Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B09: Superconductivity: Theory/Computational |
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Sponsoring Units: DCMP Chair: Brian Moritz, SLAC National Accelerator Laboratory Room: BCEC 151A |
Monday, March 4, 2019 11:15AM - 11:27AM |
B09.00001: Pairfield fluctuations in the 2D Hubbard Model Thomas Maier, Douglas J Scalapino The nature of the pseudogap phase out of which superconductivity emerges in the cuprates remains an open problem. Pairfield fluctuations above the superconducting transition temperature provide information on the nature of this phase. Here we report numerical calculations of the d-wave pairfield susceptibility of a 2D Hubbard model for dopings which have a pseudogap and for dopings which do not. One knows that in both cases there will be a region of Kosterlitz-Thouless fluctuations as the transition at T_{KT} is approached. Above this region, we find evidence that the pseudogap limits the growth of the local pairfield and provides an environment in which phase fluctuations determine the temperature dependence of the pairfield susceptibility. In contrast, in the overdoped regime where there is no pseudogap, the temperature dependence of the pairfield is consistent with Ginzburg-Landau amplitude fluctuations. We discuss an experiment that can be used to measure this characteristic difference. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B09.00002: Superconducting symmetry of the extended Hubbard model below Tc Frank Marsiglio, Joel Hutchinson The two-dimensional extended Hubbard model on a square lattice is known to host s-wave, d-wave and p-wave superconducting phases depending on the values of the on-site and nearest-neighbour interactions. By examining the free energy functional of the gap in this model, we find that these symmetries are often dependent on temperature. The critical points of this functional are highly constrained by the lattice symmetry and allow us to formulate stringent conditions on the temperature profile of the gap function, applicable to other models as well. In this talk, we discuss the finite temperature phase diagram of the extended Hubbard model, and point out the existence of first and second order symmetry transitions below Tc. Understanding such transitions may be important for assessing the symmetry of some unconventional superconductors such as UPt_{3}. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B09.00003: An accurate indicator for unconventional superconductivity using charge-spin coupling João Rodrigues, Lucas Wagner A data-based prediction model for unconventional superconductivity is constructed, which has three ingredients: a layered crystal structure, stable local magnetic moments and an intermediate spin-orbital (as opposed to spin-orbit) coupling. This classifier is sufficiently specific to clearly distinguish cuprate and iron-based superconductors from other materials in the same structural class. We discuss some of the putative false positives and whether they might be good candidates for new unconventional superconductors. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B09.00004: Ground state phase diagram of doped Hubbard model on 4-leg cylinders Yifan Jiang, Thomas Devereaux, Hong-Chen Jiang We report a large-scale density-matrix renormalization group study of the lightly doped Hubbard model on 4-leg cylinders in the presence of next-nearest hopping t'. By keeping a large number of states for long system sizes, we are able to reveal a rich phase diagram consisting of a variety of distinct phases, including (1) The Luther-Emery (LE) liquid with quasi-long-range superconductivity (SC) and charge-density-wave (CDW) order, but with a gap in the spin sector; (2) Insulating phase with "filled" charge stripe and long-range CDW order but no long-range SC, and (3) Luttinger liquid phase with dominant single-particle correlation and subdominant SC and CDW correlations. In particular, at δ=12.5% doping concentration, we found that a tiny t'∼-0.01t is enough to drive the system out of the insulating state at t'=0 to the LE phase. Aside from t', the effect of Coulomb repulsion and doping concentration has also been explored. Our results indicate that a route to robust long-range superconductivity involves destabilizing insulating charge stripes in the doped Hubbard model. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B09.00005: Study of nodal gap in t-J model via renormalized mean field theory YiHsuan Liu, Wei-Lin Tu, Ting-Kuo Lee Angle-resolved photoemission (ARPES)[1] and scanning tunnelling microscopy (STM) [2] results show that Bi_{2}Sr_{2}_{−}_{y}La_{y}CuO_{6+δ} exhibit a gap, instead of a node, near the nodal region for x < 0.1. A similar gap has also been found in lightly doped La_{2}_{−x}Sr_{x}CuO_{4}[3]. All these experiment results indicated that spin density wave (SDW) and nodal gap(NG) are closely related. However, why the NG close when the insulator-superconductor transition occurs remains unclear. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B09.00006: Single-hole wavefunction in two dimensions: A case study of the doped Mott insulator Chen Shuai We study a ground-state ansatz for the single hole doped t-J model in two dimensions via a |
