dx2-y2-wave Bose Metal induced by the next-nearest-neighbor hopping t'

TL;DR

This paper demonstrates the existence of a dx2-y2-wave Cooper pair Bose metal phase in a 2D fermionic system with anisotropic hopping, highlighting the role of Fermi surface anisotropy in its formation and suggesting potential experimental realization.

Contribution

The study introduces a dx2-y2-wave Cooper pair Bose metal phase induced by next-nearest-neighbor hopping anisotropy, revealing the importance of Fermi surface anisotropy over topology.

Findings

Bose metal phase appears for t'/t > 0.7

Maximum phase stability around t'/t ~ 0.2

Fermi surface anisotropy is key for Bose metal formation

Abstract

Superconductivity arises when electrons form Cooper pairs with phase coherence. In contrast, a lack of phase coherence in Cooper pairs can lead to an uncondensed metallic ground state known as the Bose metal state. In this study, we investigate an attractively interacting fermionic system with nearest-neighbor (NN) hopping (t) and next-nearest-neighbor (NNN) hopping (t') anisotropy between two species of spins in a two-dimensional (2D) lattice. Utilizing the constrained path quantum Monte Carlo (CPQMC) method, we demonstrate the existence of a dx2-y2-wave Cooper pair Bose metal (CPBM) phase with t'/t > 0.7. The CPBM phase exhibits a dome-like structure in the phase diagram of filling n~0.65, with the maximal region around an optimal t'/t ~ 0.2, suggesting that an appropriate value of t' facilitates the formation of the Bose metal. Furthermore, we find that a Bose metal formed by fermions with a closed Fermi surface confirms that the crucial condition for this exotic phenomenon is primarily the anisotropy of the Fermi surface, rather than its topology. Our finding of the dx2-y2-wave CPBM demonstrates the same pairing symmetry as the pseudogap behavior in cuprates, and its experimental realization in ultracold atom systems is also feasible.