Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G22: Superconductivity: Theory-II |
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Sponsoring Units: DCMP Chair: Yuli Lyanda-Geller, Purdue University Room: Room 214 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G22.00001: Pairing in 3D fermions with repulsive and non-local interactions: A tractable crossing-symmetric approach Kelly E Reidy, Thomas Ainsworth, Khandker F Quader Recent discoveries of superconductivity in novel strongly interacting systems and the prospect of unconventional pairing have generated great interest. We study general nature of pairing in strongly interacting 3D Fermi systems, with underlying repulsive and non-local interactions, using a diagrammatic crossing-symmetric equations method. This allows for the treating of competing density, spin, and current fluctuations in a self-consistent fashion, resulting in renormalized Fermi liquid interactions and, therefrom, obtaining pairing amplitudes in different angular momentum channels (viz. s, p, d). While repulsive interactions result in non-s-wave pairing, non-local interactions play important role in enhancing certain quantum fluctuations and determining the pairing symmetry, namely, switching from p-wave to s-wave pairing for sufficiently repulsive non-local interaction; and to a narrow region of d-wave pairing in the attractive case. The s-wave pairing is driven by transverse current fluctuations competing with ferromagnetic spin fluctuations, and the d-wave pairing by antiferromagnetic-like spin fluctuations. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G22.00002: Eliashberg theory in the uniform electron gas revisited Ryosuke Akashi The Eliashberg theory with the Migdal approximation has been established as a standard ab initio theory for phonon-mediated superconductor. But accurate treatment of electron-electron Coulomb interaction effects there has remained under debate. Historically the electronic interaction in nearly uniform superconductors has been of interest in the context of the plasmon superconductivity, whereas the recent interest is on a more quantitative aspect: to which extent it finally suppress or enhance Tc on top of the phonon-mediated pairing attraction. The latter is wholly a quantitative problem but has become important with the recent invention of high-temperature hydride superconductors, where the treatment of the pairing interactions affects the estimated Tc by several ten Kelvin. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G22.00003: Multiorbital superconductivity mediated by transverse optical phonons Gaurav Chaudhary, Ivar Martin Electron-phonon coupling that is responsible for most BCS superconductors typically involves longitudinal phonon mode. For the transverse phonons, typically the electron-phonon coupling vanishes to the first order. This limitation can be overcome for multi-orbital systems, where first order electron-phonon coupling can be induced in the inter-orbital channel. Here on the symmetry grounds, we present some general properties of such TO mode induced multi-orbital superconductivity. We also show that TO mode induced robust superconductivity can be stabilized even in the absence of the spin-orbit coupling, which has been the focus of the previous studies on the TO mode induced superconductivity. Using our theory for the specific case of doped quantum paraelectrics SrTiO3 and KTaO3, we highlight the relative role of spin-orbit coupling and multi-orbital physics to explain the aspects of the superconductivity in these materials. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G22.00004: Superconducting states in doped cuprates from ab initio quantum embedding Zhi-Hao Cui, Garnet K Chan Following the previous work on the electronic structure of cuprate parent states [Science 377, 1192 (2022)], we extend the ab initio quantum embedding theory to particle-number symmetry broken systems. In this talk, we will describe the application of the ab initio superconductivity formalism to the doped cuprates, without resorting to simplified models. We will show that the superconducting orders can spontaneously emerge not only in model systems but also in realistic materials with doping. We find that the multi-orbital d-wave superconducting magnitude increases with the external pressure applied to crystals and the trend connects to the magnetic degrees of freedom. Furthermore, we also explore the buffer layer effect in the single-layer and infinite-layer compounds. The work provides a promising route to study material-specific physics in high-temperature superconductivity. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G22.00005: On the Origin of Coulomb Pseudopotential: Two Wrongs Make a ``Right" Tao Wang, Xiansheng Cai, Kun Chen, Nikolay Prokof'ev, Boris Svistunov We address the outstanding problem of electron pairing in the presence of strong Coulomb repulsion at small to moderate values of the Coulomb parameter, r_s ≤ 2, and demostrate that the pseudopotential framework is fundamentally biased and uncontrolled. Instead, one has to break the net result into two distinctively different effects: the Fermi-liquid renormalization factor and the change of the effective low-energy coupling. The latter quantity is shown to behave non-monotonically with an extremum at r_s ≈ 0.75. Within the random-phase approximation, Coulomb interaction starts to enhance the effective pairing coupling at r_s >2 and the suppression of the critical temperature is entirely due to the renormalized Fermi-liquid properties. Leading vertex corrections change this picture only quantitatively. Our results call for radical reconsideration of the widely accepted repulsive pseudopotential approach, and the need for precise microscopic treatment of Coulomb interactions in the problem of superconducting instability. |
