@conference {356, title = {Signatures of Landau level crossings in a two-dimensional electron gas}, year = {2013}, month = {1{\textendash}5 Jul 2013}, pages = {MoP110}, publisher = {20th International Conference on Electronic Properties of Two-Dimensional Systems}, address = {Wroc{\l}aw University of Technology, Poland}, url = {http://www.ep2dsmss.org/}, author = {Rayda Gammag and Cristine Villagonzalo} } @article {Gammag201316, title = {Two-dimensional electron gas tilt-induced Landau level crossings}, journal = {Solid State Commun.}, volume = {156}, year = {2013}, note = {cited By 1}, pages = {16-20}, abstract = {
This work elucidates the novel behavior found in a two-dimensional electron gas (2DEG) under a tilted magnetic field in which the field{\textquoteright}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{\textdegree}. Similar new observations in Shubnikov{\textendash}de Haas experimental measurements by Hatke et al. (2012) [6] 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{\textendash}orbit interaction and the in-plane magnetic field contribution are taken into account.
}, doi = {10.1016/j.ssc.2012.12.006}, author = {Rayda Gammag and Cristine Villagonzalo} } @article {Gammag2012, title = {The interplay of Rashba spin-orbit interaction and Landau level broadening on a two-dimensional electron gas under a tilted magnetic field}, journal = {J. Phys. Conf. Ser.}, volume = {400}, number = {PART 4}, year = {2012}, note = {cited By 0}, pages = {042009}, abstract = {
A two-dimensional electron gas in a tilted magnetic field with Rashba spin-orbit interaction (RSOI) was studied. The RSOI is accredited to the asymmetry of the heterostructure where the two-dimensional electron gas is found. The effects of the disorder-attributed Landau level broadening and the RSOI on the spin splitting were identified by simulating the density of states which was assumed to take a Gaussian shape. Increased Landau level broadening obscures the spin splitting and increases the overlap between spin states resulting to stout Gaussian peaks. On the other hand, stronger RSOI amplifies the splitting and lessens the overlap between spin states of the Landau levels. The splitting, however, results to stouter peaks. The similarity in the RSOI and Landau level broadening effects can be explained by recognizing that the asymmetry of the heterostructure is in itself a form of structural disorder.
}, doi = {10.1088/1742-6596/400/4/042009}, author = {Rayda Gammag and Cristine Villagonzalo} } @article {Gammag2012, title = {Persistent spin splitting of a two-dimensional electron gas in tilted magnetic fields}, journal = {Eur. Phys. J. B}, volume = {85}, number = {1}, year = {2012}, note = {cited By 1}, pages = {22}, abstract = {
By varying the orientation of the applied magnetic field with respect to the normal of a two-dimensional electron gas, the chemical potential and the specific heat reveal persistent spin splitting in all field ranges. The corresponding shape of the thermodynamic quantities distinguishes whether the Rashba spin-orbit interaction (RSOI), the Zeeman term or both dominate the splitting. The interplay of the tilting of the magnetic field and RSOI resulted to an amplified splitting even in weak fields. The effects of changing the RSOI strength and the Landau level broadening are also investigated.
}, doi = {10.1140/epjb/e2011-20615-x}, author = {Rayda Gammag and Cristine Villagonzalo} } @article {Gammag2012757, title = {Quenching of the DOS beats in a two-dimensional electron gas in tilted magnetic fields}, journal = {Solid State Commun.}, volume = {152}, number = {9}, year = {2012}, note = {cited By 2}, pages = {757-761}, abstract = {
A two-dimensional electron gas exposed to a tilted magnetic field is considered with the Rashba spin{\textendash}orbit interaction and the Zeeman effect. An exact solution for the eigenvalues was obtained assuming that two opposite spin states of adjacent Landau levels have equal probability. No crossings between adjacent eigenenergies were observed, for the tilt angles studied here (θ<=80{\textdegree}), unlike in the perpendicular-magnetic-field case. The absence of crossings leads to quenched beating structures in the oscillations of the density of states (DOS). Persistent spin-splittings were observed at the weak magnetic field region. The splittings, however, can be effectively screened by an increased Landau level broadening. The results shed light on how spins can be controlled through the Rashba interaction strength, the disorder-related broadening and the magnetic field tilt angle.
}, doi = {10.1016/j.ssc.2012.01.047}, author = {Rayda Gammag and Cristine Villagonzalo} } @article {Villagonzalo201143, title = {The intrinsic features of the specific heat at half-filled Landau levels of two-dimensional electron systems}, journal = {J. Low Temp. Phys.}, volume = {163}, number = {1-2}, year = {2011}, note = {cited By 2}, pages = {43-52}, abstract = {
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.
}, doi = {10.1007/s10909-010-0259-3}, author = {Cristine Villagonzalo and Rayda Gammag} } @article {gammag2009a, title = {Crossover of the specific heat from the quantum Hall to the classical regime}, journal = {AIP Conf. Proc.}, volume = {1119}, year = {2009}, pages = {213}, abstract = {

The specific heat, CV, of a two-dimensional electron system in the quantum Hall effect (QHE) regime was calculated numerically. A peak was observed at temperature Tp uniform to all filling factors. This Tp signified the shift of dominance from the extended states to the localized states. After the peak decays CV rose again, this time reflecting the destruction of the QHE and the emergence of the classical counterpart. The classical Hall was characterized by a T-invariant chemical potential.

}, doi = {http://dx.doi.org/10.1063/1.3137811}, author = {Rayda Gammag and Cristine Villagonzalo} }