Direct measurement of photoinduced transient conducting state in multilayer 2H-MoTe2

TL;DR

This study uses a novel pump-probe system to directly measure the transient optical conductivity in 2H-MoTe2, revealing photoinduced insulator-metal and phase transition dynamics with high accuracy.

Contribution

Developed a near-infrared pump-THz to mid-infrared probe system to reliably measure transient optical constants in layered 2H-MoTe2, overcoming previous measurement challenges.

Findings

Photoexcitation at 690 nm induces a transient insulator-metal transition.

Photoexcitation at 2 μm has a smaller effect due to photon energy being below the band gap.

Transient response evolves towards 1T' phase at higher fluence.

Abstract

Ultrafast light-matter interaction has emerged as a powerful tool to control and probe the macroscopic properties of functional materials, especially two-dimensional transition metal dichalcogenides which can form different structural phases with distinct physical properties. However, it is often difficult to accurately determine the transient optical constants. In this work, we developed a near-infrared pump - terahertz to midinfrared (12-22 THz) probe system in transmission geometry to measure the transient optical conductivity in 2H-MoTe2 layered material. By performing separate measurements on bulk and thin-film samples, we are able to overcome issues related to nonuniform substrate thickness and penetration depth mismatch and to extract the transient optical constants reliably. Our results show that photoexcitation at 690 nm induces a transient insulator-metal transition, while photoexcitation at 2 um has a much smaller effect due to the photon energy being smaller than the band gap of the material. Combining this with a single-color pump-probe measurement, we show that the transient response evolves towards 1T' phase at higher flunece. Our work provides a comprehensive understanding of the photoinduced phase transition in the 2H-MoTe2 system.