Graphene on two-dimensional hexagonal BN, AlN, and GaN : electronic, spin-orbit, and spin relaxation properties
Zollner, Klaus (University of Regensburg. Institute for Theoretical Physics)
Cummings, Aron (Institut Català de Nanociència i Nanotecnologia)
Roche, Stephan (Institut Català de Nanociència i Nanotecnologia)
Fabian, Jaroslav (University of Regensburg. Institute for Theoretical Physics)

Data:	2021
Resum:	We investigate the electronic band structure of graphene on a series of two-dimensional hexagonal nitride insulators hXN, X=B, Al, and Ga, with first-principles calculations. A symmetry-based model Hamiltonian is employed to extract orbital parameters and spin-orbit coupling (SOC) from the low-energy Dirac bands of the proximitized graphene. While commensurate hBN induces a staggered potential of about 10 meV into the Dirac band structure, less lattice-matched hAlN and hGaN disrupt the Dirac point much less, giving a staggered gap below 100 μeV. Proximitized intrinsic SOC surprisingly does not increase much above the pristine graphene value of 12 μeV; it stays in the window of 1-16 μeV, depending strongly on stacking. However, Rashba SOC increases sharply when increasing the atomic number of the boron group, with calculated maximal values of 8, 15, and 65 μeV for B-, Al-, and Ga-based nitrides, respectively. The individual Rashba couplings also depend strongly on stacking, vanishing in symmetrically sandwiched structures, and can be tuned by a transverse electric field. The extracted spin-orbit parameters were used as input for spin transport simulations based on Chebyshev expansion of the time-evolution of the spin expectation values, yielding interesting predictions for the electron spin relaxation. Spin lifetime magnitudes and anisotropies depend strongly on the specific (hXN)/graphene/hXN system, and they can be efficiently tuned by an applied external electric field as well as the carrier density in the graphene layer. A particularly interesting case for experiments is graphene/hGaN, in which the giant Rashba coupling is predicted to induce spin lifetimes of 1-10 ns, short enough to dominate over other mechanisms, and lead to the same spin relaxation anisotropy as that observed in conventional semiconductor heterostructures: 50%, meaning that out-of-plane spins relax twice as fast as in-plane spins.
Ajuts:	European Commission 881603 Ministerio de Economía y Competitividad SEV-2017-0706
Nota:	This work was funded by the CERCA Programme/Generalitat de Catalunya.
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Llengua:	Anglès
Document:	Article ; recerca ; Versió sotmesa a revisió
Matèria:	Electron-spin relaxation ; Electronic band structure ; External electric field ; First-principles calculation ; Sandwiched structure ; Semiconductor heterostructures ; Spin-orbit parameters ; Transverse electric field
Publicat a:	Physical review B, Vol. 103, issue 7 (Feb. 2021) , art. 75129, ISSN 2469-9969

DOI: 10.1103/PhysRevB.103.075129

Preprint 18 p, 7.5 MB

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