Small size boundary effects on two-pion interferometry

The Bose-Einstein correlations of two identically charged pions are derived when these particles, the most abundantly produced in relativistic heavy ion collisions, are confined in finite volumes. Boundary effects on single pion spectrum are also studied. Numerical results emphasize that conventional formulation usually adopted to describe two-pion interferometry should not be used when the source size is small, since this is the most sensitive case to boundary effects. Specific examples are considered for better illustration.Comment: more discussion on Figure4 and diffuse boundar

Magnetoconductance Oscillations in Ballistic Semiconductor-Superconductor Junctions

The mechanism of the magnetoconductance oscillations in junctions of a ballistic semiconductor and a superconductor is discussed. The oscillations appear when both the normal and the Andreev reflection occur at the interface. The interplay between the classical cyclotron motion of a quasiparticle and the phase shift caused by the magnetic field is the origin of the conductance oscillations.Comment: 4 pages, 4 figure

Andreev Reflection in Strong Magnetic Fields

We have studied the interplay of Andreev reflection and cyclotron motion of quasiparticles at a superconductor-normal-metal interface with a strong magnetic field applied parallel to the interface. Bound states are formed due to the confinement introduced both by the external magnetic field and the superconducting gap. These bound states are a coherent superposition of electron and hole edge excitations similar to those realized in finite quantum-Hall samples. We find the energy spectrum for these Andreev edge states and calculate transport properties.Comment: 5 pages, 3 figures, RevTex, revised to include more detailed discussion of currents and transpor

Negative Echo in the Density Evolution of Ultracold Fermionic Gases

We predict a nonequilibrium critical phenomenon in the space-time density evolution of a fermionic gas above the temperature of transition into the superfluid phase. On the BCS side of the BEC-BCS crossover, the evolution of a localized density disturbance exhibits a negative echo at the point of the initial inhomogeneity. Approaching the BEC side, this effect competes with the slow spreading of the density of bosonic molecules. However, even here the echo dominates for large enough times. This effect may be used as an experimental tool to locate the position of the transition.Comment: 4 pages, 2 figure

Full Counting Statistics of Charge Transfer in Coulomb Blockade Systems

Full counting statistics (FCS) of charge transfer in mesoscopic systems has recently become a subject of significant interest, since it proves to reveal an important information about the system which can be hardly assessed by other means. While the previous research mostly addressed the FCS of non- interacting systems, the present paper deals with the FCS in the limit of strong interaction. In this Coulomb blockade limit the electron dynamics is known to be governed by a master equation. We develop a general scheme to evaluate the FCS in such case, this being the main result of the work presented. We illustrate the scheme, by applying it to concrete systems. For generic case of a single resonant level we establish the equivalence of scattering and master equation approach to FCS. Further we study a single Coulomb blockade island with two and three leads attached and compare the FCS in this case with our recent results concerning an open dot either with two and three terminals. We demonstrate that Coulomb interaction suppresses the relative probabilities of large current fluctuations.Comment: 17 pages, 16 figure

Thermodynamics of deformed AdS5_5 model with a positive/negative quadratic correction in graviton-dilaton system

By solving the Einstein equations of the graviton coupling with a real scalar dilaton field, we establish a general framework to self-consistently solve the geometric background with black-hole for any given phenomenological holographic models. In this framwork, we solve the black-hole background, the corresponding dilaon field and the dilaton potential for the deformed AdS$_5$ model with a positive/negative quadratic correction. We systematically investigate the thermodynamical properties of the deformed AdS$_5$ model with a positive and negative quadratic correction, respectively, and compare with lattice QCD on the results of the equation of state, the heavy quark potential, the Polyakov loop and the spatial Wilson loop. We find that the bulk thermodynamical properties are not sensitive to the sign of the quadratic correction, and the results of both deformed holographic QCD models agree well with lattice QCD result for pure SU(3) gauge theory. However, the results from loop operators favor a positive quadratic correction, which agree well with lattice QCD result. Especially, the result from the Polyakov loop excludes the model with a negative quadratic correction in the warp factor of ${\rm AdS}_5$.Comment: 26 figures,36 pages,V.3: an appendix,more equations and references added,figures corrected,published versio

