New driven mechanisms for STM-ESR

A. FERRON; SERGIO GOMEZ; SANTIAGO RODRIGUEZ; FERNÁNDEZ-ROSSIER, JOAQUÍN

Congreso; KPS 2022 Spring Meeting; 2022

QNS

During this talk we address the problem of electronic spin resonance of an individual atom on a surfacedriven by a scanning tunneling microscope. Several mechanisms have been proposed so far, some of thembased on the modulation of exchange and crystal field associated with a piezoelectric displacement of theadatom driven by the radio frequency (RF) tip electric field. As the distance between the tip and the adatomvaries in the experiment, the mechanisms involved should change. We know that, as the experiment is carriedout, the driven mechanisms involved will have signatures of exchange interaction, magnetic dipole interaction,modulation of the adatom’s crystal field and even some signature of the modulation of the gyromagnetic factor.We discuss thoroughly the cases of hydrogenated Ti (S= 1/2) and Fe (S= 2) on MgO, relevant forrecent experiments. We model the system using two approaches. First, we performed calculations by directdiagonalization of a many electron Hamiltonian considering the electrons in the d shell of the ad-atom. All themicroscopic models are constructed using density functional theory (DFT) calculations. Second, we obtainsome pseudoanalytical results using an effective spin model which helps us to understand some fundamentalaspects. Both, microscopic model and effective Hamiltonian, are constructed taking into account the exchangeand magnetic dipolar interaction between the ad-atom and the spin polarized tip.At the end of this talk we will sketch a model to account for the driving of ESR-STM via modulation ofexchange between a probe spin and a nearby surface spin. We also consider the exchange modulationbetween the tip an the probe spin. We work out the case of Ti-H dimer and Fe as a nearby surface spin. Wealso analyze the effect of the tip electric field on the piezoelectric displacement of both atoms, by means of DFTcalculation.