Investigation of chiral density wave mean field Hamiltonian

TL;DR

This paper analyzes the chiral density wave mean field Hamiltonian in YBCO, deriving Berry curvature, thermodynamic properties, and the anomalous Nernst effect, revealing a first-order transition with increased entropy.

Contribution

It introduces a detailed Hamiltonian model for CDW in YBCO including inter-layer tunneling and calculates related Berry curvature and thermodynamic properties.

Findings

Two Berry curvature peaks at nodal points with opposite signs.

The CDW transition is first order with increased entropy.

Theoretical prediction of anomalous Nernst effect in the CDW state.

Abstract

We start with the chiral density wave(CDW)mean field Hamiltonian in the momentum space for the pseudo-gapped state of YBCO in the absence of magnetic field, including the momentum conserving inter-layer tunneling matrix elements in the Hamiltonian for the tetragonal case, with the principal component of the order parameter corresponding to idx2-y2 and the secondary one to the dxy. With the eigenvalues and the eigenvectors of the Hamiltonian matrix we write down expression for Berry curvature(BC). Only two BC peaks of same magnitude and opposite signs are obtained at the nodal points of the reconstructed Fermi surface (RFS) for the pure idx2-y2-density wave case. We establish a relation between thermodynamic potential of the system and certain spectral functions for the CDW state. This yields an expression for entropy in closed form. We show that the transition to the CDW state is a first order one and the entropy per unit cell increases in this state. We also investigate anomalous Nernst effect theoretically.