Impurity scattering effect on charge transport in high-Tc cuprate junctions

• Datum: 2004
• Hauptverfasser: Tanaka, Y., Asano, Y., Kashiwaya, S.
• Format: Artikel
• Sprache: Englisch
• Veröffentlicht: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2004
• Schlagworte: Сверхпроводимость и мезоскопические структуры
• Online Zugang: https://nasplib.isofts.kiev.ua/handle/123456789/119832
• Назва журналу: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Zitieren: Impurity scattering effect on charge transport in high-Tc cuprate junctions / Y. Tanaka, Y. Asano, S. Kashiwaya // Физика низких температур. — 2004. — Т. 30, № 7-8. — С. 770-784. — Бібліогр.: 137 назв. — англ.

It is known that the zero-bias conductance peak (ZBCP) is expected in tunneling spectra of
 normal-metal/high-Tc cuprate junctions because of the formation of the midgap Andreev resonant
 states (MARS) at junction interfaces. In the present review, we report the recent theoretical study
 of impurity scattering effects on the tunneling spectroscopy. In the former part of the present paper,
 we discuss impurity effects in normal metal. We calculate tunneling conductance for diffusive
 normal metal (DN)/high Tc cuprate junctions based on the Keldysh Green's function technique.
 Besides the ZBCP due to the MARS, we can expect ZBCP caused by the different origin, i.e., the
 coherent Andreev reflection (CAR) assisted by the proximity effect in DN. Their relative importance
 depends on the angle α between the interface normal and the crystal axis of high-Tc superconductors.
 At α = 0, we find the ZBCP by the CAR for low transparent junctions with small Thouless
 energies in DN; this is similar to the case of diffusive normal metal/insulator/s-wave superconductor
 junctions. Under increase of α from zero to π/4, the contribution of MARS to ZBCP becomes
 more prominent and the effect of the CAR is gradually suppressed. Such complex spectral
 features would be observable in conductance spectra of high-Tc junctions at very low temperatures.
 In the latter part of our paper, we study impurity effects in superconductors. We consider impurities
 near the junction interface on the superconductor side. The conductance is calculated from the
 Andreev and the normal reflection coefficients which are estimated by using the single-site approximation
 in an analytic calculation and by the recursive Green function method in a numerical simulation.
 We find splitting of the ZBCP in the presence of the time reversal symmetry. Thus the
 zero-field splitting of ZBCP in the experiment does not perfectly prove an existence of broken time
 reversal symmetry state.