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2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 7 Apr 2020 11:15  Lara Ulcakar  KibbleZurek behavior in disordered Chern insulators 

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Even though no local order parameter in the sense of the Landau theory exists for topological quantum phase transitions in Chern insulators, the highly nonlocal Berry curvature exhibits critical behavior near a quantum critical point. We investigate the critical properties of its real space analog, the local Chern marker, in weakly disordered Chern insulators. Due to disorder, inhomogeneities appear in the spatial distribution of the local Chern marker. Their size exhibits power law scaling with the critical exponent matching the one extracted from the Berry curvature of a clean system. We drive the system slowly through such a quantum phase transition. The characteristic size of inhomogeneities in the nonequilibrium postquench state obeys the KibbleZurek scaling. In this setting, the local Chern marker thus does behave in a similar way as a local order parameter for a symmetry breaking second order phase transition. The KibbleZurek scaling also holds for the inhomogeneities in the spatial distribution of excitations and of the orbital polarization.

10 Mar 2020 11:15  Roman Rausch (Kyoto University, Japan)  Magnetic Doublon Bound States in the Kondo Lattice Model 

We present a novel pairing mechanism for electrons, mediated by magnons. These paired bound states are termed magnetic doublons. Applying numerically exact techniques (exact diagonalization and the densitymatrix renormalization group, DMRG) to the Kondo lattice model at strong exchange coupling J for different fillings and magnetic configurations, we demonstrate that magnetic doublon excitations exist as composite objects at excitation energies of the order of 3J/2 above the ground state.
The magnetic doublon is similar to the conventional doublon, a quasiparticle which arises when electrons are excited across the Mott gap in the Hubbard model, and thus has potential applications in the same areas: photovoltaics, metastable superconductivity and cooling via quantum distillation. However, it also inherits characteristics from the physics of magnetoresistance, so that its properties are in principle magnetotunable.
[1] R. Rausch, M. Potthoff, N. Kawakami, Phys. Rev. Lett. 123, 216401 (2019)
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6 Apr, 2020 Young researcher position  6 Apr, 2020 Publication: Tadic B., Andjelkovic M... Entropy 22...  6 Apr, 2020 Seminar: Apr 7: KibbleZurek be... Lara Ulcakar...  9 Mar, 2020 Seminar: Mar 10: Magnetic Doublo... Roman Rausch (Kyoto Uni...  28 Feb, 2020 Conference: SigmaPhi2020 WS3. C... Chania, Greece...  7 Feb, 2020 Publication: Bonča, J., Trugman, S.... Phys. Rev. B 100...  7 Feb, 2020 Publication: Ulcakar, L., Jernej Mr... Phys. Rev. B 100...  7 Feb, 2020 Publication: Środa, M., Prelovšek,... Phys. Rev. B 99... 

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