The present paper develops the ideas introduced in {\em cond-mat/0312673}. The construction of a hybrid discrete-continuous model of layered superconductors is briefly presented. The model bases on the classic Lawrence-Doniach scenario with admitting, however, long-range interactions between atomic planes. Moreover, apart from Josephson couplings they involve the proximity effects. The range of interactions, K, can, in principle, be arbitrary large. The solutions corresponding to the range K=2 are exposed.
The fundamental excitations are understood as deviations from stable ground states.The formulae for energy of those excitations are constructed. The possible shapes of dispersion curves are analysed. For each type of shape the corresponding values of physically measurable quantities like effective maa and bandwidth are expressed by coupling parameters.
Equations describing the resistive state of a layered superconductor with anisotropic pairing are derived. The similarity with a stack of Josephson junctions is found at small voltages only, when current density in the direction perpendicular to the layers can be interpreted as a sum of the Josephson superconducting, the Ohmic dissipative and the interference currents. In the spatially uniform state differential conductivity at higher voltages becomes negative. Nonuniformity of the current distribution generates the branch imbalance and violates the Josephson relation between frequency and vol…
The intrinsic Josephson effect in the high-Tc superconductors is studied using the layered two-dimensional t-J model. The d.c.Josephson current which flows perpendicular to the t-J planes is obtained within the mean-field approximation and the Gutzwiller approximation. We find that the Josephson current has its maximum near the optimum doping region as a function of the doping rate.
We consider dynamics of Josephson vortex lattice in layered superconductors with magnetic, charge (electrostatic) and charge-imbalance (quasiparticle) interactions between interlayer Josephson junctions taken into account. The macroscopic dynamical equations for interlayer Josephson phase differences, intralayer charge and electron-hole imbalance are obtained and used for numerical simulations. Different transformations of the vortex lattice structure are observed. It is shown that the additional dissipation due to the charge imbalance relaxation leads to the stability of triangular lattice.
We have proposed to employ the microwave S parameters method to measure phase oscillation modes (POMs) in Josephson coupled-layered superconductors. For the first time, in SmBa2Cu3O7 (SmBCO) and YBa2Cu3O7-b (YBCO) at 77 K we have directly observed some POMs far below the Josephson plasma frequency. A series of discrete modes have been observed and discussed qualitatively in the POMs. The method may be a powerful and flexible tool in this field.
The Josephson plasma resonance in layered superconductors with alternating critical current densities is investigated in a low perpendicular magnetic field. In the vortex solid phase the current densities and the squared bare plasma frequencies decrease linearly with the magnetic field. Taking into account the coupling due to charge fluctuations on the layers, we extract from recent optical data for SmLa_{1-x} Sr_x CuO_{4-delta} the Josephson penetration length lambda_{ab} approximately 1100 A parallel to the layers at T=10 K.
