Engineering Andreev Bound States for Thermal Sensing in Proximity Josephson Junctions

Abstract: The thermal response of proximity Josephson junctions (JJs) is governed by the temperature ($T$)-dependent occupation of Andreev bound states (ABS), making them promising candidates for sensitive thermal detection. In this study, we systematically engineer ABS to enhance the thermal sensitivity of the critical current ($I_c$) of proximity JJs, quantified as $|\,dI_c/dT\,|$ for the threshold readout scheme and $|\,dI_c/dT \cdot I_c^{-1}\,|$ for the inductive readout scheme. Using a gate-tunable graphene-based JJ platform, we explore the impact of key parameters -- including channel length, transparency, carrier density, and superconducting material -- on the thermal response. Our results reveal that the proximity-induced superconducting gap plays a crucial role in optimizing thermal sensitivity. Notably, we see a maximum $|\,dI_c/dT \cdot I_c^{-1}\,|$ value of $0.6\,\mathrm{K}^{-1}$ at low temperatures with titanium-based graphene JJs. By demonstrating a systematic approach to engineering ABS in proximity JJs, this work establishes a versatile framework for optimizing thermal sensors and advancing the study of ABS-mediated transport.