Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S57: Superconductivity: Unconventional TheoriesIIIRecordings Available

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Sponsoring Units: DCMP Chair: Yao Wang, Clemson University Room: Hyatt Regency Hotel Clark 
Thursday, March 17, 2022 8:00AM  8:12AM 
S57.00001: Unconventional superconductivity in systems with annular Fermi surfaces: Application to rhombohedral trilayer graphene Erez Berg, Areg Ghazaryan, Tobias Holder, Maksym Serbyn We show that in a twodimensional electron gas with an annular Fermi surface, longrange Coulomb interactions can lead to unconventional superconductivity by the KohnLuttinger mechanism. Superconductivity is strongly enhanced when the inner and outer Fermi surfaces are close to each other. The most prevalent state has chiral pwave symmetry, but dwave and extended swave pairing are also possible. We discuss these results in the context of rhombohedral trilayer graphene, where superconductivity was recently discovered in regimes where the normal state has an annular Fermi surface. Using realistic parameters, our mechanism can account for the order of magnitude of $T_c$, as well as its trends as a function of electron density and perpendicular displacement field. Moreover, it naturally explains some of the outstanding puzzles in this material, that include the weak temperature dependence of the resistivity above $T_c$, and the proximity of spin singlet superconductivity to the ferromagnetic phase. 
Thursday, March 17, 2022 8:12AM  8:24AM 
S57.00002: PolaronPlasmon Superconductivity in Strontium Titanate Alexander Edelman, Peter B Littlewood Strontium titanate (STO) is a bulk insulator that becomes a semiconducting superconductor at remarkably low carrier densities  below 10^{17} cm^{3}  with a characteristic superconducting dome as a function of doping which peaks at T_{c}~300mK, all in very close proximity to a ferroelectric quantum critical point. We investigate a scenario of superconductivity mediated by coupling to a strongly antiadiabatic longitudinal optic phonon, by extending a Fröhlich electronphonon Hamiltonian to include the effects of electronic Coulomb interactions. For the carrier densities of interest, there is a "cavity enhancement" of superconductivity by the material's own plasmons, which hybridize strongly with LO mode. Working within the cumulant expansion, we calculate the spectral signatures of this unusual regime to compare to photoemission[1] and tunneling[2] experiments, as well as the superconducting phase diagram. 
Thursday, March 17, 2022 8:24AM  8:36AM 
S57.00003: Lifetime of Scattering of Quasiparticles by Dipolons for Muon Spin Relaxation Rates in High Temperature Superconductors via Dipolon Theory Ram R sharma

Thursday, March 17, 2022 8:36AM  8:48AM 
S57.00004: Ground State Phase Diagram of the $t$$t'$$J$ Model Shengtao Jiang, Douglas J Scalapino, Steven R White We report results of large scale ground state density matrix renormalization group(DMRG) calculations on $t$$t'$$J$ cylinders with circumferences 6 and 8. We determine a rough phase diagram which appears to approximate the 2D system. While for many properties, positive and negative $t'$ values ($t'/t = \pm 0.2$) appear to correspond to electron and hole doped cuprate systems, respectively, the behavior of superconductivity itself shows an inconsistency between the model and the materials. The $t'<0$ (hole doped) region shows antiferromagnetism limited to very low doping, stripes more generally, and the familiar Fermisurface of the hole doped cuprates. However, we find $t'<0$ strongly suppresses superconductivity. The $t'>0$ (electron doped) region shows the expected circular Fermi pocket of holes around the $(\pi,\pi)$ point and a broad lowdoped region of coexisting antiferromagnetism and $d$wave pairing with a triplet $p$ component at wavevector $(\pi,\pi)$ induced by the antiferromagnetism and $d$wave pairing. The pairing for the electron lowdoped system with $t'>0$ is strong and unambiguous in the DMRG simulations. At larger doping another broad region with stripes in addition to weaker $d$wave pairing and striped $p$wave pairing appears. In a small doping region near $x=0.08$ for $t'\sim0.2$, we find a new type of stripe involving unpaired holes located predominantly on chains spaced three lattice spacings apart. The undoped twoleg ladder regions in between mimic the shortranged spin correlations seen in twoleg Heisenberg ladders. 
