Anomalous Decay of Quantum Resistance Oscillations of 2D Helical Electrons in Magnetic Field

Z D Kvon,N N Mikhailov,S Abedi,S A Vitkalov

doi:10.1038/s41598-020-64385-7

Z D Kvon, N N Mikhailov + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-64385-7

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Abstract

Shubnikov de Haas resistance oscillations of highly mobile two dimensional helical electrons propagating on a conducting surface of strained HgTe 3D topological insulator are studied in magnetic fields B tilted by angle θ from the normal to the conducting layer. Strong decrease of oscillation amplitude A is observed with the tilt: {boldsymbol{A}}sim {boldsymbol{e}}{boldsymbol{x}}{boldsymbol{p}}(,-,{boldsymbol{xi }}/{boldsymbol{c}}{boldsymbol{o}}{boldsymbol{s}}({boldsymbol{theta }})), where ξ is a constant. Evolution of the oscillations with temperature T shows that the parameter {boldsymbol{xi }} contains two terms: {boldsymbol{xi }}={{boldsymbol{xi }}}_{1}+{{boldsymbol{xi }}}_{2}{boldsymbol{T}}. The temperature independent term, {{boldsymbol{xi }}}_{{bf{1}}}, signals possible reduction of electron mean free path {l}_{q} and/or enhancement of in-homogeneous broadening of the oscillations in magnetic field B. The temperature dependent term, {{boldsymbol{xi }}}_{{bf{2}}}{boldsymbol{T}}, indicates increase of the reciprocal velocity of 2D helical electrons: delta ({v}_{F}^{-1})sim B suggesting modification of the electron spectrum in magnetic fields. Results are found in good agreement with proposed phenomenological model.

Highlights

We have introduced a phase of the SdH oscillations, φ
We have investigated the effect of the resistance normalization on results of the analysis of the angular dependence of the SdH oscillations
For very different normalizing resistance: ρN1 = ρxx(0) and ρN2 = ρxx(B⊥) we have found no difference in the extracted parameter ξ controlling the angular dependence (see Fig. 4(b))

Summary

Methods

Since HgTe films grown directly on CdTe suffer from dislocations due to the lattice mismatch, our 80 nm thick HgTe films were separated from the CdTe substrate by a 20 nm thin Cd0.7 Hg0.3 Te buffer layer. This buffer layer significantly increases the electron mobility up to 40 m2/(Vs)[14]. The structures are equipped with a TiAu gate providing the possibility to tune the Fermi energy EF inside the insulating gap ∆g≈ 15 mV14 and to change the density n = nt + nb of 2D helical electrons, where nt (nb) is the density of 2D electrons located at the top (bottom) of HgTe film. Reported in this paper measurements are done, when Fermi energy is inside the gap Δg

Results

Discussion

Conclusion