# DQMP Seminar - Prof. Georgios Varelogiannis - Quartet-Rule-Coupling and Quartet Engineering

24.10.2023 13:00 – 14:00

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 representations obey a specific rule. All quartets have essentially two regimes, the hierarchy regime where one member can be dominant and the equity regime where all members have comparable energy scales corresponding to the famous dome states in phase diagrams of correlated systems. For example, p-h asymmetry and CDW and SDW and FM was the first studied quartet coupling fundamentally charge and spin degrees of freedom that can explain colossal magnetoresistance in manganites [1] and itinerant states in oxide insulator interfaces. Particle-hole asymmetry with SDW and d-wave-SC and staggered π-triplet SC form another quartet proposed to explain the field induced SDW state in the SC state CeCoIn¬5 [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. Quartet Engineering 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 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 necessary topological quantum gates opening the path to spintronic integrated topological quantum processor devices. QRC also implies [6] that in a commensurate canted AFM state necessarily coexists an unconventional imaginary SDW state polarized in the third perpendicular axis exhibiting at the edges SOC DW and a QRC many-body magnetoelectric effect pointing to a QRC mechanism of multiferroicity in AFM materials that break inversion.

[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, http://arxiv.org/abs/1305.2976 (2013)

[4] G. Livanas, M. Sigrist and G. Varelogiannis, Sci. Rep. 9, 6259 (2019) and supplementary.

[5] G Livanas, N Vanas, M Sigrist and G Varelogiannis, Eur. Phys. J. B 95, 47 (2022)

[6] N. Vanas, C. Liu, G. Livanas, T. Kontos, M. Sigrist and G. Varelogiannis, preprint (2023)

### Lieu

Bâtiment: Ecole de Physique

Auditoire Stückelberg

### Organisé par

Département de physique de la matière quantique### Intervenant-e-s

Georges Varelogiannis , Prof. Department of Physics, National Technical University of Athens, GR-15780 Athens, Greeceentrée libre

### Classement

Catégorie: Séminaire