Monday, March 4, 2019 12:27PM - 12:39PM |
B09.00007: Superconductivity in doping the quantum paramagnet on the square lattice Hong-Chen Jiang We report a large-scale density-matrix renormalization group study of lightly doped t-J-type model on the square lattice, which hosts a quantum paramagnetic state at half-filling. We observe an interesting interplay between d-wave superconductivity and spin and charge density wave (CDW) order. Despite the tendency of CDW order on thinner cylinders is strong, our results on wider systems suggest that the CDW order may disappear in the thermodynamic limit. The spin correlations are found to decay exponentially, on the contrary, the superconducting pair-field correlations decay power-law with an exponent significantly smaller than the spatial dimension. Our results suggest that a uniform d-wave superconductivity emerges in doping the quantum paramagnet on the square lattice. The connection of our results to two dimensions is also discussed. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B09.00008: Particle-hole fluctuation corrections to BCS theory via functional integral techniques Mason Protter, Rufus Boyack, Frank Marsiglio The standard BCS approach to superconductivity considers only particle-particle pairing interactions, meaning that Cooper pairing arises as an instability of an otherwise well-defined Fermi surface. In a more generic situation, other interactions can compete with the Cooper instability and lead to a breakdown in the formation of a Fermi surface, which as a result changes the properties of the ground state. We explore a functional-integral method for rigorously incorporating particle-hole fluctuation corrections to the BCS theory of superconductivity. These corrections arise naturally as the result of a multi-channel Hubbard-Stratonovich decomposition of an attractive Hubbard interaction. Differences between this approach and previous models of particle-hole corrections to BCS theory are considered. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B09.00009: Theoretical Study on Superconductor Properties for Penrose Lattices Yongyou Zhang, Fan Yang Superconductivity in quasicrystal has been discovered in experiments [1] for Al–Zn–Mg quasicrystal with T_{c }≈ 0.05 K. In this presentation, we sytematically studied the quasicrastal superconductor properties on Penrose lattices. Within two-particle approximation the negtive U Hubbard model shows that the Cooper binding ernergy is proportional to exp(-1/U) and Anderson Law works well. Besides, the negtive U Hubbard model was studied by the mean-field method with which the superconductor gap, superconductor density of states, entropy, specific heat, and current density are analyzed. The superconductor gap decreases to zero when the temperature is larger than T_{c}, simultaneously the lines entropy and specific heat show the superconductor phase by their discontinuities. The paramagnetic and diamagnetic superconductor currents also have discontinuities at T_{c} and cancel each other when T>Tc. Different from periodical lattices the superconductor current has a finite value when T = 0, which shows the difference of the superconductor behavior between the quasicrystals and common crystals. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B09.00010: Proximity induced superconductivity in quasicrystal-superconductor hybrid rings Gautam Rai, Anuradha Jagannathan, Stephan Wolfgang Haas Quasicrystals with their exotic long range spatial order are expected to |
Monday, March 4, 2019 1:15PM - 1:27PM |
B09.00011: Bond disproportionation and electron-phonon driven oxygen-bismuth hybrid hole pairing in bismuth perovskites Kateryna Foyevtsova, Arash Khazraie, Ilya Elfimov, George Albert Sawatzky In this talk, we will present the recently developed theory^{1-3} describing the bismuth perovskites ABiO_{3} (A = Sr or Ba) as bond- (as opposed to charge-) disproportionated insulators where Bi-O hybridization and the presence of oxygen holes lead to formation of molecular orbitals and strong polaronic effects, which might be the prime mechanism driving these materials towards superconductivity upon doping. In particular, we will first use electronic structure methods to demonstrate that oxygen holes indeed condense into A_{1g} molecular orbitals centered at collapsed BiO_{6} octahedra and then to derive an appropriate tight-binding (TB) model, as well as to estimate electron-phonon coupling and an effective attraction between the two holes in the A_{1g} symmetry in this collapsed “BiO_{6} molecule”, emphasizing that these two parameters are strong enough to sustain polaronic superconductivity. We will also explore the parameter space of the TB model, finding a cross-over from the bond- into the charge-disproportionated insulating phase, as well as a metallic phase with a non-bonding character of the oxygen holes. