Berlin 2018 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 41: Frustrated Magnets - Spin Liquids - Experiments
TT 41.8: Talk
Tuesday, March 13, 2018, 12:15–12:30, H 3005
Spinon Excitations in Quantum Spin-Liquids Identified by Optical Spectroscopy — Andrej Pustogow1, Yohei Saito1, Elena Zhukova2, Boris Gorshunov2, Reizo Kato3, and •Martin Dressel1 — 11. Physikalisches Inst., Universität Stuttgart, Germany — 2Moscow Inst. Phys. Techn., Dolgoprudny, Moscow Region, Russia — 3RIKEN, Saitama, Japan
The electrodynamic response of several organic quantum spin-liquids
with highly-frustrated triangular lattices
has been measured in a wide energy range.
Even below the Mott-Hubbard gap,
large non-thermal contributions to the optical conductivity are observed
in the vicinity of the metal-insulator phase boundary;
such metallic quantum fluctuations are most pronounced
in κ-(BEDT-TTF)2Cu2(CN)3.
Only when investigating the more strongly correlated Mott insulator β′-EtMe3Sb[Pd(dmit)2]2 at
very low frequencies and temperatures, we succeeded identifying an excess conductivity
that cannot be explained by the charge response of the correlated electrons.
Upon subtracting the smooth power-law background of the Mott-Hubbard band,
a broad dome-like mode is identified,
delimited by J ≈ 20 meV at its high-energy end;
the low-frequency decrease is consistent with the ω2 dependence expected for spinons.
Due to this fast decay, the effective range of
well-defined spinons is confined to the microwave and THz energy ranges.
Our findings are in excellent agreement with recent dynamical mean field theory calculations
stating that the controversially discussed spinon
Fermi surface is damped away upon approaching the Mott metal-insulator transition.