Low Temperature Probing of On-Surface Dynamical Fluctuations with Johnson-Nyquist and Delta-T Noises

Abstract

Abstract As microelectronics evolves into nanoelectronics with faster switching speeds and the associated energy dissipation, determining local temperature and temperature gradients becomes an increasingly important challenge for solving design and manufacturing problems as well as improving reliability. Recently, experimental studies of low-temperature quantum thermal phenomena, in which heat is ruled by quantum physics, have been developing at an ever-increasing pace. A fundamental issue posed by finite temperatures is spontaneous fluctuations of electric currents occurring inside electrical conductors even in equilibrium, regardless of any applied voltage (the Johnson-Nyquist noise). Recently, a new (previously overlooked) non-equilibrium contribution to noise in a temperature-biased nanoscale conductive structure was discovered and called delta-T noise. In this paper, we argue that, along with stationary characteristics, both techniques can be successfully used to reveal on-surface dynamic processes in a cryogenic environment when other thermodynamic techniques lose sensitivity or cease to operate. Our calculations based on the scattering theory of nonlinear ac electron quantum transport show that related frequency-dependent noise spectra and their derivatives over frequency directly reflect the amplitude and the frequency of periodic current fluctuations. For practical implementations, it is proposed to use a multi-tip scanning tunneling microscope technique, which in our case needs only two tips, in contrast to the four-contact probing currently being implemented. Such nanoscale measurements, which are most effective at cryogenic temperatures, can provide important information about local thermally induced nanoscale processes useful for such applications as nanoelectronics and sensing technologies.