Russian Academy of Sciences

Landau Institute for Theoretical Physics

Seminars at the Landau Institute scientific council

Mikrovolnovye svoistva sverkhprovodnikov vblizi perekhoda v izolyator

20 October, the day after tomorrow in 11:30

L. Ioffe. M. Feigel’man

Predlozhena osnova teorii kollektivnykh mod v sil’no neuporyadochennykh sverkhprovodnikakh, nakhodyashchikhsya vblizi kvantovogo perekhoda v dielektricheskoe sostoyanie. Pokazano, chto s priblizheniem parametrov sverkhprovodnika k kvantovoi kriticheskoi tochke, v spektre vozbuzhdenii s neizbezhnost’yu voznikaet nenulevaya plotnost’ nizkolezhashchikh (s energiyami sushchestvenno nizhe sverkhprovodyashchei shcheli) sostoyanii. Pri eshche bol’shem besporyadke eti podshchelevye sostoyaniya okazyvayutsya delokalizovannymi, chto dolzhno privodit’ k zametnoi dissipatsii v mikrovolnovom otklike.

Cooper pair splitting in ballistic ferromagnetic SQUIDs

27 October in 11:30

P.L. Stroganov, Ya.V. Fominov

We consider ballistic SQUIDs with spin filtering inside half-metallic ferromagnetic arms. A singlet Cooper pair cannot pass through an arm in this case, so the Josephson current is entirely due to the Cooper pair splitting, with two electrons going to different interferometer arms. In order to elucidate the mechanisms of Josephson transport due to split Cooper pairs, we assume the arms to be single-channel wires in the short-junction limit. Different geometries of the system (determined by the length of the arms and the phases acquired by quasiparticles during splitting between the arms) lead to qualitatively different behavior of the SQUID characteristics (the Andreev levels, the current-phase relation, and the critical Josephson current) as a function of two control parameters, the external magnetic flux and misorientation of the two spin filters. The current-phase relation can change its amplitude and shape, in particular, turning to a pi-junction form or acquiring additional zero crossings. The critical current can become a nonmonotonic function of the misorientation of the spin filters and the magnetic flux (on half of period). Periodicity with respect to the magnetic flux is doubled, in comparison to conventional SQUIDs.

Helical edge transport in the presence of anisotropic magnetic impurity

17 November in 11:30

P. D. Kurilovich, V. D. Kurilovich, I. S. Burmistrov, M. Goldstein

We consider the effects of electron scattering on a quantum magnetic impurity on the current-voltage characteristics of the helical edge of a two-dimensional topological insulator. We compute the backscattering contribution to the current along the edge for a general form of the exchange interaction matrix and arbitrary value of the magnetic impurity spin. We find that the differential conductance might be a non-monotonous function of the voltage with several extrema. Effects of magnetic anisotropy for the impurity are considered.

Seminars are held on Fridays in the conference hall of Landau Institute for Theoretical Physics in Chernogolovka, beginning at 11:30.

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