Abstract
We show that the optical responses below the Mott gap can be used to probe the spin-triplet excitations in valence bond solid (VBS) phases in Mott insulators. The optical conductivity in this regime arises due to the electronic polarization mechanism via virtual electron-hopping processes. We apply this mechanism to the Hubbard model with spin–orbit couplings and/or the corresponding spin model with significant Dzyaloshinskii–Moriya (DM) interactions, and compute the optical conductivity of VBS states on both ideal and deformed Kagome lattices. In the case of the deformed Kagome lattice, we study the antiferromagnet Rb2Cu3SnF12 with the pinwheel VBS state. In case of the ideal Kagome lattice, we explore the optical conductivity signatures of the spin-triplet excitations for three VBS states with (1) a 12-site unit cell, (2) a 36-site unit cell with six-fold rotation symmetry, and (3) a 36-site unit cell with three-fold rotation symmetry, respectively. We find that increasing the DM interactions generally leads to broad and smooth features in the optical conductivity with interesting experimental consequences. The optical conductivity reflects the features of the spin-triplet excitations that can be measured in future experiments.
Highlights
In Mott insulators, small charge fluctuations exist due to virtual hopping of the electrons for any finite hopping amplitude
In case of valence bond solid (VBS) orders on the ideal Kagome lattice, we study three well known VBS states that have been studied in different contexts [21,22,23,24]: (1) a 12-site pinwheel VBS, (2) a 36-site VBS with six-fold rotation symmetry, and (3) a 36-site VBS with three-fold rotation symmetry
12-site VBS: the dimer pattern in the 12-site VBS state on the ideal Kagome lattice is essentially the same state that we considered for the deformed Kagome lattice antiferromagnet
Summary
Max-Planck Institute for the Physics of Complex Systems, Nothnitzer Str. 38, 01187 Dresden, Germany. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Keywords: optical conductivity, valence bond solid, Rb2Cu3SnF12, kagome lattice antiferromagnet
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