Abstract
Dirac fermions in condensed matter physics hold great promise for novel fundamental physics, quantum devices and data storage applications. IV-VI semiconductors, in the inverted regime, have been recently shown to exhibit massless topological surface Dirac fermions protected by crystalline symmetry, as well as massive bulk Dirac fermions. Under a strong magnetic field (B), both surface and bulk states are quantized into Landau levels that disperse as B1/2, and are thus difficult to distinguish. In this work, magneto-optical absorption is used to probe the Landau levels of high mobility Bi-doped Pb0.54Sn0.46Te topological crystalline insulator (111)-oriented films. The high mobility achieved in these thin film structures allows us to probe and distinguish the Landau levels of both surface and bulk Dirac fermions and extract valuable quantitative information about their physical properties. This work paves the way for future magnetooptical and electronic transport experiments aimed at manipulating the band topology of such materials.
Highlights
Transport and optical probes, one needs to be able to understand and rule out contributions from bulk states that may contribute similar, if not identical signatures
We performed detailed magneto-optical absorption measurements to map out the Landau level (LL) spectrum of the bulk and surface bands of high mobility (111) epitaxial Pb1-xSnxTe (x = 0.45–0.47) films grown by molecular beam epitaxy (MBE)
High mobility Pb1-xSnxTe films are grown by molecular beam epitaxy (MBE) on cleaved (111) BaF2 substrates, in a Varian Gen II system with a base pressure of 10−10 mbar
Summary
Transport and optical probes, one needs to be able to understand and rule out contributions from bulk states that may contribute similar, if not identical signatures. Previous magnetooptical[26,27] and transport studies[25,28,29] have proven difficult the task of probing, identifying and assigning the Landau levels of topological materials This is mainly due to the fact that the Fermi level in such systems is pinned to the bulk states, and the mobility is limited, requiring fields exceeding 15T to achieve clear Landau quantization[30]. After reliably mapping out all bulk contributions, we are able to identify a cyclotron resonance feature pertaining to a massless Dirac state having a Fermi velocity vf = 7.3 × 105 m/s, attributed to the Γ-point Dirac cone This is reproduced in two samples having slightly different carrier densities. Our results are in agreement with previous studies on the bulk bands in SnTe32, Pb1-xSnxTe33, and PbTe34–36 and recent calculations of the band structure of the (111) surface states in TCI systems[9,14]
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