Magnetic properties of HgTe quantum wells

Abstract

Using analytical formulas as well as a finite-difference scheme, we investigate the magnetic field dependence of the energy spectra and magnetic edge states of HgTe/CdTe-based quantum wells in the presence of perpendicular magnetic fields and hard walls for the band-structure parameters corresponding to the normal and inverted regimes. Whereas one can not find counterpropagating, spin-polarized states in the normal regime, below the crossover point between the uppermost (electronlike) valence and lowest (holelike) conduction Landau levels, one can still observe such states at finite magnetic fields in the inverted regime, although these states are no longer protected by time-reversal symmetry. Furthermore, the bulk magnetization and susceptibility in HgTe quantum wells are studied, in particular their dependence on the magnetic field, chemical potential, and carrier densities. We find that for fixed chemical potentials as well as for fixed carrier densities, the magnetization and magnetic susceptibility in both the normal and the inverted regimes exhibit de Haas-van Alphen oscillations, the amplitude of which decreases with increasing temperature. Moreover, if the band structure is inverted, the ground-state magnetization (and consequently also the ground-state susceptibility) is discontinuous at the crossover point between the uppermost valence and lowest conduction Landau levels. At finite temperatures and/or doping, this discontinuity is canceled by the contribution from the electrons and holes and the total magnetization and susceptibility are continuous. In the normal regime, this discontinuity of the ground-state magnetization does not arise and the magnetization is continuous for zero as well as finite temperatures.

Coulomb drag

“…Graphene-based double-layer devices can be used to observe Coulomb drag between massless and massive particles by coupling Dirac fermions in monolayer graphene to quasiparticles with parabolic dispersion in either bilayer graphene (Scharf and Matos-Abiague, 2012) or a usual 2DEG Scharf and MatosAbiague, 2012). Experimental realizations were reported in Fisichella et al (2014) and Gamucci et al (2014).…”

“…Theoretical analysis of Principi et al (2012) and Scharf and Matos-Abiague (2012) is based on the standard expression (77). Both works focus on the low-temperature, degenerate regime T µ.…”

Plasmonic excitations in Coulomb-coupledN-layer graphene structures

“…Substantial efforts have been directed towards the investigation of the linear response of doped graphene 24 and of the charge density excitations [25][26][27][28][29] and of such complex quasiparticles as plasmarons 30,31 and plasmon-phonon complexes 32 . Recently, the experimental realization of graphene double-layer structures coupled only via the Coulomb interaction [33][34][35][36][37][38] has attracted substantial theoretical interest in studying the double-layer plasmon effects [39][40][41][42] and the frictional drag 43 in two spatially separated graphene layers [44][45][46][47][48][49][50][51][52] as powerful tools for probing interaction effects of massless Dirac fermions.…”

Hyperfine interactions in two-dimensional HgTe topological insulators

“…[13][14][15][16][17][18] The effect of external magnetic fields have also been considered. 6,8,[19][20][21][22][23][24] The TI state in HgTe QWs was predicted by Bernevig, Hughes, and Zhang (BHZ) 25 by using a simplified k · p model containing states with S-and P -like symmetries, respectively. They found that beyond a critical thickness of the HgTe QW, the TI state would appear as confirmed experimentally.…”