Emergence of Particle-Hole Symmetry near Optimal Doping in High-Temperature Copper Oxide Superconductors

TL;DR

This paper investigates the emergence of particle-hole symmetry near optimal doping in high-temperature cuprate superconductors, linking it to spectral weight transfer and its implications for pairing mechanisms.

Contribution

It demonstrates that particle-hole symmetry arises dynamically near optimal doping due to spectral weight transfer, supported by Hubbard model calculations.

Findings

Thermoelectric power changes sign near optimal doping.

Particle-hole symmetry is linked to high-energy spectral weight transfer.

Hubbard model reproduces the sign change quantitatively.

Abstract

High-temperature copper oxide superconductors (cuprates) display unconventional physics when they are lightly doped whereas the standard theory of metals prevails in the opposite regime. For example, the thermoelectric power, that is the voltage that develops across a sample in response to a temperature gradient, changes sign abruptly near optimal doping in a wide class of cuprates, a stark departure from the standard theory of metals in which the thermopower vanishes only when one electron exists per site. We show that this effect arises from proximity to a state in which particle-hole symmetry is dynamically generated. The operative mechanism is dynamical spectral weight transfer from states that lie at least 2eV away from the chemical potential. We show that the sign change is reproduced quantitatively within the Hubbard model for moderate values of the on-site repulsion, $U$. For sufficiently large values of on-site repulsion, for example, $U=20t$, ($t$ the hopping matrix element), dynamical spectral weight transfer attenuates and our calculated results for the thermopower are in prefect agreement with exact atomic limit. The emergent particle-hole symmetry close to optimal doping points to pairing in the cuprates being driven by high-energy electronic states.