Scanning SQUID microscopy in a cryogen-free cooler

Abstract

Scanning superconducting quantum interference device (SQUID) microscopy is a powerful tool for investigating electronic states at surfaces and interfaces by mapping their magnetic signal. SQUID operation requires cryogenic temperatures, which are typically achieved by immersing the cryostat in liquid helium. Making a transition to cryogen free systems is desirable, but has been challenging, as electric noise and vibrations are increased in such systems. We report on the successful operation of a scanning SQUID microscope in a modified Montana Instruments cryogen-free cooler with a base temperature of 4.3 K. We demonstrate scanning SQUID measurements with flux noise performance comparable to a wet system and correlate the sensor-sample vibrations to the cryocooler operation frequencies. In addition, we demonstrate successful operation in a variety of SQUID operation modes, including mapping static magnetic fields, measurement of local susceptibility, and spatial mapping of current flow distribution.

Picoscale Magnetoelasticity Governs Heterogeneous Magnetic Domains in a Noncentrosymmetric Ferromagnetic Weyl Semimetal

“…The SQUID, scanner, and samples were cooled inside a Montana Instruments Fusion closed‐cycle cryostat similar to the one described by Shperber et al. [ 59 ]…”

“…The SQUID was attached to a custom-built piezoelectric scanner. The SQUID, scanner, and samples were cooled inside a Montana Instruments Fusion closed-cycle cryostat similar to the one described by Shperber et al [34] .…”

Scanning SQUID microscopy in a cryogen-free dilution refrigerator

“…The SQUID is mounted on a home-built piezoelectric scanner similar to the ones described in Refs. 15,16 , which in turn is mounted on a three-axis stack of attocube coarse positioners (see Fig. 1c).…”

“…In Ref. 15 , the authors used a cryostat with built-in mechanical isolation between the cryocooler and the cold plate on which the microscope is mounted. In Ref.…”

Isolation solution for extreme environmental vibrations for quantum-enabling cryogenic setups installed on raised frames

“…As low-temperature measurement devices advance 1 and become more sensitive [2][3][4][5][6][7][8][9] , noise due to vibrations has become of increasing concern 10,11 . Closed-cycle realization of SQUID microscopy 12,13 , scanning tunneling microscopy 14,15 , and other scanning probe techniques 2,16 demand a high level of precision, but internal and external sources of vibration remain a challenge 17 . Overall, more advanced cooling systems that are replacing conventional liquid helium technologies (due to helium unavailability and high pricing), such as those with a pulse tube, present an added element of internal vibrations.…”