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30/05/2023 - Séminaire - Georgios Varelogi

Mardi 30 Mai 2023 à 11h00, Georgios Varelogi (National Technical University of Athens, GR-15780 Athens, Greece, currently at ENS Paris) donnera un séminaire à l’auditorium TRT.

Title  :
Quartet-Rule-Coupling : from Fundamental Magnetism and Superconductivity to Quartet Engineering

Abstract :
Quartet-Rule-Coupling (QRC) that I have discovered more than two decades ago, is a universal hidden interaction that is triggered only when any three members of specific quartets of fields and/or order parameters (Ops) coexist inducing the missing fourth member. These quartets are sets of four fields and/or OPs such that all their possible representations obey a specific rule. QRC has been demonstrated analytically and we have also demonstrated numerically on dozens of different examples of quartets that QRC exhibits a universal behavior. For example, chemical potential and CDW and SDW and FM was the first studied quartet coupling fundamentally change and spin degrees of freedom that can explain colossal magnetoresistance in manganites [1]. Particle-hole asymmetry with SDW and d-wave-SC and staggered π-triplet SC form another quartet proposed to explain the high field induced SDW state in the SC state CeCoIn5 [2]. Particle-hole asymmetry with charge current and Zeeman field and antisymmetric Spin-Orbit-Coupling (SOC) form a hugely important quartet (this is quartet A in [4]) providing a fundamental generic source of SOC unrelated to relativistic effects and explaining for example the gate voltage induced sign change in spin-charge current interconversion (Nat. Mat. 2016) or even its very observation at aluminium interfaces (arXiv : 2205.08486) reported by the CNRS-Thales group.

Quartet Engineering (QE) is the invention of device schemes that exploit QRC properties and the rule that allows to predict quartets [3]. For example, the coexistence of charge current with ordinary s-SC and a Zeeman field triggers QRC inducing p-wave triplet SC. This fundamental quartet (quartet B in [4]) is groundbreaking for the whole field of SC science and technology meaning for example that that there cannot exist only s-wave or only p-wave vortices in any type II SC. Combined with other related quartets led us to the discovery of alternative paths for the realization and manipulation of Majorana fermions in ferromagnet-superconductor heterostructures without need of any material or structure with intrinsic spin-orbit coupling [4]. We proposed an original platform [5] for the manipulation of multiple Majorana qubits based on supercurrents and gate voltage manipulation of ferromagnets able to produce braiding operations for all necessary topological quantum gates with available technology opening the path to integrated topological quantum processor devices.

[1] G. Varelogiannis, Phys. Rev. Lett. 85, 4172 (2000)
[2] A. Aperis, G. Varelogiannis, P.B. Littlewood and B.D. Simons, Journal of Physics Cond. Matter. 20, 434235 (2008), A. Aperis, G. Varelogiannis and P.B. Littlewood, Phys. Rev. Lett. 104, 216403 (2010)
[3] G. Varelogiannis, Preprint at, (2013)
[4] G. Livanas, M. Sigrist and G. Varelogiannis, Sci. Rep. 9, 6259 (2019). (see also related extended supplementary material)
[5] G Livanas, N Vanas, M Sigrist and G Varelogiannis, Eur. Phys. J. B 95, 47 (2022)

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