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arXiv · 1803.01553

Low-Energy Excitations in Quantum Spin-Liquids Identified by Optical Spectroscopy

A. Pustogow·Y. Saito·E. Zhukova·B. Gorshunov·R. Kato·T. -H. Lee·S. Fratini·V. Dobrosavljević·M. Dressel
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Abstract

The electrodynamic response of organic spin liquids with highly-frustrated triangular lattices has been measured in a wide energy range. While the overall optical spectra of these Mott insulators are governed by transitions between the Hubbard bands, distinct in-gap excitations can be identified at low temperatures and frequencies which we attribute to the quantum spin liquid state. For the strongly correlated $β^{\prime}$-EtMe$_3$\-Sb\-[Pd(dmit)$_2$]$_2$, we discover enhanced conductivity below $175~{\rm cm}^{-1}$, comparable to the energy of the magnetic coupling $J\approx 250$ K. For $ω\rightarrow 0$ these low-frequency excitations vanish faster than the charge-carrier response subject to Mott-Hubbard correlations, resulting in a dome-shape band peaked at 100~\cm. Possible relations to spinons, magnons and disorder are discussed.

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A. Pustogow, Y. Saito, E. Zhukova, B. Gorshunov, R. Kato, T. -H. Lee, S. Fratini, V. Dobrosavljević, M. Dressel. 2018-08-07. Low-Energy Excitations in Quantum Spin-Liquids Identified by Optical Spectroscopy. https://doi.org/10.1103/physrevlett.121.056402

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