Dirac cone intensity asymmetry and surface magnetic field in V-doped and pristine topological insulators generated by synchrotron and laser radiation

A M Shikin,L Petaccia,A A Rybkina,P N Skirdkov,K A Zvezdin,I I Klimovskikh,O E Tereshchenko,K A Kokh,A Kimura,D A Estyunin,A G Rybkin,D M Sostina,V Yu Voroshnin,G Di Santo,A K Zvezdin

doi:10.1038/s41598-018-24716-1

Abstract

Effect of magnetization generated by synchrotron or laser radiation in magnetically-doped and pristine topological insulators (TIs) is presented and analyzed using angle-resolved photoemission spectroscopy. It was found that non-equal photoexcitation of the Dirac cone (DC) states with opposite momenta and spin orientation indicated by the asymmetry in photoemission intensity of the DC states is accompanied by the k||-shift of the DC states relative to the non-spin-polarized conduction band states located at k|| = 0. We relate the observed k||-shift to the induced surface in-plane magnetic field and corresponding magnetization due to the spin accumulation. The direction of the DC k||-shift and its value are changed with photon energy in correlation with variation of the sign and magnitude of the DC states intensity asymmetry. The theoretical estimations describe well the effect and predict the DC k||-shift values which corroborate the experimental observations. This finding opens new perspectives for effective local magnetization manipulation.

Highlights

It is well known that 2D metallic-like topological surface states (TSSs) formed at the surface of topological insulators (TIs) are characterized by the unique Dirac cone (DC) helical spin structure with opposite spin orientation for the states with opposite momentum[1,2,3,4]
Non-equal photoexcitation of the DC states with opposite momenta is followed by the hole-generated uncompensated in-plane spin accumulation with the spin locked perpendicular to momentum that induces a corresponding in-plane and out-of-plane magnetic field via spin-torque effect[15]
The direction of the induced in-plane magnetic field is aligned parallel to the generated uncompensated spin accumulation, which is determined by the asymmetry in the hole generation with opposite profiles of the intensity of the DC and bottom CB states measured at the cutting energies marked by the horizontal green and red lines

Summary

Introduction

It is well known that 2D metallic-like topological surface states (TSSs) formed at the surface of TIs are characterized by the unique DC helical spin structure with opposite spin orientation for the states with opposite momentum[1,2,3,4]. The V-doped TIs, studied in the current work, can be considered at the used temperatures (17–20 K) as materials with paramagnetic bulk and 2D surface magnetic layer For such kind of magnetic systems we study a possibility of generation of the surface in-plane magnetic field and corresponding magnetization under photoexcitation by synchrotron and laser radiation with varied photon energy at the temperatures above the bulk Curie temperature. We show that the asymmetry in the TSS intensity under photoexcitation by linearly-polarized synchrotron and laser radiation induces an effective magnetic field at the surface both in magnetically-doped and pristine TIs as indicated by the k||-shift of the Dirac point (DP) position Both the TSS intensity asymmetry and the resulting DP k||-shift show a clear dependence on the photon energy. This provide a way for changing the induced in-plane magnetic field and for switching between the spontaneous out-of-plane and the in-plane magnetization in magnetically-doped TI induced by the laser or synchrotron radiation (SR)

Methods

Results

Conclusion