Spectrally narrow, long-term stable optical frequency reference based on a Eu3+:Y2SiO5 crystal at cryogenic temperature

Using an ultrastable continuous-wave laser at 580 nm we performed spectral hole burning of Eu(3+):Y(2)SiO(5) at a very high spectral resolution. The essential parameters determining the usefulness as a macroscopic frequency reference, linewidth, temperature sensitivity, and long-term stability, were characterized using a H-maser stabilized frequency comb. Spectral holes with a linewidth as low as 6 kHz were observed and the upper limit of the drift of the hole frequency was determined to be 5±3 mHz/s. We discuss the necessary requirements for achieving ultrahigh stability in laser frequency stabilization to these spectral holes.     

The phase diagram for coexisting d-wave superconductivity and charge-density waves: cuprates and beyond

Phase diagrams of d-wave superconductivity characterized by an order parameter Δ coexisting with charge-density waves (CDWs) characterized by an order parameter Σ were constructed for the two-dimensional Fermi surface (FS) appropriate to, e.g., cuprates. CDWs were considered as an origin of the pseudogap appearing at antinodal FS sections of the d(x2-y2) superconductor. Two types of the Σ-reentrance were found: with the temperature, T, and with the opening of the CDW sector, 2α. The angular plots in the momentum space for the resulting gap profile over the FS ('gap roses') were obtained. The gap patterns are rather involved, giving insight into the difficulties of the interpretation of photoemission spectra. It was shown that the Σ-Δ coexistence region exists even for the complete dielectric gapping due to the distinction between the superconducting and CDW order parameter symmetries. The checkerboard and unidirectional CDW configurations were examined, and both the phase diagrams and the behavior with T and α of the order parameters were found to differ. A more general case with a non-zero mismatch angle β between the superconducting lobes and the CDW sectors was analyzed, the case β = π/4 corresponding to the d(xy) symmetry of the superconducting order parameter. The phase diagrams were found to be sensitive to β-variations, showing that internal strains and external pressure can drastically affect the behavior of Σ(T) and Δ(T).     

An example of dynamically induced coherent states

We consider an example where coherent states appear naturally (dynamically). We study the interaction between an arbitrary quantized matter with a quantized electromagnetic field. Using an approximation that is similar to the Hartree–Fock one and a variational principle, we demonstrate that the electromagnetic field is created by the charged matter exactly in Glauber coherent states with parameters determined by mean currents of the matter.     

The influence of geometry on the vibronic spectra of quantum aggregates

A study is presented of the localisation of excitonic states on extended molecular aggregates composed of identical monomers arising, not from disorder due to statistical energy shifts of the monomers, induced by environmental interactions (Anderson localisation), but rather simply due to changes in the orientation and geometrical arrangement of the transition dipoles. It is shown further that such small changes nevertheless can have a drastic effect on the shape of the vibronic spectrum of the aggregate. The vibronic spectra are calculated using the ‘coherent exciton scattering’ (CES) approximation whose derivation we generalise to be applicable to aggregates of arbitrary size and geometry.     

Noise spectroscopy and interlayer phase coherence in bilayer quantum Hall systems

Bilayer quantum Hall systems develop strong interlayer phase coherence when the distance between layers is comparable to the typical distance between electrons within a layer. The phase-coherent state has until now been investigated primarily via transport measurements. We argue here that interlayer current and charge-imbalance noise studies in these systems will be able to address some of the key experimental questions. We show that the characteristic frequency of current noise is that of the zero wave vector collective mode, which is sensitive to the degree of order in the system. Local electric potential noise measured in a plane above the bilayer system, on the other hand, is sensitive to finite-wave-vector collective modes and, hence, to the soft-magnetoroton picture of the order-disorder phase transition.     

Entrainment of randomly coupled oscillator networks by a pacemaker

Entrainment by a pacemaker, representing an element with a higher frequency, is numerically investigated for several classes of random networks which consist of identical phase oscillators. We find that the entrainment frequency window of a network decreases exponentially with its depth, defined as the mean forward distance of the elements from the pacemaker. Effectively, only shallow networks can thus exhibit frequency locking to the pacemaker. The exponential dependence is also derived analytically as an approximation for large random asymmetric networks.     

Rod-climbing effect in Newtonian fluids

When a rotating rod is brought into a polymer melt or concentrated polymer solution, the meniscus climbs the rod. This spectacular rod climbing is due to the normal stresses present in the polymer fluid and is thus a purely non-Newtonian effect. A similar rod climbing of an interface between two fluids has therefore been taken as a signature that one of the fluids exhibits normal stress effects. We show here, however, that the effect can occur with simple Newtonian fluids: it occurs when a Taylor-Couette instability happens in the less viscous of the two liquids but not in the more viscous one.     

Measurement of nonrandom event-by-event fluctuations of average transverse momentum in square root of (sNN)=200 GeV Au+Au and p+p collisions

Event-by-event fluctuations of the average transverse momentum of produced particles near midrapidity have been measured by the PHENIX Collaboration in square root of (sNN)=200 GeV Au+Au, and p+p collisions at the Relativistic Heavy Ion Collider. The fluctuations are observed to be in excess of the expectation for statistically independent particle emission for all centralities. The excess fluctuations exhibit a dependence on both the centrality of the collision and on the pT range over which the average is calculated. Both the centrality and pT dependence can be well reproduced by a simulation of random particle production with the addition of contributions from hard-scattering processes.     

Microscale simulation of martensitic microstructure evolution

A new model for the evolution of multivariant martensitic microstructure in single crystals and polycrystals is developed. In contrast with Landau-Ginzburg models, which are limited in practice to nanoscale specimens, this new scale-free model is valid for length scales greater than 100 nm and without an upper bound. It is based on a thermodynamic potential in the volume fractions of the martensitic variants that exhibits an instability resulting in microstructure formation. Simulated microstructures in elastic single crystals and polycrystals under uniaxial loading are in qualitative agreement with those observed experimentally.     

Exact quantum partition function of the BCS model

The exact calculation of the reduced BCS model quantum partition function (QPF) in the thermodynamic limit is carried out by the path integration method. The expression for the QPF and the phase transition temperatureT _c in the regular phase coincide with the results of Bogolyubov. In the nonregular phase a temperature singularity appears in the expression for the QPF: the QPF diverges in the region of temperaturesT _c which are smaller than some critical temperatureT _c ^* , and it turns out that in all casesT _c ^* > T _c and the differenceT _c ^* –T _c is not small. The interpretation of the temperatureT _c ^* is given.