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Journal of Physics Conference Series

Possibility of Pomeranchuk instability in staggered flux state

Kenji Kobayashi, Hisatoshi Yokoyama

Published Jul 1, 2020• 0 citations
Publisher

Abstract

Abstract In connection with the symmetry-breaking phenomena found in cuprate superconductors, the instability toward x−y and (x + y)−(x − y) anisotropy (Pomeranchuk instability) is studied for a strongly correlated Hubbard model (U/t = 12) on a square lattice with the next-nearest-neighbor transfer t′ using a variational Monte Carlo method. As a variational function, a staggered flux state ΨSF is considered, which is a candidate for the pseudogap state in cuprates. ΨSF is stabilized in a underdoped regime and reduced to the normal state (projected Fermi sea) for larger doping area. By analyzing ΨSF for t′/t = 0, ±0.3, we argue that the appearance of Pomeranchuk instability is limited to the normal state with t′/t = 0 and 0.08 ≤ δ ≤ 0.20 (σ: doping rate) in the x−y anisotropy. Band-renormalization effects (Fermi-surface modification) owing to strong correlations play a crucial role for the argument.

DOI
10.1088/1742-6596/1590/1/012017

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Abstract In connection with the symmetry-breaking phenomena found in cuprate superconductors, the instability toward x−y and (x + y)−(x − y) anisotropy (Pomeranchuk instability) is studied for a strongly correlated Hubbard model (U/t = 12) on a square lattice with the next-nearest-neighbor transfer t′ using a variational Monte Carlo method. As a variational function, a staggered flux state ΨSF is considered, which is a candidate for the pseudogap state in cuprates. ΨSF is stabilized in a underdoped regime and reduced to the normal state (projected Fermi sea) for larger doping area. By analyzing ΨSF for t′/t = 0, ±0.3, we argue that the appearance of Pomeranchuk instability is limited to the normal state with t′/t = 0 and 0.08 ≤ δ ≤ 0.20 (σ: doping rate) in the x−y anisotropy. Band-renormalization effects (Fermi-surface modification) owing to strong correlations play a crucial role for the argument.
In connection with the symmetry-breaking phenomena found in cuprate superconductors, the instability toward x-y and (x + y)-(xy) anisotropy (Pomeranchuk instability) is studied for a strongly correlated Hubbard model (U/t = 12) on a square lattice with the next-nearest-neighbor transfer t ′ , using a variational Monte Carlo method.By analyzing a normal (paramagnetic), d x 2 -y 2 -wave superconducting, and antiferromagnetic states for t ′ /t = 0, ±0.3 and 0 ≤ δ ≤ 0.3 (δ: doping rate), we argue that the possibility of Pomeranchuk instability is limited to the normal state with t ′ /t = 0 and 0.05 ≲ δ ≲ 0.20 in the x-y anisotropy.Band-renormalization effects (Fermi-surface changes), which are introduced to each state, play a crucial role for the argument.
Abstract In connection with the symmetry-breaking phenomena found in cuprate superconductors, we check whether an anisotropy spontaneously appears or not in strongly correlated electrons that exhibit superconductivity and/or antiferromagnetism. A variational Monte Carlo method is applied to the square-lattice Hubbard model (U/t = 12) with diagonal transfer t′. In the trial wave function used, we introduce band renormalization factors including adjustable parameters for the anisotropy corresponding to the fourfold rotational symmetry breaking. It is confirmed that the anisotropy appears in the overdoped regime, where the Fermi-liquid features are predominant. In the underdoped area, the anisotropy does not appear for t′/t = 0 and +0.3, whereas it possibly appears in the underdoped regime for t′/t = −0.3.
With cuprate superconductors in mind, we check whether the d -wave superconducting ( d SC) state coexists with or excludes the staggered flux (SF) state, which was revealed to be the strong candidate for the pseudogap state. To this end, we use a variational Monte Carlo method for the square Hubbard model with diagonal transfer t '. In the trial wave function, d SC and SF orders coexist, which allows a continuous description of their interplay; essential factors for Mott physics and band renormalization are also included. It is found that the SF state does not coexist with d SC and is unstable for U/t = 12 regardless of the value of t'/t within the present work.
With cuprate superconductors in mind, we check whether the d -wave superconducting ( d SC) state coexists with or excludes the staggered flux (SF) state, which was revealed to be a strong candidate for the pseudogap state. To this end, we use a variational Monte Carlo method for the square-lattice t - J model with diagonal transfer t '. We construct a trial wave function which can simultaneously represent d SC and SF orders for a continuous description of their interplay. Furthermore, a band renormalization effect is introduced into both orders independently. It is found that the SF state does not coexist with d SC and is unstable for a wide area in the parameter space. However, a strange state having both SF and antiferromagnetic orders is found to be stable for very low doping rate.
The stability of a staggered flux (SF) or d-density wave state is studied in a d-p model using a variational Monte Carlo (VMC) method. This state possesses a local circular current and possibly causes the pseudogap phase in high-Tc cuprate superconductors. We introduce into the trial function a configuration dependent phase factor, which was recently shown to be indispensable to stabilize current-carrying states. We pay attention to the energy gain as a function of adjacent O-O hopping and Cu-site coulomb repulsion U. It is found the SF state becomes stable for hole doping rates of and , owing to the reduction in kinetic energy, but seems fragile because the energy gain rapidly decays on doping holes for any . The loop current tends to increase as increases.