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DDC: 500 × Subject: quantum mechanics × WGL Institute: IFWD ×

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Now showing 1 - 3 of 3
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    Tomonaga–Luttinger liquid behavior and spinon confinement in YbAlO 3
    ([London] : Nature Publishing Group UK, 2019) Wu, L.S.; Nikitin, S.E.; Wang, Z.; Zhu, W.; Batista, C.D.; Tsvelik, A.M.; Samarakoon, A.M.; Tennant, D.A.; Brando, M.; Vasylechko, L.; Frontzek, M.; Savici, A.T.; Sala, G.; Ehlers, G.; Christianson, A.D.; Lumsden, M.D.; Podlesnyak, A.
    Low dimensional quantum magnets are interesting because of the emerging collective behavior arising from strong quantum fluctuations. The one-dimensional (1D) S = 1/2 Heisenberg antiferromagnet is a paradigmatic example, whose low-energy excitations, known as spinons, carry fractional spin S = 1/2. These fractional modes can be reconfined by the application of a staggered magnetic field. Even though considerable progress has been made in the theoretical understanding of such magnets, experimental realizations of this low-dimensional physics are relatively rare. This is particularly true for rare-earth-based magnets because of the large effective spin anisotropy induced by the combination of strong spin–orbit coupling and crystal field splitting. Here, we demonstrate that the rare-earth perovskite YbAlO3 provides a realization of a quantum spin S = 1/2 chain material exhibiting both quantum critical Tomonaga–Luttinger liquid behavior and spinon confinement–deconfinement transitions in different regions of magnetic field–temperature phase diagram.
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    Resonating holes vs molecular spin-orbit coupled states in group-5 lacunar spinels
    ([London] : Nature Publishing Group UK, 2023) Petersen, Thorben; Bhattacharyya, Pritam; Rößler, Ulrich K.; Hozoi, Liviu
    The valence electronic structure of magnetic centers is one of the factors that determines the characteristics of a magnet. This may refer to orbital degeneracy, as for jeff = 1/2 Kitaev magnets, or near-degeneracy, e.g., involving the third and fourth shells in cuprate superconductors. Here we explore the inner structure of magnetic moments in group-5 lacunar spinels, fascinating materials featuring multisite magnetic units in the form of tetrahedral tetramers. Our quantum chemical analysis reveals a very colorful landscape, much richer than the single-electron, single-configuration description applied so far to all group-5 GaM4X8 chalcogenides, and clarifies the basic multiorbital correlations on M4 tetrahedral clusters: while for V strong correlations yield a wave-function that can be well described in terms of four V4+V3+V3+V3+ resonant valence structures, for Nb and Ta a picture of dressed molecular-orbital jeff = 3/2 entities is more appropriate. These internal degrees of freedom likely shape vibronic couplings, phase transitions, and the magneto-electric properties in each of these systems.
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    Collapse of layer dimerization in the photo-induced hidden state of 1T-TaS2
    ([London] : Nature Publishing Group UK, 2020) Stahl, Quirin; Kusch, Maximilian; Heinsch, Florian; Garbarino, Gaston; Kretzschmar, Norman; Hanff, Kerstin; Rossnagel, Kai; Geck, Jochen; Ritschel, Tobias
    Photo-induced switching between collective quantum states of matter is a fascinating rising field with exciting opportunities for novel technologies. Presently, very intensively studied examples in this regard are nanometer-thick single crystals of the layered material 1T-TaS2, where picosecond laser pulses can trigger a fully reversible insulator-to-metal transition (IMT). This IMT is believed to be connected to the switching between metastable collective quantum states, but the microscopic nature of this so-called hidden quantum state remained largely elusive up to now. Here, we characterize the hidden quantum state of 1T-TaS2 by means of state-of-the-art x-ray diffraction and show that the laser-driven IMT involves a marked rearrangement of the charge and orbital order in the direction perpendicular to the TaS2-layers. More specifically, we identify the collapse of interlayer molecular orbital dimers as a key mechanism for this non-thermal collective transition between two truly long-range ordered electronic crystals.