Charge density wave with meronlike spin texture induced by a lateral superlattice in a two-dimensional electron gas

Abstract

The combined effect of a lateral square superlattice potential and the Coulomb interaction on the ground state of a two-dimensional electron gas in a perpendicular magnetic field is studied for different rational values of Γ, the inverse of the number of flux quanta per unit cell of the external potential, at filling factor ν = 1 in Landau level N = 0. When Landau level mixing and disorder effects are neglected, increasing the strength W0 of the potential induces a transition, at a critical strength W (c) 0 , from a uniform and fully spin polarized state to a two-dimensional charge density wave (CDW) with a meronlike spin texture at each maximum and minimum of the CDW. The collective excitations of this "vortex-CDW" are similar to those of the Skyrme crystal that is expected to be the ground state near filling factor ν = 1. In particular, a broken U(1) symmetry in the vortex-CDW results in an extra gapless phase mode that could provide a fast channel for the relaxation of nuclear spins. The average spin polarization Sz changes in a continuous or discontinuous manner as W0 is increased depending on whether Γ ∈ [1/2, 1] or Γ ∈ [0, 1/2] . The phase mode and the meronlike spin texture disappear at large value of W0, leaving as the ground state partially spin-polarized CDW if Γ = 1/2 or a spin-unpolarized CDW if Γ = 1/2.

Phase transitions induced by a lateral superlattice potential in a two-dimensional electron gas

“…Its electronic density n e = 1/2πℓ 2 is uniform and its Hall conductivity 12 has the quantized value σ xy = e 2 /h. In a previous work 1 , which we shall refer to as Paper 1, one of us has studied the phase transitions induced by a square grid in the interacting 2DEG at ν = 1 in the Hartree-Fock approximation. The phase diagram was studied for different rational values of Γ ≡ ϕ 0 /Ba 2 0 = 2π (ℓ/a 0 ) 2 = q/p ∈ [0, 1] , where ϕ 0 = h/e is the flux quantum, a 0 the lattice constant of the external grid and q, p are integers with no common factors.…”