Orbital and spin order in oxide two-dimensional electron gases

Abstract

We describe a variational theory of multi-band two-dimensional electron gases that captures the interplay between electrostatic confining potentials, orbital-dependent interlayer electronic hopping and electron-electron interactions, and apply it to the d-band two-dimensional electron gases that form near perovskite oxide surfaces and heterojunctions. These multi-band two-dimensional electron gases are prone to the formation of Coulomb-interaction-driven orbitally-ordered nematic groundstates. We find that as the electron density is lowered and interaction effects strengthen, spontaneous orbital order occurs first, followed by spin order. We compare our results with known properties of single-component two-dimensional electron gas systems and comment on closely related physics in semiconductor quantum wells and van der Waals heterostructures.PACS numbers: 73.20.-r,71.15.-m,71.10.-w, 73.21.-b,75.10.-b

Magnetic and Nematic Orders of the Two-Dimensional Electron Gas at Oxide (111) Surfaces and Interfaces

“…We present a Landau theory of this nematic, and discuss implications for transport measurements and superconductivity. Such nematicity induced by orbital or spin order has been previously considered for the (001) 2DEG [23,[54][55][56]. Our results should be broadly applicable to a wide class of oxide (111) 2DEGs.…”

Plasmons at the LaAlO3/SrTiO3 interface and in the graphene- LaAlO3 / SrTiOFaridi1, Asgari2 2017Phys. Rev. B140120View full textAdd to dashboardCite

“…These considerations lead to a tight-binding Hamiltonian, diagonal in orbital space with elements [Ĥ 0 ] ij = (t x,i cos kx + t y,i cos ky)δ ij where t x,2 = t y,3 = t and t x,1 = t y,1 = t y,2 = t x,3 = t [31][32][33]. Expanding the tight-binding Hamiltonian around the Γ point, a minimal model Hamiltonian of the carriers at the interface of LaAlO 3 and SrTiO 3 can be written as [34][35][36][37] …”

“…Since in this paper, we work with a density regime high enough to stay far from these points, accordingly, the tight-binding Hamiltonian of Eq. (1) can properly describe the system [35][36][37].…”

Theoretical prediction of Weyl fermions in the paramagnetic electride Y2C

“…In electrides, the looselybound electrons are easily separated from cationic atoms, thereby being trapped in void spaces along one-dimensional channels [5,6] or between two-dimensional (2D) interlayers [7,8]. Such low-dimensional anionic electrons occupying the bands near the Fermi level E F may provide unconventional playgrounds for exploration of various exotic quantum phenomena such as charge-density waves, spin ordering, superconductivity, and topological states [9][10][11][12]. Recently, Lee et al demonstrated the synthesis of a layered electride material Ca 2 N, where the anionic electrons are distributed in the interlayer spaces between positively charged [Ca 2 N] + cationic layers [13].…”