Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W48: Superconductivity: Theories and Models III |
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Sponsoring Units: DCMP Room: Mile High Ballroom 1A |
Friday, March 6, 2020 8:00AM - 8:12AM |
W48.00001: On the equivalence of Peierls and Holstein models in perovskite structures Yau Chuen Yam, Mona Berciu, George Albert Sawatzky We consider the effects of electron-phonon coupling in a perovskite ABO_3, modelled in terms of uncorrelated s-orbitals on the B sites that hybridize with ligand p-orbitals at the O sites. Both the s-p and the p-p hopping matrices are modulated by vibrations of the O, described as Einstein optical phonons. For a single B0_6 cluster, we show that the effects of this Peierls electron-phonon coupling are described well in terms of an effective Holstein model, which couples the carrier to the single "molecular" phonon with A1g symmetry. For a single polaron in an infinite crystal, however, we demonstrate that the Peierls model has sharp transitions as the coupling is varied, where the ground-state momentum jumps between different high-symmetry points of the Brillouin zone. Such transitions are impossible for a Holstein model, showing that there are regions of the parameter-space where the two types of models are not equivalent. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W48.00002: Mottness induced phase fluctuation in overdoped superconducting cuprates Wei Ku, Zijian Lang, Fan Yang Recent observations of diminishing supefluid phase stiffness in overdoped cuprate hightemperature superconductors challenges the conventional picture of superconductivity. Here, through analytic estimation and verfied via variational Monte Carlo calculation of an emergent Bose liquid, we point out that Mottness of the underlying doped holes dictates a strong phase fluctuation of the supefluid at moderate carrier density. This effect turns the expected doping-increased phase stiffness into a dome shape, in good agreement with the recent observation. Specfically, the effective mass divergence due to "jamming" of the low-energy bosons reproduces the observed nonlinear relation between phase stiffness and transition temperature. Our results suggest a new paradigm, in which the high-temperature superconductivity in the cuprates is dominated by physics of Bose-Einstein condensation, as opposed to pairing-strength limited Cooper pairing. |
Friday, March 6, 2020 8:24AM - 8:36AM |
W48.00003: Ground state properties of the Emery model in the underdoped regime Adam Chiciak, Ettore Vitali, Shiwei Zhang We perform extensive Auxiliary-Field Quantum Monte Carlo (AFQMC) calculations for the three-band Hubbard (Emery) model in the underdoped regime, in order to study the ground-state properties of Copper-Oxygen planes in the cuprates. Interfacing generalized Hartree-Fock calculations with cutting-edge AFQMC techniques in a self-consistent scheme, we are able to resolve small energy scales, which is crucial for determining the complex candidate orders in such a system. We explore the charge order, spin order, and localization properties as a function of charge-transfer energy. |
Friday, March 6, 2020 8:36AM - 8:48AM |
W48.00004: A dynamical cluster approximation study of Tc in a composite superconducting-metallic two-component model. Philip Dee, Thomas Maier Can we realize enhanced Tc in a low superfluid density superconductor by coupling it to a metal? This idea, which was postulated in [1] and shown perturbatively in [2], suggests that coupling a layer with a large pairing scale Δ0 but small phase stiffness to a non-interacting metallic layer can raise Tc to its mean-field value TMF =Δ0/2. We studied this system nonperturbatively using the dynamical cluster approximation for a 2D attractive Hubbard model coupled to a noninteracting metallic layer via interlayer hopping. In contrast to prior work, our results for Tc appear only to decrease with increasing interlayer coupling. |
Friday, March 6, 2020 8:48AM - 9:00AM |
W48.00005: Effect of non-phonon modes on the isotope effect and Hall resistivity in cuprates Da Wang Non-phonon boson modes are widely observed in cuprates. Their existence may cause many interesting phenomena. In this work, we investigate their effects on the Tc isotope coefficient and Hall resistivity. (1) The coexistence of phonon and non-phonon modes leads to anomalous isotope effect. In special, if one of the boson modes (either phonon or non-phonon) is pair-breaking, large isotope coefficient α>0.5 can be obtained and a scaling of α~ln2(Tc) as Tc →0 is predicted. This study indicates that α>0.5 may be caused by pair-breaking phonon. (2) If the non-phonon boson mode is stablized by the magnetic field, the Hall coefficient shows a strong field dependence, in special near a van Hove filling. This may challenge the current understanding of the ``Hall number'': p to 1+p or p to infinity? |
Friday, March 6, 2020 9:00AM - 9:12AM |
W48.00006: Magnetic impurities as hosts of odd-frequency superconductivity Dushko Kuzmanovski, Alexander Balatsky Odd-frequency (odd-ω) superconductivity is an example of unconventional dynamical order, where the Cooper pair correlations are both non-local and odd in relative time. Historically, the most important role regarding proximity-induced odd-ω pairing was played by superconductor-ferromagnet heterostructures. Shrinking the magnetic domain of this setup to the extreme, we demonstrate that all the necessary ingredients for generating odd-ω pairing are present in the vicinity of a paramagnetic impurity embedded in a conventional single-band bulk spin-singlet s-wave superconductor. We investigate the appearance of all possible pair amplitudes in accordance with the Berezinskii SPOT = -1 rule, which in our single-orbital case, trivially has O = +1. We study the spatial and frequency dependence of components classified by spatial parity, their evolution with impurity strength, and identify a reciprocity between different symmetries related through impurity scattering. We present calculations of physically measurable observables, such as spin-polarized local density of states, local spin susceptibility that carry signatures of odd-ω in some of their features. |
