Signature of gate-controlled magnetism and localization effects at Bi2Se3/EuS interface

Abstract

Proximity of a topological insulator (TI) surface with a magnetic insulator (MI) can open an exchange gap at the Dirac point leading to exploration of surface quantum anomalous Hall effect. An important requirement to observe the above effect is to prevent the topological breakdown of the surface states (SSs) due to various interface coupling effects and to tune the Fermi level at the interface near the Dirac point. In this work, we demonstrate the growth of high-quality c-axis oriented strain-free layered films of TI, Bi2Se3, on amorphous SiO2 substrate in proximity to an MI, europium sulfide (EuS), that show stronger weak anti-localization response from the surface than previous studies with epitaxially interfaced heterostructures. Importantly, we find gate and magnetic field cooling modulated localization effects in the SSs, attributed to the position of interface Fermi level within the band gap that is also corroborated from our positron annihilation spectroscopy measurements. Furthermore, our experiments provide a direct evidence of gate-controlled enhanced interface magnetism in EuS arising from the carrier mediated Ruderman–Kittel–Kasuya–Yosida interactions across the Bi2Se3/EuS interface. These findings demonstrate the existence of complex interfacial phenomena affecting the localization response of the SSs that might be important in proximity engineering of the TI surface to observe surface quantum Hall effects.

Recent Progress in Proximity Coupling of Magnetism to Topological Insulators

“…In this case, the TI surface states are not only affected by the magnetization, the highly coherent TSS mediate an RKKY interaction between the interface magnetic moments of the MI, enhancing its magnetic order and T c . [ 131,132 ] Some other studies even showed this exchange‐coupling mediated by the Dirac fermions can be anisotropic due to the spin‐momentum locking, and depends on the surface chemical potential. [ 133,134 ] According to another proposed mechanism, perpendicular magnetic anisotropy is induced in FMI heterostructures due to strain caused by lattice mismatch and enhanced by the spin–orbit coupling (SOC) of the TSS.…”

Progress and prospects in the quantum anomalous Hall effect

“…Extraordinary care is warranted in the TI growth, and the magnetic interfacial heterostructuring thereafter, to properly mitigate the adverse influence from residual chalcogen atoms since optimal TI demands a Se/Te-rich growth condition. This intriguing discovery has opened a vibrant arena for proximitized MI/TI heterostructures [110][111][112][113][114][115][116][117][118][119][120][121].…”

In-depth Analysis of Anisotropic Magnetoconductance in Bi$_2$Se$_3$ thin films with electron-electron interaction corrections

“…However, capping the Bi 2 Se 3 films with thick Se layer can reduce the top surface carrier concentration [48] significantly and can bring the surface E F closer to the Dirac point. This mismatch between the surface and bulk E F can further lead to a upward band bending near the top surface and can bring the bulk Fermi level closer to the conduction band-edge [26,50] making ∆/2E F → 1 for band-edge bulk states. Therefore, in our Bi 2 Se 3 thin films, bandedge WL channel and surface WAL channels may coexist.…”

“…In experiments, the WAL behaviour is observed as an upward cusp near zero field in magnetoconductance (MC) measurements [10][11][12][13][14][15][16][17]. WAL signal in the MC allows us to probe the electronic modifications in TSS due to finite film thickness [17][18][19], surface-bulk coupling [20,21], inter-surface coupling [17,22,23], magnetic doping [14,15] and magnetic proximity effect [16,[24][25][26]. Recent theoretical [27] and experimental [28,29] investigations show that a WAL signal appears from the TSSs even when magnetic field is applied parallel to the film plane due to the finite penetration depth of the surface states.…”