Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session M47: Superconductivity Theory: Cuprates and doped spin liquidsLive
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Sponsoring Units: DCMP Chair: Benjamin Fregoso, Kent State University |
Wednesday, March 17, 2021 11:30AM - 11:42AM Live |
M47.00001: Superconductivity and doping on oxygen in the three band model Nicolas KOWALSKI, A.-M. S. Tremblay, patrick Sémon Recent experimental results - using NMR measurements - have shown, across the cuprates [1], that the maximum critical temperature is much more strongly correlated with doping on the oxygen than with total doping. Using the CDMFT approximation and a finite temperature CT-HYB impurity solver, we investigate the phase diagram of the three-band Hubbard model in order to reproduce those results with theoretical means. Although the correlation is not perfect, we found such a trend, first focusing on the superconducting order-parameter and then on the critical temperature. We also discuss correlations between the spin susceptibilities and order parameter and a regime of parameters with a coexistence between pseudo-gap and superconducting phase. |
Wednesday, March 17, 2021 11:42AM - 11:54AM Live |
M47.00002: Optimizing superconductivity in the three-band Hubbard model Sidhartha Dash, David Senechal We explore the phase diagram of the three-band Hubbard model for high-Tc cuprates using Cluster Dynamical Mean Field Theory at zero temperature with an exact diagonalization solver. Our goal is to maximize the superconducting order parameter and identify the model characteristics that most enhance superconductivity. We start with realistic values of the band parameters from Weber et al [1]. We observe that the order parameter at optimal doping is monotonously related to the oxygen doping and the charge-transfer gap. We also find a marked correlation of the order parameter at optimal doping with the occupation of the upper Hubbard band. We report on the correlation of the maximum order parameter with other characteristics of the model, such as the spin susceptibility etc. |
Wednesday, March 17, 2021 11:54AM - 12:06PM Live |
M47.00003: Orbital structure of the effective pairing interaction in the high-temperature superconducting cuprates Peizhi Mai, Giovanni Balduzzi, Steven S. Johnston, Thomas Maier The nature of the effective interaction responsible for pairing in the high-temperature superconducting cuprates remains unsettled. This question has been studied extensively using the simplified single-band Hubbard model, which does not explicitly consider the orbital degrees of freedom of the relevant CuO_2 planes. Here, we use dynamic cluster approximation to study the orbital structure of the pairing interaction in the three-band Hubbard model, which treats the orbital degrees of freedom explicitly. We find that the interaction predominately acts between neighboring copper orbitals, but with significant additional weight appearing on the surrounding bonding molecular oxygen orbitals. By explicitly comparing these results to those from the simpler single-band Hubbard model, our study provides strong support for the single-band framework for describing superconductivity in the cuprates. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M47.00004: Cooperative enhancement of superconducting pairing at quarter filling by electron-electron and electron-phonon interactions Dipayan Roy, R. Torsten Clay Unbiased numerical calculations within two-dimensional Hubbard models have found no evidence for long-range superconducting order. This suggests that repulsive interactions between electrons alone are not sufficient to realize superconductivity and other interactions are required. The most likely candidate is the electron-phonon interaction. However, existing theories of superconductivity emphasize either electron-electron or electron-phonon interactions, each of which tends to cancel the effect of the other. We present direct evidence from quantum Monte Carlo calculations of cooperative, as opposed to competing, effects of electron-electron and electron-phonon interactions within the frustrated Hubbard Hamiltonian, uniquely at the band-filling of one-quarter[1]. Bond-coupled phonons and the onsite Hubbard U cooperatively |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M47.00005: Normal charge densities in cold quantum critical superfluids Eric Mefford, Blaise Gouteraux Recent experiments on overdoped LSCO by Bozovic et al. [Nature 536, 282 (2016)] have revealed an anomalously low superfluid density. Further measurements by Mahmood et al. [PRL 122, 027003 (2019)] on the low-temperature optical conductivity tie this to a large residual normal density, at odds with expectations from BCS theory and general arguments due to Legget [J. Stat. Phys 93, 927 (1998)]. We revisit these arguments in the context of superfluid hydrodynamics and demonstrate that consistently coupling the system to external sources allows for a large low-temperature normal density. As a proof-of-principle, we use gauge-gravity duality to construct an example of a strongly-coupled superfluid which has non-vanishing zero-temperature normal and superfluid densities. We find that the coexistence of the two densities at zero-temperature is a consequence of the underlying quantum critical ground state and the spectrum of irrelevant deformations around this state. Our results are in qualitative agreement with the optical conductivity as well as other previous measurements on overdoped LSCO, including the specific heat. |
Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M47.00006: Enhanced A1g Raman response in unconventional superconductors due to Higgs oscillations Matteo Puviani, Dirk Manske The Higgs in superconductors is a collective amplitude mode which can couple to light only in a non-linear Raman-like process. Despite being so far elusive in most experiments because of physical and technical reasons, in d-wave superconductors the excitation of the Higgs mode can become detectable in polarization dependent experiments. In our work, we have calculated the Raman contribution of the amplitude mode from a new perspective, including many-body dressing effects, demonstrating its role in the long-standing problem concerning the intensity of the A1g Raman spectrum in cuprates. Moreover, we apply our scheme to predict the presence of measurable characteristic oscillations in THz quench-optical probe time-dependent reflectivity experiments. |
Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M47.00007: Optical responses of Higgs and Leggett modes in multiband superconductors Takumi Kamatani, Naoto Tsuji, Sota Kitamura, Takahiro Morimoto Collective excitations in superconductors are attracting much attention recently. One typical example is the Higgs mode, which is an amplitude mode of superconducting gap function. Higgs modes in superconductors are experimentally observed by Raman spectroscopy and optical measurements of third harmonic generation [1]. In multiband superconductors, the gap function contains multiple band degrees of freedom and becomes a matrix generally. Consequently, there appears another collective mode that corresponds to the oscillation of the relative phase between different bands, which is called Leggett modes. So far, Leggett modes are observed in Raman experiments using MgB2[2], while there is no optical measurement of Leggett modes. |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M47.00008: Superconductivity in the doped quantum spin liquid on the triangular lattice Hong-Chen Jiang Broad interest in quantum spin liquid (QSL) phases was triggered by the notion that they can be viewed as insulating phases with preexisting electron-pairs, such that upon light doping they might automatically yield high temperature superconductivity. Yet despite intense efforts, definitive evidence showing that doping QSLs leads to superconductivity has been lacking. We address the problem of a lightly doped QSL through a large-scale density-matrix renormalization group study of the t-J model on the triangular lattice with a small but non-zero concentration of doped holes. We provide direct evidences that doping QSL can naturally give rise to superconductivity. The ground state is consistent with a Luther-Emery liquid with power-law superconducting and charge-density-wave correlations but short-range spin-spin correlations. Specifically, the superconducting correlations are the dominant correlations on both four-leg and six-leg cylinders, indicating that long-range superconductivity would emerge in doping QSL in two dimensions. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M47.00009: Topological superconductivity in the doped chiral spin liquid on the triangular lattice Yi-Fan Jiang, Hong-Chen Jiang It has long been proposed that doping a chiral spin liquid (CSL) or fractional quantum Hall state can give rise to topological superconductivity. Despite of intensive effort, definitive evidences still remain lacking. We address this problem by studying the t-J model supplemented by time-reversal symmetry breaking chiral interaction Jχ on the triangular lattice using density-matrix renormalization group with a finite concentration δ of doped holes. It has been established that the undoped, i.e., δ=0, system has a CSL ground state in the parameter region 0.32< Jχ/J < 0.56. Upon light doping, we find that the ground state of the system is consistent with a Luther-Emery liquid with power-law superconducting and charge-density-wave correlations but short-range spin-spin correlations. In particular, the superconducting correlations, whose pairing symmetry is consistent with d±id-wave, are dominant at all hole doping concentrations. Our results provide direct evidences that doping the CSL on the triangular lattice can naturally give rise to topological superconductivity. |
Wednesday, March 17, 2021 1:18PM - 1:30PM Live |
M47.00010: Multiorbital superconducting mechanism for a new-type cuprate Ba2CuO3+δ based on a Lieb-lattice model Kimihiro Yamazaki, Masayuki Ochi, Daisuke Ogura, Kazuhiko Kuroki, Hiroshi Eisaki, Shin-ichi Uchida, Hideo Aoki For the newly discovered cuprate superconductor Ba2CuO3+δ, we propose a lattice structure which resembles the model considered by Lieb to represent the vastly oxygen-deficient CuO2 planes [1]. We first show that the Lieb-lattice structure is nearly as stable as the chain-type structure known to exist as e.g. Sr2CuO3. Then we construct a multiorbital Hubbard model based on first-principles calculation, and apply the fluctuation-exchange approximation. We show that s-wave and d-wave pairings closely compete with each other and, more interestingly, that a coexistence of intra- and interorbital pairings arises. We also reveal an intriguing relation of the Lieb model with the two-orbital model for the usual K2NiF4-type cuprate where a close competition between s- and d-wave pairings is known to occur. We further show that s±-wave superconductivity is strongly enhanced when the d3z2−r2 band is raised in energy so that it becomes nearly “incipient” with the lower edge of the band close to the Fermi level within a realistic band filling regime. The enhanced superconductivity in the present model is in fact shown to be related to an enhancement found previously in the bilayer Hubbard model with an incipient band. |
Wednesday, March 17, 2021 1:30PM - 1:42PM Live |
