arXiv subjects

Yue Yu

Publications and source records attributed to Yue Yu.

At least 505 records · Page 28Linked to original sources

arXiv2006

Interaction broadening of Wannier functions and Mott transitions in atomic BEC

Superfluid to Mott-insulator transitions in atomic BEC in optical lattices are investigated for the case of number of atoms per site larger than one. To account for mean field repulsion between the atoms in each well, we construct an orthogonal set of Wannier functions. The resulting hopping amplitude and on-site interaction may be substantially different from those calculated with single-atom Wannier functions. As illustrations of the approach we consider lattices of various dimensionality and different mean occupations. We find that in three-dimensional optical lattices the correction to the critical lattice depth is significant to be measured experimentally even for small number of atoms. Finally, we discuss validity of the single band model.

cond-mat.soft↗

arXiv2006

Electron-like and photon-like excitations in an ultracold Bose-Fermi atom mixture

We show that the electron-like and photon-like excitations may exist in a three-dimensional Bose-Fermi Hubbard model describing ultracold Bose-Fermi atom mixtures in optical lattices. In a Mott insulating phase of the Bose atoms, these excitations are stabilized by an induced repulsive interaction between 'electrons' if the Fermi atoms are nearly half filling. We suggest to create 'external electric field' so that the electron-like excitation can be observed by measuring the linear density-density response of the 'electron' gas to the 'external field' in a time-of-flight experiment of the mixture. The Fermi surface of the 'electron' gas may also be expected to be observed in the time-of-flight.

cond-mat.other↗

arXiv2005

Short-range coherence of a lattice Bose atom gas in the Mott insulating phase

We study the short-range coherence of ultracold lattice Bose gases in the Mott insulating phase. We calculate the visibility of the interference pattern and the results agree quantitatively with the recent experimental measurement [Phys. Rev. Lett. 95, 050404 (2005)]. The visibility deviation from the inversely linear dependence on the bare on-site interaction U_0 is explained both in smaller and larger U_0. For a smaller U_0, it comes from a second order correction. For a larger U_0, except the breakdown of adiabaticity as analyzed by Gerbier et al, there might be another source to cause this deviation, which is the diversity between $U_0$ determined by the single atom Wannier function and the effective on site interaction U_eff for a multi-occupation per site.

cond-mat.other↗

arXiv2005

'Electron' and 'photon' emerging from supersymmetric neutral particles: A possible realization in ultracold Bose-Fermi atom mixture

We show that the 'electron' and 'photon' can emerge from a supersymmetric Hubbard model which is a non-relativistic theory of the neutral particles. The Higgs boson and 'photon' may not appear in the same phase of the phase diagram. In a Mott insulator phase of the boson, the 'electron' and 'photon' are stablized by an induced Coulomb interaction between 'electrons'. This emergent mechanism may be 'realized' in an ultracold Bose-Fermi atom mixture except the long range Coulomb interaction is repalced by a nearest neighbor one. We suggest to create 'external electric field' so that the 'electron' excitation can be observed by measuring the linear density-density response of the 'electron' gas to the 'external field' in the time flying experiment of the mixture. The Fermi surface of the 'electron' gas may also be expected to be observed in the time flying.

cond-mat.other↗

arXiv2005

Anisotropic transport for $ν=2/5$ FQH state at intermediate magnetic field

The $ν=2/5$ state is spin-unpolarized at weak magnetic field and fully polarized at strong field. At intermediate field, a plateau of half the maximal polarization is observed. We study this phenomenon in the frame of composite fermion theory. Due to the mixing of the composite fermion Landau levels, the unidirectional charge/spin density wave state of composite fermions is lower in energy than the Wigner crystal. It means that transport anisotropy, similar to those for electrons in higher Landau levels at half fillings, may take place at this fractional quantum Hall state when the external magnetic field is in an appropriate range. When the magnetic field is tilted an angle, the easy transport direction is perpendicular to the direction of the in-plane field. Varying the partial filling factor of composite fermion Landau level from 0 to 1, we find that the energy minimum occurs in the vicinity of one-half.

cond-mat.mes-hall↗

arXiv2005

Interaction of a surface acoustic wave with a two-dimensional electron gas

When a surface acoustic wave propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coefficient is calculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is largely dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.

cond-mat.mes-hall↗

arXiv2005

One-band Hubbard model with hopping asymmetry and the effective theory at finite U: Phase diagram and metal-insulator transition

