Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 78: Correlated Electrons: Poster Session

TT 78.31: Poster

Donnerstag, 10. März 2016, 15:00–18:30, Poster D

Optical investigations on spin liquids — •Mathias Bories — 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart

In quantum spin liquids, localized spins interact antiferromagnetically but without long-range order down to zero temperature due to quantum fluctuations. Anderson predicted this phase to have resonating valence bonds as ground state and spin 1/2 excitations called "spinons". However, experiments provided only recently evidence for its existence in a few materials, amongst which the triangular-lattice charge transfer salts κ-(BEDT-TTF)₂Cu₂(CN)₃ and EtMe₃Sb(Pd(dmit)₂)₂. Various measurements on these organic materials observed no long-range magnetic order down to the lowest temperatures which supports the proposed spin liquid behavior. Still, the nature of the ground state and its origin are still under debate. Theoretical studies have recently suggested a large spinon Fermi surface that could contribute to the optical conductivity by spin-charge interactions, leading to additional absorption within the Mott gap following a power-law frequency dependence.

We performed broadband spectroscopy at low temperatures covering the range from THz frequencies up to the visible. Special emphasis was put on the investigation of various compounds, including both inorganic and organic quantum spin liquid candidates, to possibly observe similarities or differences. The comparison gives us the possibility to pin down intrinsic features and thus enhance the current understanding of this phase, and possibly also trigger theoretical progress.