Abstract: One way to characterize quantum spin-liquids is through the fractionalization of spin excitations. A prime example of this is found in the exactly solvable Kitaev model of spin-1/2 moments with anisotropic exchange interactions on a tri-coordinated lattice. To find examples of this kind of physics in nature turns out to be challenging. The currently best-known examples of materials in which Kitaev-like physics plays a central role are the layered spin-orbit entangled J=1/2 systems Na2IrO3, α-Li2IrO3, and α-RuCl3. However, these materials all possess additional interactions, which, among other, lead to a magnetically ordered state at low temperature preventing the formation of a pure Kitaev spin-liquid (KSL) state. Apart from the ongoing quest for materials showing a true KSL ground state, one can also destabilize the magnetic order in the existing materials, which potentially can induce the sought-after KSL state. In this talk I will discuss two methods to destabilize magnetic order in α-RuCl3. The first one is through the application of an in-plane magnetic field leading to various field induced states. Though it has been shown by various authors that this indeed leads to suppression of the ordered state in α-RuCl3, the nature of the field-induced states is not fully clear. The second approach is a pump-probe method which creates holon and doublon excitations. These excitations are found to couple efficiently to magnetic excitations which in turn disorder the magnetically ordered state. For sufficiently high excitation densities the magnetic order is fully suppressed, leading to a quantum disordered magnetic state.
Biography: Paul van Loosdrecht obtained his M.Sc. in Physics from Eindhoven University of Technology and his Ph.D. from the University of Nijmegen in 1992. After receiving the prestigious NWO 'Talent' award, he held various research and educational positions at IBM's Almaden Research Center (US), Grenoble High Magnetic Field Laboratory (CNRS, France) and Aachen University (Germany). In 2003, following the receipt of the NWO 'Springplank' award, Paul was appointed as a full professor of Optical Condensed Matter Physics at the University of Groningen in the Netherlands. Since 2013, he has been a Professor of Condensed Matter Physics at the University of Cologne. Paul van Loosdrecht has held several academic leadership roles, including serving as Dean of the School of Mathematics and Natural Sciences at the University of Cologne.
Paul’s main research interests lie in the fundamental properties of complex matter and the optical manipulation of molecular and complex systems using advanced linear and non-linear spectroscopies. His current research focuses on non-equilibrium material physics and the influence of spin-orbit coupling, correlations, and topology on the physical properties of novel quantum materials. He has authored over 200 peer-reviewed papers and currently serves as an editor for Physics Reports. Paul is a founder and a lead of the research center for Control and Dynamics of Quantum Materials at Institute of Physics, University of Cologne.