A Platform for Far-Infrared Spectroscopy of Quantum Materials at Millikelvin Temperatures

TL;DR

This paper presents a new experimental platform enabling optical spectroscopy of quantum materials at millikelvin temperatures, allowing insights into quantum phases inaccessible by other methods.

Contribution

The paper introduces a novel platform combining optical spectroscopy and electronic transport at ultralow temperatures inside a dilution refrigerator, capable of studying both bulk and 2D materials.

Findings

Successful Fourier transform infrared spectroscopy on monolayer WTe₂ and multilayer 1T-TaS₂.

Spectroscopic measurements achieved at temperatures as low as 43 mK.

Spectral range from near-infrared to terahertz, with magnetic field capabilities up to 5 T.

Abstract

Optical spectroscopy of quantum materials at ultralow temperatures is rarely explored, yet it may provide critical characterizations of quantum phases not possible using other approaches. We describe the development of a novel experimental platform that enables optical spectroscopic studies, together with standard electronic transport, of materials at millikelvin temperatures inside a dilution refrigerator. The instrument is capable of measuring both bulk crystals and micron-sized two-dimensional van der Waals materials and devices. We demonstrate the performance by implementing photocurrent-based Fourier transform infrared spectroscopy on a monolayer WTe$_2$ device and a multilayer 1T-TaS$_2$ crystal, with a spectral range available from the near-infrared to the terahertz regime and in magnetic fields up to 5 T. In the far-infrared regime, we achieve spectroscopic measurements at a base temperature as low as ~ 43 mK and a sample electron temperature of ~ 450 mK. Possible experiments and potential future upgrades of this versatile instrumental platform are envisioned.