Second harmonic generation in atomically thin MoTe2

TL;DR

This study investigates second harmonic generation in atomically thin MoTe2, revealing phase-dependent symmetry effects, high nonlinear susceptibility, and potential for phase transition detection in 2D materials.

Contribution

It reports the first detailed analysis of SHG in MoTe2, highlighting phase-dependent effects and demonstrating phase transition detection via SHG.

Findings

Strong SHG in odd-layer 2H-MoTe2 due to broken inversion symmetry

High second-order nonlinear susceptibility of 2.5 nm/V in monolayer MoTe2

Distinct polarization patterns for 2H and 1T' phases

Abstract

We have studied on optical second harmonic generations (SHGs) from atomically thin MoTe2 flakes with 2H and 1T' phases. From 2H-MoTe2 samples with odd (even) numbers of layers, strong (negligible) SHGs are observed due to the layer-dependent broken inversion symmetry. When pumped by a telecom-band laser, SHG from a monolayer 2H-MoTe2 is about one order of magnitude stronger than that from a monolayer WS2; an extremely high second-order nonlinear susceptibility of 2.5 nm/V is estimated, presenting the highest value among those reported in two-dimensional materials. SHG measurements in MoTe2 are also demonstrated as an efficient way to distinguish the 2H-to-1T' phase transition. Comparing to the SHG in 2H-MoTe2, 1T'-MoTe2's SHG has much lower efficiency and the polarization dependence is changed from six-fold to two-lobe pattern.