Humboldt Research Award for Professor Andrzej M. Oleś

Professor Andrzej M. Oleś received Humboldt Research Award (Humboldt-Forschungspreis) in recognition of his entire achievements in the theoretical physics of condensed matter.

The works of A. M. Oleś advanced the field of electron correlations in transition metals, Mott insulators, and high-Tc superconductors. He introduced important concepts in the theory of quantum materials with several interacting degrees of freedom, in particular discovered the quantum aspects of spin-orbital physics, including such phenomena as fluctuations and entanglement. The most important discoveries were completed in the collaboration with his collegues from Quantum Many-Body Theory Department in Max Planck Institute for Solid State Research.

Phase diagram of the Compass-Heisenberg model in the (J<sub>x</sub>,I)-plane for fixed AF interaction J<sub>z </sub>= 1. Long-range order is stabilized by any finite Heisenberg interaction I. Square and diamond at the compass line indicate multi-critical points, where four ordered phases meet. The spin order of the different phases is depicted in a corresponding inset, and the subscript indicates the type of symmetry breaking in spin space. Straight lines separating the phases follow from symmetry; in two cases they are modified by quantum corrections.<br /><strong><em>F. Trousselet, A. M. Ole</em></strong><strong><em>ś, P. Horsch</em></strong>, Magnetic Properties of Nanoscale Compass-Heisenberg Planar Clusters, Physical Review B <strong>86</strong>, 134412 (2012). Zoom Image
Phase diagram of the Compass-Heisenberg model in the (Jx,I)-plane for fixed AF interaction Jz = 1. Long-range order is stabilized by any finite Heisenberg interaction I. Square and diamond at the compass line indicate multi-critical points, where four ordered phases meet. The spin order of the different phases is depicted in a corresponding inset, and the subscript indicates the type of symmetry breaking in spin space. Straight lines separating the phases follow from symmetry; in two cases they are modified by quantum corrections.
F. Trousselet, A. M. Oleś, P. Horsch, Magnetic Properties of Nanoscale Compass-Heisenberg Planar Clusters, Physical Review B 86, 134412 (2012).

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The selected papers listed here introduce new fundamental concepts:

The importance of novel quantum orbital fluctuations in spin-orbital systems was discovered by Feiner, Oleś, and Zaanen in [1]. The interplay between spin and orbital degrees of freedom in transition metal oxides is described in detail in [2], including some cases where the interpretation requires spin-orbital entanglement [3]. For a hole doped Mott insulator, as e. g. LaVO3, he introduced spin-orbital polarons, explaining that the orbital degrees of freedom confine the spin dynamics and generate the string potential of the joint spin-orbital character [4]. Recent research concentrates on the impact of various defect states in spin-orbital systems, including the orbital dilution in doped ruthenates [5].

[1] L. F. Feiner, A. M. Oleś, J. Zaanen
Quantum Melting of Magnetic Order due to Orbital Fluctuations
Physical Review Letters 78, 2799-2802 (1997)

[2] A. M. Oleś, G. Khaliullin, P. Horsch, L. F. Feiner
Fingerprints of Spin-Orbital Physics in Cubic Mott Insulators:
Magnetic Exchange Interactions and Optical Spectral Weights
Physical Review B 72, 214431/1-32 (2005)

[3] A. M. Oleś, P. Horsch, L. F. Feiner, G. Khaliullin
Spin-Orbital Entanglement and Violation of the Goodenough-Kanamori Rules
Physical Review Letters 96, 147205/1-4 (2006)

[4] K. Wohlfeld, A. M. Oleś, P. Horsch
Orbitally Induced String Formation in the Spin-Orbital Polarons
Physical Review B 79, 224433/1-17 (2009)
[Editor's choice and Viewpoint in Physics]

[5] W. Brzezicki, A. M. Oleś, M. Cuoco
Spin-Orbital Order Modified by Orbital Dilution in Transition Metal Oxides:
From Spin Defects to Frustrated Spins Polarizing Host Orbitals
Physical Review X 5, 011037/1-28 (2015)