Cotunneling signatures of Spin-Electric coupling in frustrated triangular molecular magnets

TL;DR

This paper proposes using cotunneling transport experiments to measure the spin-electric coupling in frustrated triangular molecular magnets, linking theoretical predictions with experimental detection of ground state splittings.

Contribution

It introduces a method to determine the spin-electric coupling strength via cotunneling conductance measurements, supported by a Hubbard-model analysis and master-equation calculations.

Findings

Electric field causes detectable ground state splitting in cotunneling conductance.

The Hubbard model relates parameters to the spin-electric coupling constant.

Predicted regimes for experimental extraction of the coupling constant.

Abstract

The ground state of frustrated (antiferromagnetic) triangular molecular magnets is characterized by two total-spin $S =1/2$ doublets with opposite chirality. According to a group theory analysis [M. Trif \textit{et al.}, Phys. Rev. Lett. \textbf{101}, 217201 (2008)] an external electric field can efficiently couple these two chiral spin states, even when the spin-orbit interaction (SOI) is absent. The strength of this coupling, $d$, is determined by an off-diagonal matrix element of the dipole operator, which can be calculated by \textit{ab-initio} methods [M. F. Islam \textit{et al.}, Phys. Rev. B \textbf{82}, 155446 (2010)]. In this work we propose that Coulomb-blockade transport experiments in the cotunneling regime can provide a direct way to determine the spin-electric coupling strength. Indeed, an electric field generates a $d$-dependent splitting of the ground state manifold, which can be detected in the inelastic cotunneling conductance. Our theoretical analysis is supported by master-equation calculations of quantum transport in the cotunneling regime. We employ a Hubbard-model approach to elucidate the relationship between the Hubbard parameters $t$ and $U$, and the spin-electric coupling constant $d$. This allows us to predict the regime in which the coupling constant $d$ can be extracted from experiment.