Emergence of nematic paramagnet via quantum order-by-disorder and pseudo-Goldstone modes in Kitaev magnets Article Swipe
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· 2020
· Open Access
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· DOI: https://doi.org/10.1103/physrevresearch.2.043023
· OA: W3013647672
The appearance of nontrivial phases in Kitaev materials exposed to an\nexternal magnetic field has recently been a subject of intensive studies. Here,\nwe elucidate the relation between the field-induced ground states of the\nclassical and quantum spin models proposed for such materials, by using the\ninfinite density matrix renormalization group (iDMRG) and the linear spin wave\ntheory (LSWT). We consider the $K \\Gamma \\Gamma'$ model, where $\\Gamma$ and\n$\\Gamma'$ are off-diagonal spin exchanges on top of the dominant Kitaev\ninteraction $K$. Focusing on the magnetic field along the $[111]$ direction, we\nexplain the origin of the nematic paramagnet, which breaks the\nlattice-rotational symmetry and exists in an extended window of magnetic field,\nin the quantum model. This phenomenon can be understood as the effect of\nquantum order-by-disorder in the frustrated ferromagnet with a continuous\nmanifold of degenerate ground states discovered in the corresponding classical\nmodel. We compute the dynamical spin structure factors using a matrix operator\nbased time evolution and compare them with the predictions from LSWT. We, thus,\nprovide predictions for future inelastic neutron scattering experiments on\nKitaev materials in an external magnetic field along the $[111]$ direction. In\nparticular, the nematic paramagnet exhibits a characteristic pseudo-Goldstone\nmode which results from the lifting of a continuous degeneracy via quantum\nfluctuations.\n
