Power-law Conductivity inside the Mott gap: application to $\kappa-(BEDT-TTF)_2Cu_2(CN)_3$

TL;DR

This paper explains the power-law optical conductivity observed in a spin-liquid insulator using U(1) gauge theory with gapless spinons, providing a theoretical framework and proposing an experimental test.

Contribution

It introduces a theoretical model linking gapless spinons to power-law conductivity and applies it to explain experimental observations in a specific organic compound.

Findings

Power-law optical conductivity inside the Mott gap due to spinons

Application of U(1) gauge theory to real materials

Proposal for an optical experiment to detect in-gap excitations

Abstract

The charge dynamics of spin-liquid states described by U(1) gauge theory coupling to fermionic spinons is discussed in this paper. We find that the gapless spinons give rise to a power law optical conductivity inside the charge gap. The theory is applied to explain the unusual optical conductivity observed recently in the organic compound $\kappa-(BEDT-TTF)_2Cu_2(CN)_3$. We also propose an optical experiment to search for the in-gap excitations in the Kagome spin liquid insulator.