[RpL 1285] IRQ'2020: 2nd 'Lecture on mesoscopic superconductivity' by Teunis Klapwijk and seminar 'Heat transmission in a proximitized nanowire' by Anton Bubis

[Alexander Semenov]

Dear all,
Today, on Thursday November 26, at 17.00 Moscow time (15.00 CET, 14.00 GMT), the second 'Lecture on mesoscopic superconductivity' will be given by Teunis Klapwijk, emeritus professor at Delft University of Technology. Instead of the abstract, you can look at several first slides of the lecture: https://drive.google.com/file/d/12XjKSAnuFraR5RwzucuoTOeKDHzuuEAl/view?usp=drivesdk
The lecture will be followed at 18.45 by seminar 'Heat transmission in a proximitized nanowire' by Anton Bubis from Skolkovo Institute of Science and Technology. Please find the abstract at the bottom of this email.
Link to Zoom meeting: https://zoom.us/j/8976647786?pwd=SjBSTVNqRG1uaCsrYjJDVit5eTduUT09
(For those who plan to get certificate and want to be counted by as accurately: 1) please check that your Zoom nick allows to identify you unambiguously; 2) after entering, send a private message via the chat, with any text,  to the person named 'Registration').
Sincerely,
On behalf of Organisers of IRQ'2020,
Alexander Semenov
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Heat transmission in a proximitized nanowire
A.V. Bubis, A.O. Denisov, S.U. Piatrusha, N.A. Titova, A.G. Nasibulin, J. Becker, J. Treu, D. Ruhstorfer, G. Koblmüller, E.S. Tikhonov, and V.S. Khrapai
Electronic transport in hybrid semiconductor-superconductor devices is getting a second breath in the context of recent topological band theory. One of the most promising directions is a realization of topological superconductivity in a proximitized semiconducting nanowire (NW), accompanied by emerging Majorana zero modes (MZMs) localized at its ends [1]. While all the prerequisites for this noble goal are there, including ballistic single-mode transport, strong spin-orbit coupling and thin superconducting shell in strong magnetic fields, the non-local character of the proposed MZMs remains hidden. The MZMs non-locality is masked in conductance measurements by the superconducting shell shunting the charge transport. By contrast, in thermal transport, thanks to the gapped nature of the superconducting shell, the topological phase transition receives a universal signature in quantized thermal conductance of the proximitized NW [2]. In this work, we demonstrate the first experimental measurement of the heat signals transmitted through the superconductor proximitized region of a single InAs NW and retrieve most of the features analytically by simple quasi-classical model [3].
Our hybrid devices are based on diffusive InAs NWs with a grounded superconducting (S) terminal in the middle and two normal (N) terminals on either side, with the proximitized center region opened towards both normal regions. Standard re-entrant behavior in local conductance and vanishing sub-gap non-local conductance evidence the dominance of the Andreev reflection of quasiparticles from the lateral S-NW interface over the normal reflection. Raising the chemical potential of the N-terminal on one side of the S-region, we detect the heat signal on the other side employing shot noise or zero-bias thermometry techniques. We demonstrate that the heat signals are mediated by sub-gap non-equilibrium Andreev quasiparticles diffusing laterally to the superconducting interface.
For the quantitative description of heat transmission we solved the diffusion equation on electron energy distribution (EED) function with proper boundary conditions. Besides resistances of both sections of NW the only one parameter, thermal conductance, determines the solution for subgap heat transport. Fitting the experimental data we obtained thermal conductance on the order of conductance quantum, proving the relevance of our approach in the context of the non-local nature of the MZMs. Moreover, the aforementioned quasi-classical approach predicts the opportunity to discover the thermal conductance even with floating S terminal, i.e. without charge-heat separation.
Finally, we will discuss how the transport of heat can interplay with non-local transport measurements. Similar to thermoelectric effect, non-equilibrium EED realized on the boundary of proximity region contributes to non-local voltage. Depending on the applied gate voltage non-local conductance response in our device is of different sign, that can also be described in terms of quasi-classical approach. Experiments accompanied by theoretical background in such geometry are in demand nowadays due to its versatile employment in Majorana setups [4].
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[1] Jason Alicea, Rep. Prog. Phys. 75, 076501 (2012)
[2] A. R. Akhmerov et al., PRL 106, 057001 (2011)
[3] K. E. Nagaev and M. Büttiker, PRB 63, 081301 (2001)
[4] G. C. Ménard et al., PRL 124, 036802 (2020)