Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C09: Superconductivity: Copper Oxide  TheoryFocus

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Sponsoring Units: DCMP Chair: Michael Sentef, Max Planck Institute for the Structure and Dynamics of Matter Room: BCEC 151A 
Monday, March 4, 2019 2:30PM  2:42PM 
C09.00001: Numerical study of the momentum and doping dependence of "hot spots" and singleparticle spectra in electrondoped cuprates Brian Moritz, Yao Wang, Edwin Huang, Thomas Devereaux We present a systematic study of the singleparticle spectral function in electrondoped cuprates determined from stateoftheart numerical calculations using cluster perturbation theory. By comparing the appearance of the "hot spots" as a function of momentum and electron filling, we conclude that the Hubbard model with an intermediate interaction U can well capture recent experimental observations from photoemission in Nd_{2x}Ce_{x}CuO_{4}. This work suggests that microscopic mechanisms similar to the holedoped cuprates may drive the shortranged antiferromagnetism, and ultimately superconductivity, even on the electron doped side, and set the stage for further theoretical explorations. 
Monday, March 4, 2019 2:42PM  2:54PM 
C09.00002: Phenomenological Theory for Pseudogap and Superconducting Phases of HighTemperature Superconductors Jianhao Zhang, Sen Li, Yao Ma, ZhengYu Weng We present a phenomenological Green's function to characterize the superconducting and pseudogap phases of the cuprates based on a microscopic theory of doped Mott insulators. In this framework, the ``Fermi arc'' and ``superconducting kink'' phenomena in ARPES experiments can be systematically obtained as a function of doping. We demonstrate that the phasestringinduced fractionalization plays a crucial role in leading to this exotic Green's function paradigm. 
Monday, March 4, 2019 2:54PM  3:06PM 
C09.00003: Intrinsic Pair Density Waves in CDMFT Improve Agreement with Cuprates Simon Verret, Alexandre Foley, Jyotirmoy Roy, Maxime Charlebois, David Senechal, AndreMarie Tremblay Cluster dynamical meanfield theory (CDMFT) is one of the most successful methods to treat strongly correlated electrons systems. It is well known, however, that CDMFT leads to an artificial breaking of translational invariance. Here, we investigate how this manifests itself. We report artificial density waves taking the shape of the cluster (cluster density waves) in all our CDMFT solutions. In particular, we report pair density waves in the superconducting solution. We discuss how these artificial density waves help the agreement of CDMFT with the lowenergy spectra of cuprate high temperature superconductors. Namely, we find subgap structures similar to those found in tunnelling experiments and a related separation between nodal and antinodal gaps in the spectral weight, as observed in photoemission experiments. This agreement with cuprates suggests that spatial inhomogeneity is an important ingredient to explain the lowenergy spectrum of cuprates, even in the strongly correlated case. 
Monday, March 4, 2019 3:06PM  3:18PM 
C09.00004: FLEX+DMFT approach for superconductivity in multiband systems: A study on bilayer Hubbard model Daisuke Ogura, Kazuhiko Kuroki Broadly speaking, to enhance the superconducting transition temperature T_{c}, a strong paring interaction and a light electron effective mass are favorable. However, the strong pairing interaction not only enhance superconductivity, but also results in the strong quasiparticle renormalization in general. As a way to circumvent this dilemma, we can consider the multiband Hubbard model as discussed in the previous studies [1, 2]. In multiband systems, spin fluctuations with finite energy arising from interband scattering channels can develop and act as an effective pairing interaction. Finite energy fluctuations do not cause an abovementioned strong competition between the quasiparticle renormalization and superconductivity. To treat both local and nonlocal correlations, we have applied the FLEX (fluctuation exchange) + DMFT (dynamical meanfield theory) method [4, 5] to the bilayer Hubbard model. In the presentation, we will discuss the correlation effects and the superconductivity arising from the interband pair scattering. 
Monday, March 4, 2019 3:18PM  3:30PM 
C09.00005: Enhancement of dwave Pairing in Cuprates by Electronphonon Couplings Xun Cai, Zixiang Li, Hong Yao The hightemperature cuprate superconductors have attracted great attentions over the past few decades. Since its discovery, the role of electronphonon couplings in the mechanism of hightemperature superconductivity in cuprates has been intensely debated. Some believe that electronphonon coupling may have a key impact on the dwave superconductivity in cuprates. We study the microscopic model of electrons on the 2D square lattice with both electronelectron and electronphonon interactions. From determinant quantum Monte Carlo simulations (DQMC), we show that dwave pairing can be significantly enhanced when the electronphonon coupling is increased. 