Friday, March 6, 2020 9:12AM - 9:24AM |
W48.00007: Harmonic Fingerprint of Unconventional Superconductivity Michael Klett, Xianxin Wu, Tilman Schwemmer, Mario Fink, Werner R Hanke, Ronny Thomale The structure of superconducting pairing is determined by microscopic details such as the interaction profile and Fermiology beyond the spatial symmetry classification along irreducible point group representations of the underlying lattice. The pairing wave function unfolds in its orbital-resolved Fourier profile which we call the harmonic fingerprint (HFP), allowing us to formulate a concise connection between microsopic parameter changes and their impact on superconductivity. We present an analysis - based on random phase approximation calculations - of twisted bilayer graphene (TBG) involving d+id, s±, and f-wave order. Including nonlocal interactions - which unavoidably enter the low-energy electronic description of TBG - increases the weight of higher lattice harmonics and furthermore has a significant effect on the orbital structure of the paring states. |
Friday, March 6, 2020 9:24AM - 9:36AM |
W48.00008: Theory of superconductivity and anomalous Hall effect in Multi-pole system CeCu2Si2 Rina Tazai, Hiroshi Kontani In heavy fermion system, multipole degree of freedom induce interesting phenomena, such as unconventional superconductivity (SC) and Anomalous Hall Effect (AHE). Recent experiments have revealed that unconventional s-wave SC state without any sigh-reversal emerges near the AFM phase in heavy fermion compound CeCu2Si2. However, this fact cannot be explained by conventional Migdal-Eliashberg (ME) theory. To overcome this difficulty, we study the microscopic SC paring mechanism in the presence of strong spin-orbit interaction (SOI) and higher-order many body effects ignored in ME theory. As a result, we find that unconventional s-wave state is realized near the AFM phase against the strong magnetic fluctuations. Moreover, obtained s-wave SC originates from interference between electric and magnetic multipole fluctuations due to the mode coupling effects given by many body effects. In addition, we propose large AHE will be induced due to the multi-orbital nature and strong SOI in the present system. [1] R. Tazai and H. kontani, J. Phys, Soc. Jpn. 88, 063701 (2019). |
Friday, March 6, 2020 9:36AM - 9:48AM |
W48.00009: Spin-orbit coupling effects on Hund's coupling induced orbital-singlet spin-triplet superconductivity Tsung-Han Lee, Nicola Lanata, Gabriel Kotliar We study the effect of spin-orbit coupling (SOC) on the Hund's coupling induced orbital-singlet spin-triplet superconductivity in the three-orbital Hubbard model with rotationally-invariant slave-boson (RISB) mean-field theory. In the absence of SOC, RISB reproduces the phase diagram similar to the one obtained from dynamical mean-field theory, where the superconducting state emerges from the Hund's metal crossover regime. In the presence of SOC, the intrinsic particle-hole asymmetry in atomic levels, introduced by SOC, leads to different superconducting behaviors for above and below half-filling; the SOC suppresses the superconductivity in these two regimes with distinct manners. We analyze how these behaviors are connected to the spin and charge fluctuations and the atomic multiplets statistics. Our results provide insight into the pairing mechanism in Sr2RuO4 and iron-based superconductors. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W48.00010: Influence of the Rutgers Relation on underdoped cuprate properties Patricia Salas Casales, M. A. Solís Within the extended Layered Boson-Fermion Model of Superconductivity [1,2] the Rutgers Relation, which relates the diference between the normal and the superconducting isobaric specific heats with the thermodynamic critical field, is combined with the first-principles relation of the critical field derivative as well as with the penetration and coherence lengths to get a novel expression for the penetration length λ(T), which is more suitable for high temperature superconductors, as we have seen after applying it to underdoped cuprate superconductors YBa2Cu3O6+x. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W48.00011: DMRG and weak coupling studies of the two-leg Hubbard ladder Yuval Gannot, Yi-Fan Jiang, Steven Kivelson The Hubbard model is of paradigmatic significance in the study of highly correlated electron systems. Hubbard ladders are particularly interesting as they exhibit a subtle interplay between multiple phases even at weak coupling. Here, we reexamine the ground state phase diagram of the two-leg ladder in the limit of asymptotically weak coupling, an approach pioneered by Balents and Fisher (BF). Among other things we find that the presence of a dangerously irrelevant operator leads to an instability of a previously predicted partially gapped phase. The result is a Luther-Emery (LE) liquid - the 1D analogue of a superconductor - characterized by a hierarchy of energy scales: the principle gap depends exponentially on 1/U in the asymptotic U → 0+ limit, as found by BA, while the additional gaps are smaller still by factors of U1/2 compared to the dominant gap. Using DMRG to study the same ladder for intermediate values of U (as small as U = 4t), we find qualitative behavior (LE phase and the existence of two distinct gap scales) similar to that predicted by the weak coupling theory. |
Friday, March 6, 2020 10:12AM - 10:24AM |
W48.00012: Beyond s- and d-waves: d + d intra- and inter-band pairing in multi-band superconductors Qimiao Si, Emilian Nica Recent experiments in multi-band Fe-based and heavy-fermion superconductors have challenged the long-standing dichotomy between standard s- and d-waves. We discuss an alternative in the form of a gapped d + d intra- and inter-band pairing which provides a natural interpolation between standard s and d-waves. We illustrate that this is equivalent to an sτ3 pairing initially proposed in the context of Fe-based superconductors [1]. We demonstrate that similar candidates are possible outside of the Fe-based family by constructing an analog for |
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