Excitonic instability of two-dimensional tilted Dirac cones

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.

arXiv comment26 pages, 5 figures, 1 supplementary file (9 pages, 3 figures)

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Cited by in corpus (9)

• Molecular Quantum Materials: Electronic Phases and Charge Dynamics in Two-Dimensional Organic Solids
• Anisotropic effects in two-dimensional materials
• Interaction-induced quantum spin Hall insulator in the organic Dirac electron system $\alpha$-(BEDT-TSeF)${}_2$I${}_3$
• Gap opening mechanism for correlated Dirac electrons in organic compounds $\alpha$-(BEDT-TTF)${}_2$I${}_3$ and $\alpha$-(BEDT-TSeF)${}_2$I${}_3$
• Thermal difference reflectivity of tilted 2D Dirac materials
• Observations of $\nu =1$ Quantum Hall Effect and Inter-Band Effects of Magnetic fields on Hall Conductivity in Organic Massless Dirac Fermion System $\alpha$-(BETS)${}_2$I${}_3$ under Pressure
• Possible Spin-Density Wave on Fermi Arc of Edge State in Single-Component Molecular Conductors [Pt(dmdt)${}_2$] and [Ni(dmdt)${}_2$]
• Excitonic instability in transition metal dichalcogenides
• Fragment-orbital-dependent spin fluctuations in the single-component molecular conductor [Ni(dmdt)${}_2$]