Optical absorption preceding resonant double photoionization of aromatic hydrocarbons hydrocarbons

We analyze resonances in the double photoionization of a variety of aromatic hydrocarbons. The resonances reflect the breakup of quasi-bound electron pairs. The basic premise of this paper is that there is a direct connection between the quasi-bound pairs and resonant peaks in the optical absorption that are associated with doubly occupied sites on the perimeter and inside the perimeter of the molecule. The optical absorption leading to the high-energy resonance (approximately 40 eV), calculated from a many-site one-dimensional Hubbard model, has a peak at U, the electrostatic interaction energy for two electrons with antiparallel spins on the same carbon atom. In the model, there are also two satellites whose separation from the main resonance is approximately +/-10 eV suggesting that unresolved satellite structure may be contributing to the linewidth of the resonant peak. The low energy resonances (approximately 10 eV) involve carbon atoms located inside the perimeter, a configuration present only in pyrene and coronene (among the hydrocarbons studied). In the case of pyrene, which has two carbon atoms inside the perimeter, we employ a two-site Hubbard model to characterize the absorption leading to the quasi-bound state. A brief analysis of the double photoionization resonance of the heterocyclic inorganic molecule 1,3,5-triazine presented. We also discuss recent results for the double photoionization of the cyclic inorganic molecule tribromoborazine and the organic molecules furan, pyrrole, selenophene, and thiophene where the 2+ ion concentration varies linearly with the difference between the photon energy and the threshold energy. A theory for the linear behavior is outlined

Coulomb Pairing and Double Photoionization in Aromatic Hydrocarbons

Recently reported anomalies in the double-photonionization spectra of the aromatic molecules partially deuterated benzene, naphthalene, anthracene, pentacene, azulene, phenanthrene, pyrene and coronene are attributed to Coulomb-pair resonances of pi electrons. The properties of the resonance in benzene are investigated in detail. The linear behavior in the 2+/1+ ion ratio above the resonance is attributed to a two-electron transition associated with excitation from the ground state to a two-electron continuum. A similar explanation accounts for the linear behavior seen in the pentagonal rings pyrrole, furan, selenophene and thiophene which do not display resonance peaks.Comment: 6 pages. arXiv admin note: substantial text overlap with arXiv:1312.049

Comments on Coulomb pairing in aromatic hydrocarbons

Recently reported anomalies in the double-photonionization spectra of aromatic molecules such as benzene, naphthalene, anthracene and coronene are attributed to Coulomb-pair resonances of pi electrons.Comment: 5 page

Linear temperature dependence of electron spin resonance linewidths in La0.7Ca0.3MnO3 and YBaMn2O6

We analyze recent electron spin resonance (ESR) experiments in La0.7Ca0.3MnO3 and YBaMn2O6 focusing on the behavior of the linewidth at high temperatures where it is a linear function of the temperature. Noting that the g-factors of the resonances are characteristic of the Mn4+ ion in a cubic environment, we make the assumption that the linewidth involves the static susceptibility of the Mn4+ spins which we analyze in the molecular field approximation. We conclude that the linear dependence on temperature is associated with the susceptibility having a Curie or Curie-Weiss form while the temperature-dependent relaxation mechanism has a microscopic rate proportional to the temperature. In La0.7Ca0.3MnO3, the Mn4+ susceptibility has the ferromagnetic Curie-Weiss form, and the static contribution to the linewidth arising from distortions of the oxygen octahedra is absent due to motional narrowing brought on by the rapid hopping of the eg polarons. In YBaMn2O6 either of two scenarios is possible. The Mn4+ susceptibility above 520 K is Curie-like and the static term is present, or the susceptibility has the antiferromagnetic Curie-Weiss form and the static term is absent due to motional narrowing. It is concluded that the Curie model, with offsetting double exchange and and superexchange Curie-Weiss parameters, is the more likely scenario. It is suggested that the linear-T variation of the linewidth in both materials arises from either a Korringa-like mechanism involving interactions with mobile carriers or from a spin-phonon process coming from interactions between the Mn4+ ions and the lattice vibrations

