Spin Induced Optical Conductivity in the Spin Liquid Candidate Herbertsmithite

Abstract

A quantum spin liquid (QSL) is a state of matter in which magnetic spins interact strongly, but quantum fluctuations inhibit long-range magnetic order even at zero temperature. A QSL has been predicted to have a host of exotic properties, including fractionalized excitations and long-range quantum entanglement. Despite the numerous theoretical studies, experimental realization of a QSL has proved to be challenging due to the lack of candidate materials. The triangular organic salts EtMe3Sb[Pd(dmit)2]2 and κ-(BEDT-TTF)2Cu2(CN)3, and kagome ZnCu3(OH)6Cl2 (Herbertsmithite) have recently emerged as promising candidates of exhibiting a QSL state, but the nature of their ground states is still elusive. Here we studied a large-area high-quality single crystal of Herbertsmithite by means of time-domain terahertz (THz) spectroscopy. We observed in the low-frequency (0.6-2.2 THz) optical conductivity evidence for the nature of the spin system. In particular, the in-plane absorption spectrum exhibits a unique frequency dependence that can be described by a power-law with an exponent of approximately 1.4, in sharp contrast with the ω^4 dependence expected for an ordered Mott insulator. The absorption is also found to increase as the temperature decreases, a behavior unexpected for conventional insulators. Such features are consistent with recent theory based on the interactions between the charge and spin degrees of freedom in a QSL system.

9 pages, 6 figures (supplementary information included)

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• Field induced magnon excitation and in gap absorption of Kitaev candidate RuCl3
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• Mechanism for subgap optical conductivity in honeycomb Kitaev materials
• Topological spin ordering via Chern-Simons superconductivity
• Cyclotron resonance inside the Mott gap: a fingerprint of emergent neutral fermions
• Electrodynamics of quantum spin liquids
• Theory of electronic magnetoelectric coupling in $d^5$ Mott insulators
• Nature of optical excitations in the frustrated kagome compound Herbertsmithite
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• Lattice dynamics in the spin-1/2 frustrated kagome compound herbertsmithite
• Signatures of fractionalization in spin liquids from interlayer thermal transport
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• Electric field control of emergent electrodynamics in quantum spin ice
• Low-Energy Excitations in Quantum Spin-Liquids Identified by Optical Spectroscopy
• Infrared phonons as a probe of a spin-liquid states in herbertsmithite ZnCu3(OH)6Cl2
• Spin liquid in twisted homobilayers group-VI gichalcogenides
• Magnetic terahertz resonances above the Néel temperature in the frustrated kagome antiferromagnet averievite
• Taking a critical look at holographic critical matter
• Fluctuating Fractionalized Spins in Quasi Two-dimensional Magnetic V0.85PS3
• The magneto-optical Faraday effect in spin liquid candidates
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• Optical conductivity and surface plasmon modes of U(1) spin liquid states with large spinon Fermi surfaces
• Universal behavior of quantum spin liquid and optical conductivity in the insulator herbertsmithite
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• Electron correlation effects and spin-liquid state in the Herbertsmithite Kagome lattice
• Spinon mediation of witness spin dynamics in herbertsmithite
• Dirac node pinning from Dzyaloshinskii-Moriya interactions in a Kagome spin liquid