconducting Qubits Antonio Puglielli, Steven Sendelbach, Taylor Klaus, Robert McDermott Low-frequency 1/f flux noise is a dominant source of dephasing in the Josephson phase and flux qubits. Recent work has revealed the presence of a high density of unpaired spins at the surfaces of superconducting thin films; it is now believed that these spins are the source of the noise, although the microscopic noise mechanism is not understood. We have recently shown that the dielectric encapsulation of the SQUID loop substantially impacts the noise magnitude and noise exponent. Here we describe experiments on SQUIDs and Josephson phase qubits designed to shed light on the underlying noise mechanism, and we describe efforts to develop Josephson phase qubits with reduced levels of 1/f flux noise and improved dephasing times. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J36.00014: Torque magnetization study of superconducting fluctuations in single-layer cuprates: new implications for the phase diagram Guichuan Yu, R. Frink, D.-D. Xia, X. Zhao, N. Bari\v{s}i\'{c}, R.-H. He, N. Kaneko, T. Sasagawa, Y. Li, A. Shekhter, M. Greven We have studied the superconducting fluctuations above the transition temperature by angle-dependent torque magnetization in single-layer La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4}}$ (LSCO), Bi$_{\mathrm{2}}$(Sr,La)$_{\mathrm{2}}$CuO$_{\mathrm{6+\delta }}$ (Bi2201), and HgBa$_{\mathrm{2}}$CuO$_{\mathrm{4+\delta }}$ (Hg1201). The latter is a more ideal compound, with a maximum $T_{\mathrm{c}}$ of 97 K, more than twice the values for LSCO and Bi2201. In all three cases, the diamagnetic signal above $T_{\mathrm{c}}$ vanishes in an unusual exponential fashion, and at a rate that is universal, despite the dramatic differences in $T_{\mathrm{c}}$ [G. Yu \textit{et al}., arXiv:1210.6942v1]. These observations suggest that anomalies observed at much higher temperatures in both LSCO and Bi2201 are not associated with superconducting fluctuations. [Preview Abstract] |
Tuesday, March 19, 2013 5:18PM - 5:30PM |
J36.00015: Effect of thermal fluctuations in topological p-wave superconductors Bela Bauer, Roman M. Lutchyn, Matthew B. Hastings, Matthias Troyer We study the effect of thermal fluctuations on the topological stability of chiral p-wave superconductors. We consider two models of superconductors: spinless and spinful with a focus on topological properties and Majorana zero-energy modes. We show that proliferation of vortex-antivortex pairs above the Kosterlitz-Thouless temperature $T_{KT}$ drives the transition from a thermal Quantum Hall insulator to a thermal metal/insulator, and dramatically modifies the ground-state degeneracy splitting. Therefore, in order to utilize 2D chiral p-wave superconductors for topological quantum computing, the temperature should be much smaller than $T_{KT}$. Within the spinful chiral p-wave model, we also investigate the interplay between half-quantum vortices carrying Majorana zero-energy modes and full-quantum vortices having trivial topological charge, and discuss topological properties of half-quantum vortices in the background of proliferating full-quantum vortices. [Preview Abstract] |
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