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Flat-band induced excitonic insulator in a carbon-based, triangulene Kagome lattice

ORAL

Abstract

Excitonic insulator (EI) is a novel cooperative phase of matter formed by coherent excitons. This phase occurs when the bound electron-hole excitations of the system have a lower energy than the normal band insulating ground state. Namely, when an electron from the valence band is put in the conduction band, the binding energy between the excited electrons and holes is larger than the bandgap of the normal state, leading to simultaneous formation and subsequent condensation of excitons. A previous work shows that a specific 2-dimensional crystal of finite-size graphene triangles, a [4]triangulene Kagome lattice, possesses negative excitation energies of triplet excitons via a GW-BSE on top of DFT-LDA calculation[1], and thus could be a candidate for EI. Here we study the coherent ground state formed by excitons using a BCS-like theory, and explore the experimental signatures of such EI state (such as the local density of state (LDOS) and other electronic properties) from first-principles calculations. Our results agree well with STM measurements performed by our experimental collaborators. We also discuss the interplay between possible magnetic state, exciton condensation state, and normal state, as well as considering substrate effects.

Reference:

[1] Gurjyot Sethi, Yinong Zhou, Linghan Zhu, Li Yang, and Feng Liu. Phys. Rev. Lett. 126, 196403 (2021)

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Presenters

  • Jingwei Jiang

    University of California, Berkeley

Authors

  • Jingwei Jiang

    University of California, Berkeley

  • Aidan Delgado

    Chemistry Department, UC Berkeley

  • Carolin Dusold

    Chemistry Department, UC Berkeley

  • Adam Cronin

    Chemistry Department, UC Berkeley

  • Felix R Fischer

    UC Berkeley, Chemistry Department, UC Berkeley and Lawrence Berkeley National Lab

  • Steven G Louie

    University of California at Berkeley, University of California, Berkeley, University Of California, Berkeley, University of California at Berkeley and Lawrence Berkeley National Lab, University of California at Berkeley; Lawrence Berkeley National Lab, UC Berkeley, University of California at Berkeley, and Lawrence Berkeley National Laboratory, UC berkeley, Lawrence Berkeley National Laboratory, Physics Department, UC Berkeley and Lawrence Berkeley National Lab, Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, LBNL & UC Berkeley