A top-loading point-contact spectroscopy probe with in-situ sample exchange for dilution refrigerators.

Abstract

We report the design and implementation of a point-contact spectroscopy 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 TiSe2 (TaxTi1-xSe2, x = 0.2), a superconductor with Tc ≈ 2.3 K and niobium with Tc ≈ 9.2 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.