Topological surface states in thick partially relaxed HgTe films

Abstract

Surface states of topological insulators (TIs) have been playing the central role in the majority of outstanding investigations in low-dimensional electron systems for more than 10 years. TIs based on high quality strained HgTe films demonstrate a variety of subtle physical effects. The strain leads to a bulk band gap, but limits a maximum HgTe strained film thickness, and, therefore, the majority of experiments were performed on the films with a thickness of less than 100 nm. Since a spatial separation of topological states is crucial for the study of a single surface response, the HgTe thickness is essential to be increased further. In this work, by combining transport measurements together with capacitance spectroscopy, we performed the analysis of a 200 nm partially relaxed HgTe film. The Drude fit of the classical magnetotransport revealed the ambipolar electron-hole transport with a high electron mobility. The detailed analysis of Shubnikov-de Haas oscillations, both in conductivity and capacitance, allowed us to distinguish three groups of electrons, identified as electrons on top and bottom surfaces and bulk electrons. The indirect bulk energy gap value was found to be close to zero. It was established that the significant gap decrease does not affect the surface states which are found to be well-resolved and spin non-degenerate. The presented techniques allow the investigations of other 3D TIs, regardless of the presence of bulk conductivity.

Weak antilocalization in partially relaxed 200-nm HgTe films

“…1 (a) we schematically show cross-section and a schematic top view of the system under study. The 200-nm HgTe film is sandwiched between thin Cd 0.6 Hg 0.4 Te barriers and is partially relaxed [25], a Ti/Au gate has been deposited on the 200-nm Si 3 N 4 plus 100-nm SiO 2 insulator grown by a low temperature chemical vapor deposition process.…”

“…Thus, the study of thicker HgTe films is also desirable because of a higher separation between the surface states, their weaker mutual electrostatic coupling, and possible hybridization. Recently [25,5], it has been shown that partially relaxed 200-nm HgTe films have a near zero bulk energy gap, but also host similar to what the strained 80-nm system has -the spin non-degenerate surface states.…”

Spin and charge transport through a helical Aharonov-Bohm interferometer with a strong magnetic impurity

“…This case corresponds to the ideal reflection of electrons on the impurity. Fourier spectrum of conductance oscillations is convenient representation for the analysis of experimental data [37,38]. Remarkably, that Fourier coefficients of the transmissions coefficient, T (n) = dφ T (φ)e i4πφn , obey universal relation…”

Terahertz Magnetospectroscopy of Cyclotron Resonances from Topological Surface States in Thick Films of CdxHg1−xTe

“…The values of sheet densities and mobilities for different types of carriers can be extracted using the two‐component classical Drude model, which was successfully implemented for thin HgTe films. [ 11,38,41 ] The values of sheet electron density obtained from such modeling are shown in Table 1. In this table, we also provide the values of average volume electron density n , which are obtained from the corresponding sheet electron densities as , where w denotes the corresponding film thicknesses (Figure 1b–f).…”