Thursday, March 17, 2022 8:48AM  9:00AM 
S57.00005: Robustness of superconductivity in the twoorbital Hubbard chain Pontus Laurell, Gonzalo Alvarez, Elbio R Dagotto Motivated by recent findings of both spinsinglet and spintriplet pairing in onedimensional multiorbital Hubbard models at intermediate interaction strengths [N. Patel et al., npj Quantum Mater. 5, 27 (2020)], we study the robustness of the superconducting phases in the twoorbital Hubbard chain. At halffilling, the model maps to the Haldane spin1 chain in the limit of large Hubbard U and Hund's coupling J_{H}, whereas superconductivity emerges upon hole doping. Here we consider the system away from the ideal limit of unit hopping and degenerate orbitals. Using DMRG calculations we explore the effects of interorbital hopping, detuned intraorbital hopping, and crystal fields expected to be present in real materials. We find that while these effects are all detrimental to the emergence of superconductivity, the presence of onsite easyplane anisotropy tends to promote hole pairing. We discuss their impact on the pairing symmetry and phase diagram. 
Thursday, March 17, 2022 9:00AM  9:12AM 
S57.00006: Superconducting pairing correlations in the 2D Hubbard model with next nearest hoping. Hao Xu, ChiaMin Chung, Mingpu Qin, Ulrich J Schollwoeck, Steven R White, Shiwei Zhang We study the superconducting pairing correlations in the ground state of the twodimensional doped Hubbard models  with nearest hoping t and next nearest hoping t'. Following the previous work on the pure Hubbard model, we again employ two computational methods, auxiliary field quantum Monte Carlo (AFQMC) and density matrix renormalization group (DMRG). These methods complement each other, and provide a powerful combination to tackle this challenging problem, where the results are sensitive to numerical details and finite size effects. We deploy our latest algorithmic advances, including a more robust procedure for self consistent constraint in AFQMC and the use of twist average boundary conditions. As a result, we achieve much higher accuracy than previously possible. We present detailed and systematic studies of the superconducting order parameter in the ground state for a number of parameter sets (t', U/t, doping), and discuss its interplay with magnetic and charge orders. 
Thursday, March 17, 2022 9:12AM  9:24AM 
S57.00007: Emergent Supersymmetry at the Boundaries in 1D Charge Conserving Superconductor Coupled to Magnetic Impurities Parameshwar R Pasnoori, Colin Rylands, Natan Andrei, Patrick Azaria Interaction induced symmetry protected topological phases exhibit distinct properties which do not exist in the non interacting limit. The topological properties emerge due to strong correlations in the bulk. A well known example is a 1D charge conserving superconductor in the spin triplet phase (STS) with open boundary conditions which features a topological phase with protected Majorana zero modes at the edges. Here we consider a superconductor in the spin singlet phase (SSS) which is considered to be topologically trivial. However upon coupling it to magnetic impurities at the two edges a topological phase will emerge induced by the interplay between the bulk and impurity fluctuations. This phase also exhibits an emergent supersymmetry at the edges in a particular regime of the boundary parameters. We discuss the effect of external fields at the edges that break the supersymmetry and reduces the topological structure to that exhibited by the STS phase 
Thursday, March 17, 2022 9:24AM  9:36AM 
S57.00008: Intertwined spin, charge and pair correlations in the twodimensional Hubbard model in the thermodynamic limit Peizhi Mai, Seher Karakuzu, Giovanni Balduzzi, Steven S Johnston, Thomas A Maier The hightemperature superconducting cuprates are governed by intertwined spin, charge, and superconducting orders. While various stateoftheart numerical methods have demonstrated that these phases also manifest themselves in doped Hubbard models, they differ on which is the actual ground state. Finite cluster methods typically indicate that stripe order dominates while embedded quantum cluster methods, which access the thermodynamic limit by treating longrange correlations with a dynamical mean field, conclude that superconductivity does. Here, we report the observation of fluctuating spin and charge stripes in the doped singleband Hubbard model using a quantum Monte Carlo dynamical cluster approximation (DCA) method. By resolving both the fluctuating spin and charge orders using DCA, we demonstrate that they survive in the doped Hubbard model in the thermodynamic limit. This discovery also provides a new opportunity to study the influence of fluctuating stripe correlations on the model's pairing correlations within a unified numerical framework. Using this approach, we also find evidence for pairdensitywave correlations whose strength is correlated with that of the stripes. 
