Development of a low temperature STM cryogenics equipped with a fast-ramping vector magnet

Molecular spins on surface are feasible systems to realize on-surface integrated nanoscale qubit devices in terms of the scalability. As a promising candidate, single molecule magnets often require a high-speed variable magnetic field to control their quantum states [1]. Here, we report a development of home-built cryogenic system for low temperature scanning tunneling microscopy (STM) in a fast-ramping magnetic field. It is equipped with a vector magnet of 1 T (in axial) and 0.25 T (in lateral) at a ramping rate up to 0.5 T/sec and 0.1 T/sec, respectively, and designed to minimize the generation of eddy current from such a fast-ramping of the field by careful selection of materials for STM head assembly. The cryostat is cooled down by the Joule-Thomson (JT) principle. Our special design of heat exchange mechanism allowed us to precool the JT stage from 100 to 5 K only in 4 hours. Using ⁴He cryogen gas, we reached at a base temperature (T_base) of 1.50 ± 0.025 K at JT stage in a continuous circulation mode. In one-shot mode, we obtained T_base = 1 K, stable for 8 hours. In addition, the cryostat is equipped with RF signal cables for electron spin resonance STM on atomic spins on surface [2]. [1] S. Thiele et al. Science (2014); [2] S. Baumann et al. Science (2015)