Abstract
Topological crystalline insulators possess metallic surface states protected by crystalline symmetry, which are a versatile platform for exploring topological phenomena and potential applications. However, progress in this field has been hindered by the challenge to probe optical and transport properties of the surface states owing to the presence of bulk carriers. Here, we report infrared reflectance measurements of a topological crystalline insulator, (001)-oriented Pb1−xSnxSe in zero and high magnetic fields. We demonstrate that the far-infrared conductivity is unexpectedly dominated by the surface states as a result of their unique band structure and the consequent small infrared penetration depth. Moreover, our experiments yield a surface mobility of 40,000 cm2 V−1 s−1, which is one of the highest reported values in topological materials, suggesting the viability of surface-dominated conduction in thin topological crystalline insulator crystals. These findings pave the way for exploring many exotic transport and optical phenomena and applications predicted for topological crystalline insulators.
Highlights
Topological crystalline insulators possess metallic surface states protected by crystalline symmetry, which are a versatile platform for exploring topological phenomena and potential applications
Dirac-like surface states (SS) that are protected by crystalline symmetry[1, 2] instead of time-reversal symmetry[18,19,20]
The spectral features in magneto-reflectance spectra below 25 meV can be attributed to a dominant resonance at ωscs / B based on theoretical study of cyclotron resonance (CR) of the SS, the frequency of which obtained from our data is quantitatively consistent with those estimated from previous scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) experiments
Summary
The actual composition is determined from the bulk band gap[4] as discussed below. Our samples are n-doped with the Fermi energy EF in the bulk conduction band[3]. The zero field σ1(ω) spectrum exhibits a Drude component below 25 meV and a threshold-like feature around 100 meV. The threshold feature in σ1(ω) can be assigned to the onset of inter-band transitions for the bulk around Einter % Δ þ EF þ mc mv as illustrated in the inset of Fig. 1c, where Δ is the bulk band gap, the Fermi energy EF is defined with respect to the bottom of the conduction band, mc and mv are effective masses of the conduction and valence band, respectively.
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