Capacitance of a Double-Heterojunction GaAs/AlGaAs Structure Subjected to In-Plane Magnetic Fields: Results of Self-Consistent Calculations

The capacitance of a double-heterojunction structure with a wide GaAs undoped layer embedded between two selectively doped AlGaAs barriers is calculated self-consistently as a function of intensity of the in-plane magnetic field. With increasing field intensity the capacitance initially increases and after reaching a maximum decreases toward a high field limit which is less than its zero field value. This behaviour is attributed to 'breathing', or charge redistribution, of the 2D electron gas at individual heterojunctions due to a combination of the confining potential and the magnetic field.Comment: LaTeX, 9 pages, 7 figs. available on request from [email protected] in 1 PS file (compressed and uuencoded

Purely orbital diamagnetic to paramagnetic fluctuation of quasi two-dimensional carriers under in-plane magnetic field

An external magnetic field, $H$, applied parallel to a quasi two-dimensional system modifies quantitatively and qualitatively the density of states. Using a self-consistent numerical approach, we study how this affects the entropy, $S$, the free energy, $F$, and the magnetization, $M$, for different sheet carrier concentrations, $N_s$. As a prototype system we employ III-V double quantum wells. We find that although $M$ is mainly in the opposite direction of $H$, the system is not linear. Surprisingly $\partial M / \partial H$ swings between negative and positive values, i.e., we predict an entirely orbital diamagnetic to paramagnetic fluctuation. This phenomenon is important compared to the ideal de Haas-van Alphen effect i.e. the corresponding phenomenon under perpendicular magnetic field.Comment: 4 pages, 6 figure

Self-Consistent Electron Subbands of Gaas/Algaas Heterostructure in Magnetic Fields Parallel to the Interface

The effect of strong magnetic fields parallel to GaAs/AlGaAs interface on the subband structure of a 2D electron layer is ivestigated theoretically. The system with two levels occupied in zero magnetic field is considered and the magnetic field induced depletion of the second subband is studied. The confining potential and the electron dispersion relations are calculated self-consistently, the electron- electron interaction is taken into account in the Hartree approximation.Comment: written in LaTeX, 8 pages, 4 figs. available on request from [email protected]

A Novel Gβγ-Subunit Inhibitor Selectively Modulates μ-Opioid- Dependent Antinociception and Attenuates Acute Morphine-Induced Antinociceptive Tolerance and Dependence

The Gβγ subunit has been implicated in many downstream signaling events associated with opioids. We previously demonstrated that a small molecule inhibitor of Gβγ-subunit-dependent phospholipase (PLC) activation potentiated morphine-induced analgesia (Bonacci et al., 2006). Here, we demonstrate that this inhibitor, M119 (cyclohexanecarboxylic acid [2-(4,5,6-trihydroxy-3-oxo-3H-xanthen-9-yl)-(9Cl)]), is selective for μ-opioid receptor-dependent analgesia and has additional efficacy in mouse models of acute tolerance and dependence. When administered by an intracerebroventricular injection in mice, M119 caused 10-fold and sevenfold increases in the potencies of morphine and the μ-selective peptide, DAMGO, respectively. M119 had little or no effect on analgesia induced by the κ agonist U50,488 or δ agonists DPDPE or Deltorphin II. Similar results were obtained in vitro, as only activation of the μ-opioid receptor stimulated PLC activation, whereas no effect was seen with the κ- and δ-opioid receptors. M119 inhibited μ-receptor-dependent PLC activation. In studies to further explore the in vivo efficacy of M119, systemic administration M119 also resulted in a fourfold shift increase in potency of systemically administered morphine. Of particular interest, M119 was also able to attenuate acute, antinociceptive tolerance and dependence in mice treated concomitantly with both M119 and morphine. These studies suggest that small organic molecules, such as M119, that specifically regulate Gβγ subunit signaling may have important therapeutic applications in enhancing opioid analgesia, while attenuating the development of tolerance and dependence

Magnetotransport in graphene on silicon side of SiC

We have studied the transport properties of graphene grown on silicon side of SiC. Samples under study have been prepared by two different growth methods in two different laboratories. Magnetoresistance and Hall resistance have been measured at temperatures between 4 and 100 K in resistive magnet in magnetic fields up to 22 T. In spite of differences in sample preparation, the field dependence of resistances measured on both sets of samples exhibits two periods of magneto-oscillations indicating two different parallel conducting channels with different concentrations of carriers. The semi-quantitative agreement with the model calculation allows for conclusion that channels are formed by high-density and low-density Dirac carriers. The coexistence of two different groups of carriers on the silicon side of SiC was not reported before.Comment: 5 pages, 6 figures, accepted for publication in the "IOP Journal of Physics: Conference series" as a contribution to the proceedings of the 20th International Conference on "High Magnetic Fields in Semiconductor Physics", HMF 2