Quantum effects on liquid dynamics as evidenced by the presence of well-defined collective excitations in liquid para-hydrogen

The origin of the well-defined collective excitations found in liquid para-H2 by recent experiments is investigated. The persistence of their relatively long lifetimes down to microscopic scales is well accounted for by calculations carried out by means of path-integral-centroid molecular dynamics. In contrast only overdamped excitations are found in calculations carried within the classical limit. The results provide fully quantitative evidence of quantum effects on the dynamics of a simple liquid.     

The Microscopic Model of Composite Fermion-Type Excitations for υ = l/m Edge States

We derive a microscopic theory of the composite fermion-type quasiparticles describing the low-lying edge excitations in the fractional quantdm Hall liquid with υ = 1/m. Using the composite fermion transformation, one finds that the edge states of the system in a disc sample are described by the Calogero-Sutherland-like model (CSLM) in the one-dimensional limit. This result presents the consistency between one-dimensional and two-dimensional statistics. It is shown that the low-lying excitations, indeed, have the chiral Luttinger liquid behaviors because there is a gap between the right-and left-moving excitations of the CSLM.     

Momentum dependence of the spin and charge excitations in the two dimensional Hubbard model

The low energy spin and charge excitations in the 2D Hubbard model near half filling are analyzed. The RPA spectra derived from inhomoheneous mean field textures are analyzed. Spin excitations show a commensurate peak at half filling, incommensurate peaks near half filling, and a broad background typical of a dilute Fermi liquid away from half filling. Charge excitations, near half filling, are localized near (0,0), and they occupy a small portion of the Brillouin Zone, in a way consistent with the existence of a small density of carriers, and a small Fermi surface. At higher hole densities, they fill the entire BZ, and can be understood in terms of a conventional Fermi liquid picture. The results are consistent with the observed features of the high-T_c superconductors.     

Interacting particles as neither bosons nor fermions: A microscopic origin for fractional exclusion statistics

We study a quantum liquid of particles interacting via a long-ranged two-body potential in three dimensions where the original particles are supposed to be either bosons or fermions. We show that such liquids exhibit the nature of a quantum liquid with fractional exclusion statistics. In both quantum liquids enlarged pseudo-Fermi surfaces are formed from bosons and fermions, although with different excitations. Hence, we conclude that the microscopic origin of exclusion statistics comes from the nature of long-ranged two-body interactions between the particles.     

Exact microscopic wave function for a topological quantum membrane

The higher dimensional quantum Hall liquid constructed recently supports stable topological membrane excitations. Here we introduce a microscopic interacting Hamiltonian and present its exact ground state wave function. We show that this microscopic ground state wave function describes a topological quantum membrane. We also construct variational wave functions for excited states using the noncommutative algebra on the four sphere. Our approach introduces a nonperturbative method to quantize topological membranes.     

Correlations and confinement of excitations in an asymmetric Hubbard ladder

Correlation functions and low-energy excitations are investigated in the asymmetric two-leg ladder consisting of a Hubbard chain and a noninteracting tight-binding (Fermi) chain using the density matrix renormalization group method. The behavior of charge, spin and pairing correlations is discussed for the four phases found at half filling, namely, Luttinger liquid, Kondo-Mott insulator, spin-gapped Mott insulator and correlated band insulator. Quasi-long-range antiferromagnetic spin correlations are found in the Hubbard leg in the Luttinger liquid phase only. Pair-density-wave correlations are studied to understand the structure of bound pairs found in the Fermi leg of the spin-gapped Mott phase at half filling and at light doping but we find no enhanced pairing correlations. Low-energy excitations cause variations of spin and charge densities on the two legs that demonstrate the confinement of the lowest charge excitations on the Fermi leg while the lowest spin excitations are localized on the Hubbard leg in the three insulating phases. The velocities of charge, spin, and single-particle excitations are investigated to clarify the confinement of elementary excitations in the Luttinger liquid phase. The observed spatial separation of elementary spin and charge excitations could facilitate the coexistence of different (quasi-)long-range orders in higher-dimensional extensions of the asymmetric Hubbard ladder.     

