Observation of quantum-tunnelling-modulated spin texture in ultrathin topological insulator Bi2Se3 films

Abstract

Understanding the spin-texture behaviour of boundary modes in ultrathin topological insulator films is critically essential for the design and fabrication of functional nanodevices. Here, by using spin-resolved photoemission spectroscopy with p-polarized light in topological insulator Bi 2 Se 3 thin films, we report tunnelling-dependent evolution of spin configuration in topological insulator thin films across the metal-to-insulator transition. We report a systematic binding energy-and wavevector-dependent spin polarization for the topological surface electrons in the ultrathin gapped-Dirac-cone limit. The polarization decreases significantly with enhanced tunnelling realized systematically in thin insulating films, whereas magnitude of the polarization saturates to the bulk limit faster at larger wavevectors in thicker metallic films. We present a theoretical model that captures this delicate relationship between quantum tunnelling and Fermi surface spin polarization. Our high-resolution spin-based spectroscopic results suggest that the polarization current can be tuned to zero in thin insulating films forming the basis for a future spin-switch nanodevice.

Fermi-level electronic structure of a topological-insulator/cuprate-superconductor based heterostructure in the superconducting proximity effect regime

“…No Dirac point gap is seen, which indicates that the 6 QL film is above the limit at which the two surfaces couple to each other, consistent with the previous report. 35,36 Fermi surface mapping over a wide momentum-space window is shown in Fig. 1e.…”

Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

“…Understanding the key parameters of a material that are relevant to its nontrivial topology is vital for utilizing the protected surface states in applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] . A topological crystalline insulator (TCI) is a new symmetry protected topological phase that is protected by crystalline space group symmetries [16][17][18] .…”

Edge states of a three-dimensional topological insulator

“…We have chosen k y > 0 and b x < 0 so that the states appears near the corner at (20,20) where the analysis around Eqs. (43)(44)(45)(46)(47)(48) is applicable. In accordance with the statement made after Eq.…”

“…For a given value of k y , we can think of the two Hamiltonians in Eqs. (43) as being unitarily equivalent to a one-dimensional Dirac equation with a mass term proportional to v k y +b x /2 on one side (the top surface) and to v k y on the other side (the side surface). (We are ignoring the orbital term (e/c)B x z here).…”

“…Junctions of different surfaces of TIs (which are sometimes separated by a geometrical step or a magnetic domain wall) [24][25][26][27][28][29][30][31][32] , polyhedral surfaces 33 , and junctions of surfaces of a TI with normal metals or magnetic materials 34 or superconductors 35,36 have also been studied. Effects of finite sizes [37][38][39][40][41][42][43] and different orientations 31,32,[44][45][46][47][48] on the surface states have been studied. Zero energy states at the edges of a thin strip have been studied in Ref.…”