Experimental search for one-dimensional edge states at surface steps of the topological insulator Bi2Se3 : Distinguishing between effects and artifacts

Abstract

The results of a detailed study of the topological insulator Bi2Se3 surface state energy structure in the vicinity of surface steps using scanning tunneling microscopy and spectroscopy methods are presented. An increase in the chemical potential level µ near the step edge is observed. The value of the increase δµ ∼ 0.1 eV is found to correlate with the step height. The effect is caused by redistribution of electron wave functions between the outer and inner edges of surface steps, as known for normal metals. The smaller value of the chemical potential shift and its larger characteristic length of ∼ 10 nm reflect specifics of the helical surface states. This increase is accompanied by enlargement of the normalized differential tunneling conductance in the helical surface states energy region and thereby produces the illusion of the appearance of edge states. We show that the enlargement is reproduced in the framework of the tunneling model taking into account the tunneling gap transparency change when the chemical potential moves away from the Dirac point. arXiv:1609.08911v5 [cond-mat.mtrl-sci]

Fermi Level Manipulation through Native Doping in the Topological Insulator Bi2Se3

“…As the spectra are acquired over a 1 μm 2 area, it is likely that some of the measured positions were close to step edges. Previous studies have shown that the E F behavior close to these step edges deviates from E F on the Bi 2 Se 3 terraces and may be more susceptible to chalcogen loss . This may explain the wider E C – E F spread observed in samples after high-temperature anneals.…”

Connection topology of step edge state bands at the surface of a three dimensional topological insulator

“…Bound states at quintuple layer step edges have been observed for the related TIs Bi 2 Se 3 and Bi 2 Te 3 [16,38], and a recent STM analysis has been interpreted to suggest that they may be a form of 1D electron gas brought on by an effective scalar potential at the step [38]. The in-gap surface states of these materials have large wavelengths (λ>5 nm), meaning that the real-space structure of the step edge potential is not well resolved on this basis.…”

Structural Characterization of Defects in the Topological Insulator Bi2Se3 at the Picometer Scale

“…Imaging parameters: V b = −200 mV, I = 20 pA. (c) Differential conductance spectrum measured on the Bi 2 Se 3 sample with a metallic tip with a flat density of states. The vertical dashed line marks the minimum in the band gap at V b = −335 mV, which can be associated with the Dirac point. ,, The slight kink marked by the black arrow at around V b = −100 mV is caused by the onset of the bulk conduction band. , Both spectral features lie below V b = 0 V, which shows the n-type doping of the Bi 2 Se 3 sample.…”

“…The spectrum was measured with a metal tip with a flat density of states and the d I /d V signal is therefore directly proportional to the local density of states of the Bi 2 Se 3 sample . In contrast to the idealized band structure of Bi 2 Se 3 shown in ref , the onset of the bulk conduction band (marked by the black arrow in Figure c) lies below the Fermi level (corresponding to a bias voltage of V b = 0 V), and the Dirac point, which corresponds to the minimum in the d I /d V spectrum (dashed line), is located at V b = −335 mV. ,, …”