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arXiv · 1702.00097

Anomalous Spin Correlations and Mass-Generating Excitonic Instability of Interacting Weyl Fermions

Michihiro Hirata·Kyohei Ishikawa·Genki Matsuno·Akito Kobayashi·Kazuya Miyagawa·Masafumi Tamura·Claude Berthier·Kazushi Kanoda
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Abstract

Recent advances in the study of nodal Weyl fermions (WFs), quasi-relativistic massless particles, constitute a novel realm of quantum many-body phenomena. The Coulomb interaction in such systems, having a zero density of states at the Fermi level, is of particular interest, since in contrast to conventional correlated metals, its long-ranged component is unscreened. Here, through nuclear-magnetic-resonance (NMR) measurements, we unveil the exotic spin correlations of two-dimensional WFs in an organic material, causing a divergent increase of the Korringa ratio by a factor of 1000 upon cooling, in striking contrast with conventional metallic behaviors. Combined with model calculations, we show that this divergence stems from the interaction-driven velocity renormalization that almost exclusively suppresses the zero-momentum spin fluctuations. At low temperatures, the NMR rate shows a remarkable increase, which is shown by numerical analyses to correspond to inter-node excitonic fluctuations, precursor of a transition from massless to massive quasiparticles.

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Michihiro Hirata, Kyohei Ishikawa, Genki Matsuno, Akito Kobayashi, Kazuya Miyagawa, Masafumi Tamura, Claude Berthier, Kazushi Kanoda. 2017-02-01. Anomalous Spin Correlations and Mass-Generating Excitonic Instability of Interacting Weyl Fermions. https://doi.org/10.1126/science.aan5351

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