Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F48: Superconductivity: General Theory 
Hide Abstracts 
Sponsoring Units: DCMP Chair: Khadijeh Najafi, Virginia Tech Room: Mile High Ballroom 1A 
Tuesday, March 3, 2020 8:00AM  8:12AM 
F48.00001: How Alfven's theorem explains the Meissner effect Jorge Hirsch Alfven's theorem states that in a perfectly conducting fluid magnetic field lines move with the fluid without dissipation. When a metal becomes superconducting in the presence of a magnetic field, magnetic field lines move from the interior to the surface (Meissner effect) in a reversible way. This indicates that a perfectly conducting fluid is flowing outward. I explain the nature of this fluid and show that it carries neither charge nor mass, but carries effective mass. This implies that the effective mass of carriers is lowered when a system goes from the normal to the superconducting state, which agrees with the prediction of the unconventional theory of hole superconductivity, with optical and photoemission experiments in some superconducting materials, and with Bardeen's first theory of superconductivity. The 60year old conventional understanding of the Meissner effect ignores Alfven's theorem and for that reason I argue that it does not provide a valid understanding of real superconductors. 
Tuesday, March 3, 2020 8:12AM  8:24AM 
F48.00002: Superconductivity induced by fluctuations of momentumbased multipoles Shuntaro Sumita, Youichi Yanase Recent studies of superconductivity have focused on spin fluctuation, instead of electronphonon coupling, as an origin of attractive interaction between electrons. 
Tuesday, March 3, 2020 8:24AM  8:36AM 
F48.00003: Multiple solutions of pairing gap equation in quantum critical metals. YiMing Wu, Artem G Abanov, Yuxuan Wang, Andrey Chubukov We use Eliashberg theory to analyze superconductivity for a class of quantumcritical models of itinerant fermions interacting with collective massless bosons, with varying scaling dimension γ of a boson (the γ model). A conventional wisdom holds that there is a single T_{c} for the pairing in a given symmetry channel. We find in this study that at the critical point the situation is different: the linearized gap equation has a cascade of solutions at T=T_{c}^{(n)} . These solutions have the same spatial symmetry, but they are topologically distinct by the number of sign changes as functions of Matsubara frequency. The transition temperatures T_{c}^{(n)} decrease exponentially with increasing number of nodes n, and the largest T_{c}^{(0) } has no nodes. We further show that below a given T_{c}^{(n)} , the corresponding solution Δ(ω_{n}) of the linearized gap equation grows in magnitude, but maintains the number of sign changes, which in this respect acts as a topological invariant. We discuss how these oscillating solutions evolve with increasing scaling dimension γ, and how they contribute to destruction of long range superconducting order. 
Tuesday, March 3, 2020 8:36AM  8:48AM 
F48.00004: The dielectric function method for superconducting materials Dietrich Elst, Sergei N. Klimin, Jacques Tempere The dielectric function method (DFM), which uses a nonadiabatic approach to calculate the critical temperatures for superconductivity, has been quite successful in describing superconductors at low carrier densities. This semiphenomenological theory uses the dielectric function of the material to describe the interelectron interaction and obtains very BCSlike equations for the superconducting gap and the critical temperature. However, DFM uses an interaction of arbitrary form, instead of a constant attraction in a Debye window as is the case for BCS. We investigate the application of DFM to the linear dispersion of single layer graphene. This is done using an interaction potential that uses the Random Phase Approximation dielectric function and thus allows for plasmonic interactions which are most relevant at low carrier doping. 
Tuesday, March 3, 2020 8:48AM  9:00AM 
F48.00005: Odd–Parity Spin–Triplet Superconductivity in Antiferromagnetic Metals Lacking Effective TimeReversal Symmetries Seung Hun Lee, BohmJung Yang We propose a route to achieve oddparity spintriplet superconductivity in metallic collinear antiferromagnets with inversion symmetry. Owing to the existence of hidden antiunitary symmetries, which we call the effective timereversal symmetries (eTRS), the Fermi surfaces of such systems are generally spindegenerate. However, by introducing a local inversion symmetry breaking perturbation that also breaks the eTRS, we can lift the degeneracy to obtain spinpolarized Fermi surfaces. In the weakcoupling limit, the spinpolarized Fermi surfaces constrain the electrons to form spintriplet Cooper pairs with oddparity. Furthermore, we find that the oddparity superconducting states host nontrivial band topology. We also solve the finitesize tightbinding models to show the boundary modes appear as a consequence of the bulk topology. 
