@conference {358, title = {Long range disorder effects on the heat capacity of two-dimensional electron systems}, year = {2010}, month = {12{\textendash}15 Dec 2010}, pages = {66-67}, publisher = {9th Asia-Pacific Workshop on Materials Physics}, address = {Hanoi University of Science, Vietnam}, abstract = {Broadening of Landau levels of two dimensional electron systems at low temperature and at high perpendicular magnetic fields causes perceptible variations in their interlevel and intralevel excitations as seen in their heat capacity. At a characteristic temperature, the interlevel excitations become negligible and the effect of a small broadening on the energy spectrum vanishes. In this work, a long-range disorder is considered. This can be modeled for the two-dimensional electron gas via a Lorentzian density of states or a Gaussian density of states whose broadening is much larger than kT. The temperature dependence of the heat capacity is derived at half-filled Landau levels or when the chemical potential is a constant. The heat capacity behavior of a system with a long-range disorder is compared to the case of impurity-free quantum Hall systems.}, url = {http://www.iop.vast.ac.vn/theor/conferences/apwmp/files/Detailed\%20Program.pdf}, author = {Cristine Villagonzalo and Rayda P Gammag} } @inproceedings {257, title = {Uncertainty relation of the momentum components of a two-dimensional electron system under a tilted magnetic field}, booktitle = {Proceedings of the 28th Samahang Pisika ng Pilipinas Physics Congress}, year = {2010}, month = {25{\textendash}27 Oct 2010}, pages = {SPP-2010-005}, address = {Meralco Management and Leadership Development Center, Antipolo City}, abstract = {
A two-dimensional electron gas along the xy-plane is considered. When an applied perpendicular magnetic field, directed along the z-axis, is turned on, the electrons move in cyclotron orbits and the components of the momentum along the x- and y-axes do not commute. This work shows that if the applied magnetic field is tilted at an angle\ θ\ with respect to the z-axis, the uncertainty in simultaneous measurements of the momentum components becomes dependent on\ θ.
}, author = {Rayda P Gammag and Cristine Villagonzalo} } @inproceedings {gammag-spp-2009, title = {Sensitivity of the specific heat to the electronic density of states}, booktitle = {Proceedings of the 27th Samahang Pisika ng Pilipinas Physics Congress}, year = {2009}, month = {28{\textendash}30 Oct 2009}, pages = {SPP-2009-062}, address = {Development Academy of the Philippines Convention Center, Tagaytay City}, abstract = {
The effect of an anomalous shape of the electronic density of states near the Fermi energy on the specific heat for bulk solids is investigated in this work. The density of states was simulated using a superposition of the usual square-root-energy-dependent function, and an additional Gaussian function centered in the region about the Fermi energy. The results show an enhanced specific heat when the anomalous density of states{\textquoteright} peak is located after but near the Fermi energy. If this peak is narrow, the specific heat displays an extra maximum with temperature. A large specific heat is suitable for applications wherein it is preferred to keep a system at constant temperature despite a large thermal energy exchange with its environment.
}, author = {Rayda P Gammag and Cristine Villagonzalo} } @inproceedings {gammag-spp-2008, title = {The 2DES chemical potential: Revealing the link from the classical to the quantum Hall regime}, booktitle = {Proceedings of the 26th Samahang Pisika ng Pilipinas Physics Congress}, year = {2008}, month = {22{\textendash}24 Oct 2008}, pages = {SPP-2008-026}, address = {University of the Phlippines Baguio, Baguio City}, abstract = {
A two-dimensional electron system under a magnetic field was studied numerically particularly, the temperature dependence of its chemical potential. For all fillings ν the chemical potential μ saturated to a common value at high temperature T - the classical Hall region. Approaching low T, the quantum Hall regime, μ followed varying paths depending on ν. For the complete fillings, μ showed a knee temperature Tν pointing to the juncture between the two regimes. This crossover, characterized by Tν being constant, indicates the balance between the localization and delocalization effects of the magnetic field and temperature, respectively.
}, author = {Rayda P Gammag and Cristine Villagonzalo} } @article {Gammag2008487, title = {The interplay of Landau level broadening and temperature on two-dimensional electron systems}, journal = {Solid State Commun.}, volume = {146}, number = {11-12}, year = {2008}, note = {cited By 5}, pages = {487-490}, abstract = {
This work investigates the influence of low temperature and broadened Landau levels on the thermodynamic properties of two-dimensional electron systems. The interplay between these two physical parameters on the magnetic field dependence of the chemical potential, the specific heat and the magnetization is calculated. In the absence of a complete theory that explains the Landau level broadening, experimental and theoretical studies in literature perform different model calculations of this parameter. Here it is presented that different broadening parameters of Gaussian-shaped Landau levels cause width variations in their contributions to interlevel and intralevel excitations. Below a characteristic temperature, the interlevel excitations become negligible. Likewise, at this temperature range, the effect of the Landau level broadening vanishes.
