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arXiv · 1910.08999

Excitonic instability of two-dimensional tilted Dirac cones

Daigo Ohki·Michihiro Hirata·Takehiro Tani·Kazushi Kanoda·Akito Kobayashi
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Abstract

The electron-electron Coulomb interaction in Dirac-Weyl semimetals harbours a novel paradigm of correlation effects that hybridizes diverse realms of solid-state physics with their relativistic counterpart. Driving spontaneous mass acquisition, the excitonic condensate of strongly-interacting massless Dirac fermions is one such example whose exact nature remains debated. Here, by focussing on the two-dimensional tilted Dirac cones in the organic salt $\alpha$-(BEDT-TTF)$_2$I$_3$, we show that the excitonic instability is controlled by a small chemicalpotential shift and an in-plane magnetic field. In combined analyses based on renormalization-group approaches and ladder approximation, we demonstrate that the nuclear relaxation rate is an excellent probe of excitonic-spin fluctuations in an extended parameter region. Comparative nuclear magnetic resonance (NMR) experiments show good agreements with this result, jointly revealing the importance of intervalley nesting between field-induced, spin-split Fermi pockets of opposite charge polarities. Our work provides an accurate framework to search for excitonic instability of strongly-interacting massless fermions.

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Daigo Ohki, Michihiro Hirata, Takehiro Tani, Kazushi Kanoda, Akito Kobayashi. 2019-10-20. Excitonic instability of two-dimensional tilted Dirac cones. https://doi.org/10.1103/physrevresearch.2.033479

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