Tuesday, March 7, 2023 12:30PM - 12:42PM Author not Attending |
G22.00006: Robust d-wave superconductivity from the Su-Schrieffer-Heeger-Hubbard model: possible route to high-temperature superconductivity Hong Yao, Hao-Xin Wang, Yi-Fan Jiang Increasing numerical studies showed that the pure Hubbard model on the square lattice with strong repulsion may not exhibit high-temperature superconductivity (SC). |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G22.00007: Superconductivity out of a non-Fermi liquid. Free energy analysis. Shang-Shun Zhang, Andrey V Chubukov, Artem G Abanov, Yi-Ming Wu We present an in-depth analysis of the condensation energy for a superconductor in a situation when superconductivity emerges out of a non-Fermi liquid due to pairing mediated by a massless boson. This is the case for electronic-mediated pairing near a quantum-critical point in a metal, for pairing in SYK-type models, and for phonon-mediated pairing in the properly defined limit, when the dressed Debye frequency vanishes. We consider a subset of these quantum-critical models, in which the pairing in a channel with a proper spatial symmetry is described by an effective 0+1 dimensional model with the effective dynamical interaction V(Ωm)=1/[Ωm]γ, where γ is model-specific (the γ-model). We have argued that the pairing in the γ-model is qualitatively different from that in a Fermi liquid, and the gap equation at T=0 has an infinite number of topologically distinct solutions, Δn(ωm), where an integer n, running between 0 and infinity, is the number of zeros of Δn(ωm) on the positive Matsubara axis. This gives rise to the set of extrema of the condensation energy at each solution, of which the sign-preserving solution is the global minimum. The condensation spectrum is discrete for a generic γ<2, but becomes continuous at γ= 2-0. We discuss the profile of the condensation energy near each saddle point and the transformation from a discrete to a continuous spectrum as γ approaches 2. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G22.00008: Local condensation of charge-4e superconductivity at a nematic domain wall Matthias Hecker, Rafael M Fernandes, Roland Willa, Joerg Schmalian Multi-component superconductivity is realized in various materials, such as doped Bi2Se3 and possibly twisted bilayer graphene. This type of superconductivity naturally generates bilinear composite order parameters that are either nematic, time-reversal symmetry-breaking (TRSB), or even charge-4e superconducting – the latter remains an elusive quantum state of matter. Here, to determine whether charge-4e order can emerge above the superconducting transition temperature, we consider a paradigmatic two-component superconductor in a tetragonal crystal. By solving this model with a variational approach, we find that although the s- and d-wave charge-4e pairing channels can be attractive, they are always subleading to an instability towards nematic or TRSB order. Nevertheless, using a real-space variational method, we find that charge-4e order can locally condense in the vicinity of a nematic domain wall, where the competing nematic order naturally melts. We assess the conditions under which this scenario is realized, and discuss its experimental manifestations. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G22.00009: Magnetization amplification in interlayer superconductivity Chunxiao Liu, Shubhayu Chatterjee, Thomas Scaffidi, Erez Berg, Ehud Altman A recent experiment on the bulk compound 4Hb-TaS$_2$ reveals an unusual time-reversal-symmetry-breaking superconducting state that possesses a magnetic memory not manifest in the normal state [1]. Here we provide a possible mechanism for this observation by studying the magnetic and electronic properties of 4Hb-TaS$_2$. We discuss the criterion for a vanishingly small magnetization in the normal state in terms of the spin and orbital magnetizations. Based on 4Hb-TaS$_2$'s centrosymmetry and Fermi surface structure, we propose a simple mechanism that gives rise to the experimentally observed magnetic memory in the 4Hb-TaS$_2$ superconducting state: ferromagnetism mediated interlayer superconductivity that leads to amplified magnetization in the superconducting state. We discuss how this superconducting state can be probed experimentally in terms of spin polarized superconducting vortices. |
Tuesday, March 7, 2023 1:18PM - 1:30PM Author not Attending |