We study the one-band Hubbard model at half filling with hopping asymmetry and its effective model at finite but large U up to the second order of tmix/U. Two variational wave functions, the resonating valence bond (RVB) wave function and antiferromagnetic (AF) RVB coexisted wave function, are studied by variational Monte Carlo method on L*L square lattices up to L=12. Based on these two wave functions, the phase diagrams for both models are presented. For the Hubbard model, we find that there is a metal-insulator transition when the hopping parameter tmix which changes the local double occupant vanishes while only a metal-insulator crossover is explored for any finite tmix. For the effective model in which the perturbation expansion is up to the second order of tmix/U, a clear metal-insulator transition can be identified for both variational wave functions and the phase diagram can be drawn accordingly. In both models, we find that the systems are dominated by AF-RVB wave function when U is large while the RVB wave function is favored when U is small.

cond-mat.str-el↗

arXiv2005

Phase diagram of ultracold atoms on optical lattice: Comparative study to slave fermion and slave boson for Bose Hubbard modelPhase diagram of ultracold atoms in optical lattices: Comparative study of slave fermion and slave boson approaches to Bose-Hubbard model

We perform a comparative study of the finite temperature behavior of ultracold Bose atoms in optical lattices by the slave fermion and the slave boson approaches to the Bose Hubbard model. The phase diagram of the system is presented. Although both approaches are equivalent without approximations, the mean field theory based on the slave fermion technique is quantitatively more appropriate. Conceptually, the slave fermion approach automatically excludes the double occupancy of two identical fermions on the same lattice site. By comparing to known results in limiting cases, we find the slave fermion approach better than the slave boson approach. For example, in the non-interacting limit, the critical temperature of the superfluid-normal liquid transition calculated by the slave fermion approach is closer to the well-known ideal Bose gas result. At zero-temperature limit of the critical interaction strength from the slave fermion approach is also closer to that from the direct calculation using a zero-temperature mean field theory.

cond-mat.str-el↗

arXiv2005

Incompressible excitonic superfluid of ultracold Bose atoms in an optical lattice: a new superfluid phase in the one-component Bose-Hubbard model

We predict that a new superfluid phase, the incompressible excitonic superfluid (IESF), in the phase diagram of ultracold Bose atoms in $d>1$ dimensional optical lattices, which is caused by the spontaneous breaking of the symmetry of translation of the lattice. Within mean field theory, the critical temperature of the phase transition from this IESF to the normal fluid (NF) is calculated and the triple-critical point of the three phases is determined. We also investigate both configuration and gauge field fluctuations and show the IESF state is stable against these fluctuations. We expect this IESF phase can be experimentally observed by loading cold Bose atoms into a two-dimensional lattice where the atom filling fraction deviates slightly from exact commensurations. The signatures distinguishing this IESF from the common atom superfluid (ASF) are that (i) the critical temperature of the IEST/NF transition is independent of interaction, unlike the ASF/NF transition; (ii) the IESF is incompressible while the ASF is compressible.

cond-mat.stat-mech↗

arXiv2004

Gapped spin liquid states in a one-dimensional Hubbard model with antiferromagnetic exchange interaction

We study the phase diagram of a one-dimensional extended Hubbard model with antiferromagnetic exchange interaction analytically and numerically. The bosonization and transfer-matrix renormalization group methods are used in the corresponding coupling regimes. At half-filling, the system is a Mott insulator with a finite spin excitation gap if the on-site Coulomb repulsion is fairly smaller than the antiferromagnetic exchange J. This Mott-insulator is characterized by the bond-charge-density-wave order or spontaneously dimerization. In the weak-coupling regime where the spin-charge separation holds approximately, the critical point separating the gapless and gapped spin liquid phases is U_c\sim J/2. However, as J increases, the spin-charge couplings become important and the critical point U_c is significantly suppressed and eventually tends to zero as J\to \infty. Away from half-filling, the charge gap completely collapses but the spin gap persists.

cond-mat.str-el↗

arXiv2004

Temperature dependence of the conductivity of the electronic crystal

We study the temperature dependence of the conductivity of the 2D electronic solid. In realistic samples, a domain structure forms in the solid and each domain randomly orients in the absence of the in-plane field. At higher temperature, the electron transport is governed by thermal activation form of $σ_{xx}(T)\propto e^{-Δ_0/k_BT}$. The impurities will localize the electron states along the edges of the crystal domains. At sufficient low temperature, another transport mechanism called Mott's variable range hopping mechanism, similar to that in a disorder insulator takes effect. We show that as the temperature decreases, a crossover from the fixed range hopping of the transport to the variable range hopping of transport in the 2D electron system may be experimentally observed.

