Coherent diffraction of thermal currents in Josephson tunnel junctions

Abstract

We theoretically investigate heat transport in temperature-biased Josephson tunnel junctions in the presence of an in-plane magnetic field. In full analogy with the Josephson critical current, the phase-dependent component of the heat flux through the junction displays coherent diffraction. Thermal transport is analyzed in three prototypical junction geometries highlighting their main differences. Notably, minimization of the Josephson coupling energy requires the quantum phase difference across the junction to undergo \pi-slips in suitable intervals of magnetic flux. An experimental setup suited to detect thermal diffraction is proposed and analyzed.Comment: 6.5 pages, 4 color figures, updated versio

A quantum diffractor for thermal flux

“…Specifically, thermal diffraction manifests itself with a modulation of the electron temperature in a small metallic electrode nearby contacted to a thermally biased Josephson junction (JJ) when sweeping the magnetic flux F. Remarkably, the observed temperature dependence exhibits symmetry under F reversal and a clear reminiscence with a Fraunhofer-like modulation pattern, as expected fingerprints for a quantum diffraction phenomenon. Our results confirm a recent prediction of heat transport 8 and, joined with double-junction heat interferometry demonstrated in ref. 6, exemplify the complementary proof of the existence of phase-dependent thermal currents in Josephson-coupled superconductors.…”

“…heat transport and pave the way for the investigation of more exotic junction geometries 18,26,27 . These might provide tunable temperature diffraction patterns and should represent a powerful tool for tailoring and managing heat currents at the nanoscale 8,[29][30][31] . Besides offering insight into energy transport in quantum nanosystems, our experimental findings set the complementary demonstration of the 'thermal' Josephson effect in weakly coupled superconductors, similarly to what it was done 50 years ago for its 'electric' counterpart.…”

“…The latter, together with Rowell's observations, constituted the unequivocal demonstration of the Josephson supercurrent-phase relation. Yet, the Josephson effect has further profound implications going well beyond electrical transport, as the phase of the Cooper pair condensate is encoded in the wave functions of the un-paired Bogoliubov quasiparticles that transport thermal energy as well as electrical charge [4][5][6][7] Here we report the first realization of Fraunhofer diffraction for thermal currents 8 . Specifically, thermal diffraction manifests itself with a modulation of the electron temperature in a small metallic electrode nearby contacted to a thermally biased Josephson junction (JJ) when sweeping the magnetic flux F. Remarkably, the observed temperature dependence exhibits symmetry under F reversal and a clear reminiscence with a Fraunhofer-like modulation pattern, as expected fingerprints for a quantum diffraction phenomenon.…”

Radiation comb generation with extended Josephson junctions

“…In such a case the self-field genarXiv:1502.07122v2 [cond-mat.mes-hall] 15 Sep 2015 erated by the Josephson current in the weak-link can be neglected with respect to the externally applied magnetic field and no traveling solitons are originated 8,13 . We choose a coordinate system such that the applied magnetic field (H), directed along the x direction, is parallel to a symmetry axis of the junction whose electrodes planes lies in the xy plane [see Fig.…”

“…1(a), and consists of an extended Josephson tunnel junction composed of two identical superconducting electrodes [8][9][10][11][12] . We denote by λ and t the London penetration depth and the thickness of the superconductors S, respectively, which satisfy the condition t > λ .…”