One-Dimensional Magnetic Excitonic Insulators

TL;DR

This paper investigates the possibility of Bose-Einstein condensation of excitons in one-dimensional materials, providing theoretical proofs, deriving critical temperatures, and predicting specific material behaviors through first-principles calculations.

Contribution

It offers a statistical proof of exciton condensation in 1D, derives a general critical temperature formula across dimensions, and predicts new excitonic insulator states in specific materials.

Findings

Existence of 1D exciton condensation proven statistically.

Critical temperature increases as dimensionality decreases.

Predicted antiferromagnetic and ferromagnetic excitonic insulators in specific wires.

Abstract

Dimensionality significantly affects exciton production and condensation. Despite the report of excitonic instability in one-dimensional materials, it remains unclear whether these spontaneously produced excitons can form Bose-Einstein condensates. In this work, we first prove statistically that one-dimensional condensation exists when the spontaneously generated excitons are thought of as an ideal neutral Bose gas, which is quite different from the inability of free bosons to condense. We then derive a general expression for the critical temperature in different dimensions and find that the critical temperature increases with decreasing dimension. We finally predict by first-principles $GW$-BSE calculations that experimentally accessible single-chain staircase Scandocene and Chromocene wires are an antiferromagnetic spin-triplet excitonic insulator and a ferromagnetic half-excitonic insulator, respectively.