Sputtering-induced reemergence of the topological surface state inBi2Se3

Abstract

We study the fate of the surface states of Bi 2 Se 3 under disorder with strength larger than the bulk gap, caused by neon sputtering and nonmagnetic adsorbates. We find that neon sputtering introduces strong but dilute defects, which can be modeled by a unitary impurity distribution, whereas adsorbates, such as water vapor or carbon monoxide, are best described by Gaussian disorder. Remarkably, these two disorder types have a dramatically different effect on the surface states. Our soft x-ray angle-resolved photoemission spectroscopy (ARPES) measurements combined with numerical simulations show that unitary surface disorder pushes the Dirac state to inward quintuplet layers, burying it below an insulating surface layer. As a consequence, the surface spectral function becomes weaker but retains its quasiparticle peak. This is in contrast to Gaussian disorder, which smears out the quasiparticle peak completely. At the surface of Bi 2 Se 3 , neon sputtering adds additional unitary scatterers to the Gaussian disorder of the adsorbates. Since the introduced unitary disorder pushes the surface state to inward layers, the effects of Gaussian disorder are reduced. As a result the ARPES signal becomes sharper upon sputtering.

Spin- and angle-resolved photoemission on topological materials

“…In real space this topological protection can be followed in the response to defects. The interface states will move around the defects by shifting away from the interface [8][9][10][11] , similar to the simplified picture for the edge state in the quantum hall effect. In momentum space, a topologically protected state has to cross the band gap and this crossing can't be lifted by small perturbations.…”

Effect of surface disorder on the chiral surface states of a three-dimensional quantum Hall system

“…In this work, we study the effect of surface disorder on the 2D chiral surface states using a 3D tight-binding lattice model 35,36 . Surface disorder has also been considered in the context of topological insulators [37][38][39][40][41][42] . Since surface disorder does not alter the bulk gap which protects the surface states, the surface conductance remains quantized, independent of the disorder strength 39,41 .…”

Electronic band structure of the buried SiO2/SiC interface investigated by soft x-ray ARPES

“…Wave functions of the STderived interface states, on the other hand, will oscillate and extend into the SiC bulk typically over a few unit cells or more (see Figure 1(c)) similar to ST surface states on Al (100) ($5nm) 7 or topological surface states on Bi 2 Se 3 (001) ($3nm). 16 Protected by the SiC bulk from their randomization by amorphous SiO 2 , the ST-derived interface states will show well-defined energies and band k-dispersions. 14 The different character of the DB-and ST-derived SiO 2 / SiC interface states will then determine the different photoemission (PE) response hU f jU i i.…”

“…Therefore, even at high energies, their hU f jU i i product, and thus high-energy photoemission response, is similar to those of the bulk SiC states. Related examples are Al (100) and Bi 2 Se 3 (001) surface states 7,16 which retain a significant photoemission response up to at least 1 keV, with the intensity oscillations as af u n c t i o no fh reflecting their Fourier composition. Hence, SX-ARPES is mostly sensitive to the ST-derived interface states with their sharp k-dispersions.…”

“…Hence, SX-ARPES is mostly sensitive to the ST-derived interface states with their sharp k-dispersions. 6,7,16 Figure 2 shows angle-integrated photoemission (PE) spectra of the Si 2p core levels, for the 4 nm thick oxide, measured through a series of increasing h as well as increasing photoelectron emission angle H relative to the surface normal. The spectra are acquired at p-polarization of the incident X-rays and aligned in binding energy E B to compensate for sample charging depending on h. The low-E B peak is attributed to the Si atoms in SiC and the high-E B peak to SiO 2 .…”