Bogolyubov’s theory of superfluidity

The Bogolyubov model of liquid helium is considered. We derive sufficient conditions which ensure an appearance of the Bose condensate in the model. For some temperatures and some positive values of the chemical potential there is the gapless Bogolyubov spectrum of elementary excitations, leading to the proper microscopic interpretation of the superfluidity.     

Equilibration of Luttinger liquid and conductance of quantum wires

Luttinger liquid theory describes one-dimensional electron systems in terms of noninteracting bosonic excitations. In this approximation thermal excitations are decoupled from the current flowing through a quantum wire, and the conductance is quantized. We show that relaxation processes not captured by the Luttinger liquid theory lead to equilibration of the excitations with the current and give rise to a temperature-dependent correction to the conductance. In long wires, the magnitude of the correction is expressed in terms of the velocities of bosonic excitations. In shorter wires it is controlled by the relaxation rate.     

On the low-temperature behavior of condensed Bose systems

A microscopic derivation of theT ²-law for the low-temperature behavior of the condensate depletion in an interacting Bose liquid is given using the knownT=0 low-lying single-particle excitations. TheT ²-term gives no contribution to the orderT ³ in the microscopic proof of Landau'sT ³-law for the specific heat of an interacting Bose liquid.     

A comparative study of optic phonon-like excitations in liquid mixtures and molten salts

We report a study of collective excitations in an equimolar Lennard–Jones liquid mixture KrAr and a molten salt NaCl within the parameter-free generalized collective modes (GCM) approach. It is shown that the high-frequency propagating modes in liquid KrAr and molten NaCl correspond to optic phonon-like excitations, caused by fast mass-concentration (charge in NaCl) fluctuations. Dispersion curves for optic collective excitations are discussed.     

Spin-plasmons in topological insulator

Collective plasmon excitations in a helical electron liquid on the surface of strong three-dimensional topological insulator are considered. The properties and internal structure of these excitations are studied. Due to spin-momentum locking in helical liquid on a surface of topological insulator, the collective excitations should manifest themselves as coupled charge- and spin-density waves.     

Electromagnetic response of broken-symmetry nanoscale clusters

A microscopic, nonlocal response theory is developed to model the interaction of electromagnetic radiation with inhomogeneous nanoscale clusters. The breakdown of classical continuum-field Mie theory is demonstrated at a critical coarse-graining threshold, below which macroscopic plasmon resonances are replaced by molecular excitations with suppressed spectral intensity.     

Manipulating transmission and reflection properties of a photonic crystal doped with quantum dot nanostructures

We consider excitations that exist, in addition to phonons, in the ideal Bose gas at zero temperature. These excitations are vortex rings whose energy spectrum is similar to the roton one in liquid helium.     

Dancing "atoms" and "molecules" of luminous gas-discharge spots

Highly localized, dynamic particle-like excitations are observed in a dc-driven, quasi-two-dimensional gas-discharge system. These localized excitations undergo a transition from isolated to aggregated state as the discharge current is increased. Although they provide us a macroscopic analogue of microscopic atoms and molecules, they are quite distinct from the latter in the point that they exhibit a rich variety of complex dynamics. The fact that these localized excitations can show synchronous dynamics even in distant places, together with recent theoretical studies, indicates that a global coupling plays an important role on the dynamics of such localized excitations.     

Is superdense fluid hydrogen a molecular metal?

Recent experiments on the compression of liquid hydrogen in reverberating shock waves, which indicate the transition into a metallic state at about nine times the liquid H₂ density [S. T. Weir, A. C. Mitchell, and W. J. Nellis, Phys. Rev. Lett. 76, 1860 (1996)], have been interpreted by a microscopic percolation in a virtual molecular structure with a continuous spectrum of the electron excitations. The scaling dependence of the electron mobility on the energy above the percolation threshold has been used to qualitatively describe the electrical conductivity of fluid molecular hydrogen in the vicinity of the insulator-metal transition point. Zh. éksp. Teor. Fiz. 113, 1094–1100 (March 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.