Thursday, March 17, 2022 9:36AM  9:48AM 
S57.00009: Higher angular momentum pairings in interorbital shadowedtriplet superconductors: Application to Sr_{2}RuO_{4} Jonathan Clepkens, Austin W Lindquist, Xiaoyu Liu, HaeYoung Kee In multiorbital systems with significant Hund’s and spinorbit coupling, evenparity interorbital spintriplet pairing emerges as a relevant instability. Spinorbit coupling generates an intraband pseudospinsinglet component of pairing, resulting in both singlet and triplet character and can also influence the pairing symmetry [1]. A natural question is whether higher angular momentum pairing symmetries such as d and gwave, proposed in candidate systems, can be realized from local spintriplet pairing. We examine the interplay between spinorbit coupling and the electronic dispersions in correlated metals such as Sr_{2}RuO_{4} to demonstrate how they can be realized. The competition among pairing states is determined as multiple spinorbit coupling parameters are tuned, and the presence of both d and gwave pairings, including a d+ig state, are found when the spinorbit coupling with dwave character is increased [2]. 
Thursday, March 17, 2022 9:48AM  10:00AM 
S57.00010: Superconducting pairing from repulsive interactions of fermions in a flat band system Iman Mahyaeh, Thomas Koehler, Annica M BlackSchaffer, Adrian Kantian Manybody quantum systems of fermions with flat bands at the Fermi level are intensely studied for their potential to boost superconductivity by enhancement of the density of states. We use quasiexact numerical methods to show that repulsive interactions between spinless fermions in a model onedimensional flat band system, the Creutz ladder, lead to a finite pairing energy that increases with repulsion. Pure repulsion however leaves chargeorder as the dominant quasiorder over the superconductivity. Adding an additional attractive component to the interaction shifts the balance fully in favor of superconductivity. In this regime we find that the interactions of two flat bands further yields a remarkable enhancement to superconductivity far above and outside the known paradigms for onedimensional fermions. 
Thursday, March 17, 2022 10:00AM  10:12AM 
S57.00011: Correcting the fatal flaw in BCS theory HyunTak Kim Cooper pair is formed by two electrons outside E_{F} due to the phonon and the screened Coulomb fields[1]. The screened Coulomb field is very weak, which makes the electron density n_{N} outside E_{F} small. Thus, the Cooper pair density, n_{Cooper}, becomes very small, the pair coherence length ξ becomes very large, the double potential structure is made. We assert the weak screened Coulomb field is the fatal flaw in BCS theory not explaining superconductivity[2]. To correct the flaw, we apply the onsite Coulomb interaction U in the BrinkmanRice(BR) picture[3]. When U increases, discontinuity[=m/m*=1(U/U_{c})^{2})] at E_{F} decreases, then n_{N} rapidly increases, n_{Cooper} becomes much larger, ξ becomes much smaller, a single potential well structure is generated. Thus T_{c_BR_BCS}[2] can explain the superconductivity. [1]PRL 104(1956)1189. [2]ScientificReport 11(2021)10329. [3]PRB 2(1970)4302. 
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