Hidden order in 1D bose insulators

We investigate the phase diagram of spinless bosons with long range (variant 1/r(3)) repulsive interactions, relevant to ultracold polarized atoms or molecules, using density matrix renormalization group. Between the two conventional insulating phases, the Mott and density wave phases, we find a new phase possessing hidden order revealed by nonlocal string correlations analogous to those characterizing the Haldane gapped phase of integer spin chains. We develop a mean field theory that describes the low-energy excitations in all three insulating phases. This is used to calculate the absorption spectrum due to oscillatory lattice modulation. We predict a sharp resonance in the spectrum due to a collective excitation of the new phase that would provide clear evidence for the existence of this phase.     

Localization and the origin of paramagnetic centers in 1D conductors

It is shown that the appearance of paramagnetic centers is an intrinsic property of 1D conductors with static defects of a non-magnetic origin. The concentration of paramagnetic centers is determined by the fact that in the 1D case all electron states in the field of defects are localized and the Coulomb repulsion leads to the appearance of a certain number of single occupied states. Power temperature dependences for a number of thermodynamic quantities, in particular, for susceptibility are obtained     

Computational comparison of charge neutralisations of conductors and insulators with corona ionisers

We report a numerical investigation of phenomena of charge neutralisations of insulators and conductors with a balanced DC or AC ioniser using 2-D cylindrical electrohydrodynamic modelling. The early-phase phenomena of the insulator charge neutralisation are complicated and significantly different from the conductor ones, which indicates that the evaluation by the standard test may lead to potential problems in practical applications. In addition, the results of simulations demonstrated that, in the insulator charge neutralisation, ionisers themselves can cause latent hazards during neutralisation. We propose proper use of ionisers and the standard test to avoid such hazards.     

Temperature dependence of multiphonon absorption in ionic insulators

We present a calculation for a simple model of the temperature dependence of the absorption in the high frequency wing of the reststrahlen absorption band in NaCl and NaF. The theoretical results are in qualitative agreement with the experimental results.     

Electron localization in 1D conductors due to the phonon scattering

Electron localization in 1D conductors due to scattering by dispersionless optical phonons at low temperatures has been studied by applying the Berezinsky diagram technique. The large localization length l_loc, much longer than the mean free path l, has been found. The low frequency optical absorption is described by the law: Re σ(ω) ～ ω² |ln³ω|.     

Interband excitations in the 1D limit of two-band fractional Chern insulators

We investigate the stability of the one-dimensional limit of $\nu =1/3$ Laughlin-like fractional Chern insulator with respect to the interband interaction. We propose a construction for the excitations in the infinite-interaction case and show that the energy gap remains finite in the thermodynamic limit. Next, by means of exact diagonalization and Density Matrix Renormalization Group approaches, we consider deviations from ideal dimerization and show that they reduce the stability of the FCI-like states. Finally, to show that our approach is not restricted to one model, we identify the dimer structure behind the thin-torus limit of other system – the checkerboard lattice.     

Infrared absorption in ionic insulators due to multiphonon processes

The absorption β in ionic insulators due to multiphonon processes is examined for frequencies higher than several times the reststrahl frequency. The frequency dependence and temperature dependence of β are calculated for simple models which include approximations appropriate to ionic insulators: anharmonic potential and an estimate of the influence of a small quadratic term in the dipole moment operator. The frequency dependence of β is found to be approximately exponential with a slope given by the log of the ratio of atomic displacement to a distance characterizing the onset of the anharmonicity in the potential. The calculated values of β are found to be in good agreement with the experimental results for reasonable values of the parameters in the models.     

