A theory of spin polarized tunneling spectroscopy based on a scattering theory is given for tunneling junctions between ferromagnets and d-wave superconductors. The spin filtering effect of an exchange field in the insulator is also treated. We clarify that the properties of the Andreev reflection are largely modified due to a presence of an exchange field in the ferromagnets, and consequently the Andreev reflected quasiparticle shows an evanescent-wave behavior depending on the injection angle of the quasiparticle. Conductance formulas for the spin current as well as the charge current are given as a function of the applied voltage and the spin-polarization in the ferromagnet for arbitrary barrier heights. It is shown that the surface bound states do not contribute to the spin current and that the zero-bias conductance peak expected for a d-wave superconductor splits into two peaks under the influence of the exchange interaction in the insulator.

We construct the phase diagram of a homogeneous two component Fermi gas with population imbalance under a Feshbach resonance. In particular, we study the physics and stability of the Larkin-Ovchinnikov phase. We show that this phase is stable over a much larger parameter range than what has been previously reported by other authors.

Tunneling conductance in ferromagnet / unconventional superconductor junctions is studied theoretically as a function of temperatures and spin-polarization in ferromagnets. In d-wave superconductor junctions, a zero-energy Andreev bound state drastically affects the temperature dependence of the zero-bias conductance (ZBC). In p-wave superconductor junctions, numerical results show various temperature dependence of the ZBC depending on the direction of the magnetic moment in ferromagnets and the pairing symmetry in superconductors such as px, py and px + ipy-wave symmetries. The last one is a candidate for the pairing symmetry of Sr2RuO4. From these characteristic features in the conductance, we may obtain the information about the degree of spin-polarization in ferromagnets and the direction of the d-vector in spin-triplet superconductors.

A theory of tunneling conductance in ferromagnetic-metal/insulator/triplet-superconductor junctions is presented for unitary and non-unitary spin triplet pairing states which are promising candidates for the superconducting pairing symmetry of Sr 2 RuO 4 . As the magnitude of the exchange interaction in the ferromagnetic metal is increased, the conductance for the unitary pairing state below the energy gap is reduced in contrast to that for the non-unitary pairing state. This is due to the fact that the retro-reflectivity in the Andreev reflection for unitary pairing state is broken due to the influence from the exchange interaction.KEYWORDS: triplet superconductor, unitary pair potential, non-unitary pair potential, ferromagnetic metal, Andreev reflectionAndreev reflection, which occurs at the interfaces between normal metals and superconductors, 1)is one of the most important elemental processes in electron transport through the superconducting junction. It is an interesting problem to clarify the expected for a tunneling effect in ferromagnet/insulator/superconductor (F/I/S) junctions, since the retro-reflectivity of the Andreev reflection is broken due to an exchange interaction in the ferromagnets. For s-wave superconductors, these properties are well understood and new aspects of the Andreev reflection have been revealed. 2) On the other hand, stimulated by the establishment of d-wave symmetry in high-T C superconductors, theories of the tunneling conductance of anisotropic superconductor junctions have been developed, which fully take into account the anisotropy of the pair potential. 3,4,5,6,7) In anisotropic superconductors, the change in sign of the pair potential induces remarkable effects, i.e., a zero-bias conductance peak (ZBCP) 8) in tunneling experiments of high T C superconductors, due to the formation of zero-energy states (ZES). Recently, previous theories have been extended to F/I/S junctions with d-wave superconductors, 9,10,11) and the influences of the exchange interaction on transport properties have been clarified. 11) However, these theories treat only spin singlet superconductors.The recent discovery of superconductivity in Sr 2 RuO 4 12) has attracted much theoretical and experimental attention because this material is the first example of a noncuprate layered perovskite 1

The current fluctuations in normal metal / d-wave superconductor junctions are studied for various orientation of the crystal by taking account of the spatial variation of the pair potentials. Not only the zero-energy Andreev bound states (ZES) but also the non-zero energy Andreev bound states influence on the properties of differential shot noise. At the tunneling limit, the noise power to current ratio at zero voltage becomes 0, once the ZES are formed at the interface. Under the presence of a subdominant s-wave component at the interface which breaks time-reversal symmetry, the ratio becomes 4e.

Abstract. -The superconducting current-phase relation (CPR) of Nb/Au/(001)YBa2Cu3Ox heterojunctions prepared on epitaxial c-axis oriented YBa2Cu3Ox thin films has been measured in a single-junction interferometer. For the first time, the second harmonic of the CPR of such junctions has been observed. The appearance of the second harmonic and the relative sign of the first and second harmonics of the CPR can be explained assuming, that the macroscopic pairing symmetry of our YBa2Cu3Ox thin films is of the d + s type.Introduction. It is now well established that the dominant component of the superconducting order parameter in the cuprates has d-wave symmetry (see [1] and references therein). Moreover, it has become clear that in orthorhombic materials such as YBa 2 Cu 3 O x (YBCO), a finite component with s-wave symmetry is admixed to the dominant d-wave order parameter. The early in-plane phase sensitive experiments imply that the d-wave component remains coherent through the whole sample [1], while an elegant c-axis tunneling experiment shows directly that the s-wave order parameter component does change sign across the twin boundary [2].The above picture of the YBCO pairing state is challenged by the experimental observation of a finite c-axis Josephson current between heavily twinned YBCO and a Pb counterelectrode [3]. Namely, the contribution of the s-wave part of the YBCO order parameter to

A bstractT he transportproperti esbetween ferrom agnetsand hi gh-T c superconductors were i nvesti gated i n La 0:67juncti ons i n the geom etry ofcross-stri p l i nes. T he conductance spectra show zero-bi as conductance peaks (ZB C P),re ecti ng the charge transport i n the ab-pl ane.W hen an externalm agneti c el d i sappl i ed to thejuncti ons,theconductance spectra show two notabl e features,i. e. ,an i ncrease ofbackground conductance and an asym m etri c ZB C P spl i tti ng w hose am pl i tude responds nonl i nearl y to the appl i ed el d. It i s show n that the m agneti c el d response are consi stent w i th a theoreti cal predi cti on of tunnel i ng spectroscopy w hen the presence ofa ferrom agneti c barri er between a spi n-pol ari zed ferrom agnet and a d-wave superconductor i s assum ed. 74. 50. + r,74. 80. Fp

A method for identifying the parity of unconventional superconductors based on tunneling spectroscopy is proposed. For a model of calculation, we adopt a ferromagnet/superconductor (F/S) junction, the tunneling current of which is spin polarized. The tunneling conductance spectra are shown to be quite sensitive to the direction of the magnetization axis in the ferromagnet only when the superconductor has odd parity. Therefore, it is possible to distinguish the parity of the superconductor by performing tunneling spectroscopy in F/S junctions.