M47.00011: Photoinduced η-pairing at finite temperatures Satoshi Ejima, Tatsuya Kaneko, Florian Lange, Seiji Yunoki, Holger Fehske We numerically prove photoinduced η-pairing in a half-filled fermionic Hubbard chain at both zero and finite temperature. The result, obtained by combining the matrix-product-state-based infinite time-evolving block decimation technique and the purification method, applies to the thermodynamic limit. Exciting the Mott insulator by a laser electric field docked on via the Peierls phase, we track the time evolution of the correlated many-body system and determine the optimal parameter set for which the nonlocal part of the η-pair-correlation function becomes dominant during the laser pump at zero and low temperatures. These correlations vanish at higher temperatures and long times after pulse irradiation. In the high laser frequency strong Coulomb coupling regime we observe a remnant enhancement of the Brillouin-zone boundary pair-correlation function also at high temperatures, if the Hubbard interaction is about a multiple of the laser frequency, which can be attributed to an enhanced double occupancy in the virtual Floquet state. |
Wednesday, March 17, 2021 1:42PM - 1:54PM Live |
M47.00012: Quatonic and SpinQuatonic Superconductors: Twisted Bilayer Graphene and Cuprates Sang-Boo Nam A novel superconducting transition temperature Tc=nVBCS/4 and energy gap Δ(T)=2Tctanh[Δ(T)/2T] are presented, based on BCS framework [the cut-off energy Td ≤2Tc], where n is the carrier filling number in the primitive unit cell. The virtual exchange of Quaton (QT) [SpinQuaton (SQ)], (4 charges [spins] of 2 electrons and 2 holes on tetrahedron corners), induced by exciton [magnon], between the carriers involved, yields VBCS = 2EQT[ESQ] (eigenenergy of QT [SQ]). For twisted bilayer graphene (TBG), EQT=2Ex (exciton energy), Ex is μ, the chemical potential energy, defined by the carrier density for n=½, and Tc=μ/2. Using μ=-0.3meV calculated by Wu et al., Phys. Rev. Lett. 121, 257001 (2018), Tc(TBG)=1.74K in excellent agreement with 1.7K observed by Cao et al., Nature 556, 43 (2018). For cuprates, assigning the modes at 47meV (TlBCO) and 41 – 34meV (YBCO) in the neutron and Raman scatterings, as the respective SQs, for n=1/2, Tc (TlBCO)=135K and Tc (YBCO)=119 – 98K are in agreement with the experiments. The carrier specific heat jump [Cs/Cn -1] at Tc is found to be 1.823 (BCS value 1.43). The result of Tc=N(0)TdVBCS/2 [Nam, Phys. Lett. A193, 111 (1994), ibid(E) A197, 458 (1995)] is recovered with n=2N(0)Td, where N(0) is the density of states/spin at the reference energy. |
Wednesday, March 17, 2021 1:54PM - 2:06PM Live |
M47.00013: Fluctuating Pair-Density Wave in anisotropic strongly coupled pairing system Laura Fanfarillo, Chandan Setty, Peter Hirschfeld In weakly coupled BCS superconductors, only electrons within a tiny energy window around the Fermi energy form Cooper pairs. This may not be the case in strong coupling superconductors such as FeSe, SrTiO3 or cold atom condensates where the pairing scale becomes comparable or even larger than the Fermi energy. In this talk I will discuss an analytically solvable model to examine possible pairing phases in the strongly coupled regime in the presence of anisotropic interactions. I will illustrate the properties of a novel finite temperature phase where local pair correlations have non-zero center-of-mass momentum but lack long-range order. Below a critical temperature such a fluctuating pair-density wave phase can condense either to a uniform d-wave superconductor or to a pair-density wave phase depending on the strength of the pairing interaction. I will conclude discussing possible realizations of our mechanism, including cuprates, where the pseudogap phase has been postulated to be a form of incoherent pair density wave. |
Wednesday, March 17, 2021 2:06PM - 2:18PM Live |
M47.00014: Finding Tc in an attractive-U Hubbard-metallic bilayer system. Philip Dee, Steven S. Johnston, Thomas Maier An intriguing route to higher temperature superconductivity is via coupling layers of different material properties. From a model standpoint, others have shown coupling layers with a large pairing scale, and weak superfluid stiffness to a metal can recover part of the mean-field transition temperature when coupled to a thin metallic film. But how general is this result? We examine this question by studying a bilayer system comprised of an attractive Hubbard layer and a metallic layer coupled with an interlayer hopping using the dynamical cluster approximation. Focusing on the regime where the interaction magnitude is comparable to the electronic bandwidth, we find that coupling between the layers suppresses Tc and that the transition evolves from a Kosterlitz-Thouless type to a logarithmic BCS (mean-field) type transition. We will discuss the reasons for this suppression and potential future directions. |
Wednesday, March 17, 2021 2:18PM - 2:30PM Not Participating |
M47.00015: Large scale simulations of topological defects in pair density waves YiHsuan Liu, Ting-Kuo Lee, Gia-wei Chern Pair density wave (PDW) has been in the central stage of high-Tc cuprate since its direct experimental observation. A PDW is a unique superconducting state in which the electron pairing function varies periodically as a function of position. Experimentally, density-wave states of cuprates have been shown to be highly inhomogeneous, indicating the importance of both quenched disorder and topological defects. To investigate the effects of spatial inhomogeneity, we combine the kernel polynomial method (KPM), which offers linear-scaling electronic structure calculation, with the renormalized mean-field theory (RMFT) for $t$-$J$ model. This allows us to perform unprecedented large-scale simulations, with number of lattice sites up to $N\sim 10^5$, of PDW states. In particular, we are trying to investigate the solutions with fractionalized half-vortices with a dislocation of the charge stripes. We also compute the local electronic density of states of these novel inhomogeneous PDW states. |
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