Euclid Asteroseismology and Kuiper Belt Objects

Euclid, which is primarily a dark-energy/cosmology mission, may have a microlensing component, consisting of perhaps four dedicated one-month campaigns aimed at the Galactic bulge. We show that such a program would yield excellent auxilliary science, including asteroseimology detections for about 100,000 giant stars, and detection of about 1000 Kuiper Belt Objects (KBOs), down to 2--2.5 mag below the observed break in the KBO luminosity function at I ~26. For the 400 KBOs below the break, Euclid will measure accurate orbits, with fractional period errors <~ 2.5%.Comment: 8 pages, 4 figures, submitted to JKA

Bose condensation in flat bands

We derive effective Hamiltonians for lattice bosons with strong geometrical frustration of the kinetic energy by projecting the interactions on the flat lowest Bloch band. Specifically, we consider the Bose Hubbard model on the one dimensional sawtooth lattice and the two dimensional kagome lattice. Starting from a strictly local interaction the projection gives rise to effective long-range terms stabilizing a supersolid phase at densities above nu_c=1/9 of the kagome lattice. In the sawtooth lattice on the other hand we show that the solid order, which exists at the magic filling nu_c=1/4, is unstable to further doping. The universal low-energy properties at filling 1/4+delta nu are described by the well known commensurate-incommensurate transition. We support the analytic results by detailed numerical calculations using the Density Matrix Renormalization Group and exact diagonalization. Finally, we discuss possible realizations of the models using ultracold atoms as well as frustrated quantum magnets in high magnetic fields. We compute the momentum distribution and the noise correlations, that can be extracted from time of flight experiments or neutron scattering, and point to signatures of the unique supersolid phase of the kagome lattice.Comment: 18 pages, 13 figure

Dynamics of an Ensemble of Noisy Bistable Elements with Global Time-Delayed Coupling

The dynamics of an ensemble of bistable elements with global time-delayed coupling under the influence of noise is studied analytically and numerically. Depending on the noise level the system undergoes ordering transitions and demonstrates multi-stability. That is, for a strong enough positive feedback it exhibits a non-zero stationary mean field and a variety of stable oscillatory mean field states are accessible for positive and negative feedback. The regularity of the oscillatory states is maximal for a certain noise level, i.e., the system demonstrates coherence resonance. While away from the transition points the system dynamics is well described by a Gaussian approximation, near the bifurcation points a description in terms of a dichotomous theory is more adequate.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. Let

Anomalous Fermi arcs in a periodically driven Weyl system

Three dimensional Weyl semimetals exhibit open Fermi arcs on their sample surfaces connecting the projection of bulk Weyl points of opposite chirality. The canonical interpretation of these surfaces states is in terms of chiral edge modes of a layer quantum Hall effect: The two-dimensional momentum-space planes perpendicular to the momentum connecting the two Weyl points are characterized by a non-zero Chern number. It might be interesting to note, that in analogy to the known two-dimensional Floquet anomalous chiral edge states, one can realize open Fermi arcs in the absence of Chern numbers in periodically driven system. Here, we present a way to construct such anomalous Fermi arcs in a concrete model

Observation of phononic helical edge states in a mechanical 'topological insulator'

A topological insulator is characterized by a dichotomy between the interior and the edge of a finite system: While the bulk has a non-zero energy gap, the edges are forced to sustain excitations traversing these gaps. Originally proposed for electrons governed by quantum mechanics, it has remained an important open question if the same physics can be observed for systems obeying Newton's equations of motion. Here, we report on measurements that characterize the collective behavior of mechanical oscillators exhibiting the phenomenology of the quantum spin hall effect. The phononic edge modes are shown to be helical and we demonstrate their topological protection via the stability against imperfections. Our results open the door to the design of topological acoustic meta-materials that can capitalize on the stability of the surfaces phonons as reliable wave guides.Comment: 6 pages, 4 figure

Universal Dephasing of Many-Body Rabi Oscillations of Atoms in One-Dimensional Traps

We study a quantum quench in a system of two coupled one-dimensional tubes of interacting atoms. After the quench the system is out of equilibrium and oscillates between the tubes with a frequency determined by microscopic parameters. Despite the high energy at which the system is prepared we find an emergent long time scale responsible for the dephasing of the oscillations and a transition at which this time scale diverges. We show that the universal properties of the dephasing and the transition arise from an infrared orthogonality catastrophe. Furthermore, we show how this universal behavior is realized in a realistic model of fermions with attractive interactions.Comment: 4 pages, 2 figure