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B09.00012: Pressure-enhanced high temperature superconductivity in XH3 (X=As, Se, Br, Sb, Te and I) Po-Hao Chang, Swabir Silayi, Dimitrios A Papaconstantopoulos, Michael Mehl The discovery of high critical temperature T_{c} superconductivity in highly compressed H3S has |
Monday, March 4, 2019 1:39PM - 1:51PM |
B09.00013: First-principles evolutionary structural searches for new high-pressure phases of Nb_{3}Al Jianjun Mao, Yue Chen High cost and poor stability have inhibited the large-scale applications of high-temperature cuprate superconductors. Intermetallic niobium compounds such as Nb_{3}Sn and Nb_{3}Al attract significant research interest due to their potential superconducting applications. Herein, we have combined evolutionary algorithms with density functional theory to perform structural searches for ground-state crystal structures of Nb_{3}Al under high pressures. At ambient pressure and low temperature, a new phase with distorted Nb atomic chains is found to be energetically more stable than the well-known A15 phase. Because the Nb atomic chains are believed to be closely related to the superconducting properties, the electron-phonon coupling of this new phase has been further studied using density functional perturbation theory. Moreover, we identify a pressure-induced structural phase transition of Nb_{3}Al under high pressures. Base on ab-initio molecular dynamics simulations, the temperature effects on the structural phase transitions of Nb_{3}Al have also been investigated. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B09.00014: Magnetism of the low-dimensional orbital-selective Mott insulators Jacek Herbrych, Jonas Heverhagen, Maria Daghofer, Gonzalo Alvarez, Adriana Moreo, Elbio R Dagotto The magnetic properties of low-D iron-based superconductors belonging to the 122 (Rb_{x}Fe_{y}Se_{2}) and 123 (BaFe_{2}Se_{3}) families [1-2] proved to be a challenge for the theoretical description. Investigation of the orbital-selective Mott phase in 1D (relevant for 123 family) [3,4] revealed the existence of an exotic block spin order, namely AFM coupled FM spin islands. In parallel, inelastic neutron scattering experiments on quasi-1D BaFe_{2}Se_{3} [2] and 2D Rb_{x}Fe_{y}Se_{2} [1] confirmed the relevance of these spin-block phases. The theoretical description of the latter requires long-range interaction and strong dimerization if within spin-wave models. In our work [4,5] we show that the magnetic properties of the orbital-selective Mott phase can be properly described by (short-range) multiorbital Hubbard models. Furthermore, we argue that the electronic correlations of itinerant orbitals are important for block-magnetism and that the minimal model which properly captures such a physics is the generalized Kondo-Heisenberg model. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B09.00015: Hetero-crystals, a new type of composite alloys: a case study of the 1144-phase TM-phosphides and -arsenides. Boqun Song, Manh Cuong Nguyen, Cai-Zhuang Wang, Paul Canfield, Kai-Ming Ho The recently discovered 1144-phase [1-2] suggests a new type of composite alloys, namely hetero-crystals. The author will present its definition and demonstrate wide existence. The hetero-crystals consist of the layered skeleton and hetero-cations alternatively located on both sides of the skeleton. Tuning cation species leads to significant modifications to structures, granting an exceptional chance to manipulate the emerging phases. The 1144-phase is examined as a case study of hetero-crystals. Various 1144-arsenide and phosphides are examined by combining first principle calculation and ideal solution approximation, wherein configurational, vibrational and electronic degrees of freedom are fully considered. Remarkably, the seemingly random occurrence of the 1144 phases is governed by a rule that involves two factors: elastic distortion and charge balance. Derived from 1144-phosphides, the rule, nevertheless, is heuristic and generic, which leads to an outlook of other hetero-crystals promising to be stabilized. [1] B. Q. Song, et. al. Physical Review B 97 (9), 094105 (2018). [2] B. Q. Song, et. al. Physical Review Materials 2 (10), 104802 (2018) |
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