We analyze the charge and spin transport through a ballistic ferromagnet/insulator/superconductor junction by means of the Bogoliubov-de Gennes equations. For the ferromagnetic side we assume that ferromagnetism may be driven by an unequal mass renormalization of oppositely polarized carriers, i.e. a spin bandwidth asymmetry, and/or by a rigid splitting of up-and down-spin electron bands, as in a standard Stoner ferromagnet, whereas the superconducting side is assumed to exhibit a d-wave symmetry of the order parameter, which can be pure or accompanied by a minority component breaking time-reversal symmetry. Several remarkable features in the charge conductance arise in this kind of junction, providing useful information about the mechanism of ferromagnetism in the ferromagnetic electrode, as well as of the order parameter symmetry in the superconducting one. In particular, we show that when a time-reversal symmetry breaking superconductor is considered, the use of the two kinds of ferromagnet mentioned above represents a valuable tool to discriminate between the different superconducting mixed states. We also explain how this junction may mimic a switch able to turn on and off a spin current, leaving the charge conductance unchanged, and we show that for a wide range of insulating barrier strengths, a spin bandwidth asymmetry ferromagnet may support a spin current larger than a standard Stoner one.

We analyze the dc Josephson effect in a ballistic superconductor/ferromagnet/superconductor junction by means of the Bogoliubov-de Gennes equations in the quasiclassical Andreev approximation. We consider the possibility of ferromagnetism originating from a mass renormalization of carriers of opposite spin, i.e. a spin bandwidth asymmetry. We provide a general formula for Andreev levels which is valid for arbitrary interface transparency, exchange interaction, and bandwidth asymmetry and analyze the current-phase relation, free energy, and critical current, in the short junction regime. We compare the phase diagrams and the critical current magnitudes of two identical junctions differing only in the mechanism by which the mid-layer becomes magnetic. We show that a larger number of 0 − π transitions caused by a change in junction width or polarization magnitude is expected when ferromagnetism is driven by spin bandwidth asymmetry compared to Stoner magnetism. Moreover, we show that these features can be present also for ferromagnets of the Stoner type having only a partial bandwidth asymmetry. PACS numbers: 74.50.+r,74.45.+c,72.25.-b,74.25.Dw arXiv:1012

We describe the superconducting proximity effect taking place in a contact between a noncentrosymmetric superconductor and a diffusive normal/ferromagnetic metal within the quasiclassical theory of superconductivity. By solving numerically the Usadel equation with boundary conditions valid for arbitrary interface transparency, we show that the analysis of the proximity-modified local density of states in the normal side can be used to obtain information about the exotic superconductivity of noncentrosymmetric materials. We point out the signatures of triplet pairing, the coexistence of triplet and singlet pairing, and particular orbital symmetries of the pair potential. Exploiting the directional dependence of the spin polarization pair breaking effect on the triplet correlations, we show how the order relation between triplet and singlet gaps can be discriminated and that an estimation of the specific gap ratio is possible in some cases.Comment: 11 pages, 4 figure

A ferromagnet/insulator/superconductor ballistic junction is used to distinguish the contributions due to exchange splitting and spin-dependent mass renormalization of up-and down-spin bands in itinerant ferromagnets. The study is performed within the Blonder-Tinkham-Klapwijk approach and by solving the corresponding Bogoliubov-de Gennes equations in a way to get the current flux across the junction. The averaged differential conductance is shown to exhibit features that depend on the strength of the mass and the exchange splitting while the knowledge of the transmission critical angle provides a mean to measure the mass asymmetry among up and down carriers.

The discovery of noncentrosymmetric superconductors, such as CePt 3 Si, and chiral superconductors, such as Sr 2 RuO 4 , calls for experimental methods to identify the presence of spin-triplet pairing. We here demonstrate a method which accomplishes this in an appealingly simple manner: a spin-sensitive proximity effect in a ferromagnet|triplet superconductor bilayer. It is shown how the orientation of the field can be used to unambiguously distinguish between different spin-triplet states. Moreover, the proximity effect becomes long-ranged in spite of the presence of an exchange field and even without any magnetic inhomogeneities, in contrast to conventional S|F junctions. Our results can be verified by STM-spectroscopy and could be useful as a tool to characterize the pairing state in unconventional superconducting materials. PACS numbers:Superconductivity may be defined as conventional or unconventional depending on the properties of the pairing state and whether or not multiple broken symmetries are present in the system. In conventional superconductors, the pairing state belongs to the trivial representation of the point-group and the system ground state breaks the U(1) gauge symmetry. On the other hand, unconventional superconductors display pairing symmetries belonging to higher-dimensional representations of the point group and may also exhibit multiple broken symmetries in the ground state. Examples of the latter are ferromagnetic superconductors [1] with simultaneously broken U(1) and SU(2) symmetries due to the presence of an intrinsic magnetization, and noncentrosymmetric superconductors [2], where the absence of a definite parity of the lattice leads to the mixing of even-and odd-parity superconducting order parameters.In order to characterize the properties of a superconducting system, much relies on determining the orbital-and spinsymmetry of the order parameter (OP), a topic currently under intense investigation [3][4][5][6][7]. To acquire information about the order parameter, it is often useful to study how the superconducting correlations behave when placed in proximity to a non-superconducting material such as a normal metal. This idea has been employed previously in several works studying e.g. normal metal|non-centrosymmetric superconductor (N|NCS) junctions [8][9][10][11] in order to look for unique signatures of the superconducting OP. However, the nonsuperconducting material does not necessarily have to be a simple normal metal. Instead, it may feature intrinsic properties, such as magnetism, which then provide an arena for studying the interplay between superconductivity and different types of electronic ordering [12].A natural question arises: could such an interplay be useful in order to extract information about the superconducting state? In this Letter, we demonstrate that a ferromagnet|triplet superconductor bilayer provides an appealingly simple and powerful method of clearly distinguishing between different types of triplet pairing states, thus providing information about the natu...