cond-mat.mes-hall↗

arXiv2004

Density-induced reorientation of the stripe at half-filled high Landau levels

The effect of a unidirectional periodic potential on the orientation of the stripe state is studied for the two-dimensional electron system at half-filled high Landau levels. By considering a quantum well with two electric subbands, it is found that the stripe is parallel to the external potential for weak modulation and is orthogonal for strong modulation. In the intermediate range, the orientation of the stripe changes from orthogonal to parallel as the electron density is increased. This result explains the recent experiment performed by J. Zhu {\it et al} that the anisotropy axis at half-filled high Landau levels rotates by $90^0$ by increasing the electron density. It also supports the suggestion that the stripes is pinned by the native surface morphology at the interface of the heterojunction.

cond-mat.mes-hall↗

arXiv2004

Luttinger liquid with strong spin-orbital coupling and Zeeman splitting in quantum wires

We study a one-dimensional interacting electron gas with the strong Rashba spin-orbit coupling and Zeeman splitting in a quantum well. A bosonization theory is developed for this system. The tunneling current may deviate from a simple power law which is that in an ordinary Luttinger liquid. The microscopic interacting coupling and the spin-orbital parameter may be measured by varying the external magnetic field in the tunneling experiment.

cond-mat.str-el↗

arXiv2004

Time-evolution stability of order parameters and phase diagrams of bosons on optical lattice

Stemming from the Heisenberg equations of motion, we study the time-evolution stability of the order parameters for the cold atoms on optical lattices. The requirement of this stability of the order parameters endows the phase diagram with a fruitful structure in the superfluid phase. For the one-component Bose-Hubbard model, we see that this stability of order parameter leads to a physically receivable phase diagram. For two-component bosons, we show that the molecules are preformed in the atomic superfluid and then condenses into a molecular superfluid phase at a critical repulsive inter-species interaction, which resembles the pre-pairing mechanism in high $T_c$ superconductor of Cu-O cuprates.

cond-mat.soft↗

arXiv2003

Comments on `Rashba precession in quantum wire with interaction'

In a recent Rapid Communication (Phys. Rev. B {\bf 63}, 121210(R) (2001)), Haüsler showed that the interaction between electrons in quantum wires may enhance the persistent spin current arising from Rashba spin-orbital coupling. In this Comments, we would like to point out that this 'enhancement' comes from a misunderstanding to the boosting persistent current in the Luttinger liquid theory. A correct calculation will not give such an enhancement of the persistent spin current. Meanwhile, we provide a Luttinger liquid theory with Rashba spin-orbital interaction by bosonization, which may show how the Rashba precession is in a Luttinger liquid.

cond-mat.mes-hall↗

arXiv2003

Co-ordination between Rashba spin-orbital interaction and space charge effect and enhanced spin injection into semiconductors

We consider the effect of the Rashba spin-orbital interaction and space charge in a ferromagnet-insulator/semiconductor/insulator-ferromagnet junction where the spin current is severely affected by the doping, band structure and charge screening in the semiconductor. In diffusion region, if the the resistance of the tunneling barriers is comparable to the semiconductor resistance, the magnetoresistance of this junction can be greatly enhanced under appropriate doping by the co-ordination between the Rashba effect and screened Coulomb interaction in the nonequilibrium transport processes within Hartree approximation.

cond-mat.mes-hall↗

arXiv2003

Electron space charge effect on spin injection into semiconductors

We consider spin polarized transport in a ferromagnet-insulator/semiconductor/insulator-ferromagnet (F1-I-S-I-F2) junction. We find that the spin current is strongly dependent on the spin configurations, the doping and space charge distribution in the semiconductor. When the ferromagnet-semiconductor interface resistance is comparable to the semiconductor resistance, the magnetoresistance ratio of this junction can be greatly enhanced under appropriate doping when the space charge effect in the nonequilibrium transport processes is taken into consideration.

cond-mat.mes-hall↗

arXiv2003

From Hubbard model to t-J-U model: a canonical transformation formalism, the metal-insulator transition and mean-field state

We prove that the t-J-U model can be deduced from the Hubbard model at a large but finite U by a canonical transformation. We argue that the system may have a metal-insulator transition at a critical on-site Coulomb interaction whose value, however, is smaller than that in previous calculations in which the kinetic energy has a double counting. In a mean field theory and a special choice of the parameters, we show that the metallic state may be equivalent to the gossamer superconducting state proposed by Laughlin recently.

cond-mat.str-el↗