arXiv subjects

Yue Yu

Publications and source records attributed to Yue Yu.

540 records · Page 30Linked to original sources

arXiv1999

Bosonization Based on Bethe Ansatz Equations and Spin-Charge Separation in the Hubbard Model with Finite U

We develop a bosonization approach for one-dimensional models based on Bethe ansatz equations. The operator formalism of the exact soluble models in the low energy limit provides a systematic method to calculate the asymptotic correlation functions. As examples with and without internal degrees of freedom, the Calogero-Sutherland (C-S) model and the repulsive Hubbard model are considered respectively. We verify that the low energy behavior of the C-S model is controlled by two classes of c=1 conformal field theories, depending on whether the C-S interactions are among bosons or among fermions. For the Hubbard model, we show the explicit charge-spin separation at low energy for arbitrary U>0. The low energy behavior of the system is described by the (semi-) direct product of two independent Virasoro algebras with c=1.

cond-mat.str-el↗

arXiv1999

Effective mass of composite fermion: a phenomenological fit in with anomalous propagation of surface acoustic wave

We calculate the conductivity associated with the anomalous propagation of a surface acoustic wave above a two-dimensional electron gas at $ν=1/2$. Murthy-Shankar's middle representation is adopted and a contribution to the response functions beyond the random phase approximation has been taken into account. We give a phenomenological fit for the effective mass of composite fermion in with the experimental data of the anomalous propagation of surface acoustic wave at $ν=1/2$ and find the phenomenological value of the effective mass is several times larger than the theoretical value $m_{th}^*=6ε/e^2l_{1/2}$ derived from the Hartree-Fock approximation. We compare our phenomenologically fitting composite fermion effective mass with those appeared in the measurements of the activation energy and the Shubnikov-de Haas effect and find that our result is fairly reasonable.

cond-mat.mes-hall↗

arXiv1999

From Composite Fermions to Calogero-Sutherland Model: Edge of Fractional Quantum Hall Liquid and the Dimension Reduction

We derive a microscopic model describing the low-lying edge excitations in the fractional quantum Hall liquid with $ν=\frac{ν^*} {\tildeϕν^*+1}$. For $ν^*>0$, it is found that the composite fermion model reduces to an SU$(ν^*)$ Calogero-Sutherland model in a dimension reduction, whereas it is not exact soluble for $ν^*<0$. However, the ground states in both cases can be found and the low-lying excitations can be shown the chiral Luttinger liquid behaviors. On the other hand, we shows that the finite temperature behavior of $G-T$ curve will deviate from the prediction of the chiral Luttinger liquid. We also point out that the suppression of the `spin' degrees of freedom agrees with very recent experiments by Chang et al. The two-boson model of Lee and Wen is described microscopically.

cond-mat.mes-hall↗

arXiv1999

A Microscopic Model of Edge States of Fractional Quantum Hall Liquid: From Composite Fermions to Calogero-Sutherland Model

Based on the composite fermion approach, we derive a microscopic theory describing the low-lying edge excitations in the fractional quantum Hall liquid with $ν=\frac{ν^*}{\tildeϕν^*+1}$. For $ν^*>0$, it is found that the composite fermion model reduces to an SU$(ν^*)$ Calogero-Sutherland model in the one-dimensional limit, whereas it is not exact soluble for $ν^*<0$. However, the ground states in both cases can be found and the low-lying excitations can be shown the chiral Luttinger liquid behaviors since a gap exists between the right- and left-moving sectors in each branch of the azimuthal excitations.

cond-mat.mes-hall↗

arXiv1999

Schwinger boson mean field theory of the Heisenberg Ferrimagnetic Spin Chain

The Schwinger boson mean field theory is applied to the quantum ferrimagnetic Heisenberg chain. There is a ferrimagnetic long range order in the ground state. We observe two branches of the low lying excitation and calculate the spin reduction, the gap of the antiferromagnetic branch, and the spin fluctuation at $T=0K$. These results agree with the established numerical results quite well. At finite temperatures, the long range order is destroyed because of the disappearance of the Bose condensation. The thermodynamic observables, such as the free energy, magnetic susceptibility, specific heat, and the spin correlation at $T>0K$, are calculated. The $Tχ_{uni}$ has a minimum at intermediate temperatures and the spin correlation length behaves as $T^{-1}$ at low temperatures. These qualitatively agree with the numerical results and the difference is small at low temperatures.

