Anomalous proximity effect in an inhomogeneous disordered superconductor

By combining very low temperature scanning tunneling microscopy and spectroscopy on a TiN film we have observed a nonuniform state comprising of superconducting (S) and normal (N) areas. The local density of states displays a spatial dependence between S and N different from the usual proximity effect. We conclude that mesoscopic fluctuations might play a major role in accordance with recent theories describing superconductor-normal-metal quantum transition.     

Inverse proximity effect in a strongly correlated electron system

An anomalous superconducting proximity effect between a strongly correlated electron system and a normal metal is demonstrated. The model system is a 2D ultrathin superconducting quench-condensed Pb film. Such a highly disordered film has a reduced transition temperature (T(c) = 1.7 K) due to the strong e(-)-e(-) interaction. Instead of weakening the superconductivity, an overlayer of Ag on Pb induces an increase of both the T(c) and the gap. The restoration of the electron screening brought about by the quasiparticles from the normal metal can explain this striking inverse proximity effect.     

The proximity effect for weak itinerant ferromagnets

The Curie temperature T_c of a proximity sample composed of a thin film of a weak itinerant ferromagnet of thickness d_f in contact with a thick film of an enhanced parmagnetic metal is calculated using the Hubbard model in the Hartree-Fock approximation. The sample is paramagnetic for values of d_f less than a critical thickness d_f⁰ of the order of the coherence length. The shape of the curve of T_c vs. d_f for d_f > d_f⁰ depends on whether the bulk ferromagnet exhibits a Curie-Weiss or a Pauli susceptibility above the bulk Curie temperature. The letter is concluded by comments on the experimental situation.     

Anomalous proximity effect in superconducting oxide structures with an antiferromagnetic layer

The electrophysical parameters of superconductor/antiferromagnetic insulator structures based on the Nb/Au/Ca_1?x Sr _x CuO₂/YBa₂Cu₃O_7?δ hybrid heterostructure have been examined. YBa₂Cu₃O_7?δ and Ca_1?x Sr _x SuO₂ epitaxial films are grown by the laser ablation method on NdGaO₃ single crystal substrates, the thickness of the Ca_1?x Sr _x CuO₂ layer varies from 20 to 50 nm, and x = 0.15 and 0.5. The superconducting pair potential in the interface between the YBa₂Cu₃O_7?δ superconductor and Ca_1?x Sr _x CuO₂ antiferromagnet is found to penetrate into the antiferromagnet at distances much larger than the coherence length calculated for the ferromagnetic layer. The critical current of the superconducting transition manufactured at such an interface is highly sensitive to the magnetic field.     

Giant proximity effect in cuprate superconductors

Using an advanced molecular beam epitaxy system, we have reproducibly synthesized atomically smooth films of high-temperature superconductors and uniform trilayer junctions with virtually perfect interfaces. We found that supercurrent runs through very thick barriers. We can rule out pinholes and microshorts; this "giant proximity effect" (GPE) is intrinsic. It defies the conventional explanation; it might originate in resonant tunneling through pair states in an almost-superconducting barrier. GPE may also be significant for superconducting electronics, since thick barriers are easier to fabricate.     

Anomalous proximity effect in d-wave superconductors

The anomalous proximity effect between a d-wave superconductor and a thin disordered normal layer is studied theoretically in the framework of Eilenberger equations. It is shown that disorder of the quasiparticle reflection from this thin layer leads to the formation of an s-wave component localized near the boundary. The angular and spatial structure of the pair potential near the interface is studied. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 478–483 (10 April 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Triplet proximity effect in FSF trilayers

We study the critical temperature T _c of FSF trilayers (F is a ferromagnet, S is a singlet superconductor), where the triplet superconducting component is generated at noncollinear magnetizations of the F layers. An exact numerical method is employed to calculate T _c as a function of the trilayer parameters, in particular, mutual orientation of magnetizations. Analytically, we consider limiting cases. Our results determine the conditions necessary for the existence of recently investigated odd triplet superconductivity in SF multilayers.     

Magnetic proximity effect in EuO-Cs interface

In the surface of the ferromagnetic insulator EuO is covered with a small amount of cesium, the photoelectric magnetization curves P(H) show magnetic saturation in contrast to those of the pure surface. The proximity of the Cs film causes the paramagnetism of the clean EuO surface to disappear.     