We consider the ground state configurations of the Josephson vortex lattice in layered superconductors. Due to commensurability effects with the layered structure, the lattice has multiple configurations, both aligned with layers and rotated at finite angle. At low fields the lattice switches between these configurations via first-order phase transitions. These transitions become more frequent at smaller fields. With increasing magnetic field a dilute lattice transforms first into a sheared dense lattice. With further increase of field, the shear deformation smoothly vanishes at a second-order…
The Josephson-plasma and vortex modes in layered superconductors have been studied theoretically for low magnetic fields parallel and perpendicular to layers. The two modes belong to the same lowest-frequency branch of collective-mode spectrum localized near vortices. This is the Josephson-plasma resonance if pancakes are strongly pinned and cannot move. Otherwise the lowest-frequency mode is a vortex mode governed by pancake pinning and the vortex mass. The latter is strongly enhanced by wandering of a vortex line around its average direction. The recently observed jump of the magnetoabsorpti…
The coupling of Josephson oscillations in layered superconductors is studied with help of a tunneling Hamiltonian formalism. The general form of the current density across the barriers between the superconducting layers is derived. The induced charge fluctuations on the superconducting layers lead to a coupling of the Josephson oscillations in different junctions. A simplified set of equations is then used to study the non-linear dynamics of the system. In particular the influence of the coupling on the current-voltage characteristics is investigated and upper limits for the coupling strength …
A general phenomenological theory describing dynamics of Josephson vortices coupled to wide class of linear waves in layered high-T$_c$ superconductors is developed. The theory is based on hydrodynamic long wave approximation and describes interaction of vortices with electromagnetic, electronic and phonon degrees of freedom on an equal footing. In the limiting cases the proposed theory degenerates to simple models considered earlier. In the framework of the suggested model we undertook the numerical simulation of resistive state in layered superconductors placed in external magnetic field and…
Light scattering by Josephson vortices is theoretically predicted. An experimental set-up for the observation of the effect is proposed. The magnetic field should be parallel to the CuO_2 layers and the crystal surface. The falling light should be at grazing angles, and the Bragg scattering must be almost backscattering. The distance between the columns of the Josephson vortices must be slightly smaller than the light-wavelength. The surface should be very clean and flat in order light scattering by surface terraces and surface roughness to give the relatively small background.
Phase transitions of a flux lattice in layered superconductors with magnetic field perpendicular to the layers and in presence of disorder are studied. We find that the Josephson coupling between layers leads to a strongly pinned Josephson glass (JG) phase at low temperatures and fields. The JG phase undergoes either a decoupling transition with increasing field or a depinning transition with increasing temperature. The resulting phases undergo further depinning and decoupling transitions, respectively, resulting in a phase diagram with a multicritical point where four phases meet. The phase d…
Conductivity mechanism in the regime of the intrinsic Josephson effect in layered superconductors with singlet d-wave pairing is studied theoretically. The cases of coherent and incoherent interlayer tunneling of electrons are considered. The theory with coherent tunneling describes main qualitative features of the effect observed in highly anisotropic high-T$_c$ superconductors at voltages smaller than the amplitude of the superconducting gap, mechanism of the resistivity being related to excitations of the quasiparticles via the d-wave gap. At voltages of the order of the gap amplitude and l…
In this publication a microscopic theory for the coupling of intrinsic Josephson oscillations in layered superconductors with longitudinal c-axis-phonons is developed. It is shown that the influence of lattice vibrations on the c-axis transport can be fully described by introducing an effective longitudinal dielectric function. Resonances in the I-V-characteristic appear at van Hove singularities of both acoustical and optical longitudinal phonon branches. This provides a natural explanation of the recently discovered subgap structures in the I-V-characteristic of highly anisotropic cuprate su…
We predict a novel type of Josephson effect to occur in triplet superconductor - ferromagnet - triplet superconductor Josephson junctions. We show that the Josephson current, I_J, exhibits a rich dependence on the relative orientation between the ferromagnetic moment and the d-vectors of the superconductors. This dependence can be used to build several types of Josephson current switches. Moreover, we predict an unconventional temperature dependence of I_J in which I_J changes sign with increasing temperature
