Proximity nanovalve with large phase-tunable thermal conductance

Abstract

We propose a phase-controlled heat-flux quantum valve based on the proximity effect driven by a superconducting quantum interference proximity transistor (SQUIPT). Its operation relies on the phase-dependent quasiparticle density of states in the Josephson weak-link of the SQUIPT which controls thermal transport across the device. In a realistic Al/Cu-based setup the structure can provide efficient control of thermal current inducing temperature swings exceeding ∼ 100 mK, and flux-to-temperature transfer coefficients up to ∼ 500 mK/Φ 0 below 100 mK. The nanovalve performances improve by lowering the bath temperature, making the proposed structure a promising building-block for the implementation of coherent caloritronic devices operating below 1 K.Phase-dependent manipulation of heat in solid-state nanodevices is nowadays one of the major challenges of coherent caloritronics 1 , and plays a key role in determining the physical properties of mesoscopic systems at low temperature. Toward this direction, the prototype for a heat interferometer has been recently realized with a superconducting quantum interference device (SQUID) where the modulation of the thermal current has been achieved thanks to the Josephson coupling 2-5 . Yet, phase-dependent thermal transport has been also demonstrated in Andreev interferometers 6-8 where the proximity effect in a normal metal affects its thermal conductance, and is controlled via a magnetic field.Here we propose an alternative approach to control heat transport by envisioning a thermal nanovalve based on proximity effect but phase-controlled by a SQUIPT 9-12 . Differing from SQUID-based and Andreev interferometers our device allows a drastic quenching of the thermal conductance which makes our proposal an efficient phase-tunable thermal nanovalve. Specifically, we expect an improvement of the temperature swing (up to ∼ 100 mK) and a flux-to-temperature transfer function exceeding 500 mK/Φ 0 at 100 mK.A sketch for the proximity nanovalve is shown in Fig. 1(a) and consists of a SQUIPT composed by a superconducting (S) ring interrupted by a diffusive normal metal (N) wire of length L. We assume the wire transverse dimensions to be negligible in comparison to its length so that it can be considered as quasi-onedimensional. Superconducting correlations are induced in the N wire owing to proximity effect from the S loop a) Electronic

Coherent transport properties of a three-terminal hybrid superconducting interferometer

“…The phase-controlled density of states (DOS) of the proximized nanowire makes the SQUIPT an ideal building block for the realization of heat nanovalves [4] or very sensitive and ultra-low-power dissipation magnetometers [5][6][7][8] able to succeed the state-of-the-art SQUID technologies, with particular interest in single-spin detection [9].…”

Normal metal tunnel junction-based superconducting quantum interference proximity transistor

“…Yet, it has been recently predicted that coherent thermal valves based on the proximity effect privilege SQUIPTs realized with a normal metal probe (N-SQUIPT), as the presence of the superconducting junction in the conventional S-SQUIPT design would severely limit the heat flow across the structure 24 . The N-SQUIPT appears therefore as a highly-promising candidate to implement future phasecoherent caloritronic devices such as heat transistors, rectifiers, thermal splitters and phase-tunable electron coolers 25 .…”

“…ii) The typical operating power, fully modulated from fW to aW levels, gives the opportunity of using the N-SQUIPT as a magnetometer for condensed matter systems 41 characterized by low-energy excitations, which are vulnerable to disruption by measurement back-action. iii) The choice of a normal metal probe has been shown to improve drastically the transport properties of a heat nanovalve 24 due to the lack of a superconducting gap in the probe itself. More generally, a normal density of states provides a natural opportunity of realizing a thermal reservoir in which the electron temperature can be tuned and probed to its fullest extent.…”

Mesoscopic Josephson junctions with switchable current-phase relation

“…4(a) demonstrate that the kinetic inductance of the Josephson weak link can be tuned by h ex , and maximized around ∼ π. This is indeed essential to provide a robust and well-defined phase drop across the junction in a number of nanodevices 32,[35][36][37][38][39] …”

“…−1 ] in a region of phases (ϕ ∼ π) very important for several phase-controlled devices 32,[35][36][37][38][39] . In order to quantify the relative deviation of the CPR from the sinusoidal behavior we plot in Fig.…”