Tuesday, March 3, 2020 9:00AM  9:12AM 
F48.00006: Suppression of superfluidity by dissipation – An application to failed superconductor Kou Misaki, Naoto Nagaosa The ground states of bosons have been classified into superfluid, Mott insulator, and bose glass. Recent experiments in twodimensional superconductors strongly suggest the existence of the fourth quantum state of Cooper pairs, i.e., bose metal or quantum metal, where the resistivity remains constant at lowest temperature. However, its theoretical understanding remains unsettled. In this talk, we show theoretically that the bosons in the dilute limit subject to dissipation can lose the superfluidity and remain metallic, utilizing the Feynman's picture of superfluidity in the first quantized formulation. This result is relevant to the quantum vortices under an external magnetic field in twodimensional superconductors with the finite resistivity of the normal core as the source of dissipation. 
Tuesday, March 3, 2020 9:12AM  9:24AM 
F48.00007: SP^{*}OT^{*} symmetry and unconventional pairing in nonHermitian superconductors Sumanta Bandyopadhyay, Alexander V Balatsky Novel physics with nontrivial topology and nodal structures emerge in the nonhermitian system. In this work, we investigate the role of damping as a mean to induce dynamics in the superconducting system. We find both odd (Berezinskii) and even (BCS) frequency (ω) states emerge as a result of damping in the superconductors. Odd ω pairing emerges as a result of SP^{*}OT^{* }symmetry ^{[1]}. To properly introduce Berezinskii classification in the nonhermitian superconductors, this classification should be extended to include particlehole conjugation (C^{*}). C^{*}SP^{*}OT^{*} =1. This symmetry constraint allows us to predict new kinds of order parameters in dynamic systems with damping. We have identified the natural occurrence of odd ω superconductivity (OFSc) in the nonhermitian systems such as odd ω swave spintriplet superconducting state. We also propose experimental observables related to OFSc in such a nonhermitian system. 
Tuesday, March 3, 2020 9:24AM  9:36AM 
F48.00008: Spontaneous TimeReversal Symmetry Breaking in unconventional Superconductors Meng Zeng, LunHui Hu, Congjun Wu Timereversal symmetry plays a crucial role in the study of unconventional superconductivity in strongly correlated systems. When two superconducting order parameters with different pairing symmetries compete, timereversal symmetry can be spontaneously broken due to a 2^{nd} order Josephson coupling between the competing order parameters. In this work, we show that timereversal symmetry breaking transition can occur due to superconducting phase fluctuations before the onset of superconductivity. To illustrate this phenomenon, we employ the GinzburgLandau theory, and use an effective twocomponent XYmodel to perform a renormalization group analysis to study superconducting phase fluctuations. In the timereversal symmetry breaking normal state, neither of the pairing orders develops phase coherence, but their relative phase is pinned at ±π/2. 
Tuesday, March 3, 2020 9:36AM  9:48AM 
F48.00009: Electromagnetic response of superconductors in the presence of multiple collective modes Rufus Boyack, Pedro Lopes Collectivemode fluctuations play an essential role in ensuring the electromagnetic response of superfluids is gauge invariant. The contribution of these fluctuations, however, is known to drop out from the Meissner response of uniform superfluids. The same phenomenon is not so established in the context of nonuniform superfluids. To clarify this issue, we revisit how collective modes appear in the Meissner effect. We find that their contributions vanish both in uniform and nonuniform systems, unless an external length scale is present  as in FuldeFerrell or finite sized superfluids. As examples, we consider $s$ and $p$wave superconductors. To facilitate this analysis, we formulate a pathintegral matrix methodology for computing the response of fermionic fluids in the presence of multiple collective modes. Closedform expressions are provided, incorporating effects from phase and amplitude of the superconducting order parameter and electronic density fluctuations. All microscopic symmetries and invariances are manifestly satisfied in this approach, and it can be straightforwardly extended to other scenarios. 
Tuesday, March 3, 2020 9:48AM  10:00AM 
F48.00010: Calculating the Superconducting Superheating Field within Eilenberger Theory Alden Pack, Mark Transtrum For Type II superconductors in an applied magnetic field, the superconducting Meissner state can persist metastably up to a theoretical maximum, "superheating field", Hsh. Superconducting Resonance Frequency (SRF) cavities are a critical component of particle accelerators for which Hsh represents a fundamental limit to performance. As the accelerator community explores materials for nextgeneration cavities, such as Nb3Sn, better estimates of Hsh are needed for candidate materials. Previous calculations have used GinzburgLandau theory (valid near Tc), however SRF cavities often operate well below the critical temperature. Extensions to Eilenberger theory (valid at all temperatures) in the highkappa and dirty limits have also been done. Here, we discuss the calculation of Hsh in Eilenberger theory in the clean limit. In addition to an accurate temperature dependence, the clean limit of the Eilenberger theory includes materialspecific parameters for the density of states at the Fermi surface. I discuss implications for SRF cavity development. 