cond-mat.str-el↗

arXiv1999

Pseudogap phase in the U(1) gauge theory with incoherent spinon pairs

The pseudogap effect of underdoped high-$T_c$ superconductors is studied in the U(1) gauge theory of the t-J model including the spinon pairing fluctuation. The gauge fluctuation breaks the long range correlation between the spinon pairs. The pairing fluctuation, however, suppresses significantly the low-lying gauge fluctuations and leads to a stable but phase incoherent spin gap phase which is responsible for the pseudogap effects. This quantum disordered spin gap phase emerges below a characteristic temperature $T^{*}$ which is determined by the effective potential for the spinon pairing gap amplitude. The resistivity is suppressed by the phase fluctuation below $% T^{*}$, consistent with experiments.

cond-mat.str-el↗

arXiv1998

Phenomenological Understanding of a Transport Regime with Reflection Symmetry in the Quantum Hall System in a Composite Fermion Picture

In this paper, we present a phenomenological picture based on the composite fermion theory, in responding to the recent discovery by Shahar et al. of a new transport regime near the transition from a $ν=1$ quantum Hall liquid to a Hall insulator(ref[8]). In this picture, the seemingly unexpected reflection symmetry in the longitudinal resistivity $ρ_{xx}$ can be understood clearly as due to the symmetry of the gapful excitations which dominate $σ_{xx}$ across the transition, and the abrupt change in $σ_{xy}$ at the transition. The parameter $α$ in the linear fit of $ν_0(T)$ in ref[8] is also given a simple physical meaning and the effective mass can be calculated from $α$, which gives a reasonable value of several electron band mass. When taking into account the result of network model, the almost invariant Hall resistivity $ρ_{xy}$ across the transition is also well-understood.

cond-mat.mes-hall↗

arXiv1998

A Systematic Improvement for Calculation to Conductivity in Anomalous Propagation of Surface Acoustic Wave at $ν={1/2}$

We report a systematic improvement to calculate the conductivity which associates to the anomaly of the propagation of surface acoustic waves at $ν={1/2}$ above a two-dimensional electron gas. We try to resolve the discrepancy between theoretical and experimental values for the magnitude of $σ_{xx}(q)$ by considering the contribution to the response functions from the self-interaction among the Chern-Simons gauge fluctuations.

cond-mat↗

arXiv1997

Comparative Study of the Insulator-Hall Liquid-Insulator Transitions: Composite Boson Picture vs Composite Fermion Picture

Based on a newly advanced phenomenological understanding of the high-field insulator- Hall liquid transition in a composite fermion picture, we extend its composite boson counterpart to the analysis of the low-field insulator-Hall liquid transition. We thus achieve a comparative study of these two transitions. In this way, the similar reflection symmetries in filling factors in both transitions are understood consistently as due to the symmetry of the gapful excitations which dominate $σ_{xx}$ across the transitions, and the abrupt change in $σ_{xy}$ at the transitions. The substantially different characteristic energy scales involved in these two transitions can be attributed to the differences in critical filling factors $ν_c$ and the effective masses. The opposite temperature-dependences of the critical longitudinal resistivities are also well-understood, which can be traced to the opposite statistical natures of the composite fermion and the composite boson. We also give a tentative discussion of the zero-temperature dissipative conductivity. The above results are supported by a recent experiment (cond-mat/9708239).

cond-mat.mes-hall↗

arXiv1997

Phase Structures of Magnetic Impurity Models with Two-Body Hybridization

The most general model with a magnetic impurity coupled to hybridizing and screening channels of a conduction band is considered. The partition function of the system is asymptotically equivalent to that of the multi-component kink plasma with a weak external field. The scaling properties of the models for finite $U$ are sketched by using the Anderson-Yuval-Hamann-Cardy poor man's scaling theory. We point out that it is proper to include a two-body hybridization in order to obtain correct renormalization flows. The phase structures are studied graphically for the general model and various reduced models. A Fermi-non-Fermi liquid phase transition is found for all the models. We also show all possible phases with different finite temperature behaviors though they have the same Fermi liquid fixed point at low temperature. We also discuss the fixed point behaviors in the mixed valence state regime.

cond-mat↗

arXiv1997

Generalized Variable Range Hopping Near Two-Dimensional Metal-Insulator Transitions

In an attempt to understand quantitatively the remarkable discoveries of metal-insulator transitions in two-dimensional systems, we generalize Mott's variable range hopping theory to the situation with strong Coulomb interaction. In our formulation, the Gaussian form is adopted into the expression of the hopping probability, and the effect of Coulomb gap is also considered. After taking account of the newly proposed scaling consideration, we produce the dynamical and localization length exponents, which are consistent with the experiments. We then clarify the physical content of our formulation and explain the universality of the localization length exponent suggested by a series of experiments. We also discuss the general scaling function of both temperature and electrical field on the insulating side of the transition.

cond-mat.str-el↗

arXiv1997

Effective Mass of Composite Fermions and Fermionic Chern-Simons Theory in Temporal Gauge