Local anisotropy and giant enhancement of local electromagnetic fields in fractal aggregates of metal nanoparticles

We have shown within the quasistatic approximation that the giant fluctuations of local electromagnetic field in random fractal aggregates of silver nanospheres are strongly correlated with a local anisotropy factor S which is defined in this paper. The latter is a purely geometrical parameter which characterizes the deviation of local environment of a given nanosphere in an aggregate from spherical symmetry. Therefore, it is possible to predict the sites with anomalously large local fields in an aggregate without explicitly solving the electromagnetic problem. We have also demonstrated that the average (over nanospheres) value of S does not depend noticeably on the fractal dimension D, except when D approaches the trivial limit D=3. In this case, as one can expect, the average local environment becomes spherically symmetrical and S approaches zero. This corresponds to the well-known fact that in trivial aggregates fluctuations of local electromagnetic fields are much weaker than in fractal aggregates. Thus, we find that, within the quasistatics, the large-scale geometry does not have a significant impact on local electromagnetic responses in nanoaggregates in a wide range of fractal dimensions. However, this prediction is expected to be not correct in aggregates which are sufficiently large for the intermediate- and radiation-zone interaction of individual nanospheres to become important.Comment: 9 pages 9 figures. No revisions from previous version; only figure layout is change

Spin Nematic Phase in S=1 Triangular Antiferromagnets

Spin nematic order is investigated for a S=1 spin model on triangular lattice with bilinear-biquadratic interactions. We particularly studied an antiferro nematic order phase with three-sublattice structure, and magnetic properties are calculated at zero temperature by means of bosonization. Two types of bosonic excitations are found. One is a gapless excitation with linear energy dispersion around $k \sim 0$, and this leads to a finite spin susceptibility at T=0 and would have a specific heat $C(T) \sim T^2$ at low temperatures. These behaviors can explain many of characteristic features of recently discovered spin liquid state in the triangular magnet, NiGa2S4

Andreev reflection and cyclotron motion at superconductor -- normal-metal interfaces

We investigate Andreev reflection at the interface between a superconductor and a two--dimensional electron system (2DES) in an external magnetic field such that cyclotron motion is important in the latter. A finite Zeeman splitting in the 2DES and the presence of diamagnetic screening currents in the superconductor are incorporated into a microscopic theory of Andreev edge states, which is based on the Bogoliubov--de Gennes formalism. The Andreev--reflection contribution to the interface conductance is calculated. The effect of Zeeman splitting is most visible as a double--step feature in the conductance through clean interfaces. Due to a screening current, conductance steps are shifted to larger filling factors and the formation of Andreev edge states is suppressed below a critical filling factor.Comment: 8 pages, 6 figure

Numerical Study of Impurity Effects on Quasiparticles within S-wave and Chiral P-wave Vortices

The impurity problems within vortex cores of two-dimensional s-wave and chiral p-wave superconductors are studied numerically in the framework of the quasiclassical theory of superconductivity and self-consistent Born approximation under a trial form of the pair potential. The dispersion and impurity scattering rate (the inverse of the relaxation time) of the Andreev bound state localized in vortex cores are deduced from the angular-resoloved local density of states. The energy dependence of the impurity scattering rates depends on the pairing symmetry; particularly, in the chiral p-wave vortex core where chirality and vorticity have opposite sign and hence the total angular momentum is zero, the impurities are ineffective and the scattering rate is vanishingly small. Owing to the cancellation of angular momentum between chirality and vorticity, the chiral p-wave vortex core is similar to locally realized s-wave region and therefore non-magnetic impurity is harmless as a consequence of Anderson's theorem. The results of the present study confirm the previous results of analytical study (J. Phys. Soc. Jpn. {\bf 69} (2000) 3378) in the Born limit.Comment: 8pages, 9figures, submitted to J. Phys. Soc. Jp