23 июня 2019 г.

В четверг 27 июня 2019 г. в 15:00 в Конференц-зале НТЦ УП состоится научный семинар по акустической и оптической спектроскопии.

С докладом на тему «Hidden order in boron-doped superconducting nanocrystalline diamond films» выступит Somnath Bhattacharyya (Nano-Scale Transport Physics Laboratory, School of Physics, and DST/NRF Centre of Excellence in Strong Materials, (University of the Witwatersrand, Johannesburg, South Africa), Университет «МИСиС», Москва)

Аннотация: Nanocrystalline diamond films can be described as a granular superconducting system with the association of Josephson’s tunneling between two superconducting carbon (diamond) grains separated by a very thin layer of graphene-like carbon. Graphene on diamond has been suggested as a good candidate for topological insulator. Hence the superconducting nanodiamond heterostructures can form some topological qubits in addition to flux qubits of superconducting diamond. Presently we concentrate on electrical transport properties of heavily boron–doped nanocrystalline diamond films around the superconducting transition temperature measured as a function of magnetic fields and the applied bias current and establish chiral superconductivity in these materials. We tune the transport properties in heavily boron-doped nanocrystalline diamond films near to the superconducting transition point by changing the orientation and magnitude of the applied magnetic field and also with the finite bias current that suggests non-s wave symmetry of order parameter in this system. Observations include an anomalous resistance peak near to the superconducting transition temperature as well as a strong zero bias anomaly. The occurrence of the Berezinskii-Kosterlitz-Thouless transition is investigated through a combination of current-voltage and resistance measurements which is related to vortex pinning. The magnetoresistance (MR) of these films was found to change from negative to a positive value at a particular temperature close to this transition which is explained through the transition from weak localization to weak anti-localization effect. Additionally we report on the observation of anomalous Hall resistance as well as strong zero bias conductance peak which is sensitive to the applied magnetic fields. Through the application of a low bias current negative magnetoresistance (MR) features can be seen with some periodic oscillatory features which can be attributed to tunnelling associated with non-s wave order parameters in a multi-junction system. Presence of an odd frequency superconducting order parameter has been claimed from pronounced zero bias conductance peak (ZBCP) as well as spin valve-like effect in MR. Ultimately from the angle-dependent change of critical temperature as well as the MR peaks we demonstrate signature of spin triplet superconductivity in these films. The transition from a spin singlet state to a triplet state is explained via a transition of 0-pphase of Josephson current confirms nanodiamond films as unconventional superconductors that matches with some recent experimental observations and theoretical models of a 2D bilayer system recently proposed in this system also related a topologically protected surface state.

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