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Regensburg 2019 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 38: Methods in Computational Materials Modelling (methodological aspects, numerics)

MM 38.4: Vortrag

Donnerstag, 4. April 2019, 15:45–16:00, H44

Exchange-driven dimerization, magnetism and insulating state in diamond(111)betul pamuk1 and •matteo calandra21School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA — 2Sorbonne Université, CNRS, Institut des Nanosciences de Paris, UMR7588, F-75252, Paris, France

Strong electron-electron interaction in ultraflat edge states can be responsible for correlated phases of matter, such as magnetism, charge density wave or superconductivity. Here we consider the diamond(111) surface that after Pandey reconstruction, presents zig-zag carbon chains, generating a very flat surface band. By performing full structural optimization with hybrid functionals, we find that a substantial dimerization (0.076 Å  bond disproportionation in the HSE06, 0.09 Å  in PBE0) occurs on the chains; a structural effect absent in calculations based on the LDA/GGA functionals. This dimerization is the primary mechanism for the opening of an insulating gap. Neglecting spin polarization, the single-particle direct gap is 1.672 in PBE0 (1.0 in HSE06), smaller than the experimental data that are compatible with a 1.57−1.87 (including 0.1−0.4 eV of excitonic effects). However, the exchange interaction stabilizes a ferrimagnetic order along the Pandey π-chains with magnetic moments as large as 0.285 µB, opening a direct band gap of approximately 2.1 eV in PBE0, in agreement with experiments. Our work is relevant for systems with flat bands in general and wherever the interplay between structural and electronic degrees of freedom is crucial, as in twisted bilayer graphene, IVB atoms on IVB(111) surfaces such as Pb/Si(111) or molecular crystals.

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