Dresden 2017 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 3: Transport: Topological Insulators (jointly with DS, MA, HL, O)

HL 3.5: Talk

Monday, March 20, 2017, 10:30–10:45, HSZ 204

Perfect filter for triplet superconductivity on the surface of a 3DTI — •Daniel Breunig¹, Pablo Burset¹, François Crépin², and Björn Trauzettel¹ — ¹Institute for Theoretical Physics and Astrophysics, Wuerzburg University, 97074 Wuerzburg, Germany — ²Laboratoire de Physique Théorique de la Matière Condensée, UPMC, Sorbonne Universités, 75252 Paris, France

We study a NSN junction on the surface of a 3D topological insulator (TI), where N is a normal region and S is a s-wave proximity-induced superconducting region. Spin-orbit coupling in the TI breaks spin rotational symmetry and induces unconventional triplet superconductivity.

From the anomalous Green function, we identify the singlet and triplet pairing amplitudes and perform a symmetry classification on these quantities. Pauli exclusion principle demands the antisymmetry of the Green function under simultaneous exchange of its space, time and spin variables. The pairing amplitudes can thus be classified as ESE, OSO, ETO or OTE. Here, the first (last) letter specifies the time/frequency (parity) symmetry (Even or Odd) and the second one describes the spin (Singlet or Triplet). A special feature of our system is the emergence of the exotic odd-frequency pairing.

Interestingly, we find that for a bipolar junction, where the chemical potentials in the N leads only differ in their signs, the non-local singlet pairing amplitude is completely suppressed and only triplet pairing occurs. As a result, the non-local conductance across the junction can be dominated by purely spin triplet crossed Andreev reflections, while electron cotunneling is absent.