N. Kitaura

Nagoya University, Nagoya, Aichi, Japan

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Publications (4)4.08 Total impact

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    ABSTRACT: Effects of impurity scattering on tunneling conductance in dirty normal-metal/insulator/superconductor junctions are studied based on the Kubo formula and the recursive Green function method. The zero-bias conductance peak (ZBCP) is a consequence of the unconventional pairing symmetry in superconductors. The impurity scattering in normal metals suppresses the amplitude of the ZBCP. The degree of the suppression agrees well with results of the quasiclassical Green function theory. When superconductors have $d$+is-wave pairing symmetry, the time-reversal symmetry is broken in superconductors and the ZBCP splits into two peaks. The random impurity scattering reduces the height of the two splitting peaks. The position of the splitting peaks, however, almost remains unchanged even in the presence of the strong impurity scattering. Thus the two splitting peaks never merge into a single ZBCP. Comment: 12 pages, 5 figures, using jpsj2.cls and overcite.sty
    Journal of the Physical Society of Japan 03/2003; · 2.09 Impact Factor
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    ABSTRACT: We numerically calculate the tunnel conductance in N/I/D(pi/4) junctions in the presence of randomness in N part, where N, I, D(pi/4) are normal metals, insulators and d-wave superconductors with the orientation angle being pi/4, respectively. When N are in the diffusive regime, the zero-bias conductance peak (ZBCP) in conductance spectra of N/I/D(pi/4) junctions still can be observed. The height of the ZBCP, however, is suppressed and the shape of the ZBCP is broadened. When N are in the localization regime, the ZBCP tends to split into two peaks.
    01/2003;
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    ABSTRACT: Tunneling conductance at zero voltage in diffusive normal metal (DN)/insulator/s-wave superconductor junctions is calculated for various situations based on the quasiclassical (QC) theory. In QC theory, the generalized boundary condition introduced by Nazarov [Superlattices and Microstructures 25 1221 (1999)] is applied, where ballistic theory by Blonder Tinkham and Klapwijk and diffusive theory by Volkov Zaitsev and Klapwijk based on the boundary condition by Kupriyanov and Lukichev are naturally reproduced. It is shown that with the increase of the magnitude of resistance of DN (RD), normalized tunneling conductance is enhanced (suppressed) for low (high) transparent barrier. When the length of DN is larger than that of localization length, tunneling conductance obtained by numerical simulation deviates from that by QC theory.
    Physica C Superconductivity 01/2003; · 0.72 Impact Factor
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    ABSTRACT: We calculate tunnel conductance for disordered normal metal/unconventional superconductor junctions where superconducting order parameter has broken time reversal symmetry (BTRS), i.e., dx2−y2+is. It is shown that reflectionless tunneling phenomena appears since zero-energy resonant states caused by the internal phase of dx2−y2-pair potential is broken by BTRS states. It is also shown that splitting of zero bias conductance peak due to BTRS in conductance spectra remains whereas the height of the peak is suppressed by the randomness.
    Physica B Condensed Matter 01/2003; 329:1451-1452. · 1.28 Impact Factor