We find systematic signatures suggesting a different superconducting nature for a triple-layered cuprate Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ with respect to a double-layer through the properties of intrinsic Josephson junctions (IJJs). Our measurements on the current-voltage characteristics reveal that the $c$-axis maximum Josephson current density is sensitive to the superfluid density in outer planes while the critical temperature and the superconducting gap remain unaffected. Switching dynamics of stacked IJJs exhibit that the fluctuation in gauge-invariant phase difference of an IJJ implies…
The present paper is an extension of 'cond-mat/0312673'. The construction of a hybrid discrete-continuous model of layered superconductors is presented. The model bases on the classic Lawrence-Doniach scenario with admitting, however, long-range interactions between atomic planes. Moreover, apart from Josephson couplings they involve the proximity effects. The range of interactions can, in principle, be arbitrary large. The solutions corresponding to the range K=2 are found. The mechanism of enhancement of superconductivity caused by the proximity effect and the presence of higher Josephson co…
To reveal the influence of the exchange interaction on the Josephson effect, the d.c. Josephson current in unconventional-superconductor / ferromagnet / unconventional-superconductor junctions is studied. When the two superconductors have d-wave symmetry, the Josephson current is drastically suppressed with the increase of the exchange interaction. On the other hand, when the two superconductors have different parities, e.g. s-wave and p-wave, an enhancement of the Josephson current is obtained with the increment of the exchange interaction due to the break-down of SU(2) symmetry in the spin s…
We predict that the Josephson current in a clean s-wave superconductor-normal metal-d-wave superconductor junction is periodic in superconducting phase difference $ϕ$ with period $π$ instead of $2π$. The frequency of non-stationary Josephson effect is correspondingly $2ω_J = 4eV.$ The effect is due to coexistence in the normal layer of current carrying Andreev levels with phase differences $ϕ$ and $ϕ+π.$
We calculate the field dependence of the critical current for the dense Josephson vortex lattice which is created by large magnetic field $B$ applied along the layers of atomically layered superconductors. In clean samples a finite critical current appears due to the interaction of the lattice with the boundaries. The boundary induces an alternating deformation of the lattice decaying inside the sample at the typical length, which is larger than the Josephson length and increases proportional to the magnetic field. The exact shape of this deformation and the total current flowing along the sur…
We investigate Josephson junctions among conventional superconducting wires, in the presence of externally applied Zeeman fields and supercurrents. We demonstrate that the critical Josephson current and the current-phase relation of the junction depends on the relative orientation of the applied Zeeman fields and supercurrents. The controllability of the Josephson current relies on the stabilization of conventional superconductivity in high magnetic fields, due to the restoration of the opposite momentum opposite spin projection resonance at the Fermi level. We assert that our results can lead…
We calculate Ic(T) and Rn for both coherent and incoherent electron tunneling across a c-axis break junction between nu=s,d_x^2-y^2-wave superconducting half spaces, each with c-axis bandwidth 2J. Coherent quasiparticle tunneling only occurs for voltages V<2J/e, leading to difficulties in measuring Rn for underdoped samples. The coherent part of Ic(0) is independent of Delta_nu(0) for J/Delta_nu(0)<<1, and can be large. Our results are discussed with regard to recent experiments.
A thin ferromagnetic layer on a bulk equal-spin-pairing triplet superconductor is shown to mediate a Josephson coupling between the spin $\uparrow$ and $\downarrow$ condensates of the superconductor. By deriving analytic expressions for the bound states at the triplet superconductor-ferromagnet interface, we show that this spin Josephson effect establishes an effective anisotropy axis in the ferromagnetic layer. The associated Josephson spin current is predicted to cause a measurable precession of the magnetization about the vector order parameter of the triplet superconductor.
The Josephson effect between triplet and singlet superconductors is studied. Josephson current can flow between triplet and singlet superconductors due to the spin-orbit coupling in the spin-triplet superconductor but it is finite only when triplet superconductor has $L_z=-S_z=\pm 1$, where $L_z$ and $S_z$ are the perpendicular components of orbital angular momentum and spin angular momentum of the triplet Cooper pairs, respectively. The recently observed temperature and orientational dependence of the critical current through a Josephson junction between UPt$_3$ and Nb is investigated by cons…
We study the Josephson effect between a conventional s-wave superconductor and a non-centrosymmetric superconductor with Rashba spin-orbit coupling. Rashba spin-orbit coupling affects the Josephson pair tunneling in a characteristic way. The Josephson coupling can be decomposed into two parts, a `spin-singlet-like' and a `spin-triplet-like' component. The latter component can lead to shift of the Josephson phase by πrelative to the former coupling. This has important implications on interference effects and may explain some recent experimental results for the Al/CePt3Si junction.
