Download Asano_Abstract - Superconducting hybrid nanostructures

MIPT Conference 2016 “Superconducting hybrid nanostructures: physics and application”
Anomalous magnetic response and electric transport due to
odd-frequency Cooper pairs
Y. Asano1,3, S.-I.Suzuki1, S. IKegaya1, A. Sasaki1, and Y. Tanaka2,3
1
Department of Applied Physics, Hokkaido University, Sapporo, 060-8628, Japan
2
Department of Applied Physics, Nagoya University, 462-8602, Japan
3
Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia
Unconventional superconductor hosts the Andreev bound states at its surface.
Simultaneously odd-frequency Cooper pairs appear at the surface as a
subdominant pairing correlation. We discuss the anomalous magnetic response
and electric transport of a unconventional superconductor physics, which are
responsible for odd-frequency pairs. At first, we demonstrate the paramagnetic
response of a small unconventional superconductor [1]. This unusual effect
stems from the paramagnetic property of an odd-frequency pair. We also briefly
discuss the robustness of the paramagnetic effect under the surface roughness.
Secondly, we show that the presence of an odd-frequency pair in a two-band
superconductor. The band hybridization generates odd-frequency pairs. Although
odd-frequency pairs are paramagnetic (thermodynamically instable), they stay in
the uniform ground state. As a consequence, the transition temperature
decreases with increasing in the amplitude of odd-frequency pairs[2]. Thirdly we
discuss the quantization of conductance minimum in an NS junction consisting of
an unconventional superconductor. In the limit of strong impurity scatterings in
the normal metal, the quantized conductance value is characterized by the
Atihya-Singer index in mathematics. The Atihya-Singer index theorem relates a
topological invariant and an invariant defined by the solutions of a differential
equation. We propose a novel invariant characterizes the physical
phenomenon[3]. The unusual behavior of the zero-bias conductance is a
common property of odd-parity superconductor known as the anomalous
proximity effect. We show that the penetration of odd-frequency Cooper pairs into
the dirty normal metal causes the perfect Andreev reflection.
[1] S.-I. Suzuki and Y. Asano, Phys. Rev. B 89, 184508 (2014); Phys. Rev. B 91, 214510 (2015).
[2] A. Sasaki and Y. Asano, Phys. Rev. B 92, 224508 (2015).
[3] S. Ikegaya, S.-I. Suzuki, Y. Tanaka, and Y. Asano, Phys. Rev. B 94, 054512 (2016).
[4] S. Ikegaya, Y. Asano, and Y. Tanaka, Phys. Rev. B 91, 174511 (2015).
1