Two-dimensional electron gas tilt-induced Landau level crossings

This work elucidates the novel behavior found in a two-dimensional electron gas (2DEG) under a tilted magnetic field in which the field's angle becomes the dominant factor in tuning the spin-splitting rather than the strength of the spin-orbit interaction. The 2DEG eigenvalues are derived with Rashba and Zeeman interactions for various tilt angles and they show crossing-free levels except at very high tilt. Moreover, concomitant with the crossings is the appearance of beats in the 2DEG density of states. The crossings from different levels occur consecutively at around 87^{\circ}. Similar new observations in Shubnikov-de Haas experimental measurements by Hatke et al. [1] attributed such phenomena to an in-plane-magnetic-field-induced increase in the effective mass. We show here that this behavior is inherent to a 2DEG where spin-orbit interaction and the in-plane magnetic field contribution are taken into account.Comment: 5 pages, 5 figure

The intrinsic features of the specific heat at half-filled Landau levels of two-dimensional electron systems

The specific heat capacity of a two-dimensional electron gas is derived for two types of the density of states, namely, the Dirac delta function spectrum and that based on a Gaussian function. For the first time, a closed form expression of the specific heat for each case is obtained at half-filling. When the chemical potential is temperature-independent, the temperature is calculated at which the specific heat is a maximum. Here the effects of the broadening of the Landau levels are distinguished from those of the different filling factors. In general, the results derived herein hold for any thermodynamic system having similar resonant states.Comment: 11 pages, 1 figure, to appear in J Low Temp Phys (2010

Distribution of critical temperature at Anderson localization

Based on a local mean-field theory approach at Anderson localization, we find a distribution function of critical temperature from that of disorder. An essential point of this local mean-field theory approach is that the information of the wave-function multifractality is introduced. The distribution function of the Kondo temperature (T-K) shows a power-law tail in the limit of T-K -> 0 regardless of the Kondo coupling constant. We also find that the distribution function of the ferromagnetic transition temperature (T-c) gives a power-law behavior in the limit of T-c -> 0 when an interaction parameter for ferromagnetic instability lies below a critical value. However, the T-c distribution function stops the power-law increasing behavior in the T-c -> 0 limit and vanishes beyond the critical interaction parameter inside the ferromagnetic phase. These results imply that the typical Kondo temperature given by a geometric average always vanishes due to finite density of the distribution function in the T-K -> 0 limit while the typical ferromagnetic transition temperature shows a phase transition at the critical interaction parameter. We propose that the typical transition temperature serves a criterion for quantum Griffiths phenomena vs smeared transitions: Quantum Griffiths phenomena occur above the typical value of the critical temperature while smeared phase transitions result at low temperatures below the typical transition temperature. We speculate that the ferromagnetic transition at Anderson localization shows the evolution from quantum Griffiths phenomena to smeared transitions around the critical interaction parameter at low temperatures.1111sciescopu