An ultrahigh-vacuum cryostat for simultaneous scanning tunneling microscopy and magneto-transport measurements down to 400mK

TL;DR

This paper describes a compact, ultrahigh-vacuum cryostat with a scanning tunneling microscope capable of operating at 400 mK, enabling detailed spectroscopic and magneto-transport measurements on microstructured samples.

Contribution

It introduces a novel cryostat design integrating STM and magneto-transport capabilities in a compact setup suitable for low-temperature physics research.

Findings

Achieved an energy resolution of 120 meV in tunneling spectroscopy.

Demonstrated stable operation with a vertical noise of 1 pm rms.

Operated near the physical noise limit with a feature size of 60 mV in Josephson measurements.

Abstract

We present the design and calibration measurements of a scanning tunneling microscope setup in a 3He ultrahigh-vacuum cryostat operating at 400 mK with a hold time of 10 days. With 2.70 m in height and 4.70 m free space needed for assembly, the cryostat fits in a one-story lab building. The microscope features optical access, an xy table, in situ tip and sample exchange, and enough contacts to facilitate atomic force microscopy in tuning fork operation and simultaneous magneto-transport measurements on the sample. Hence, it enables scanning tunneling spectroscopy on microstructured samples which are tuned into preselected transport regimes. A superconducting magnet provides a perpendicular field of up to 14 T. The vertical noise of the scanning tunneling microscope amounts to 1 pmrms within a 700 Hz bandwidth. Tunneling spectroscopy using one superconducting electrode revealed an energy resolution of 120 mueV. Data on tip-sample Josephson contacts yield an even smaller feature size of 60 mueV, implying that the system operates close to the physical noise limit.