Anomalous Decay of Quantum Resistance Oscillations of Two Dimensional Helical Electrons in Magnetic Field

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 $\theta$ from the normal to the conducting layer. Strong decrease of oscillation amplitude A is observed with the tilt: $A\sim \exp (-\xi /cos(\theta ))$, where $\xi$ is a constant. Evolution of the oscillations with temperature T shows that the parameter $\xi$ contains two terms: $\xi ={\xi }_1+{\xi }_{2}T$. The temperature independent term, ${\xi }_1$, describes reduction of electron mean free path in magnetic field B pointing toward suppression of the topological protection of the electron states against impurity scattering. The temperature dependent term, ${\xi }_{2}T$, indicates increase of the reciprocal velocity of 2D helical electrons suggesting modification of the electron spectrum in magnetic fields.

5 pages, 5 figures