Monday, March 4, 2019 3:30PM  3:42PM 
C09.00006: Quantifying Quantum Order Transitions in Cuprate HighTc Superconductor ZhenSu She, Rong Li Wall turbulence and cuprates HTSC are similar for they are both complex systems with many degrees of freedom, and in nonequilibrium state with strong fluctuations. Here, we identify a new similarity between the two: both display symmetrybreaking transition embedded in nontrivial transport. First, we present a recent structural ensemble dynamics (SED) theory of wall turbulence that yields unified and accurate description of mean velocity and turbulent intensities profiles across the entire domain of turbulent boundary layer, using a multilayer formula of a length order function quantifying turbulent eddy size (She et al., JFM, 2017,2018). Then, we extend the SED theory to cuprates HTSC to predict a similar length order function, which successfully describes transitions between several dominant quantum orders such as spin order, charge order and superconductivity, as validated by resistivity data (see also another contributed talk, Li and She, 'New mechanism of umklapp scattering in cuprate HTSC' ). We conclude that wall turbulence and cuprates HTSC share similar selforganized symmetrybreaking feature, which can be effectively described through length order function. 
Monday, March 4, 2019 3:42PM  3:54PM 
C09.00007: Instabilities of Bogoliubovde Gennes quasiparticles in the zeroth Landau level of nodal superconductors under strain Emilian Nica, Onur Erten Landau levels have recently been predicted [12] to emerge in 2D nodal superconductors under applied strain or doping gradients. In contrast to more conventional cases, timereversal symmetry is preserved in the absence of interactions. We study the interactiondriven instabilities of the Bogoliubovde Gennes quasiparticles in the flat, zeroth Landaulevel. We focus on ferromagnetic and valleypolarized states and show that the resulting phase diagram depends on the direction of the applied strain. 
Monday, March 4, 2019 3:54PM  4:06PM 
C09.00008: Projected BCS theory for hightemperature superconductivity HyunWoong Kwon, Kwon Park At the core of the problem of hightemperature superconductivity lies the relationship between strong correlation and superconductivity. One of the most exciting prospects on their relationship is that strong correlation is the very source of hightemperature superconductivity. To investigate the validity of this prospect, we perform a variational analysis of the BCS model Hamiltonian projected onto the constrained Hilbert space with infinitely strong correlation, or no double occupancy. This is also known as the Gutzwiller projection. For convenience, let us call such an analysis the projected BCS theory. By computing the overlap between the exact ground states of the projected BCS theory and those of the tJ model via exact diagonalization, here, we show that the projected BCS theory provides excellent variational states for the ground states of the tJ model in the entire range of hole concentration including both half filling and finite doping. It is emphasized that the resonating valence bond (RVB) state, i.e., the projected BCS wave function is closely related to the ground state of the projected BCS theory, while quite different at low doping. What makes the difference is whether the projection is applied to the ground state of the Hamiltonian or the Hamiltonian itself. 

C09.00009: ABSTRACT WITHDRAWN

(Author Not Attending)

C09.00010: Vortex structure and Hall conductivity in dwave superconductors Vladimir Kalnitsky, Netanel Lindner, Erez Berg, Sebastian D Huber The Hall conductivity σ_{xy} serves as an important experimental probe for determining the sign of charge carriers in materials. In type II superconductors models of vortex dynamics predicted σ_{xy} to have the same sign as in the normal state; that is, the same as the charge carriers. However, Hall measurements showed that σ_{xy} changes sign as a function of temperature in YBCO and other cuprates, in contradiction to these predictions. Recently it was shown that a sign reversal of σ_{xy} occurs in a generic model for an swave superconductor, due to a topological transition in the vortex core. We show that a similar effect occurs in a model for a dwave superconductor, and find a rich phase diagram of σ_{xy} as a function of interaction strength and doping p: in addition to a sign reversed phase, we find a phase in which σ_{xy }∼ p . While such a relation implies a small Fermi surface, the model does not exhibit a bulk Fermi surface reconstruction. 
