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We study heat transport in hybrid normal metal - superconductor - normal metal (NSN) structures. We find the thermal conductance of a short superconducting wire to be strongly enhanced beyond the BCS value due to inverse proximity effect. The measurements agree with a model based on the quasiclassical theory of superconductivity in the diffusive limit. We determine a crossover temperature below which quasiparticle heat conduction dominates over the electron-phonon relaxation.
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The superconducting proximity effect has played an important role in recent work searching for Majorana modes in thin semiconductor devices. Using transport measurements to quantify the changes in the semiconductor caused by the proximity effect provides a measure of dynamical processes such as screening and scattering. However, in a two terminal measurement the resistance due to the interface conductance is in series with resistance of transport in the semiconductor. Both of these change, and it is impossible to separate them without more information. We have devised a new three terminal device that provides two resistance measurements that are sufficient to extract both the junction conductance and the two dimensional sheet resistance under the superconducting contact. We have compared junctions between Nb and InAs and Nb and 30% InGaAs all grown before being removed from the ultra high vacuum molecular beam epitaxy growth system. The most transparent junctions are to InAs, where the transmission coefficient per Landauer mode is greater than 0.6. Contacts made with ex-situ deposition are substantially more opaque. We find that for the most transparent junctions, the largest fractional change as the temperature is lowered is to the resistance of the semiconductor.
We study the proximity effect between the fully-gapped region of a topological insulator in direct contact with an s-wave superconducting electrode (STI) and the surrounding topological insulator flake (TI) in Au/Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$/Nb devices. The conductance spectra of the devices show the presence of a large induced gap in the STI as well as the induction of superconducting correlations in the normal part of the TI on the order of the Thouless energy. The shape of the conductance modulation around zero-energy varies between devices and can be explained by existing theory of s-wave-induced superconductivity in SNN (S is a superconductor, N a superconducting proximized material and N is a normal metal) devices. All the conductance spectra show a conductance dip at the induced gap of the STI.
Realization of topological superconductors (TSCs) hosting Majorana fermions is a central challenge in condensed-matter physics. One approach is to use the superconducting proximity effect (SPE) in heterostructures, where a topological insulator contacted with a superconductor hosts an effective p-wave pairing by the penetration of Cooper pairs across the interface. However, this approach suffers a difficulty in accessing the topological interface buried deep beneath the surface. Here, we propose an alternative approach to realize topological superconductivity without SPE. In a Pb(111) thin film grown on TlBiSe2, we discover that the Dirac-cone state of substrate TlBiSe2 migrates to the top surface of Pb film and obtains an energy gap below the superconducting transition temperature of Pb. This suggests that a BCS superconductor is converted into a TSC by the topological proximity effect. Our discovery opens a route to manipulate topological superconducting properties of materials.
We theoretically investigate the tunneling conductance of the $d+ip$-wave superconductor which is recently proposed to be realised at the (110) surface of a high-$T_c$ cuprate superconductor. Utilizing the quasiclassical Eilenberger theory, we obtain the self-consistent pair potentials and the differential conductance of the normal-metal/$d+ip$-wave superconductor junction. We demonstrate that the zero-bias peak of a $d$-wave superconductor is robust against the spin-triplet $p$-wave surface subdominant order even though it is fragile against the spin-singlet $s$-wave one. Comparing our numerical results and the experimental results, we conclude the spin-triplet $p$-wave surface subdominant order is feasible.
In this work, magnetization dynamics is studied in superconductor/ferromagnet/superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement technique. It is shown that in presence of both superconducting layers and of superconducting proximity at both superconductor/ferromagnet interfaces a massive shift of the ferromagnetic resonance to higher frequencies emerges. The phenomenon is robust and essentially long-range: it has been observed for a set of samples with the thickness of ferromagnetic layer in the range from tens up to hundreds of nanometers. The resonance frequency shift is characterized by proximity-induced magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the drop of magnetization. The shift and the corresponding uniaxial anisotropy grow with the thickness of the ferromagnetic layer. For instance, the anisotropy reaches 0.27~T in experiment for a sample with 350~nm thick ferromagnetic layer, and about 0.4~T in predictions, which makes it a ferromagnetic film structure with the highest anisotropy and the highest natural resonance frequency ever reported. Various scenarios for the superconductivity-induced magnetic anisotropy are discussed. As a result, the origin of the phenomenon remains unclear. Application of the proximity-induced anisotropies in superconducting magnonics is proposed as a way for manipulations with a spin-wave spectrum.
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