arXiv subjects

Jinwu Ye

Publications and source records attributed to Jinwu Ye.

82 records · Page 5Linked to original sources

arXiv1998

Coulomb interactions at quantum Hall critical points of systems in a periodic potential

We study the consequences of long-range Coulomb interactions at the critical points between integer/fractional quantum Hall states and an insulator. We use low energy theories for such transitions in anyon gases in the presence of an external periodic potential. We find that Coulomb interactions are marginally irrelevant for the integer quantum Hall case. For the fractional case, depending upon the anyon statistics parameter, we find behavior similar to the integer case, or flow to a novel line of fixed points with exponents $z=1$, $ν> 1$ stable against weak disorder in the position of the critical point, or run-away flow to strong coupling.

cond-mat.mes-hall↗

arXiv1998

On two channel flavor anisotropic and one channel compactified Kondo models

We reinvestigate the two channel flavor anisotropic model (2CFAK) and one channel compacitified Kondo model (1CCK). For these two models, all the possible fixed points and their symmetries are identified; the finite size spectra, the electron conductivity and pairing susceptibility are calculated. It is shown that the only non-fermi liquid (NFL) fixed point of the 2CFAK is the NFL of the two channel Kondo model (2CK) with the symmetry $O(3) \times O(5)$. Any flavor anisotropies between the two channels drive the system to the fermi-liquid (FL) fixed point with the symmetry $O(4) \times O(4)$ where one of the two channels suffers the phase shift π/2 and the other remains free. The NFL fixed point of the 1CCK has the symmetry $O(3) \times O(1)$ and has the same thermodynamics as the NFL fixed point of the 2CK. However, in contrast to the 2CK, its conductivity shows $T^{2}$ behavior and there is no pairing susceptibility divergence. Any anisotropies between the spin and isospin sectors drive the system to the FL fixed point with the symmetry O(4) where the electrons suffer the phase shift π/2. The connection and differences between the two models are explicitly demonstrated. The recent conjectures and claims on the NFL behaviors of the two models are commented.

cond-mat.str-el↗

arXiv1998

Solution of effective Hamiltonian of impurity hopping between two sites in a metal

We analyze in detail all the possible fixed points of the effective Hamiltonian of a non-magnetic impurity hopping between two sites in a metal obtained by Moustakas and Fisher(MF). We find a line of non-fermi liquid fixed points which continuously interpolates between the 2-channel Kondo fixed point(2CK) and the one channel, two impurity Kondo (2IK) fixed point. The additional non-fermi liquid fixed point found by MF has the same symmetry as the 2IK, The system is shown to flow to a line of fermi-liquid fixed points which continuously interpolates between the non-interacting fixed point and the 2 channel spin-flavor Kondo fixed point (2CSFK) discussed by the author previously. The effect of particle-hole symmetry breaking is discussed. The effective Hamiltonian in the external magnetic field is analysed. The scaling functions for the physical measurable quantities are derived in the different regimes; their predictions for the experiments are given. Finally the implications are given for a non-magnetic impurity hopping around three sites with triangular symmetry discussed by MF.

cond-mat.str-el↗

arXiv1997

Solution of two channel spin-flavor Kondo model

We investigate a model where an impurity couples to both the spin and the flavor currents of the two channel conduction electrons. This model can be used as a prototype model of a magnetic impurity tunneling between two sites in a metal and of some heavy fermion systems where the ground state of the impurity has a fourfold degeneracy. The system is shown to flow to a doubly degenerate non fermi-liquid(NFL) fixed point; the thermodynamic quantities show NFL behaviors, but the transport quantities show fermi liquid (FL) behaviors . A spin-flavor coupling double tensor term is shown to drive the system to one of the two singlet FL fixed points. The relation with SU(4) Coqblin-Schrieffer model is studied. The implications on the possible experiments are given.

cond-mat.str-el↗

arXiv1997

Abelian bosonization approach to quantum impurity problems

Using Abelian Bosonization, we develop a simple and powerful method to calculate the correlation functions of the two channel Kondo model and its variants. The method can also be used to identify all the possible boundary fixed points and their maximum symmetry, to calculate straightforwardly the finite size spectra, to demonstrate the physical picture at the boundary explicitly. Comparisons with Non-Abelian Bosonization method are made. Some fixed points corresponding to 4 pieces of bulk fermions coupled to s=1/2 impurity are listed.

