Signatures of in-plane and out-of-plane magnetization generated by synchrotron radiation in magnetically doped and pristine topological insulators

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

doi:10.1103/physrevb.97.245407

Abstract

Possibility of in-plane and out-of-plane magnetization generated by synchrotron radiation (SR) in magnetically doped and pristine topological insulators (TIs) is demonstrated and studied by angle-resolved photoemission spectroscopy. We show experimentally and by ab initio calculations how nonequal depopulation of the Dirac cone (DC) states with opposite momenta in V-doped and pristine TIs generated by linearly polarized SR leads to the hole-generated uncompensated spin accumulation followed by the SR-induced magnetization via spin-torque effect. Moreover, the photoexcitation of the DC is asymmetric, and it varies with the photon energy. We find a relation between the photoexcitation asymmetry, the generated spin accumulation, and the induced in-plane and out-of-plane magnetic field. Experimentally the SR-generated in-plane and out-of-plane magnetization is confirmed by the ${k}_{\ensuremath{\parallel}}$ shift of the DC position and by the gap opening at the Dirac point even above the Curie temperature. Theoretical predictions and estimations of the measurable physical quantities substantiate the experimental results.

Highlights

The photoexcitation by laser or synchrotron radiation is accompanied by depopulation of the initial states, which influences the electronic structure observed in photoemission (PE) measurements
We show experimentally and by ab initio calculations how nonequal depopulation of the Dirac cone (DC) states with opposite momenta in V-doped and pristine topological insulators (TIs) generated by linearly polarized synchrotron radiation (SR) leads to the hole-generated uncompensated spin accumulation followed by the SR-induced magnetization via spintorque effect
In materials with helical spin structure like topological insulators (TIs) [1,2,3,4] the imbalance in photoexcitation of the DC states with opposite momenta created by circularly polarized laser or SR can be effectively used for generation of the surface spin-polarized currents that depend on the helicity of the radiation polarization [5,6,7,8,9,10]

Summary

INTRODUCTION

The photoexcitation by laser or synchrotron radiation is accompanied by depopulation of the initial states, which influences the electronic structure observed in photoemission (PE) measurements. We relate this phenomenon to an asymmetry in the depopulation of the DC states with opposite momenta, which leads to a hole-generated uncompensated spin accumulation. The oblique incidence of SR breaks the symmetry of the angular distribution of the photocurrent, and the different photoemission intensity at k and −k [26,27] can be a source of the SR-generated uncompensated spin accumulation and an induced magnetization This problem is especially important for magnetically doped TIs, because the DP gap opening due to the TRS breaking, its value and origin (magnetization or hybridization derived) are being actively discussed; see, for instance, Ref. In the current work we analyze how the local surface in-plane and out-of-plane magnetic field can be developed in such kind of 2D magnetic materials under nonequal photoexcitation of the DC states with opposite momenta at different photon energy

ASYMMETRY IN THE INTENSITY OF THE DC STATES VS PHOTON ENERGY

Findings

METHODS