Nonlocal Cooper pair Splitting in a pSn Junction

Perfect Cooper pair splitting is proposed, based on crossed Andreev reflection (CAR) in a p-type semiconductor - superconductor - n-type semiconductor (pSn) junction. The ideal splitting is caused by the energy filtering that is enforced by the bandstructure of the electrodes. The pSn junction is modeled by the Bogoliubov-de Gennes equations and an extension of the Blonder-Tinkham-Klapwijk theory beyond the Andreev approximation. Despite a large momentum mismatch, the CAR current is predicted to be large. The proposed straightforward experimental design and the 100% degree of pureness of the nonlocal current open the way to pSn structures as high quality sources of entanglement

Thermal rectification of electrons in hybrid normal metal-superconductor nanojunctions

We theoretically investigate heat transport in hybrid normal metal-superconductor (NS) nanojunctions focusing on the effect of thermal rectification. We show that the heat diode effect in the junction strongly depends on the transmissivity and the nature of the NS contact. Thermal rectification efficiency can reach up to 123% for a fully-transmissive ballistic junction and up to 84% in diffusive NS contacts. Both values exceed the rectification efficiency of a NIS tunnel junction (I stands for an insulator) by a factor close to 5 and 3, respectively. Furthermore, we show that for NS point-contacts with low transmissivity, inversion of the heat diode effect can take place. Our results could prove useful for tailoring heat management at the nanoscale, and for mastering thermal flux propagation in low-temperature caloritronic nanocircuitry.Comment: 4+ pages, 3 color figure

Fine structure of the local pseudogap and Fano effect for superconducting electrons near a zigzag graphene edge

Motivated by recent scanning tunneling experiments on zigzag-terminated graphene this paper investigates an interplay of evanescent and extended quasiparticle states in the local density of states (LDOS) near a zigzag edge using the Green's function of the Dirac equation. A model system is considered where the local electronic structure near the edge influences transport of both normal and superconducting electrons via a Fano resonance. In particular, the temperature enhancement of the critical Josephson current and 0-pi transitions are predicted.Comment: 5 pages, 5 figures, to be published in Phys. Rev.

Re-entrant localization of single particle transport in disordered Andreev wires

We study effects of disorder on the low energy single particle transport in a normal wire surrounded by a superconductor. We show that the heat conductance includes the Andreev diffusion decreasing with increase in the mean free path $\ell$ and the diffusive drift produced by a small particle-hole asymmetry, which increases with increasing $\ell$. The conductance thus has a minimum as a function of $\ell$ which leads to a peculiar re-entrant localization as a function of the mean free path.Comment: 4 pages, 2 figure

Crossed Andreev reflection in diffusive contacts

Crossed Andreev reflection in multiterminal structures in the diffusive regime is addressed within the quasiclassical Keldysh-Usadel formalism. The elastic cotunneling and crossed Andreev reflection of quasiparticles give nonlocal currents and voltages (depending on the actual biasing of the devices) by virtue of the induced proximity effect in the normal metal electrodes. The magnitude of the nonlocal processes is found to scale with the square of the barrier transparency and to decay exponentially with interface spacing. Nonlocal cotunneling and crossed Andreev conductances are found to contribute equally to the nonlocal current, which is of relevance to the use of normal metal-superconducting heterostructures as sources of entanglement

Ferromagnetic features on zero-bias conductance peaks in ferromagnet/insulator/superconductor junction

We present a formula for tunneling conductance in ballistic ferromagnet/ferromagnetic insulator/superconductor junctions where the superconducting state has opposite spin pairing symmetry. The formula can involve correctly a ferromagnetism has been induced by effective mass difference between up- and down-spin electrons. Then, this effective mass mismatch ferromagnet and standard Stoner ferromagnet have been employed in this paper. As an application of the formulation, we have studied the tunneling effect for junctions including spin-triplet p-wave superconductor. The conductace spectra show a clear difference between two ferromagnets depending upon the way of normalization of the conductance. Especially, a essential difference is seen in zero-bias conductance peaks reflecting characteristics of each ferromagnets. From obtained results, it will be suggested that the measurements of the tunneling conductance in the junction provide us a useful information about the mechanism of itinerant ferromagnetism in metal.Comment: 8 pages, 8 figures, references added to the first versio

On the spectrum of facet crystallization waves at the smooth 4He crystal surface

The wavelike processes of crystallization and melting or crystallization waves are well known to exist at the 4He crystal surface in the rough state. Much less is known about crystallization waves for the 4He crystal surface in the smooth well-faceted state below the roughening transition temperature. To meet the lack, we analyze here the spectrum of facet crystallization waves and its dependence upon the wavelength, perturbation amplitude, and the number of possible facet steps distributed somehow over the wavelength. All the distinctive features of facet crystallization waves from conventional waves at the rough surface result from a nonanalytic cusplike behavior in the angle dependence for the surface tension of smooth crystal facets.Comment: 7 pages, 3 figures, 1 tabl

Andreev reflections on Y1-xCaxBa2Cu3O7-delta evidence for an unusual proximity effect

We have measured Andreev reflections between an Au tip and Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7 - \delta} thin films in the in-plane orientation. The conductance spectra are best fitted with a pair potential having the "d_{x^{2}-y^{2}+is" symmetry. We find that the amplitude of the "is" component is enhanced as the contact transparency is increased. This is an indication for an unusual proximity effect that modifies the pair potential in the superconductor near the surface with the normal metal.Comment: 4 pages, 4 figure