Low-noise large-bandwidth transimpedance amplifier for measuring scanning tunneling shot noise spectra in cryogenic STM and its applications

Abstract

Shot noise is a powerful tool to study quantum systems. In this work, a design of transimpedance amplifier (TIA) for a cryogenic scanning tunneling microscope (CryoSTM) is proposed to meet the requirements of the shot noise measurements for quantum systems. In the TIA, the preamplifier is made of the low-noise low-power cryogenic high electron mobility transistors. With the high transimpedance gain of 1 GΩ, the bandwidth of the proposed TIA is larger than 300 kHz. In the CryoSTM, the TIA with the tip-sample component is called as CryoSTM-TIA. The bandwidth of the proposed CryoSTM-TIA is still larger than 300 kHz. Its equivalent input noise current power spectral density is less than 30(fA)2/Hz at 100 kHz. It is detailed, for quantum systems, by using the CryoSTM-TIA, how to measure scanning tunneling current spectra, scanning tunneling differential conductance spectra, and scanning tunneling noise current power spectra, in atomic scale, and then extract their scanning tunneling shot noise spectra. Thus, it is possible to study novel quantum phenomena in various quantum systems by measuring shot noise with the CryoSTM-TIA, such as the Andreev reflection in atomic scale, the Kondo effect in a single molecular magnet, and the existence of Majorana bound states, etc.