Determining the temperature of a millikelvin scanning tunnelling microscope junction

Abstract Cooling the junction of a scanning tunneling microscope to millikelvin temperatures is fundamental for high-resolution spectroscopy. However, accurately determining temperature has proven elusive, due microscopic dimension and its continuous energy exchange with surrounding environment. Here, we employ tunnelling cooled by an adiabatic demagnetization refrigerator. Using normal-metal superconducting tips, perform spectroscopy on atomically clean surface Al(100) in state. By varying refrigerator between 30 mK 1.2 K, show that decoupled from To corroborate our findings, simulate data P ( E ) theory determine 77 mK, despite environment being at 1.5 K.