We analytically study stability of sliding lattice of Josephson vortices driven by a transport current in the stack direction in strong in-plane magnetic field. In contrast to recent findings we obtain that there are no diverse configurations of stable vortex lattices, and, hence, the stable sliding vortex lattice can not be selected by boundary conditions. We find that only the triangular (rhombic) lattice can be stable, its stability being limited by a critical velocity value. At higher velocities there are no simple stable lattices with single flux line per unit cell. Oblique sliding lattic…
Many superconducting materials are composed of weakly coupled conducting layers. Such a layered structure has a very strong influence on the properties of vortex matter in a magnetic field. This review focuses on the properties of the Josephson vortex lattice generated by the magnetic field applied in the layers direction. The theoretical description is based on the Lawrence-Doniach model in the London limit which takes into account only the phase degree of freedom of the superconducting order parameter. In spite of its simplicity, this model leads to an amazingly rich set of phenomena. We rev…
It is generally believed that superconductivity can occur in materials irrespective of whether the charge carriers in the material are electrons or holes. Here we point out that Josephson tunneling would not occur between superconductors with charge carriers of opposite sign. Consequently, observation of Josephson tunneling between two superconductors implies that their charge carriers have the same sign. We propose that this has profound implications for the understanding of superconductivity and in particular is consistent with the theory of hole superconductivity.
We discuss the Josephson current between two noncentrosymmetric superconductors. The coexistence of superconducting order parameters between spin-singlet $Δ_{\text{S}}$ and helical p-wave spin-triplet $Δ_{\text{T}}$ enriches a variety of low-temperature behavior of Josephson current depending on their relative amplitudes. We will show that characteristic behaviors of the Josephson current for $Δ_{\text{S}} > Δ_{\text{T}}$ are clearly different from those for $Δ_{\text{S}} < Δ_{\text{T}}$. The topologically protected zero-energy surface bound states are responsible for the clear difference. We …
In the frame of an exactly solvable model we calculate electric and magnetic fields created by uniformly moving lattice of Josephson vortices driven by the transport current in the magnetic field parallel to conducting layers. The distribution of fields and currents is strongly modified at large velocities of the vortex lattice, plasma oscillations of superconducting electrons being excited by flux flow at low temperatures. This modifies the flux flow resistivity and results in interference features in I-V curves, thus regions of negative differential conductivity appear in which the uniform m…
For certain orientations of Josephson junctions between two p_x-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4pi-periodic relation between the Josephson current I and the phase difference phi: I ~ sin(phi/2). Consequently, the ac Josephson current has the fractional frequency eV/h, where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs…
We study vortex matter in layered superconductors in the limit of zero Josephson coupling. The long range of the interaction between pancake vortices in the c-direction allows us to employ a mean-field method: all attractive inter-layer interactions are reduced to an effective substrate potential, which pancakes experience in addition to the same-layer pancake repulsion. We perform numerical simulations of this mean-field model using two independent numerical implementations with different simulation methods (Monte-Carlo sampling and Langevin molecular dynamics). The substrate potential is upd…
We present an exact mathematical description of Josephson vortices and of the Meissner effect in periodic thin-layer superconductor/insulator structures with an arbitrary number of identical junctions N-1 (N is the number of superconducting layers) in terms of localized solutions to a system of differential equations for phase differences. We establish a general criterion of the existence of localized solutions. We show that Meissner solutions are characterized by several Josephson lengths [N/2 lengths for even N, and (N-1)/2 lengths for odd N]. We derive an exact expression for the superheati…
Due to the difference in the momenta of the superconducting order parameters, the Josephson current in a Josephson junction between a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor and a conventional BCS superconductor is suppressed. We show that the Josephson current may be recovered by applying a magnetic field in the junction. The field strength and direction at which the supercurrent recovery occurs depend upon the momentum and structure of the order parameter in the FFLO state. Thus the Josephson effect provides an unambiguous way to detect the existence of an FFLO state, and to m…
We demonstrate the manifestations of the nonlinear features in magnetic dynamics and IV-characteristics of the $φ_0$ Josephson junction in the ferromagnetic resonance region. We show that at small values of system parameters, namely, damping, spin-orbit interaction, and Josephson to magnetic energy ratio, the magnetic dynamics is reduced to the dynamics of the scalar Duffing oscillator, driven by the Josephson oscillations. The role of increasing superconducting current in the resonance region is clarified. Shifting of the ferromagnetic resonant frequency and the reversal of its damping depend…
A possible scenario for an ac Josephson effect initiated by the flow of dislocations through a mechanically loaded but electrically unbiased superconductor is proposed. The characteristic voltages due to the motion of dislocations in loaded (under the applied stress of 10^7N/m^2) YBCO crystals are estimated to be of the order of a few picovolts (which corresponds to the Josephson frequency of 10 kHz).
