Superconductivity due to cooperation of electron-electron and electron-phonon interactions at quarter filling

Abstract

We present the results of Quantum Monte Carlo calculations for a two dimensional frustrated Hubbard model coupled to bond phonons. The model is known to have a d-wave superconducting ground state in the limit of large phonon frequency for sufficiently strong electron-phonon coupling. In the absence of electron-phonon coupling the Hubbard interaction U enhances superconducting pairing in the quarter-filled (density ρ = 0.5) band. We show here that at ρ = 0.5 electron-electron and electron-phonon interactions cooperatively reinforce d-wave pairing, while competing with each other at all other densities. Cooperative degrees of freedom are found in many phase transitions and are essential to understanding superconductivity in strongly correlated materials.

Absence of Superconductivity in the Hubbard Dimer Model for κ-(BEDT-TTF)2X

“…DMRG calculations on a width-three triangular lattice found evidence for p-wave and d-wave SC in the density range 0.40∼0.65 [58], which would appear to agree with the conclusion from the previous work [41]. Additionally, electron-electron and electron-bond phonon interactions act cooperatively at this bandfilling to enhance superconducting pair correlations, even as they compete with one another at all other fillings [59]. These results are encouraging and suggest further research along this direction.…”

Absence of superconductivity in the Hubbard dimer model for kappa-(BEDT-TTF)_2X

“…Calculations on an anisotropic triangular lattice [40] as well as on κ-lattices [41,55] have indeed found that superconducting pair correlations are enhanced by the Hubbard U uniquely at 1 4 -filling. Additionally, electron-electron and electron-bond phonon interactions act co-operatively at this bandfilling to enhance superconducting pair correlations, even at they compete with one another at all other fillings [56]. These results are encouraging and suggest further research along this direction.…”

Exact Self-Similar Patterns of Atomic-Layer Boron Nitride with Koch Fractal Complexity

“…According to atomic configuration analysis in Figure b, under the nonequilibrium condition (low source concentration), the B and N atom preferential growth direction would deviate from the lowest barrier B-terminated (100) direction (3-fold symmetry) to the high barrier B–N armchair edge (110) direction (6-fold symmetry), forming the ideal 2D Koch snowflakes (Figure d). In addition, in critical phenomena, e.g., superconductivity , or bacterial collective motion patterns, − interactions between agents (electrons and bacteria) play a critical role in their emergent behaviors. Similar to the above phenomenon, the exact self-similar Koch curve formation in this work is inextricably linked to the asymmetric interaction introduced by the mirror symmetry of the h-BN armchair edge of the growth front (Figure b), which could facilitate long-range correlations of atomic reaction-diffusion processes (i.e., trigger the KPZ interaction).…”