Low-Noise Large-Bandwidth Transimpedance Amplifier for Measuring Scanning Tunneling Shot Noise Spectra in Cryogenic STM and its Applications
摘要：散粒噪声是一个研究量子体系的强有力的手段。本文提出一种用于低温扫描隧道显微镜 (CryoSTM)的跨阻放大器(TIA)，可满足散粒噪声测量的需要。在该TIA中，前置放大器(Pre-Amp)由超低噪声低功率低温高电子迁移率晶体管(HEMTs)构成。以1Gohm的高跨阻增益，所设计的TIA的带宽超过300 kHz。在CryoSTM中，这个TIA连同针尖-样品组件和输入信号被称为CryoSTM-TIA。它的带宽仍然超过300kHz，并且它的等效输入噪声电流功率谱密度在100 kHz小于30 (fA)2/Hz。该CryoSTM-TIA能够用于测量扫描隧道电流谱和扫描隧道微分电导谱。本文又特别阐述了如何用该CryoSTM-TIA测量量子体系的扫描隧道噪声电流功率谱和散粒噪声谱。这就使得用低温CryoSTM-TIA通过测量散粒噪声来研究各种量子体系中的新奇量子现象成为可能，例如在局域尺度中的Andreev反射、在单分子磁体中的Kondo效应，等等。特别是把它用于研究与实现拓扑量子计算有关的Majorana零能模的存在性。
英文摘要: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 preamplfier is made of the low-noise low-power cryogenic high electron mobility transistors. With the high transimpedance gain of 1 Gohm, 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.