Quantum spin metal state on a decorated honeycomb lattice

TL;DR

This paper introduces a modified exactly solvable Kitaev model on a decorated honeycomb lattice, revealing a spin metal state with a Fermi-circle, and analyzes its thermodynamic and dynamic properties.

Contribution

It presents a new exactly solvable spin model exhibiting a spin metal ground state with a Fermi-circle, expanding understanding of quantum spin liquids.

Findings

The model's Majorana fermions form a 2D gapless state with a Fermi-circle.

Low-temperature heat capacity scales linearly with temperature, C(T) ~ T.

Dynamic spin susceptibility shows a power-law peak near resonance frequency.

Abstract

We present a modification of exactly solvable spin-(1/2) Kitaev model on the decorated honeycomb lattice, with a ground state of "spin metal" type. The model is diagonalized in terms of Majorana fermions; the latter form a 2D gapless state with a Fermi-circle those size depends on the ratio of exchange couplings. Low-temperature heat capacity C(T) and dynamic spin susceptibility \chi(\omega,T) are calculated in the case of small Fermi-circle. Whereas C(T)\sim T at low temperatures as it is expected for a Fermi-liquid, spin excitations are gapful and \chi(\omega,T) demonstrate unusual behaviour with a power-law peak near the resonance frequency. The corresponding exponent as well as the peak shape are calculated.