Normal and superfluid fractions of inhomogeneous nonequilibrium quantum fluids

We present a theoretical analysis of the normal and superfluid fractions of quantum fluids described by a nonequilibrium extension of the Gross-Pitaevskii equation in the presence of an external potential. Both disordered and regular potentials are considered. The normal and superfluid fractions are defined by the response of the nonequilibrium quantum fluid to a vector potential, in analogy with the equilibrium case. We find that the physical meaning of these definitions breaks down out of equilibrium. The normal and superfluid fractions no longer add up to one and for some types of external potentials, they can even become negative.Comment: 6 pages, 5 figure

The spatial coherence of weakly interacting one-dimensional non-equilibrium Bosonic quantum fluids

We present a theoretical analysis of spatial correlations in a one-dimensional driven-dissipative non-equilibrium condensate. Starting from a stochastic generalized Gross-Pitaevskii equation, we derive a noisy Kuramoto-Sivashinsky equation for the phase dynamics. For sufficiently strong interactions, the coherence decays exponentially in close analogy to the equilibrium Bose gas. When interactions are small on a scale set by the nonequilibrium condition, we find through numerical simulations a crossover between a Gaussian and exponential decay with peculiar scaling of the coherence length on the fluid density and noise strength.Comment: 5 pages, 2 figures, supplemental materia

Noise-induced transition from superfluid to vortex state in two-dimensional nonequilibrium polariton condensates -- semi-analytical treatment

We develop a semi-analytical description for the Berezinskii-Kosterlitz-Thouless (BKT) like phase transition in nonequilibrium Bose-Einstein condensates. Our theoretical analysis is based on a noisy generalized Gross-Pitaevskii equation. Above a critical strength of the noise, spontaneous vortex-antivortex pairs are generated. We provide a semi-analytical determination of the transition point based on a linearized Bogoliubov analysis, to which some nonlinear corrections are added. We present two different approaches that are in agreement with our numerical calculations in a wide range of system parameters. We find that for small losses and not too small energy relaxation, the critical point approaches that of the equilibrium BKT transition. Furthermore, we find that losses tend to stabilize the ordered phase: keeping the other parameters constant and increasing the losses leads to a higher critical noise strength for the spontaneous generation of vortex-antivortex pairs. Our theoretical analysis is relevant for experiments on microcavity polaritons

Temporal coherence of one-dimensional non-equilibrium quantum fluids

We theoretically investigate the time dependence of the first order coherence function for a one-dimensional driven dissipative non-equilibrium condensate. Simulations on the generalized Gross-Pitaevskii equation (GGPE) show that the characteristic time scale of exponential decay agrees with the linearized Bogoliubov theory in the regime of large interaction energy. For very weak interactions, the temporal correlation deviates from the linear theory, and instead respects the dynamic scaling of the Kardar-Parisi-Zhang universality class. This nonlinear dynamics is found to be quantitatively captured by a noisy Kuramoto-Sivashinsky equation for the phase dynamics.Comment: 5 pages, 4 figure

Paramagnetic Meissner effect in ZrB12 single crystal with non-monotonic vortex-vortex interactions

The magnetic response related to paramagnetic Meissner effect (PME) is studied in a high quality single crystal ZrB12 with non-monotonic vortex-vortex interactions. We observe the expulsion and penetration of magnetic flux in the form of vortex clusters with increasing temperature. A vortex phase diagram is constructed which shows that the PME can be explained by considering the interplay among the flux compression, the different temperature dependencies of the vortex-vortex and the vortex-pin interactions, and thermal fluctuations. Such a scenario is in good agreement with the results of the magnetic relaxation measurements.Comment: accepted by New Journal of Physic

High magnetic field cyclotron resonance in CdS: explanation of the non-monotonic temperature dependence of the cyclotron mass

Recent cyclotron resonance expts. in n-type CdS at ultra-high magnetic fields revealed a well-pronounced max. of the electron cyclotron mass as a function of temp. These exptl. data are interpreted within a model which takes into account the interaction of the conduction electrons with LO phonons and with nonpolar optical phonons. The piezoelec. electron-phonon interaction and the electron scattering by randomly distributed defects with a short-range potential are also treated. The obsd. behavior of the cyclotron mass can be explained in terms of an interplay between several scattering mechanisms

Variability of adult cerebrum mass of the Saratov-city residents

The research aimed to study the age-gender variability and extreme variants of individual cerebrum mass of Saratov citizens. Material and methods – Cerebrum preparations from 191 dead bodies of adults of 21-90 years were used as a material for the research. The whole material was divided into 4 age groups: the 1st group – the 1st adult period and 43 cerebrum preparations (26 male, 17 female); the 2nd group – the 2nd adult period – 82 preparations (66 male, 16 female); the 3rd group – the elderly age period – 34 preparations (16 male, 18 female); the senium age – 32 preparations (16 male and 16 female). The cerebrum was taken apart from the spinal cord at the border with the medulla oblongata and was weighed on analytical balance to within the accuracy of 1.0 g. Results – The cerebrum mass of Saratov adult citizens was 1323.69±19.81 g (M±SD) (without including gender and age groups). For men it was 1371.05±20.39 g, for women – 1236.05±32.51 g, i.e. the cerebrum mass of men is more than the women’s one in average for 135 g (10.9 %) (Р>0.05). The cerebrum mass decrease is registered at the 2nd adult period, which becomes more evident at the senium age. Thus the cerebrum mass at the 1st and the 2nd adult periods differs authentically from its value at the senium age, and at the 1st adult period it differs from its value at the elderly age as well (P<0.05). Considerable individual cerebrum mass variability has aroused the necessity to specify the groups of its extreme variables. An average cerebrum mass is at 47.1 % of Saratov citizens. Small, extremely small, and below average cerebrum mass is registered at 25.2 % of Saratov citizens, and large, above average, and extremely large mass – at 13.6 %. Conclusion – Thus the cerebrum mass of Saratov citizens subjected to age-gender variability which lies in the fact that male cerebrum is heavier comparing with female cerebrum, and the cerebrum mass is been decreased from the 2nd adult period. The described cases of a large cerebrum mass at an elderly age, and of small and extremely small cerebrum mass at the 1st and 2nd adult periods, as we think, are connected with the individual variability of subjects' skull forms and volume