Suppression of Ground-State Magnetization in Finite-Sized Systems Due to Off-Diagonal Interaction Fluctuations

TL;DR

This paper demonstrates that off-diagonal interaction fluctuations in finite disordered fermionic systems suppress ground-state magnetization, leading to a spin gap and potential experimental signatures in Coulomb blockade measurements.

Contribution

It reveals how off-diagonal interaction fluctuations compete with exchange effects, influencing ground-state spin configurations in finite disordered systems.

Findings

Off-diagonal fluctuations favor low-spin ground states at large interaction amplitudes.

A spin gap larger for odd-spin ground states is predicted due to these fluctuations.

Suppression of magnetization is observable in Coulomb blockade transport experiments.

Abstract

We study a generic model of interacting fermions in a finite-sized disordered system. We show that the off-diagonal interaction matrix elements induce density of states fluctuations which generically favor a minimum spin ground state at large interaction amplitude, $U$. This effect competes with the exchange effect which favors large magnetization at large $U$, and it suppresses this exchange magnetization in a large parameter range. When off-diagonal fluctuations dominate, the model predicts a spin gap which is larger for odd-spin ground states as for even-spin, suggesting a simple experimental signature of this off-diagonal effect in Coulomb blockade transport measurements.