Monday, March 4, 2019 4:30PM  4:42PM 
C09.00011: Electronic States Induced by Doping a Mott Insulator in the Presence of Antiferromagnetic Order Masanori Kohno Recent theoretical studies on the Mott transition suggest that magnetically excited states emerge in the Mott gap in the singleparticle spectrum with the dispersion relation shifted by the Fermi momenta following the doping of a Mott insulator [14]. This characteristic is difficult to explain in terms of meanfield quasiparticles in antiferromagnetic order. Here, by taking into account spin fluctuation in the randomphase approximation, electronic states exhibiting momentumshifted spinwave dispersion relation are shown to emerge in the Mott gap following the doping of a Mott insulator even though antiferromagnetic order persists [5]. The results imply that the emergence of electronic states exhibiting momentumshifted magnetic dispersion relation is a general and fundamental characteristic of the Mott transition regardless of whether antiferromagnetic order exists or not. 
Monday, March 4, 2019 4:42PM  4:54PM 
C09.00012: High Tc superconductivity in strong electronphonon interacting systems with frustrated charge order Zixiang Li, Marvin L Cohen, Dunghai Lee In this talk, I will discuss how geometric frustration inhibits charge order and allows superconductivity to benefits from strong electronphonon coupling. We perform signproblemfree Quantum Monte Carlo simulation to study Holstein model with strong electronphonon coupling on triangular and square lattices. Our simulation indicates that geometric frustration of charge density wave enables strong superconductivity to exist under much wider conditions in temperature and electronphonon coupling strength. In particular, under geometric frustration a novel coexistence phase where superconducting coherence develops within a charge ordered state exists in a strong electronphonon coupling regime. 
Monday, March 4, 2019 4:54PM  5:06PM 
C09.00013: Continuing search for the origin of HTSC: DFT studies of selected copper oxide proxy structures reviewed and paths forward suggested Paul Grant In this presentation, we review our past attempts to uncover the pairing mechanism underlying high temperature superconductivity in copper oxide compounds and suggest possible paths forward.^{1, 2} One such path would be to derive and generalize pairing coupling functions to apply to DFT + U computed eigenstates in order to estimate Cooper pair coupling strengths arising from a combination of both lattice and spin excitations. Interestingly, such interactions were found in transition metal alums some 78 years ago as manifested in linking their respective Debye and Curie temperatures.^{3 } We suggest repeating such experiments today on the copper oxide compounds as a function of hole/electron concentration, along with a possible computational strategy to pursue in the interpretation of the results^{4} to finally resolve the fundamental origin of high temperature superconductivity. 
Monday, March 4, 2019 5:06PM  5:18PM 
C09.00014: Singlet s±wave pairing in quasionedimensional ACr_{3}As_{3} (A=K, Rb, Cs) superconductors LiDa Zhang, Xiaoming Zhang, JuanJuan Hao, Wen Huang, Fan Yang The recent discovery of quasi1D Crbased superconductivity has generated much excitement. We study in this work the superconducting instabilities of a representative compound, the newly synthesized KCr_{3}As_{3} superconductor. Based on inputs from DFT calculations, we first construct an effective multiorbital TB Hamiltonian to model its lowenergy band structure. We then employ standard RPA calculations to investigate the superconducting instabilities of the resultant multiorbital Hubbard model. We find the leading pairing symmetry realized in this material is singlet s±wave pairing. This singlet pairing is driven by spindensity wave fluctuations enhanced by FS. We design a phasesensitive measurement to identify the swave pairing. The s±wave pairing in KCr_{3}As_{3} shall also exhibit a subgap spin resonance mode near the nesting vector, which can be tested by inelastic neutron scattering measurements. We also propose further application of KCr_{3}As_{3} by utilizing it to induce TRI TSC via proximity effect. Our study shall be of general relevance to all superconductors in the family of ACr_{3}As_{3} (A=K, Rb, Cs). Reference: arXiv: 1809.07117 
Monday, March 4, 2019 5:18PM  5:30PM 
C09.00015: Superconductivity in systems exhibiting the AltshulerAronov anomaly Richard Hlubina, Branislav Rabatin Dirty superconductors close to the metalinsulator transition frequently exhibit a pseudogap in the normal state due to the AltshulerAronov (AA) effect. In this talk we show that, making use of generalized Eliashberg equations, the AA effect and superconductivity can be described on equal footing. We derive explicit expressions for the Coulomb pseudopotential in 3D, taking into account also the anomalous diffusion. We present a full numerical solution for two normalstate and two anomalous selfenergies. In the normal state, we amend the known results for the purely electronic AA effect; with electronphonon coupling turned on, we find additional anomalies in the density of states close to the phonon energy. We study how the critical temperature and density of states of strongly disordered 3D superconductors change with normalstate resistivity. We find that the type of transition from the superconducting to the insulating state depends on the strength of electronphonon coupling: at weak coupling there exists an intermediate normal state, whereas at strong coupling the transition is direct. 
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