Российский Квантовый Центр Russian Quantum Center

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Open RQC colloquium. Lecture 41


The Forty First lecture "Spin impurities near a helical edge: Kondo screening vs. RKKY interaction" in Open RQC Colloquium will be held in National University of Science and Technology MISIS (Moscow, Leninsky Avenue, 4) lecture hall № Б-534 (5th floor), on 18th of May 2018 at 10:00 a.m by Vladimir Yudson, Chief Research Fellow in the Laboratory for Condensed Matter Physics (HSE), at Institute for Spectroscopy RAS and in the Many-body Theory Group (RQC).




Abstract

The seminal Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect interaction between magnetic impurities (local spins) plays the fundamental role in physics of conductors. In the paradigmatic approach, RKKY is described in terms of an effective spin Hamiltonian. Common wisdom states that there is a broad interval of distances where RKKY overwhelms screening of an individual magnetic impurity by the cloud of electrons (the well-known Kondo screening). We show that this commonly accepted physical picture and the paradigmatic description of RKKY fail in strongly correlated one-dimensional helical systems (like edge states in two-dimensional topological insulators ). Helical electrons possess the lock-in relation between their spin and direction of propagation. We demonstrate that helicity may lead to a new regime where the Kondo effect dominates over RKKY interaction at all distances. The crossover occurs when the (effective) electron interaction becomes larger than some critical value. The unexpected failure of the common wisdom is one of the peculiarities of physics of strongly correlated systems

Biography

Vladimir Yudson graduated from Moscow Physical-Technical Institute in 1973 and got the PhD degree in 1990. From 1973 till 2016 he was working in the theoretical department of the Institute of Spectroscopy RAS (ISAN). From the Fall 2016 he has been working as a сhief research fellow in the Laboratory of Condensed Matter Physics of the Faculty of Physics of National research university Higher School of Economics, keeping a part of his responsibilities in ISAN. He is also a сhief research fellow in the Many-body Theory Group of RQC. His research interests include low-dimensional electron systems, many-body theory, electron and light propagation in disordered media, localization and mesoscopic phenomena, linear and nonlinear spectroscopy of solids, nonlinear quantum optics. Among his scientific achievements there is prediction of a Wigner crystallization of a two-dimensional electron gas (2DEG) in a strong magnetic field, interaction and dark states of resonant atoms (qubits) in one-dimensional waveguides, discovery of instability of nonlinear sigma-model of the weak localization theory caused by high gradient vertices and etc.

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