Contribution of forbidden orbits in the photoabsorption spectra of atoms and molecules in a magnetic field

In a previous work [Phys. Rev. A \textbf{66}, 0134XX (2002)] we noted a partial disagreement between quantum R-matrix and semiclassical calculations of photoabsorption spectra of molecules in a magnetic field. We show this disagreement is due to a non-vanishing contribution of processes which are forbidden according to the usual semiclassical formalism. Formulas to include these processes are obtained by using a refined stationary phase approximation. The resulting higher order in $\hbar$ contributions also account for previously unexplained ``recurrences without closed-orbits''. Quantum and semiclassical photoabsorption spectra for Rydberg atoms and molecules in a magnetic field are calculated and compared to assess the validity of the first-order forbidden orbit contributions.Comment: 12 pages, 6 figure

Semiclassical cross section correlations

We calculate within a semiclassical approximation the autocorrelation function of cross sections. The starting point is the semiclassical expression for the diagonal matrix elements of an operator. For general operators with a smooth classical limit the autocorrelation function of such matrix elements has two contributions with relative weights determined by classical dynamics. We show how the random matrix result can be obtained if the operator approaches a projector onto a single initial state. The expressions are verified in calculations for the kicked rotor.Comment: 6 pages, 2 figure

Semiclassical quantization of the hydrogen atom in crossed electric and magnetic fields

The S-matrix theory formulation of closed-orbit theory recently proposed by Granger and Greene is extended to atoms in crossed electric and magnetic fields. We then present a semiclassical quantization of the hydrogen atom in crossed fields, which succeeds in resolving individual lines in the spectrum, but is restricted to the strongest lines of each n-manifold. By means of a detailed semiclassical analysis of the quantum spectrum, we demonstrate that it is the abundance of bifurcations of closed orbits that precludes the resolution of finer details. They necessitate the inclusion of uniform semiclassical approximations into the quantization process. Uniform approximations for the generic types of closed-orbit bifurcation are derived, and a general method for including them in a high-resolution semiclassical quantization is devised

A Search for the Electric Dipole Moment of the Tau-Lepton

Using the ARGUS detector at the e+e- storage ring DORIS II, we have searched for the real and imaginary part of the electric dipole formfactor d_tau of the tau lepton in the production of tau pairs at q^2=100 GeV^2. This is the first direct measurement of this CP violating formfactor. We applied the method of optimised observables which takes into account all available information on the observed tau decay products. No evidence for CP violation was found, and we derive the following results: Re(d_tau)=(1.6+-.9)*10^(-16) ecm and Im(d_tau)=(-0.2+-0.8)*10^(-16) ecm, where statistical and systematic errors have been combined.Comment: 8 pages, 5 figures (10 subfigures

Intermittency and Chaos in Monte-Carlo Based Simulations of Low Temperature Impurity Breakdown

International audienc

Microscopic analysis of noise and nonlinear dynamics in p -type germanium

International audienc

Scaled-energy spectroscopy of helium vertical bar M vertical bar=1 Rydberg atoms in a static electric field

We present scaled-energy spectra on helium Rydberg atoms in a static electric field. /M/ = 1 states were studied in excitation from the 2 S-1(0) metastable state. Spectra were recorded for epsilon = -2.940(4), epsilon = -2.350(4), both below the saddle point, and epsilon = -1.760(4), above the saddle point. Closed-orbit theory was applied to interpret the spectra. A recent extension to closed-orbit theory, incorporating core effects, was used. This significantly improved agreement between experiment and theory. [S1050-2947(98)02610-9]

Intermittent breakdown of current-oscillation tori in n-type GaAs epitaxial layers

Self-sustained current oscillations in high-purity n-type GaAs epitaxial layers were investigated for intermittent behavior in the control parameter plane constituted by the constant bias voltage and an external magnetic field. Intermittent windows were observed in a sequence of Hopf bifurcations. Quasiperiodic and frequency-locked oscillations were found to follow an intermittency type-II or type-III route to chaos in the Pomeau-Manneville classification scheme. Additionally, intermittent bursts due to noise were observed at voltages well below the threshold of bifurcation