We consider a simple model of a multidomain superconductor-ferromagnet-superconductor (SFS) Josephson junction. Sign-alternating magnetization $M$ in domains leads to a spatial modulation of the phase difference $ϕ(x)$. Due to this modulation the Josephson critical current $I_{c}$ may have a different sign depending on the ratio of the magnetic flux in a domain, 4$πMa(2d_{F}),$ to the magnetic flux quantum. This phase modulation, but not a nonmonotonic dependence of the local critical current density $j_{c}$, may be the reason for oscillations of the current $I_{c}$ {\bf \}as a function of the…
We present a theory of the Josephson effect in a twofold-tilted Josephson junction made by d-wave anisotropic layered superconductors. We find the appearance of an intrinsic electrical resistance that arises from the misalignment of the superconductive planes (the CuO_2 planes in YBCO) in the two electrodes. This intrinsic contribution to the tunnel barrier has several non-trivial consequences. The result is relevant for understanding the electric transport properties of [100] tilt and [100] tilt-tilt Josephson junctions based on d-wave superconductors.
Using the functional integral method, we construct a theory of heterotic SIS Josephson junctions between single- and two-gap superconductors. The theory predicts the presence of in-phase and out-of-phase collective oscillation modes of superconducting phases. The former corresponds to the Josephson plasma mode whose frequency is drastically reduced for $\pm$ s-wave symmetry, and the latter is a counterpart of Leggett's mode in Josephson junctions. We also reveal that the critical current and the Fraunhofer pattern strongly depend on the symmetry type of the two-gap superconductor.
A formula for the Josephson current between two superconductors with anisotropic pairing symmetries is derived based on the mean-field theory of superconductivity. Zero-energy states formed at the junction interfaces is one of basic phenomena in anisotropic superconductor junctions. In the obtained formula, effects of the zero-energy states on the Josephson current are taken into account through the Andreev reflection coefficients of a quasiparticle. In low temperature regimes, the formula can describe an anomaly in the Josephson current which is a direct consequence of the exsitence of zero-e…
We study the Josephson effect in spin-singlet superconductor/helical $p$-wave superconductor junctions with a ferromagnetic barrier using the quasiclassical Green function method. It is found that both $\sinϕ$-type and $\cosϕ$-type current-phase relations always exist, irrespective of the gap symmetries in superconductors. The indispensable condition for the $\sinϕ$-type and $\cosϕ$-type current is that the magnetization must have a component parallel to the crystallographic $a$ or $b$ axis, which is distinct from the case of $p$-wave superconductor described by a $\vect{d}$-vector with a unif…
Current - voltage characteristics in magnetic field for layered superconductor with intrinsic pinning of Josephson vortices
M.N. Mikheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences（俄罗斯科学院乌拉尔分校 M.N. 米凯耶夫金属物理研究所）；National Research Nuclear University MEPhI（国立核研究大学莫斯科工程物理学院）
We develop a detailed microscopic theory describing dc Josephson effect and Andreev bound states in superconducting junctions with a half-metal. In such systems the supercurrent is caused by triplet pairing states emerging due to spin-flip scattering at the interfaces between superconducting electrodes and the half-metal. For sufficiently clean metals we provide a detailed non-perturbative description of the Josephson current at arbitrary transmissions and spin-flip scattering parameters for both interfaces. Our analysis demonstrates that the behavior of both the Josephson current and Andreev …
In superconductors with three or more bands, time-reversal symmetry (TRS) may be broken in the presence of repulsive interband couplings, resulting in a pair of degenerate states characterized by opposite chiralities. We consider a Josephson junction between a three-band superconductor with broken TRS and a single-band superconductor. Phenomena such as asymmetric critical currents, subharmonic Shapiro steps and symmetric Fraunhhofer patterns are revealed theoretically. Existing experimental results are discussed in terms of the present work.
