"Bad Metal" Conductivity of Hard Core Bosons

TL;DR

This paper investigates the high-temperature resistive behavior of two-dimensional hard core bosons, revealing a breakdown of quasiparticle transport and identifying features in the dynamical conductivity related to fluctuations and potential parallels with cuprate superconductors.

Contribution

It provides a non-perturbative analysis of the dynamical conductivity of hard core bosons, uncovering a broad resistive regime and spectral features linked to order parameter fluctuations.

Findings

Resistivity increases linearly with temperature over a broad range.

Dynamical conductivity becomes broad and featureless at high temperatures.

A high-frequency peak in conductivity relates to order parameter fluctuations.

Abstract

Two dimensional hard core bosons suffer strong scattering in the high temperature resistive state at half filling. The dynamical conductivity is calculated using non perturbative tools such as continued fractions, series expansions and exact diagonalization. We find a large temperature range with linearly increasing resistivity and broad dynamical conductivity, signaling a breakdown of Boltzmann-Drude quasiparticle transport theory. At zero temperature, a high frequency peak in the dynamical conductivity appears above a "Higgs mass" gap, and corresponds to order parameter magnitude fluctuations. We discuss the apparent similarity between conductivity of hard core bosons and phenomenological characteristics of cuprates, including the universal scaling of Homes et. al. (Nature 430, 539 (2004)).