}, doi = {10.1016/j.ssc.2008.03.042}, author = {Rayda P Gammag and Cristine Villagonzalo} } @inproceedings {gammag-spp-2007, title = {The influence of the level broadening on the chemical potential and the heat capacity of two-dimensional electron system}, booktitle = {Proceedings of the 25th Samahang Pisika ng Pilipinas Physics Congress}, year = {2007}, month = {24{\textendash}26 Oct 2007}, pages = {SPP-2007-179}, address = {University of the Phlippines Los Ba{\~n}os, Laguna}, abstract = {
Experiments on two dimensional electron systems (2DES) in a magnetic field show a broadening of an otherwise delta-like density of states. This broadening has been attributed as an effect of impurity scattering, electron-electron interactions, electron transfers into a reservoir of electronic states, or disorder, among others. As this broadening is usually present in 2DES, this work incorporates the Landau level broadening to have a more realistic electron system. Its effect on the chemical potential and the heat capacity is simulated. Under strong magnetic fields B and fixed electron concentration, both the chemical potential and the heat capacity are found to oscillate with B at constant temperature.
}, author = {Rayda P Gammag and Cristine Villagonzalo} } @inproceedings {gammag-spp-2006, title = {Thermodynamic properties of a two-dimensional electron gas in the fractional quantum Hall regime}, booktitle = {Proceedings of the 24th Samahang Pisika ng Pilipinas Physics Congress}, year = {2006}, month = {25{\textendash}27 Oct 2006}, pages = {SPP-2006-69}, address = {Ateneo de Davao University, Davao City}, abstract = {
We investigate the chemical potential μ and specific heat CV of a two-dimensional electron gas at temperatures T\<1 K subject to high magnetic fields B that correspond to filling factors ν\<1. We found out that at ν=1/2, the chemical potential is pinned at ℏω_c/2 which is equal to the energy of the first Landau level. The μ(T) increases when ν\>1/2 and decreases when ν\<1/2. This behavior is dictated by the change in the number of states available to the electrons. We also found out that μ(B) converged at ℏω_c/2 and this trend has a negligible T-dependence. When this behavior of the chemical potential was used in calculating the specific heat at the fractional quantum Hall filling factors, CV(T) exhibited a humpy behavior as compared to its smoothly increasing trend at the integral quantum Hall regime. This trend is a direct consequence of the discontinuities in the chemical potential.
}, author = {Rayda P Gammag and Cristine Villagonzalo} } @inproceedings {gammag-spp-2005, title = {Magnetic field effects on the chemical potential and specific heat of a 2DEG}, booktitle = {Proceedings of the 23rd Samahang Pisika ng Pilipinas Physics Congress}, year = {2005}, month = {26{\textendash}28 Oct 2005}, pages = {SPP-2005-040}, address = {Central Philippine University, Iloilo City}, abstract = {
We investigate the effect of the filling factors on the chemical potential and the specific heat of a two-dimensional electron gas in an external magnetic field. At integer and half-integer filling factors ν the chemical potential is found to jump with an increment of ℏω_c from one Landau level to the next as the magnetic field is increased. In between these special ν{\textquoteright}s the chemical potential tends to infinitesimally increase or decrease in a stepwise manner. This behavior of the chemical potential, in turn, caused the specific heat to vary its behavior with temperature.
}, author = {Rayda P Gammag and Cristine Villagonzalo} } @inproceedings {gammag-spp-2004, title = {The specific heat of a 2DEG in a magnetic field}, booktitle = {Proceedings of the 22nd Samahang Pisika ng Pilipinas Physics Congress}, year = {2004}, month = {25{\textendash}27 Oct 2004}, pages = {154}, address = {Bohol Tropics Resort, Tagbilaran City}, abstract = {
We investigate the specific heat of a two-dimensional electron gas (2DEG) and how it varies with the system{\textquoteright}s temperature and chemical potential in the presence of an external magnetic field. In this work, we take into account the dependence of the chemical potential with temperature. We show that the specific heat of the system exhibits a two-peak behavior at low T regardless of the field{\textquoteright}s magnitude if μ~T^2 and that this is consistent with results in the literature where the broadening of Landau levels was considered. The underlying processes may be different but the effect on CV is similar.
}, author = {Rayda P Gammag and Cristine Villagonzalo} }