Dielectric capping effects on binary and ternary topological insulator surface states

Abstract

Using a density-functional-based electronic structure method, we study the effect of crystalline dielectrics on the metallic surface states of Bismuth-and chalcogen-based binary and ternary three-dimensional topological insulator (TI) thin films. Crystalline quartz (SiO 2 ) and boron nitride (BN) dielectrics were considered. Crystalline approximation to the amorphous quartz allows one to study the effect of oxygen coverage or environmental effects on the surface-state degradation, which has gained attention recently in the experimental community. We considered both symmetric and asymmetric dielectric cappings to the surfaces of TI thin films. Our studies suggest that BN and quartz cappings have negligible effects on the Dirac cone surface states of both binary and ternary TIs, except in the case of an oxygen-terminated quartz surface. Dangling bond states of oxygens in oxygen-terminated quartz dominate the region close to Fermi level, thereby distorting the TI Dirac cone feature and burying the Dirac point in the quartz valence-band region. Passivating the oxygen-terminated surface with atomic hydrogen removes these dangling bond states from the Fermi-surface region, and consequently the clear Dirac cone is recovered. Our results are consistent with recent experimental studies of TI surface degradation in the presence of oxygen coverage.

Large Enhancement of Thermal Conductivity and Lorenz Number in Topological Insulator Thin Films

“…Therefore, in the BTS221 TI films, surface electrons and bulk phonons are the major heat carriers. It remains a concern that the SiO2 dielectric layer underneath the TI film during the electrical measurements could alter the electronic properties of the surface states, for example by shifting the fermi level relative to the Dirac point 29,30 . There is also a concern that the BTS221 device fabrication process for the electrical measurements could alter the BTS221 films.…”

Tuning the vertical location of helical surface states in topological insulator heterostructures via dual-proximity effects

“…Recently, a number of peculiar quantum phenomena have been discovered in various TI-based heterostructures1415161718192021272829303132333435, such as Majorana fermions induced by the superconducting proximity effect19, topological magnetoelectric effect4, quantized anomalous Hall effect14, and electron reservoir effect of TSS in surface catalysis21. Although the TSS was confirmed to be robust as the TI surface is intruded under diverse conditions provided that time reversal symmetry is preserved212728293031, its properties can be largely modified due to the tunability in the magnitude of interfacial coupling within the heterostructures.…”

Density functional study of ternary topological insulator thin films

“…It is interesting to note that the predicted induced gaps in Tl-based TIs, for the same film thickness, are larger than the binary Bi-based TIs. 20 To understand the origin of the gap at the Dirac point with decreasing film thickness, we first map out the surface state Figs. 1(a) and 1(b).…”