Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W52: Superconductivity: General Theory |
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Sponsoring Units: DCMP Chair: Ronny Thomale, University of Wurzburg Room: Mile High Ballroom 1F |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W52.00001: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W52.00002: Nodeless versus Nodal Scenarios of Possible Triplet Superconductivity in the Quasi-One-Dimensional Layered Conductor Li$_{0.9}$Mo$_6$O$_{17}$ Otar Sepper, Andrei Lebed We solve a theoretical problem of the upper critical magnetic field, parallel to a conducting axis of a layered, quasi-one-dimensional (Q1D) superconductor. In particular, we consider two cases: a triplet superconducting order parameter with and without zeros on the Q1D Fermi surface. We demonstrate [1,2] that the orbital destructive effects can destroy the superconducting state with parallel magnetic fields much higher than the so-called Clogston-Chandrasekhar paramagnetic limit, and that the nodeless order parameter is in a better quantitative agreement with the recent experimental data [3]. Our results indicate strong evidence in favor of triplet superconducting pairing in the layered Q1D superconductor Li$_{0.9}$Mo$_6$O$_{17}$. This work was supported by the NSF under Grant DMR-1104512.\\[4pt] [1] O. Sepper and A. G. Lebed, Phys. Rev. B 88, 094520 (2013.)\\[0pt] [2] A. G. Lebed and O. Sepper, Phys. Rev. B (Rapid Communications) 87, 100511(R) (2013).\\[0pt] [3] J. F. Mercure et al., Phys. Rev. Lett. 108, 187003 (2012). [Preview Abstract] |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W52.00003: Superconductivity and Gutzwiller correlations in a two band Hubbard-Fr\"{o}hlich model Tao Qin, Michele Fabrizio, S. Shahab Naghavi, Erio Tosatti We studied the two-band Hubbard-Fr\"{o}hlich model with the hopping parameters from the first-principle calculation for La-Phenanthrene. The mean-field approximation shows that two-band superconductivity with opposite signs is possible even with the presence of a large Hubbard $U$. Using Gutzwiller approximation, we show that the Hubbard $U$ can help the superconductivity in this system. When $U$ is too large, it will go into the insulator state. Roughly, we determined the critical $U$ for this superconductor-insulator (SI) transition. We further shows that before the SI transition, the antiferromagnetic order will come into being. However, there is still a large range of $U$ for the superconductivity to win. We also discussed the possibility to apply our model to other polycyclic aromatic hydrocarbons. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W52.00004: A $\frac{1}{4}$-filled band model for the organic superconductor $\kappa$-(ET)$_2$X R. Torsten Clay, S. Mazumdar The minimal model usually assumed for the conducting layers of the organic charge transfer solid superconductor $\kappa$-(ET)$_2$X is a $\frac{1}{2}$-filled anisotropic triangular lattice Hubbard model, where a dimer of molecules is replaced with a single effective site. Within this frustrated $\frac{1}{2}$-filled model a metal to antiferromagnetic (AFM) phase transition is found, but calculations beyond the mean field level do not find evidence for superconductivity. Recent dielectric constant measurements suggest that a coupling is present between AFM order and ferroelectric charge ordering. Such a charge order would lead to unequal charge densities on the ET molecules within each dimer and can not be described within the effective model. We present the results of correlated calculations on the full $\frac{1}{4}$-hole-filled $\kappa$-(ET)$_2$X lattice using the Path Integral Renormalization Group (PIRG) method. We show that AFM order does occur within the $\frac{1}{4}$-filled model and investigate the possibility that charge order can cooperatively enhance the AFM state. We further present results for superconducting pair-pair correlations within this model. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W52.00005: Chiral p-wave superconductivity in 2D lattices of magnetic atoms on a superconductor Jian Li, Bogdan Bernevig We investigate chiral p-wave superconductivity in 2D lattices of magnetic atoms on an s-wave superconductor. We identify criteria of obtaining topologically nontrivial phases in such systems. In particular, we prove that a non-commuting helix pattern along the x and y directions is a necessary condition. When such a condition is satisfied, the system displays a rich phase diagram that generically allows for an arbitrary Chern number. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W52.00006: First-order chiral to non-chiral transition in the angular dependence of the upper critical induction of the Scharnberg-Klemm $p$-wave pair state Richard Klemm, Jingchuan Zhang, Christopher Lorscher, Qiang Gu We calculate the temperature $T$ and angular $(\theta,\phi)$ dependence of the upper critical induction $B_{c2}(\theta,\phi,T)$ for parallel-spin superconductors with an axially symmetric $p$-wave pairing interaction pinned to the lattice and a dominant ellipsoidal Fermi surface (FS). When both parallel-spin states are allowed, the chiral Scharnberg-Klemm state $B_{c2}(\theta,\phi,T)$ exceeds that of the chiral Anderson-Brinkman-Morel state for all FS anisotropies, and exhibits a kink at $\theta=\theta^{*}(T,\phi)$, indicative of a first-order transition from its chiral, nodal-direction behavior to its non-chiral, antinodal-direction behavior. Potential applicability to Sr$_2$RuO$_4$, UCoGe, and topological superconductors is discussed. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W52.00007: Theory of the magnetic ground states of TMTTF$_2$X Andrew Ward, R. Torsten Clay, Sumit Mazumdar As a function of pressure the ground state of the TMTTF$_2$X salts is either one of two different antiferromagnetic (AFM) phases, spin-Peierls (SP), or superconducting. Pressure is usually thought to increase the dimensionality of the TMTTF stacks. The occurrence of the SP phase is then counterintuitive, as it enters at higher pressure than the first AFM state. Here we examine a model for the pressure dependent phase of TMTTF$_2$X salts, the extended Hubbard model on a two dimensional lattice with inter- and intra-site electron-phonon coupling. Previous calculations have suggested that two distinct SP phases with different charge and bond distortions occur in this model. We argue that two distinct SP phases are not supported by experiment, and are a result of unsuitable parameter choices and finite-size effects within calculations. We present the results of further numerical calculations and investigate the effect of magnetic frustration on the AFM and SP phases. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W52.00008: Enhanced anti-ferromagnetic exchange between magnetic impurities in a superconducting host Jay Sau, Norman Yao, Leonid Glazman, Eugene Demler, Mikhail Lukin It is generally believed that superconductivity only weakly affects the indirect exchange between magnetic impurities. If the distance $r$ between impurities is smaller than than the superconducting coherence length $(r<\xi)$, this exchange is thought to be dominated by RKKY interactions, identical to the those in a normal metallic host. This perception is based on a perturbative treatment of the exchange interaction. Here, we discuss a non-perturbative analysis and demonstrate that the presence of Yu-Shiba-Rusinov bound states induces a strong $1/r^2$ anti-ferromagnetic interaction that can dominate over conventional RKKY even at distances significantly smaller than the coherence length $(r\ll\xi)$. Experimental signatures, implications and applications are discussed. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W52.00009: Unconventional Superconductivity in TiSe$_2$: a renormalization group approach R. Ganesh, Dmitry Efremov, Jeroen van den Brink, G. Baskaran TiSe$_2$ is a quasi-two dimensional material which hosts CDW and superconducting orders. Motivated by recent studies of single-layer transition metal dichalcogenides, we study the effect of electronic correlations in single-layer TiSe$_2$. This is a hexagonal system with an elegant band structure -- one hole-like Fermi pocket and three electron-like pockets at the edge centres of the Brillouin zone. We use Renormalization Group (RG) analysis to examine low energy interactions in this configuration. RG flow is governed by three fixed points corresponding to different long range orders: (i) The most exciting fixed point corresponds to `chiral superconductivity' -- the three electron-like pockets undergo pairing but each pair of Fermi pockets differs in phase by 2$\pi$/3. The phase increases as we move clockwise or anticlockwise. The state breaks time reversal symmetry and has interesting properties. (ii) Another fixed point corresponds to s$_{+-}$ superconductivity, in which the order parameter on the central pocket has its sign reversed. (iii) The third fixed point corresponds to CDW order. We discuss situations in which RG flow may be cutoff, possibly also giving SDW order. We suggest that TiSe$_2$ may host one of two possible superconducting orders, both unconventional. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W52.00010: Spin-orbit scattering in inhomogeneous superconductors Charles Agosta, Daniel Ellowitz, Steven Butler, Evan Palmer Spin-orbit scattering is important in all superconductors (SC) to understand the critical magnetic field. In most SC, the application of a magnetic field will eventually destroy the SC mostly due to the formation of vortices. At higher fields, when the Zeeman Energy is closer to the SC energy gap, singlet Cooper pairs are separated due to Pauli paramagnetism. One would expect that when the magnetic energy equals the SC energy gap, all SC would be destroyed, and that limit is called the Chandrasakhar-Clogston Pauli paramagnetic limit. In the case that the orbital effects can be suppressed, Pauli paramagnetism can become the dominant cause of the destruction of SC, and an inhomogeneous SC can result. An inhomogeneous SC has an order parameter with nonzero pair momentum that oscillates periodically as a function of distance, unlike traditional SC where the order parameter is uniform. Furthermore, an inhomogeneous SC can form an exotic SC state above the paramagnetic limit. We have studied a class of anisotropic organic SC that have an exotic inhomogeneous SC state. Spin-orbit scattering has a strong affect on Pauli paramagnetism and must be taken into account carefully when developing model theories. We will discuss how we extract spin-orbit scattering amplitudes from our data. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W52.00011: Effects of columnar defects on fluctuation phenomena in superconductors Alexey Galda, Alexei Koshelev, Andrey Varlamov We investigate thermodynamic properties of superconducting materials with columnar defects in presence of external magnetic field. The defects, which can be produced by ion irradiation, have a dramatic effect on vortex pinning and critical parameters of the superconductor. We account for superconducting fluctuations in the system and calculate their effect on thermodynamic properties (e.g. specific heat, etc.) The results are valid for high-T$_{\mathrm{c}}$ superconductors. We compare our results with the recent experiments. [Preview Abstract] |
Thursday, March 6, 2014 4:42PM - 4:54PM |
W52.00012: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 4:54PM - 5:06PM |
W52.00013: The Casimir effect across a superconducting transition Zachary Raines, Andrew Allocca, Victor Galitski We show that Casimir effect can be used as a means to probe electronic correlations. In particular, we consider an interacting electron system which undergoes a superconducting transition and calculate the Casimir force it exerts on a normal metal. We found an interesting non-analytic behavior of the Casimir force as a function of temperature across the superconducting transition. [Preview Abstract] |
Thursday, March 6, 2014 5:06PM - 5:18PM |
W52.00014: Hall conductivity in the normal and topological superconducting phases of the Rashba system Suk Bum Chung, Rahul Roy The study of the intrinsic Hall conductivity in superconductors is attracting considerable theoretical and experimental efforts in recent years. In this paper we focus on the effect of Cooper pairing on a metallic system with non-zero intrinsic Hall conductivity - the Rashba metal with under the perpendicular Zeeman field. We find that there is a qualitatively larger change in the intrinsic Hall conductivity when there is interband pairing, with the change in magnitude linear in the pairing gap. Since the topologically non-trivial phase is unlikely to allow for significant interband pairing, our work leads to an interesting prediction : that the observation or lack thereof of the linear dependence of the intrinsic Hall conductivity on the pairing gap could be used to determine if the Rashba superconductor is topologically trivial or not. Our results are consistent with other investigations of interband pairing in the context of the proposed chiral $p$-wave superconducting state of Sr$_2$RuO$_4$. [Preview Abstract] |
Thursday, March 6, 2014 5:18PM - 5:30PM |
W52.00015: Gravity at a Kelvin: the generalized rigidity of superconducting quantum nematics Kai Wu, Aron Beekman, Vladimir Cvetkovic, Jan Zaanen There is experimental evidence for the existence of zero temperature nematic quantum liquids. Resting on field theoretic dualities we demonstrate that its rigidity theory is closely related to linearized gravity. The difference is in the loss of Lorentz invariance and we show that the gravitons merge into a richer world of collective excitations such as rotational Goldstone modes deconfining at the crystal-nematic phase transition, yet to be detected experimentally. [Preview Abstract] |
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