cond-mat.str-el↗

arXiv1996

On Emery-Kivelson line and universality of Wilson ratio of spin anisotropic Kondo model

Yuval-Anderson's scaling analysis and Affleck-Ludwig's Conformal Field Theory approach are applied to the $k$ channel {\em spin anisotropic} Kondo model. Detailed comparisons with the available Emery-Kivelson's Abelian Bosonization approaches are made. It is shown that the EK line exists for any $k$, although it can be mapped to free fermions only when $k=1$ or $2$. The Wilson ratio is universal if $k=1$ or $2$, but {\em not} universal if $k>2$. The leading low temperature correction to the electron resistivity is {\em not} affected by the spin anisotropy for {\em any} $k$. A new universal ratio for $k>2$ is proposed to compare with experiments.

cond-mat↗

arXiv1994

Theory of Two-Dimensional Quantum Heisenberg Antiferromagnets with a Nearly Critical Ground State

We present the general theory of clean, two-dimensional, quantum Heisenberg antiferromagnets which are close to the zero-temperature quantum transition between ground states with and without long-range Néel order. For Néel-ordered states, `nearly-critical' means that the ground state spin-stiffness, $ρ_s$, satisfies $ρ_s \ll J$, where $J$ is the nearest-neighbor exchange constant, while `nearly-critical' quantum-disordered ground states have a energy-gap, $Δ$, towards excitations with spin-1, which satisfies $Δ\ll J$. Under these circumstances, we show that the wavevector/frequency-dependent uniform and staggered spin susceptibilities, and the specific heat, are completely universal functions of just three thermodynamic parameters. Explicit results for the universal scaling functions are obtained by a $1/N$ expansion on the $O(N)$ quantum non-linear sigma model, and by Monte Carlo simulations. These calculations lead to a variety of testable predictions for neutron scattering, NMR, and magnetization measurements. Our results are in good agreement with a number of numerical simulations and experiments on undoped and lightly-doped $La_{2-δ} Sr_δCu O_4$.

cond-mat↗

arXiv1992

Gapless Spin-Fluid Ground State in a Random Quantum Heisenberg Magnet

We examine the spin-$S$ quantum Heisenberg magnet with Gaussian-random, infinite-range exchange interactions. The quantum-disordered phase is accessed by generalizing to $SU(M)$ symmetry and studying the large $M$ limit. For large $S$ the ground state is a spin-glass, while quantum fluctuations produce a spin-fluid state for small $S$. The spin-fluid phase is found to be generically gapless - the average, zero temperature, local dynamic spin-susceptibility obeys $\barχ (ω) \sim \log(1/|ω|) + i (π/2) \mbox{sgn} (ω)$ at low frequencies. This form is identical to the phenomenological `marginal' spectrum proposed by Varma {\em et. al.\/} for the doped cuprates.

cond-mat↗

arXiv1992

A Solvable Spin-Glass of Quantum Rotors

We examine a model of $M$-component quantum rotors coupled by Gaussian-distributed random, infinite-range exchange interactions. A complete solution is obtained at $M=\infty$ in the spin-glass and quantum-disordered phases. The quantum phase transition separating them is found to possess logarithmic violations of scaling, with no further modifications to the leading critical behavior at any order in $1/M$; this suggests that the critical properties of the transverse-field Ising model (believed to be identical to the $M\rightarrow 1$ limit) are the same as those of the $M=\infty$ quantum rotors.

cond-mat↗

arXiv1992

Universal quantum critical dynamics of two-dimensional antiferromagnets

The universal dynamic and static properties of two dimensional antiferromagnets in the vicinity of a zero-temperature phase transition from long-range magnetic order to a quantum disordered phase are studied. Random antiferromagnets with both Néel and spin-glass long-range magnetic order are considered. Explicit quantum-critical dynamic scaling functions are computed in a 1/N expansion to two-loops for certain non-random, frustrated square lattice antiferromagnets. Implications for neutron scattering experiments on the doped cuprates are noted.

cond-mat↗