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Author: van Wezel, Jasper × Start date: 2020 × DDC: 530 × Type: Text × Publisher: College Park, MD : APS ×

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    Thermalization by a synthetic horizon
    (College Park, MD : APS, 2022) Mertens, Lotte; Moghaddam, Ali G.; Chernyavsky, Dmitry; Morice, Corentin; van den Brink, Jeroen; van Wezel, Jasper
    Synthetic horizons in models for quantum matter provide an alternative route to explore fundamental questions of modern gravitational theory. Here we apply these concepts to the problem of emergence of thermal quantum states in the presence of a horizon, by studying ground-state thermalization due to instantaneous horizon creation in a gravitational setting and its condensed matter analog. By a sudden quench to position-dependent hopping amplitudes in a one-dimensional lattice model, we establish the emergence of a thermal state accompanying the formation of a synthetic horizon. The resulting temperature for long chains is shown to be identical to the corresponding Unruh temperature, provided that the postquench Hamiltonian matches the entanglement Hamiltonian of the prequench system. Based on detailed analysis of the outgoing radiation we formulate the conditions required for the synthetic horizon to behave as a purely thermal source, paving a way to explore this interplay of quantum-mechanical and gravitational aspects experimentally.
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    Horizon physics of quasi-one-dimensional tilted Weyl cones on a lattice
    (College Park, MD : APS, 2022) Könye, Viktor; Morice, Corentin; Chernyavsky, Dmitry; Moghaddam, Ali G.; van den Brink, Jeroen; van Wezel, Jasper
    To simulate the dynamics of massless Dirac fermions in curved space-times with one, two, and three spatial dimensions, we construct tight-binding Hamiltonians with spatially varying hoppings. These models represent tilted Weyl semimetals where the tilting varies with position, in a manner similar to the light cones near the horizon of a black hole. We illustrate the gravitational analogies in these models by numerically evaluating the propagation of wave packets on the lattice and then comparing them to the geodesics of the corresponding curved space-time. We also show that the motion of electrons in these spatially varying systems can be understood through the conservation of energy and the quasiconservation of quasimomentum. This picture is confirmed by calculations of the scattering matrix, which indicate an exponential suppression of any noncontinuous change in the quasimomentum. Finally, we show that horizons in the lattice models can be constructed also at finite energies using specially designed tilting profiles.
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    Observation of orbital order in the van der Waals material 1T−TiSe2
    (College Park, MD : APS, 2022) Peng, Yingying; Guo, Xuefei; Xiao, Qian; Li, Qizhi; Strempfer, Jörg; Choi, Yongseong; Yan, Dong; Luo, Huixia; Huang, Yuqing; Jia, Shuang; Janson, Oleg; Abbamonte, Peter; van den Brink, Jeroen; van Wezel, Jasper
    Besides magnetic and charge order, regular arrangements of orbital occupation constitute a fundamental order parameter of condensed matter physics. Even though orbital order is difficult to identify directly in experiments, its presence was firmly established in a number of strongly correlated, three-dimensional Mott insulators. Here, reporting resonant x-ray-scattering experiments on the layered van der Waals compound 1T-TiSe2, we establish that the known charge density wave in this weakly correlated, quasi-two-dimensional material corresponds to an orbital ordered phase. Our experimental scattering results are consistent with first-principles calculations that bring to the fore a generic mechanism of close interplay between charge redistribution, lattice displacements, and orbital order. It demonstrates the essential role that orbital degrees of freedom play in TiSe2, and their importance throughout the family of correlated van der Waals materials.