Bose-Einstein condensates in 1D optical lattices

We discuss the Bloch-state solutions of the stationary Gross-Pitaevskii equation and of the Bogoliubov equations for a Bose-Einstein condensate in the presence of a one-dimensional optical lattice. The results for the compressibility, effective mass and velocity of sound are analysed as a function of the lattice depth and of the strength of the two-body interaction. The band structure of the spectrum of elementary excitations is compared with the one exhibited by the stationary solutions (Bloch bands). Moreover, the numerical calculations are compared with the analytic predictions of the tight binding approximation. We also discuss the role of quantum fluctuations and show that the condensate exhibits 3D, 2D or 1D features depending on the lattice depth and on the number of particles occupying each potential well. We finally show how, using a local density approximation, our results can be applied to study the behaviour of the gas in the presence of harmonic trapping.Received: 15 July 2003, Published online: 8 October 2003PACS: 03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow - 03.75.Lm Tunneling, Josephson effect, Bose-Einstein condensates in periodic potentials, solitons, vortices and topological excitations     

1D Bose gases in an optical lattice

We report on the study of the momentum distribution of a one-dimensional Bose gas in an optical lattice. From the momentum distribution we extract the condensed fraction of the gas and thereby measure the depletion of the condensate and compare it with a theoretical estimate. We have measured the coherence length of the gas for systems with average occupation >1 and <1 per lattice site. PACS 05.30.Jp; 03.75.Kk; 03.75.Lm; 73.43.NqThis revised version was published in November 2004 due to a typesetting mistake in the abstract.     

Transition to 1D conduction with decreasing thickness of the crystals of TaS3 and NbSe3 quasi-1D conductors

It is found that, with decreasing thickness of the crystals of TaS₃ and NbSe₃ quasi-1D conductors, the dependences of the conductivity of these crystals on temperature and electric field change from the form typical of bulk samples to a nearly power law behavior typical of 1D electron systems.     

Charge-transfer states and optical absorption

The intensities of the Laporte-forbidden transitions in complexes like RhCl₆ ^3-, IrBr₆ ^2-, etc. are connected to the energies of the initial, final and charge-transfer states by the approximate relation, intensity α(E_f - E_i ) (E_C - E_f )^-2. This is due to the mixing in of the odd, bonding states into the even, anti-bonding ones through the vibrations of the complex. An analysis of the electronic states of these strongly covalent complexes and of the allowed, charge-transfer transitions is also presented. From this it is concluded that the dipole moment of the transitions is largely due to the presence of the charges in the anti-bonding states on the ligand due to covalent bonding.     

Dynamics of amplitude and phase mode and infrared absorption of linear conductors

The dynamics of the Amplitude and Phase mode in the incommensurate case is reduced to the dynamics of a diatomic molecule. Using this Hamiltonian, σ(ω) is given as a canonical average for a Penn model with fluctuating gap.     

Single atom transistor in a 1D optical lattice

We propose a scheme utilizing a quantum interference phenomenon to switch the transport of atoms in a 1D optical lattice through a site containing an impurity atom. The impurity represents a qubit which in one spin state is transparent to the probe atoms, but in the other acts as a single atom mirror. This allows a single-shot quantum nondemolition measurement of the qubit spin.     

Superfluid fermi gas in a 1D optical lattice

We calculate the superfluid transition temperature for a two-component 3D Fermi gas in a 1D tight optical lattice and discuss a dimensional crossover from the 3D to quasi-2D regime. For the geometry of finite size discs in the 1D lattice, we find that even for a large number of atoms per disc the critical effective tunneling rate for a quantum transition to the Mott insulator state can be large compared to the loss rate caused by three-body recombination. This allows the observation of the Mott transition, in contrast to the case of Bose-condensed gases in the same geometry.     

Measurement-induced disturbance and thermal negativity in 1D optical lattice chain

We study the measurement-induced disturbance (MID) in a 1D optical lattice chain with nonlinear coupling. Special attention is paid to the difference between the thermal entanglement and MID when considering the influences of the linear coupling constant, nonlinear coupling constant and external magnetic field. It is shown that MID is more robust than thermal entanglement against temperature T$T$ and external magnetic field B$B$, and MID may reveal more properties about quantum correlations of the system, which can be seen from the point of view that MID can be nonzero when there is no thermal entanglement and MID can detect the critical point of quantum phase transition at finite temperature.