| Brief Bio of the Speaker | Thierry Valet is a distinguished engineer and physicist renowned for his expertise in the field of spintronics, after a 35+ year career in the electronic industry and academia, both in Europe and the United States. His achievements include the seminal theory of perpendicular magnetoresistance in magnetic multilayers developed with Nobel prize winner Prof. Albert Fert while at Thales (FR), the first demonstration of the HAMR technology while leading the Optical Storage Group at Seagate Research (US), and his contribution to the first demonstration of spin transfer torque magnetization switching in MTJ while serving as Chief Scientist at Grandis (US). Valet's work has garnered extensive citations, underscoring the impact of his findings on condensed matter physics. His patented innovations in magnetic memory and magneto resistive transducers demonstrate a blend of theoretical insight and practical application, advancing the frontiers of spintronics and its applications in modern technology. His significant contributions to the field have been recognized with the awarding of the MAINZ Visiting Professorship in 2015. While maintaining strong link with the industry as an entrepreneur and technology consultant, Valet is still pursuing more fundamental endeavors, with the recent development of a quantum kinetic theory of electronic systems with non-trivial quantum geometry, in collaboration with Pr. Roberto Raimondi (IT), with key implications for the rapidly growing field of orbitronics. |
Abstract |
In a recent work [1], we have established the foundations of a U(1) x SU(N) gauge invariant quantum kinetic theory of general N-bands electron systems, driven by classical electromagnetic fields slowly varying in time and space on atomic scales. In this talk, we will start with a general overview of the salient new features of this formalism, insisting on how we have recently extended it to weakly disordered systems, and how we can insure full equivalence with Kubo linear response theory under some well-defined hypothesis. Then, we will illustrate the power of this framework on selected examples in spintronics. Namely, we will show how concrete calculations shed new light on the subtle interplay between quantum geometry and disorder, in modulating the spin Hall effect [2] and the spin-orbit torque effect [3]. The importance of vertex corrections, and how our approach captures them seamlessly, will be specially discussed. We will then turn our focus to orbitronics [4], with the derivation of a new mechanism responsible for out-of-equilibrium orbital coherence, which may explain the recent observations of current induced edge orbital accumulation in thin films of centrosymmetric normal metals [5]. In conclusion, we would like to open a perspective towards the development of new numerical simulation capabilities, whose theoretical underpinning is provided by our formalism, and that we believe will help bridge the current gap between microscopic material modeling (DFT-Wannier) and device modeling at the mesoscopic scale. [1] T. Valet and R. Raimondi,Semiclassical kinetic theory for systems with non-trivial quantum geometry and the expectation value of physical quantities, EPL, 143, 26004 (2023). [2] R. Raimondi, C. Gorini, P. Schwab, and M. Dzierzawa, Quasiclassical approach to the spin Hall effect in the two-dimensional electron gas, Phys. Rev. B, 74, 035340 (2006). [3] D. G. Ovalle, A. Pezo and A. Manchon,Spin-orbit torque for field-free switching in C3v crystals, Phys. Rev. B, 107, 094422 (2023). [4] D. Go, D. Jo, H.-W. Lee, M. Klaui and Y. Mokrousov,Orbitronics: Orbital currents in solids, EPL, 135, 37001 (2021). [5] I. Lyalin, S. Alikhah, M. Berritta, P. M. Oppeneer, and R. K. Kawakami,Magneto-Optical Detection of the Orbital Hall Effect in Chromium, Phys. Rev. Lett., 131, 156702 (2023) |