We study theoretically the effects of interfacial Rashba and Dresselhaus spin-orbit coupling in superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions---with allowing for tunneling barriers between the layers---by solving the Bogoljubov-de Gennes equation for a realistic heterostructure and applying the Furusaki-Tsukada technique to calculate the electric current at a finite temperature. The presence of spin-orbit couplings leads to out- and in-plane magnetoanisotropies of the Josephson current, which are giant in comparison to current magnetoanisotropies in similar normal-state…
We analyze consequences of dynamical modulations of Josephson current by non-polar lattice mode in the Josephson junction barrier. In the high $T_c$ junctions, the effect of such modulations can be anomalously strong due to the proximity of the insulating barrier to the superconducting state. Accordingly, the interconversion of sound (as well as other non-polar phonons) and the Josephson plasma oscillations mediated by stationary Josephson currents, which may be present in the junction due to various reasons, becomes possible. We suggest that this effect can be employed for imaging of the stat…
We show that the two-band nature of noncentrosymmetric superconductors leads naturally to an anomalous Josephson current appearing at zero phase difference in a clean noncentrosymmetric superconductor/ferromagnet/noncentrosymmetric superconductor junction. The two-band nature provides two sets of Andreev bound states which carry two supercurrents with different amplitudes. When the magnetization direction of the ferromagnet is suitably chosen, two supercurrents experience opposite phase shifts from the conventional sinusoidal current-phase relation. Then the total Josephson current results in …
We examine a Josephson junction involving two arbitrary equal-spin-pairing unitary triplet superconductors and a ferromagnetic tunneling barrier. Using perturbation theory, we show how the interaction of the barrier moment with the spin of the tunneling triplet Cooper pairs can reverse the sign of the Josephson charge current. This also results in a Josephson spin current, which contains a phase-independent contribution due to reflection processes at the barrier. We verify our analytic predictions using a non-perturbative Bogoliubov-de Gennes method.
We study the Josephson effect in a triplet superconductor--ferromagnet--singlet superconductor junction. We show that the interaction of tunneling Cooper pairs with the interface magnetization can permit a Josephson current at the lowest order of a tunneling Hamiltonian perturbation theory. Two conditions must be satisfied for this to occur: the magnetization of the ferromagnet has a component parallel to the ${\bf d}$-vector of the triplet superconductor, and the gaps of the superconductors have the same parity with respect to the interface momentum. The resulting charge current displays an u…
We develop a model for high-Tc superconductors based on an electronic phase separation where low-and high-density domains are formed. At low temperatures this system may act as a granular superconductor forming an array of Josephson junctions. Cuprates are also known to have low superfluid densities and strong correlation effects. Both characteristics activate a negative Josephson coupling due to frustration that leads to spontaneous currents responsible for the weak ferromagnetic order. This original approach reproduces the observed onset of spontaneous magnetic signal and its dependence on t…
Charge and spin Josephson currents in a ballistic superconductor-ferromagnet-superconductor junction with spin-triplet pairing symmetry are studied using the quasiclassical Eilenberger equation. The gap vector of superconductors has an arbitrary relative angle with respect to magnetization of the ferromagnetic layer. We clarify the effects of the thickness of ferromagnetic layer and magnitude of the magnetization on the Josephson charge and spin currents. We find that 0-πtransition can occur except for the case that the exchange field and d-vector are in nearly perpendicular configuration. We …
A novel time-reversal symmetry breaking state is found theoretically in the Josephson junction between the two-gap superconductor and the conventional s-wave superconductor. This occurs due to the frustration between the three order parameters analogous to the two antiferromagnetically coupled XY-spins put under a magnetic field. This leads to the interface states with the energies inside the superconducting gap. Possible experimental observations of this state with broken time-reversal symmetry are discussed.
