Berlin 2018 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 4: Spin structures and magnetic phase transitions
MA 4.5: Vortrag
Montag, 12. März 2018, 10:30–10:45, EB 202
Optical study of vibronic coupling in the quantum spin liquid candidate Tb2Ti2O7 — •Evan Constable1,2, R. Ballou1, J. Robert1, L Bergen2, C. Decorse3, J.-B. Brubach4, P. Roy4, E. Lhotel1, V. Simonet1, S. Petit5, and S. deBrion2 — 1Institut Néel, CNRS and Université Grenoble Alpes, Grenoble, France — 2Institute of Solid State Physics, Vienna University of Technology, Vienna, Austria — 3ICMMO, Université Paris-Sud, Orsay, France — 4Synchrotron SOLEIL, Gif-sur-Yvette, France — 5Laboratoire Léon Brillouin, CEA, CNRS, Université Paris-Saclay, Gif-sur-Yvette, France
Vibronic coupling describes the interaction between electronic energy levels and phonon modes, often leading to a ground state that is considerably perturbed. In magnetic rare-earth pyrochlores (RE2Ti2O7, RE = Dy, Ho), large crystal field splitting of the electronic energy levels leads to exotic magnetic behaviour in the form of a highly degenerate spin ice ground state. The possibility that quantum fluctuations due to vibronic coupling could melt the spin ice state forming a quantum spin liquid, is an interesting prospect. It is thought that this process could be present in Tb2Ti2O7 as it does not appear to feature long range order nor a spin ice phase. Indeed, our investigations reveal favourable symmetry and energy conditions for vibronic coupling. Using optical spectroscopic techniques we find evidence of a hybridisation of crystal-field-phonon modes present across a broad temperature range. This vibronic process supports a collective state between the ground and excited levels, which provides a crucial path for quantum spin-flip fluctuations that inhibit the stabilisation of conventional magnetism.