High quality-factor mechanical resonators based on WSe2 monolayers

TL;DR

This study demonstrates that monolayer WSe2 resonators exhibit exceptionally high quality factors at cryogenic temperatures, surpassing graphene, and enables new opto-mechanical applications involving 2D materials.

Contribution

The paper reports the first measurement of high Q-factors in monolayer WSe2 resonators at cryogenic temperatures, revealing their potential for advanced quantum opto-mechanical systems.

Findings

Q-factor reaches 1.6E4 at liquid nitrogen temperature

Q-factor reaches 4.7E4 at liquid helium temperature

Thermal contraction causes significant increase in resonant frequency

Abstract

Suspended monolayer transition metal-dichalcogenides (TMD) are membranes that combine ultra-low mass and exceptional optical properties, making them intriguing materials for opto-mechanical applications. However, the low measured quality factor of TMD resonators has been a roadblock so far. Here, we report an ultrasensitive optical readout of monolayer TMD resonators that allows us to reveal their mechanical properties at cryogenic temperatures. We find that the quality factor of monolayer WSe2 resonators greatly increases below room temperature, reaching values as high as 1.6E^4 at liquid nitrogen temperature and 4.7E^4 at liquid helium temperature. This surpasses the quality factor of monolayer graphene resonators with similar surface areas. Upon cooling the resonator, the resonant frequency increases significantly due to the thermal contraction of the WSe2 lattice. These measurements allow us to experimentally study the thermal expansion coefficient of WSe2 monolayers for the first time. High Q-factors are also found in resonators based on MoS2 and MoSe2 monolayers. The high quality-factor found in this work opens new possibilities for coupling mechanical vibrational states to two-dimensional excitons, valley pseudospins, and single quantum emitters, and for quantum opto-mechanical experiments based on the Casimir interaction.