Effect of electron-hole asymmetry on ${\Delta }_T$ noise in metal/quantum point contact/metal and metal/quantum point contact/superconductor junctions

Abstract

This work examines charge ${\Delta }_T$ noise in two-terminal hybrid nanostructures featuring a quantum point contact (QPC), realized either between two normal metallic leads (NQN) or between a normal metal and a superconducting lead (NQS). The energy-dependent transmission of a QPC breaks electron-hole (e-h) symmetry, leading to a finite thermovoltage under an applied temperature and voltage bias. In contrast, in earlier studies on hybrid junctions incorporating insulating barriers, as electron-hole symmetry is preserved, have vanishing thermovoltage, and consequently, charge ${\Delta }_T$ noise is calculated at zero thermovoltage. In our setup, the broken e-h symmetry allows for a finite thermovoltage, at which we compute the corresponding charge ${\Delta }_T$ noise. Unlike earlier studies restricted by electron-hole symmetry and vanishing thermovoltage, our work establishes a self-consistent thermoelectric noise framework in mesoscopic hybrid junctions, revealing how Andreev reflection fundamentally reshapes charge ${\Delta }_T$ noise once electron-hole symmetry is broken. This broad access to charge fluctuation signatures provides a more comprehensive understanding of non-equilibrium transport in linear response. To the best of our knowledge, this is the first work that systematically explores the interplay between Andreev reflection and electron-hole symmetry breaking in the context of quantum noise and ${\Delta }_T$ noise in mesoscopic hybrid structures.

26 pages, 23 figures, 1 table; accepted for publication in Physical Review B