Evidence of topological gap opening in the surface state of Bi₂Se₃ by proximity to a magnetic insulator

Out-of-plane magnetism at the Bi₂Se₃/EuS interface is experimentally demonstrated and theoretically proposed [1,2,3], that is expected to break time-reversal-symmetry of topologically protected surface states (SSs). However, an exchange gap (EG) opening at the Dirac point due to proximity effect of the magnetic insulator (MI), EuS, is not observed before using transport studies, primarily due to dominant bulk conduction over the SSs. By using bottom gate voltage and external magnetic field studies, we report evidence of a metal-to-insulator transition at Bi₂Se₃/EuS interface, attributed to the opening of EG, with the signature of half-integer quantum Hall effect when Fermi level is tuned into the EG [4]. Our study also shows a gate-controlled enhanced interface magnetism at Bi₂Se₃/EuS interface which we attribute to the conduction carrier-mediated RKKY interactions [3]. Our efforts in this direction with suitable MI/TI/MI device will possibly allow us to demonstrate a switchable topological electronic device using magnetic proximity effect studies.
[1]Wei et al., Phys. Rev. Lett. 110, 186807 (2013)
[2]Katmis et al., Nature 533, 513 (2016)
[3]Kim et al., Phys. Rev. Lett. 119, 027201 (2017)
[4]Mathimalar et al., arXiv:1907.12770