Unconventional proximity effect and inverse spin-switch behavior in a model manganite-cuprate-manganite trilayer system

The proximity effect in a model manganite-cuprate system is investigated theoretically. We consider a situation in which spin-polarized electrons in manganite layers antiferromagnetically couple with electrons in cuprate layers as observed experimentally. The effect of the interfacial magnetic coupling is found to be much stronger than the injection of spin-polarized electrons into the cuprate region. As a result, the superconducting transition temperature depends on the thickness of the cuprate layer significantly. Since the magnetic coupling creates negative polarization, an applied magnetic field and the negative polarization compete, resulting in the inverse spin-switch behavior where the superconducting transition temperature is increased by applying a magnetic field.     

Fully developed triplet proximity effect

We present a model for the fully developed proximity effect in superconductor-ferromagnet heterostructures. Within the circuit-theory approximation, we evaluate the Green functions, the density of states, and the Josephson current which depend essentially on the magnetic configuration.     

Superconducting proximity effect in Ag—Mn

The proximity effect was studied by measuring the thermal conductivity of double layers films made of a normal metal (Ag or Ag—Mn) and a superconductor (Pb–5% Bi), in the temperature range of 0.3–2 K.Thermal conductivity ratios have been used to estimate induced energy gap in silver and in dilute silver manganese alloys. No evidence for bound states in the presence of magnetic impurities was observed.     

Dynamic ferromagnetic proximity effect in photoexcited semiconductors

The spin dynamics of photoexcited carriers in semiconductors in contact with a ferromagnet is treated theoretically and compared with time-dependent Faraday rotation experiments. The long-time response of the system is found to be governed by the first tens of picoseconds in which the excited plasma interacts strongly with the intrinsic interface between the semiconductor and the ferromagnet in spite of the existence of a Schottky barrier in equilibrium.     

Giant proximity effect in a phase-fluctuating superconductor

When a tunneling barrier between two superconductors is formed by a normal material that would be a superconductor in the absence of phase fluctuations, the resulting Josephson effect can undergo an enormous enhancement. We establish this novel proximity effect by a general argument as well as a numerical simulation and argue that it may underlie recent experimental observations of the giant proximity effect between two cuprate superconductors separated by a barrier made of the same material rendered normal by severe underdoping.     

Spin dynamics in a superconductor-ferromagnet proximity system

The ferromagnetic resonance of thin sputtered Ni80Fe20 films grown on Nb is measured. By varying the temperature and the thickness of the Nb the role of the superconductivity on the whole ferromagnetic layer in these heterostructures is explored. The change in the spin transport properties below the superconducting transition of the Nb is found to manifest itself in the Ni80Fe20 layer by a sharpening in the resonance of the ferromagnet, or a decrease in the effective Gilbert damping coefficient, showing that the superconductivity affects the macrospin of the ferromagnetic layer. We interpret this in terms of the spin-pumping model.     

Universal gap fluctuations in the superconductor proximity effect

Random-matrix theory is used to study the mesoscopic fluctuations of the excitation gap in a metal grain or quantum dot induced by the proximity to a superconductor. We propose that the probability distribution of the gap is a universal function in rescaled units. Our analytical prediction for the gap distribution agrees well with exact diagonalization of a model Hamiltonian.     

Spin proximity effect in ultrathin superconducting Be-Au bilayers

We present a detailed study of the effects of interface spin-orbit coupling on the critical field behavior of ultrathin superconducting Be/Au bilayers. Parallel field measurements were made in bilayers with Be thicknesses in the range of d=2-30 nm and Au coverages of 0.5 nm. Though the Au had little effect on the superconducting gap, it produced profound changes in the spin states of the system. In particular, the parallel critical field exceeded the Clogston limit by an order of magnitude in the thinnest films studied. In addition, the parallel critical field unexpectedly scaled as [FORMULA: SEE TEXT], suggesting that the spin-orbit coupling energy was proportional to Delta0/d2. Tilted field measurements showed that, contrary to recent theory, the interface spin-orbit coupling induces a large in-plane superconducting susceptibility but only a very small transverse susceptibility.     

Influence of an interface double electric layer on the superconducting proximity effect in ferromagnetic metals

The electric field within the double electric layer that occurs when two conductors with different work functions come into contact induces interface spin-orbit coupling. In the case of contact of a conventional, s-wave superconductor with a ferromagnetic metal, the coupling is predicted to give rise to the appearance of triplet superconductivity on both sides of the interface. The form of the triplet component of the condensation amplitude is determined, and the ability of the triplet superconductivity to penetrate into the ferromagnet on the usual coherence length is shown.