Detailed balance condition and ultraviolet stability of scalar field in Horava-Lifshitz gravity

Detailed balance and projectability conditions are two main assumptions when Horava recently formulated his theory of quantum gravity - the Horava-Lifshitz (HL) theory. While the latter represents an important ingredient, the former often believed needs to be abandoned, in order to obtain an ultraviolet stable scalar field, among other things. In this paper, because of several attractive features of this condition, we revisit it, and show that the scalar field can be stabilized, if the detailed balance condition is allowed to be softly broken. Although this is done explicitly in the non-relativistic general covariant setup of Horava-Melby-Thompson with an arbitrary coupling constant $\lambda$, generalized lately by da Silva, it is also true in other versions of the HL theory. With the detailed balance condition softly breaking, the number of independent coupling constants can be still significantly reduced. It is remarkable to note that, unlike other setups, in this da Silva generalization, there exists a master equation for the linear perturbations of the scalar field in the flat Friedmann-Robertson-Walker background.Comment: Some typos are corrected. To appear in JCA

On the origin of the A1g_{1g} and B1g_{1g} electronic Raman scattering peaks in the superconducting state of YBa2_{2}Cu3_{3}O7−δ_{7-\delta}

The electronic Raman scattering has been investigated in optimally oxygen doped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ single crystals as well as in crystals with non-magnetic, Zn, and magnetic, Ni, impurities. We found that the intensity of the A$_{1g}$ peak is impurity independent and their energy to $T_{c}$ ratio is almost constant ($2\Delta/k_{B}T_{c}\sim5$). Moreover, the signal at the B$_{1g}$ channel is completely smeared out when non-magnetic Zn impurities are present. These results are qualitatively interpreted in terms of the Zeyher and Greco's theory that relates the electronic Raman scattering in the A$_{1g}$ and B$_{1g}$ channels to \textit{d}-CDW and superconducting order parameters fluctuations, respectively.Comment: Submited to Phys. Rev. Let

Alkali doping leads to charge-transfer salt formation in a two-dimensional metal–organic framework

Efficient charge transfer across metal–organic interfaces is a key physical process in modern organic electronics devices, and characterization of the energy level alignment at the interface is crucial to enable a rational device design. We show that the insertion of alkali atoms can significantly change the structure and electronic properties of a metal–organic interface. Coadsorption of tetracyanoquinodimethane (TCNQ) and potassium on a Ag(111) surface leads to the formation of a two-dimensional charge transfer salt, with properties quite different from those of the two-dimensional Ag adatom TCNQ metal–organic framework formed in the absence of K doping. We establish a highly accurate structural model by combination of quantitative X-ray standing wave measurements, scanning tunnelling microscopy, and density-functional theory (DFT) calculations. Full agreement between the experimental data and the computational prediction of the structure is only achieved by inclusion of a charge-transfer-scaled dispersion correction in the DFT, which correctly accounts for the effects of strong charge transfer on the atomic polarizability of potassium. The commensurate surface layer formed by TCNQ and K is dominated by strong charge transfer and ionic bonding and is accompanied by a structural and electronic decoupling from the underlying metal substrate. The consequence is a significant change in energy level alignment and work function compared to TCNQ on Ag(111). Possible implications of charge-transfer salt formation at metal–organic interfaces for organic thin-film devices are discussed

Spin Transport in Two Dimensional Hopping Systems

A two dimensional hopping system with Rashba spin-orbit interaction is considered. Our main interest is concerned with the evolution of the spin degree of freedom of the electrons. We derive the rate equations governing the evolution of the charge density and spin polarization of this system in the Markovian limit in one-particle approximation. If only two-site hopping events are taken into account, the evolution of the charge density and of the spin polarization is found to be decoupled. A critical electric field is found, above which oscillations are superimposed on the temporal decay of the total polarization. A coupling between charge density and spin polarization occurs on the level of three-site hopping events. The coupling terms are identified as the anomalous Hall effect and the recently proposed spin Hall effect. Thus, an unpolarized charge current through a sheet of finite width leads to a transversal spin accumulation in our model system.Comment: 15 pages, 3 figure

Quantum Computing with Atomic Josephson Junction Arrays

We present a quantum computing scheme with atomic Josephson junction arrays. The system consists of a small number of atoms with three internal states and trapped in a far-off resonant optical lattice. Raman lasers provide the "Josephson" tunneling, and the collision interaction between atoms represent the "capacitive" couplings between the modes. The qubit states are collective states of the atoms with opposite persistent currents. This system is closely analogous to the superconducting flux qubit. Single qubit quantum logic gates are performed by modulating the Raman couplings, while two-qubit gates result from a tunnel coupling between neighboring wells. Readout is achieved by tuning the Raman coupling adiabatically between the Josephson regime to the Rabi regime, followed by a detection of atoms in internal electronic states. Decoherence mechanisms are studied in detail promising a high ratio between the decoherence time and the gate operation time.Comment: 7 figure

Hadron Structure on the Lattice

A few chosen nucleon properties are described from a lattice QCD perspective: the nucleon sigma term and the scalar strangeness in the nucleon; the vector form factors in the nucleon, including the vector strangeness contribution, as well as parity breaking effects like the anapole and electric dipole moment; and finally the axial and tensor charges of the nucleon. The status of the lattice calculations is presented and their potential impact on phenomenology is discussed.Comment: 17 pages, 9 figures; proceedings of the Conclusive Symposium of the Collaborative Research Center 443 "Many-body structure of strongly interacting systems", Mainz, February 23-25, 201