Shubnikov-de Haas oscillations in Digital Magnetic Heterostructures

Abstract

In this paper we theoretically investigate the magnetic-field and temperature dependence of the Shubnikov-de Haas oscillations in group II-VI modulation-doped Digital Magnetic Heterostructures. We self-consistently solve the effective-mass Schrödinger equation within the Hartree approximation and calculate the electronic structure and the magneto-transport properties. Our results show i) a shift of the Shubnikov-de Haas minima to lower magnetic fields with increasing temperature, and ii) an anomalous oscillation which develops when two opposite Landau levels cross near the Fermi energy. Both of these are consistent with recent magneto-transport measurements in such heterostructures [R. Knobel et al., Phys. Rev. B 65, 235327 (2002)].

Ringlike structures in the density–magnetic‐field ρ xx diagram of two‐subband quantum Hall systems

“…1(a)]. We do not find any hysteresis or discontinuities in the DFT-LSDA Landau-level fan diagram, which would indicate easy-axis (Ising) quantum Hall ferromagnetism in the system [4][5][6][7]. However, we cannot rule out the possibility for easy-plane ferromagnetism.…”

“…However, our SDFT/LSDA simulations do not show ferromagnetic phase transitions. The Landau fan diagram and the resistivities (ρ xx and ρ xy ) do not show any hysteresis or discontinuities which would signal an easy-axis (Ising-like) ferromagnetic transition [4][5][6][7]. In addition, the spin-polarization at the center of the rings are too small to be understood as an easy-axis ferromagnetic phase.…”

“…Within the usual implementation of the SDFT/LSDA formulation in the context of the effective mass approximation, we self-consistently solve the Kohn-Sham equations for the conduction electrons in an external potential. Because of the translational symmetry in the xy plane of the 2DEG, the problem is separable [7]. For the z direction we have two (spin up and down) coupled one-dimensional Schrödinger equations…”

“…Corresponding dips or bumps in ρ xy are sometimes reported. Most importantly, these features in ρ xx and ρ xy are hysteretic in many cases thus signaling Ising-like ferromagnetism [4][5][6][7].…”

Magnetic phase structure of Mn-doped III-V semiconductor quantum wells

“…1,2 By spatial modulation of the doping profile and magnetic impurity concentration, DMS quantum structures can lead to a spinpolarized many-particle system. [3][4][5][6] This would consist of n electrons of majority spin (↓) and n electrons of minority spin (↑) per unit area and show a variety of unique properties which are absent in conventional nonmagnetic structures. The effect of an additional degree of freedom associated with the exchange coupling of itinerant carriers and magnetic impurities in the DMS QW can be varied at finite temperatures.…”