Exact non-magnetic ground state and residual entropy of S = 1/2 Heisenberg diamond spin lattices

TL;DR

This paper presents exactly solvable frustrated quantum spin models on diamond lattices, revealing their ground states, excitation gaps, and residual entropy, with implications for experimental synthesis.

Contribution

It introduces new exactly solvable models with macroscopic degeneracy and calculates their excitation gaps and residual entropy, extending to arbitrary dimensions.

Findings

Ground states are tetramer-dimer states with macroscopic degeneracy.

The excitation gap lower bound is exactly finite.

Residual entropy ranges from 0 to about 8.4% of high-temperature entropy.

Abstract

Exactly solvable frustrated quantum spin models consisting of a diamond unit structure are presented. The ground states are characterized by tetramer-dimer states with a macroscopic degeneracy in a certain range of isotropic exchange interaction. The lower bound of the excitation gap is exactly calculated to be finite and the bulk entropy in the limit of zero temperature remains finite depending on the shape of the boundary of system. Residual entropy is in a range of 0~6.1% of the entropy at high temperature for hexagonal diamond lattice and 0~8.4% for square diamond lattice. These diamond lattices are generalized to any dimensions and it is likely to be synthesized experimentally.