Negative differential thermal conductance and heat amplification in superconducting hybrid devices

TL;DR

This paper explores a superconducting Josephson junction that exhibits negative differential thermal conductance, enabling thermal modulation, memory, switching, and amplification, advancing the development of coherent caloritronics nanocircuits.

Contribution

It demonstrates the first use of a simple superconducting junction to achieve NDTC and heat amplification, paving the way for thermal logic and memory devices.

Findings

Achieved a peak-to-valley ratio of ~3 in heat current

Demonstrated temperature modulation up to 80 mK at 50 mK bath temperature

Designed thermal transistor with heat amplification factor >1

Abstract

We investigate the thermal transport properties of a temperature-biased Josephson tunnel junction composed of two different superconductors. We show that this simple system can provide a large negative differential thermal conductance (NDTC) with a peak-to-valley ratio of $\sim 3$ in the transmitted electronic heat current. The NDTC is then exploited to outline the caloritronic analogue of the tunnel diode, which can exhibit a modulation of the output temperature as large as 80 mK at a bath temperature of 50 mK. Moreover, this device may work in a regime of thermal hysteresis that can be used to store information as a thermal memory. On the other hand, the NDTC effect offers the opportunity to conceive two different designs of a thermal transistor, which might operate as a thermal switch or as an amplifier/modulator. The latter shows a heat amplification factor $>1$ in a 500-mK-wide working region of the gate temperature. After the successful realization of heat interferometers and thermal diodes, this kind of structures would complete the conversion of the most important electronic devices in their thermal counterparts, breaking ground for coherent caloritronics nanocircuits where heat currents can be manipulated at will.