Tuesday, March 3, 2020 10:00AM  10:12AM 
F48.00011: Enhanced Superconductivity in Quasiperiodic Crystals Zhijie Fan, GiaWei Chern, Shizeng Lin It is ubiquitous that superconductivity emerges in materials with incommensurate structure. Here we study superconductivity in a family of onedimensional incommensurate system with swave pairing interaction. The incommensurate potential changes the characteristics of the electronic wave function either to extended, critical or localized states. Through standard Bogoliubovde Gennes calculations and analytical analysis utilizing Anderson's idea of pairing the timereversed exact eigenstates, we find that superconductivity is enhanced when the electronic wave functions are critical. The superconducting transition temperature obeys an unconventional power law relation with respect to the pairing interaction. Consequently, there exists a superconducting dome around the localization transition when the amplitude of the incommensurate potential is tuned, or near the mobility edge when the chemical potential is varied. Our results suggest a way to enhance superconducting transition temperature by introducing an incommensurate potential. 
Tuesday, March 3, 2020 10:12AM  10:24AM 
F48.00012: Dynamic PairBreaking Current in Superconductors Ahmad Sheikhzada, Alexander V Gurevich We calculated a dynamic pairbreaking current density $J_d$ and a critical condensate velocity $v_d$ in a thin film superconducting strip or a filament carrying a largeamplitude ac current $J(t)=J_0\sin\omega t$. Here $J_d(T,\omega)$ and $v_d(T,\omega)$ in a dirty superconductor at $T\approx T_c$ were computed by numerical simulations of the timedependent GinzburgLandau (TDGL) equations, as well as the full timedependent Usadel and kinetic equations that take into account both a nonequilibrium distribution function of quasiparticles and nonlinear current pairbreaking effects. It is shown that superconductivity is destroyed at $J_0>J_d$, where the dynamic pairbreaking current density $J_d(T,\omega)$ approaches $\sqrt{2}J_{GL}(T)$ at $\omega\tau > 1$. Here $J_{GL}(T)$ is the GL dc depairing current density and $\tau(T)$ is the energy relaxation time of quasiparticles on phonons. Nonlinear electromagnetic response of a nonequilibrium superconductor and intermodulation at $J<J_d$ were also calculated. 
Tuesday, March 3, 2020 10:24AM  10:36AM 
F48.00013: Collective modes in Bogoliubov Fermi surfaces without gapless Goldstone modes Jay Sau, Brian Swingle We study collective modes of a finite temperature Bogoliubov Fermi surface with no symmetries. The Bogoliubov Fermi surface is assumed to form in a superconductor with Coulomb interactions, so that the plasmon is gapped and there is no low lying Goldstone mode in the system. Despite this we find the existence of a gapless second sound, which is a collective mode of energy and momentum fluctuations that is not related to any Goldstone mode. This is different from previously discussed second sound modes in either superfluids or crystals, where the second sound coexists with and is related to a spontaneously broken symmetry with a gapless Goldstone mode. Thus these modes are an example of collective modes that are solely related to conservation of energy/momentum. 
Tuesday, March 3, 2020 10:36AM  10:48AM 
F48.00014: Floquet theory of periodicallydriven superconductors Danilo Liarte, James Maniscalco, Michelle Kelley, Nathan Sitaraman, Tomas Arias, Matthias Ulf Liepe, James Patarasp Sethna We use Floquet theory to describe dynamics and losses of superconductors under extremely high fields and frequencies. Periodicallydriven superconductors at high fields provides an unexplored theoretical territory relevant in modern applications (lower cryogenic costs for particle accelerators), allowing for experimental validation using SuperconductingRadioFrequency (SRF) cavities. We use the Floquet formalism to solve the Cooper problem in the limit of strong AC fields (in which linearresponse analysis does not apply). We also discuss preliminary results combining BCS and Floquet theories to develop an experimentallyverifiable new approach for periodicallydriven superconductors that provides explanation and control of dissipation, with relevance for condensed matter physics and the ‘positive Q slope’ of SRF cavities. 

F48.00015: Effect of Defects in Superconducting Phase of Twisted Bilayer Graphene Hui Yang, ZhiQiang Gao, Fa Wang In this work we study the effect of impurity in the superconducting phases of the twisted bilayer graphene (TBG) by analysing bound states induced by the impurity. As a comparison with the superconducting phase, we first consider the impurity effect in the TBG without superconductivity in the scheme of a low energy effective theory. For superconductivity, our basis is a fourband model2 with different superconducting pairing symmetries. Then we construct the effective impurity Hamiltonian and compute the local density of state (DOS). We find that for different kind of pairing symmetries the numbers of bound states are different. These results can in principle be detected in scanning tunnelling microscopy (STM) experiments, and therefore the pairing symmetry may be determined. Finally we consider the multiimpurity effect and compute phase diagrams in terms of effective gap and the strength and density of impurities. We find that in (p + ip)wave and (d + id)wave phases superconductivity will be destroyed by impurities with strong strength or concentration 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2024 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700