Observation of Optical and Electrical In-plane Anisotropy in High-mobility Few-layer ZrTe5

TL;DR

This study reveals significant optical and electrical in-plane anisotropy in few-layer ZrTe5, a 3D Dirac semimetal, with implications for understanding its exotic physical phenomena and potential applications.

Contribution

It provides the first detailed exploration of optical and electrical anisotropy in mechanically exfoliated few-layer ZrTe5, including experimental measurements and theoretical analysis.

Findings

Strong in-plane optical anisotropy observed via Raman spectroscopy.

Electrical conductance varies by 50% along different in-plane directions.

High electron mobility up to 44,000 cm2/Vs detected in magneto-resistance measurements.

Abstract

Transition metal pentatelluride ZrTe5 is a versatile material in condensed-matter physics and has been intensively studied since the 1980s. The most fascinating feature of ZrTe5 is that it is a 3D Dirac semimetal which has linear energy dispersion in all three dimensions in momentum space. Structure-wise, ZrTe5 is a layered material held together by weak interlayer van der Waals force. The combination of its unique band structure and 2D atomic structure provides a fertile ground for more potential exotic physical phenomena in ZrTe5 related to 3D Dirac semimentals. However the physical properties of its few-layer form have yet to be thoroughly explored. Here we report strong optical and electrical in-plane anisotropy of mechanically exfoliated few-layer ZrTe5. Raman spectroscopy shows significant intensity change with sample orientations, and the behavior of angle-resolved phonon modes at the gamma point is explained by theoretical calculation. DC conductance measurement indicates a 50% of difference along different in-plane directions. The diminishing of resistivity anomaly in few-layer samples indicates the evolution of band structure with reduced thickness. Low-temperature Hall experiment sheds lights on more intrinsic anisotropic electrical transport, with hole mobility of 3,000 and 1,500 cm2/Vs along a-axis and c-axis respectively. Pronounced quantum oscillations in magneto-resistance are observed at low temperatures with highest electron mobility up to 44,000 cm2/Vs.