A Top-Loading Point-Contact Spectroscopy Probe with In-Situ Sample Exchange for Dilution Refrigerators

TL;DR

This paper presents a cryogenic point-contact spectroscopy system integrated with a dilution refrigerator, enabling stable, in-situ measurements of quantum materials at millikelvin temperatures and high magnetic fields.

Contribution

The authors develop a novel PCS probe with in-situ sample exchange and demonstrate its effectiveness on a superconductor at ultra-low temperatures.

Findings

Successful operation at 30 mK demonstrating stable point contacts.

Spectroscopic features consistent with superconductivity in Ta-doped TiSe2.

The platform enables detailed studies of quantum materials at millikelvin temperatures.

Abstract

We report the design and implementation of a point-contact spectroscopy (PCS) system integrated with a dilution refrigerator, enabling measurements down to 30 mK. The setup employs a needle-anvil geometry with a cryogenic piezo-driven nanopositioner for in-situ formation of mesoscopic point contacts. We discuss the thermal anchoring strategies that enable efficient cooling of the probe to ultra-low temperatures and reliable measurements. We also address positioner-related challenges and the solutions implemented to ensure stable operation at millikelvin temperatures. The performance of the probe is demonstrated through point contact spectroscopy on Ta-doped TiSe$_2$ (Ta$_x$Ti$_{1-x}$Se$_2$, $x = 0.2$), a superconductor with $T_c \approx 2.3$ K. The spectra exhibit well-defined superconducting features that systematically diminish with increasing temperature and magnetic field. The platform provides a robust and versatile tool for spectroscopic investigations of superconductors and other quantum materials at millikelvin temperatures and high magnetic fields.