We report on the successful terahertz emission (0.6$\sim$1 THz) that is continuous and tunable in its frequency and power, by driving Josephson vortices in resonance with the collective standing Josephson plasma modes excited in stacked Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ intrinsic Josephson junctions. Shapiro-step detection was employed to confirm the terahertz-wave emission. Our results provide a strong feasibility of developing long-sought solid-state terahertz-wave emission devices.
Topological superconductors are gapped superconductors with protected Majorana surface/edge states on the boundary. In this paper, we study the Josephson coupling between time-reversal invariant topological superconductors and s-wave superconductors. The Majorana edge/surface states of time-reversal invariant topological superconductors in all physical dimensions 1, 2, 3 have a generic topological property which we named as time-reversal anomaly. Due to the time-reversal anomaly, the Josephson coupling prefers a nonzero phase difference between topological and trivial superconductors. The nont…
The low energy excitation spectrum is found for a layered superconductor vortex with a small number of impurities inside the vortex core. All levels are found to be correlated. This leads to the strong enhancement of conductivity in superclean layered superconductors.
For certain orientations of Josephson junctions between two p_x-wave or two d-wave superconductors, the subgap Andreev bound states produce a 4pi-periodic relation between the Josephson current I and the phase difference phi: I sin(phi/2). Consequently, the ac Josephson current has the fractional frequency eV/h, where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. …
We report the first experimental observation of the two-node thickness dependence of the critical current in Josephson junctions with a ferromagnetic interlayer. Vanishings of the critical current correspond to transitions into pi-state and back into conventional 0-state. The experimental data allow to extract the superconducting order parameter oscillation period and the pair decay length in the ferromagnet. We develope a theoretical approach based on Usadel equations, which takes into account the spin-flip scattering. Results of numerical calculations are in good agreement with the experimen…
Structural and physical properties of layered chalcogenide superconductors are summarized. In particular, we review the remarkable properties of the Fe-chalcogenide superconductors, FeSe and FeTe-based materials. Furthermore, we introduce the recently-discovered new BiS2-based layered superconductors and discuss its prospects.
Theoretical studies of a planar tunnel junction between two superconductors with antisymmetric spin-orbit coupling are presented. The half-space Green's function for such a superconductor is determined. This is then used to derive expressions for the dissipative current and the Josephson current of the junction. Numerical results are presented in the case of the Rashba spin-orbit coupling, relevant to the much studied compound CePt$_3$Si. Current-voltage diagrams, differential conductance and the critical Josephson current are presented for different crystallographic orientations and different…
We find a mapping of the layered sine-Gordon model to an equivalent gas of topological excitations and determine the long-range interaction potentials of the topological defects. This enables us to make a detailed comparison to the so-called layered vortex gas, which can be obtained from the layered Ginzburg-Landau model. The layered sine-Gordon model has been proposed in the literature as a candidate field-theoretical model for Josephson-coupled high-T_c superconductors, and the implications of our analysis for the applicability of the layered sine-Gordon model to high-T_c superconductors are…
