Non-equilibrium spin-crossover in copper phthalocyanine

TL;DR

This paper demonstrates how tip-induced manipulation can control the spin state of copper phthalocyanine on an insulator, revealing a non-equilibrium spin crossover driven by electronic correlations and population inversion.

Contribution

It introduces a method to induce and observe spin state changes in CuPc via STM tip control, accounting for electronic correlations and population inversion effects.

Findings

Spin state of CuPc can be controlled by STM tip.

Population inversion leads to spin crossover.

Experimental signatures include nodal planes and current suppression.

Abstract

We demonstrate the tip induced control of the spin state of copper phthalocyanine (CuPc) on an insulator coated substrate. Accounting for electronic correlations, we find that, under the condition of energetic proximity of neutral excited states to the anionic groundstate, the system can undergo a population inversion towards these excited states. The resulting state of the system is accompanied by a change in the total spin quantum number. Experimental signatures of the crossover are the appearance of additional nodal planes in the topographical STM images as well as a strong suppression of the current near the center of the molecule. The robustness of the effect against moderate charge conserving relaxation processes has also been tested.