A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade

We provide a framework for analyzing the problem of interacting electrons in a ballistic quantum dot with chaotic boundary conditions within an energy $E_T$ (the Thouless energy) of the Fermi energy. Within this window we show that the interactions can be characterized by Landau Fermi liquid parameters. When $g$, the dimensionless conductance of the dot, is large, we find that the disordered interacting problem can be solved in a saddle-point approximation which becomes exact as $g\to\infty$ (as in a large-N theory). The infinite $g$ theory shows a transition to a strong-coupling phase characterized by the same order parameter as in the Pomeranchuk transition in clean systems (a spontaneous interaction-induced Fermi surface distortion), but smeared and pinned by disorder. At finite $g$, the two phases and critical point evolve into three regimes in the $u_m-1/g$ plane -- weak- and strong-coupling regimes separated by crossover lines from a quantum-critical regime controlled by the quantum critical point. In the strong-coupling and quantum-critical regions, the quasiparticle acquires a width of the same order as the level spacing $\Delta$ within a few $\Delta$'s of the Fermi energy due to coupling to collective excitations. In the strong coupling regime if $m$ is odd, the dot will (if isolated) cross over from the orthogonal to unitary ensemble for an exponentially small external flux, or will (if strongly coupled to leads) break time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we are treating charge-channel instabilities in spinful systems, leaving spin-channel instabilities for future work. No substantive results are change

Magnetic Field Penetration Depth in the Heavy-Electron Superconductor U Be

We report the observation of a T2 temperature dependence of the magnetic field penetration depth in UBe13 at low temperatures. We show that this behavior is consistent with an anisotropic gap function for an axial P-wave state. Our results further show that the Landau parameter Fls appears to be small. © 1986 The American Physical Society

Upper critical magnetic field of the heavy-electron superconductors U

The temperature T dependence of the upper critical magnetic field Hc2 of the heavy-electron superconductors U1-xThxBe13 (x=0 and 2.9%) doped with various concentrations of Gd has been determined from low-frequency ac magnetic susceptibility measurements in magnetic fields up to 60 kOe. The Hc2(T) curves for U1-xGdxBe13 samples deviate from the Hc2(T) curves of UBe13 near Tc, which is consistant with the depairing of superconducting electrons via the Zeeman interaction between the spins of the superconducting electrons and the exchange field associated with the Gd spins. This suggests that UBe13 exhibits singlet superconductivity. In contrast, the Hc2(T) curves for (U0.97Th0.03)Be13 doped with Gd scale with Hc2(T) of pure (U0.97Th0.03)Be13 and do not reflect superconducting depairing by the Gd ions. These results are consistent with either strong spin-orbit scattering due to the presence of Th in UBe13, or to a qualitatively different type of superconductivity involving triplet spin pairing in (U0.97Th0.03)Be13. Measurements of the temperature dependence of Hc2 for U1-xRxBe13 compounds where R=La, Lu, and Ce for various compositions x as well as U0.985R0.015Be13 compounds for R=Tb, Dy, Ho, and Er are also presented and compared with the Gd-doped UBe13 system. The results of low-temperature specific-heat measurements of UBe13 doped with various concentrations of Gd are also discussed. © 1991 The American Physical Society

PHARMACOLOGICAL EVALUATION OF ANTIDEPRESSANT ACTIVITY OF AQUEOUS EXTRACT OF ROSA CENTIFOLIA PETALS IN MICE

ABSTRACT To study the antidepressant activity with aqueous extract of Rosa centifolia. The extract was primarily subjected for preliminary phytochemical investigation and for Maximum Tolerance Dose (MTD). Antidepressant activity was evaluated in various animal models like Forced swim test, Tail suspension test, Apomorphine induced hypothermia and 5-HTP potentiation of head twitches in mice. The aqueous extract of Rosa centifolia was positively identified with carbohydrates, tannins, proteins, amino acids, alkaloids, flavonoids, flavanone, glycosides and phenolic compounds. The extract was subjected for maximum tolerance dose upto the dose level of 2000mg/kg has not produced any mortality. The extract of Rosa centifolia showed significant antidepressant activity at high dose (100 mg/kg) in Tail suspension test, Forced swim test and Potentiation of 5-HTP induced head twitches. The extract didn't antagonized the hypothermia induced by apomorphine