G22.00010: Superconductivity mediated by longitudinal hybrid-polar-modes in doped ferroelectrics Stephen E Rowley Quantum phase transitions may be reached in many ferroelectric systems by supressing the Curie temperature to absolute zero using a quantum tuning parameter such as chemical substitution or hydrostatic pressure. We present experimental and model results revealing the nature of the quantum critical regime which persists over wide ranges in temperature and tuning parameter and includes a low temperature quantum polar-elastic phase. The occurrence of superconductivity in electron-doped SrTiO3 and related materials at low carrier densities points to the presence of an unusually strong pairing interaction that has puzzled scientists for several decades. We discuss new experiments on the pressure dependence of the resistivity and superconducting transition temperature, Tc, that sheds light on the nature of the interaction. We find that Tc increases dramatically when the energy gap of ferroelectric critical modes is suppressed, i.e., as the ferroelectric quantum critical point is approached, in a way reminiscent of behaviour observed in magnetic counterparts. However, in contrast to the latter, the coupling of itinerant electrons to the critical modes in ferroelectrics is predicted to be small. We present a superconductivity model to make quantitative comparisons with experiments and show that an enhancement of Tc near to a ferroelectric quantum critical point arises due to the virtual exchange of longitudinal hybrid-polar-modes, even in the absence of a direct coupling to the transverse critical modes. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G22.00011: Phononic Role of Alkaline-earth Metal in High Tc Cuprate Superconductors Sungwoo Lee, Woojin Choi, YeongJae Kim, Gun-Do Lee Although many years have passed since the discovery of high Tc superconductors, the underlying mechanism is still unknown. The B1g phonon anomaly in high Tc cuprate has been studied for a long time, but the correlation between the B1g anomaly and the superconductivity has not yet been revealed clearly. In here, we reproduced successfully B1g anomaly in YBa2Cu3O7 (YBCO) using ab initio molecular dynamics simulation and temperature-dependent effective potential method. Beside B1g anomaly, it is found that Ag mode by Ba atoms showed a more severe anomaly than B1g mode and most out-of-plane modes were suppressed at low temperatures. We also found that Ba atoms are electronically and thermally isolated in YBCO at low temperatures. Ba atoms play an important phononic role in heat phenomena in YBCO. We also reveal that the distance between Ba atom and CuO2 plane is closely related to the superconducting dome. Our findings could present a new paradigm for the understanding of high Tc superconductivity. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G22.00012: Anisotropic Thermal Transport in Superconductors with Coexisting Spin Density Waves Sean Peterson, Yves U Idzerda Thermal conductivity measurements can provide key and experimentally verifiable insight into the electronic transport of unconventional superconductors. In this work, electronic thermal transport of two-dimensional tight-binding metallic systems with coexisting s- or d-wave superconducting (SC) and antiferromagnetic spin density wave (SDW) orders with nesting vector Q = (π/2,π/2) or (π,0) are considered. The coexisting SC and SDW orders are modelled at the mean-field level. Thermal conductivities are numerically calculated within Boltzmann kinetic theory in the weak impurity scattering (Born) limit. These SDW nesting vectors are chosen for their unique property of anisotropically gapping the Fermi surface (FS) parallel to Q and preserving the metallic FS perpendicular to the nesting vector. This leads to anisotropic electronic thermal conductivities parallel and perpendicular to Q, which also depend on the presence or absence of additional gapless excitations exclusive to the coexistence phase. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G22.00013: The Wiedemann-Franz law in doped Mott insulators without quasiparticles Wen O Wang, Jixun K Ding, Yoni Schattner, Edwin W Huang, Brian Moritz, Thomas Devereaux Many metallic quantum materials display anomalous transport phenomena violating Fermi liquid and Boltzmann theory. We discuss transport in the doped Hubbard model where we observe a cross-over separating high- and low-temperature behavior in both thermal and charge transport. Distinct from the incoherent behavior at high temperatures, as T→0, the Lorenz number obeys the Wiedemann-Franz law, even in a doped Mott insulator that lacks well-defined quasiparticles. By analyzing contributions to thermal diffusivity, we find that the potential energy strongly affects thermal transport at high temperatures, while at low temperatures, the behavior of both thermal and charge transport is controlled primarily by the electronic kinetic energy. Our result helps to clarify the interpretation of transport experiments beyond Boltzmann theory in non-Fermi liquid strange metals. |
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