The definitions of the effective mass of the composite fermion are discussed for the half-filled Landau level problem. In a recent work, Shankar and Murthy show a finite effective mass of the composite fermion by a canonical transformation while the perturbative calculation gives the logarithmic divergence of the effective mass at the Fermi surface. We will emphasize that the different definition of the effective mass has the different physical processes. The finite one could be defined for any momentum of the composite fermion while the divergence only appears at the Fermi surface. We work with the standard Halperin-Lee-Read model but in the temporal gauge. The advantage of this gauge to be employed is that the finite effective mass could be calculated in the Hartree-Fock approximation. Furthermore, it is precisely equal to the result that Shankar and Murthy obtained which is well-fit with the numerical calculation from the ground state energy analysis and a semi-classical estimation. However, if we consider the random phase approximation, one sees that the divergence of the effective mass of the quasiparticle at the Fermi surface emerges again no matter that we work on the temporal or Coulomb gauges. We develop an effective theory where the finite effective mass serves as a `bare' effective mass and show that the same divergence of the RPA effective mass. On the other hand, the correct behavior of the response functions in the small band mass limit could be seen clearly in the temporal gauge since there is a self-interaction among the magnetoplasmons.

cond-mat.mes-hall↗

arXiv1997

Temperature-dependent crossover in fractional quantum Hall edges in the presence of Coulomb interaction

Based on a newly derived microscopic fractional quantum Hall edge model, we study its thermodynamics at finite temperature. For the dressed energy spectrum a critical energy scale determined by the temperature exists, below which the refractive dispersion which is essential to the model's bosonization to a Luttinger liquid is smeared. According to this observation, a temperature-dependent crossover picture is proposed, and applied to the analysis of a recent tunneling experiment in comparison with the standard Luttinger liquid theory, and a better fit to the features of the measured conductance-temperature curve is achieved. We also consider the role of the Coulomb interaction in the thermodynamics and find that a crossover exists during which the influence of the Coulomb interaction is suppressed with the increase of temperature.

cond-mat.mes-hall↗

arXiv1997

The Microscopic Picture of Chiral Luttinger Liquid: Composite Fermion Theory of Edge States

We derive a microscopic theory of the composite fermions describing the low-lying edge excitations in the fractional quantum Hall liquid. Using the composite fermion transformation, one finds that the edge states of the $ν=1/m$ system in a disc sample are described by, in one dimensional limit, the Calogero-Sutherland model with other interactions between the composite fermions as perturbations. It is shown that a large class of short-range interactions renormalize only the Fermi velocity while the exponent $g=ν=1/m$ is invariant under the condition of chirality. By taking the sharp edge potential into account, we obtain a microscopic justification of the chiral Luttinger liquid model of the fractional quantum Hall edge states. The approach applied to the $ν=1/m$ system can be generalized to the other edge states with odd denominator filling factors.

cond-mat.mes-hall↗

arXiv1997

The Microscopic Model of Composite Fermion Type Excitations for ν=1/m Edge States

We derive a microscopic theory of the composite fermion type quasiparticles describing the low-lying edge excitations in the fractional quantum Hall liquid with $ν=1/m$. 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 shows 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.

cond-mat↗

arXiv1996

Mean-Field and Perturbation Theory of Vortex-like Composite Fermions

We develop a field theory for a partially filled Landau level based on composite fermions with a finite vortex core, whose mean-field states are exactly those described by well-tested trial wave functions. Despite non-orthogonality of free composite-fermion states and non-Hermiticity of the mean-field Hamiltonian, a consistent perturbation theory is formulated and the mean-field Fermi sea at half filling is shown to be stable. While the low-energy and long-distance physics is the same as in the Chern-Simons fermion theory, new physics is expected to show up for larger wave vectors.

cond-mat↗

arXiv1995

Bosonization of One-Dimensional Exclusons and Characterization of Luttinger Liquids

We achieve a bosonization of one-dimensional ideal gas of exclusion statistics $λ$ at low temperatures, resulting in a new variant of $c=1$ conformal field theory with compactified radius $R=\sqrt{1/λ}$. These ideal excluson gases exactly reproduce the low-$T$ critical properties of Luttinger liquids, so they can be used to characterize the fixed points of the latter. Generalized ideal gases with mutual statistics and non-ideal gases with Luttinger-type interactions have also similar behavior, controlled by an effective statistics varying in a fixed-point line.

cond-mat↗

arXiv1995

Scaling Law for a Magnetic Impurity Model with Two-Body Hybridization

We consider a magnetic impurity coupled to the hybridizing and screening channels of a conduction band. The model is solved in the framework of poor man's scaling and Cardy's generalized theories. We point out that it is important to include a two-body hybridization if the scaling theory is to be valid for the band width larger than $U$. We map out the boundary of the Fermi-non-Fermi liquid phase transition as a function of the model parameters.

cond-mat↗