arXiv subjects

Jianhui Dai

Publications and source records attributed to Jianhui Dai.

81 records · Page 5Linked to original sources

arXiv2008

The Bose-Fermi Kondo model with a singular dissipative spectrum: Exact solutions and their implications

Quantum dissipation induces a critical destruction of a Kondo screened state, which is of interest in the contexts of quantum critical heavy fermion metals and magnetic nanostructures. The sub-ohmic Bose-Fermi Kondo model provides a setting to study this effect. We find that this many-body problem is exactly solvable when the spectrum of the dissipative bosonic bath, J(ω), is singular, corresponding to J(τ)=const.. We determine the local spin correlation functions, showing that the singular LONGITUDINAL fluctuations of the bosonic bath dominate over the transverse ones. Our results provide evidence that the local quantum critical solution, derived within the extended dynamical mean field approach to the Kondo lattice model, has a zero residual entropy.

cond-mat.str-el↗

arXiv2005

Quantum Nonlinear Sigma Model for Arbitrary Spin Heisenberg Antiferromagnets

In this Letter, we derive a quantum nonlinear sigma model (QNLSM) for quantum Heisenberg antiferromagnets (QHA) with arbitrary S (spin) values. A upper limit of the low temperature is naturally carried out for the reliability of the QNLSM. The S dependence of the effective coupling constant and the spin wave velocity in the QNLSM are also obtained explicitly. The resulting spin wave velocity for 2-dim spin-1/2 QHA highly concurs with the experimental data of high $T_c$ compound La2CuO4. The predicted correlation lengths for 2d QHA and spin-gap magnitudes for 1d QHA also agrees with the accurate numerical results.

cond-mat.str-el↗

arXiv2005

Quantum Monte Carlo Simulations on S=1/2 antiferromagnetic-Ferromagnetic Random Alternating spin chain

The S=1/2 Heisenberg chain with bond alternation and randomness of antiferromagnetic (AFM) and ferromagnetic (FM) interactions is investigated by quantum Monte Carlo simulations of loop/cluster algorithm. Our results have shown interesting finite temperature magnetic properties of this model. The relevance of our study to the observed results of the material (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$ is discussed.

cond-mat.dis-nn↗

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↗

arXiv2000

Absence of overscreened Kondo effect in ferromagnetic host

We study the low temperature behavior of a boundary magnetic impurity S'=1/2 in an open ferromagnetic Takhatajian-Babujian spin-S chain. For antiferromagnetic Kondo coupling, it is show via Bethe ansatz solution that the impurity spin is always locked into the critical behavior the bulk. At low temperature, a local composite of spin S-1/2 forms near the impurity site and its contribution to specific heat is of simple power law T^{1/2}. The absence of overscreened Kondo effect is due to the large correlation length of host spins which is divergent near the quantum critical point.

cond-mat.str-el↗

arXiv2000

Logarithmic corrections from ferromagnetic impurity ending bonds of open antiferromagnetic host chains

We analyze the logarithmic corrections due to ferromagnetic impurity ending bonds of open spin 1/2 antiferromagnetic chains, using the density matrix renormalization group technique. A universal finite size scaling $\sim {\frac 1 {L \log L}}$ for impurity contributions in the quasi-degenerate ground state energy is demonstrated for a zigzag spin 1/2 chain at the critical next nearest neighbor coupling and the standard Heisenberg spin 1/2 chain, in the long chain limit. Using an exact solution for the latter case it is argued that one can extract the impurity contributions to the entropy and specific heat from the scaling analysis. It is also shown that a pure spin 3/2 open Heisenberg chain belongs to the same universality class.

cond-mat.str-el↗

arXiv1999

Kondo effect in a quantum critical ferromagnet

We study the Heisenberg ferromagnetic spin chain coupled with a boundary impurity. Via Bethe ansatz solution, it is found that (i) for J>0, the impurity spin behaves as a diamagnetic center and is completely screened by 2S bulk spins in the ground state, no matter how large the impurity spin is; (ii) The specific heat of the local composite (impurity plus 2S bulk spins which form bound state with it) shows a simple power law $C_{loc}\sim T^{3/2}$. (iii)For J<0, the impurity is locked into the critical behavior of the bulk. Possible phenomena in higher dimensions are discussed.

cond-mat.str-el↗

arXiv1998

Exactly solvable Kondo problem in the open $t-J$ chains

We study the problem of a boundary magnetic impurity coupled with the solvable $t-J$ chains. Our model provides a good start point to understand the Kondo problem in a Luttinger liquid as well as in a strongly correlated host. The Kondo coupling constant $J$ can take arbitrary values, which allows us to study the ferromagnetic and antiferromagnetic Kondo problems simultaneously. It is shown that both the Kondo coupling and the scalar potential effectively reconcile the spin dynamics at low temperatures. Generally, the impurity spin is split into two ghost spins via coupling effect. The residual entropy, which can be exactly derived for the present model, is strongly interaction-dependent. This hints the local spin configuration is very complicated and very different from that in the conventional Kondo problem. An unscreening phenomenon in the antiferromagnetic regime is found, which reveals the impurity potential plays an important role for the Kondo problem in a strongly correlated host. The low temperature specific heat is calculated in the framework of local Landau-Luttinger liquid theory.

cond-mat.str-el↗

arXiv1997

Exact Results for a Kondo Problem in One Dimensional t-J Model

We propose an integrable Kondo problem in a one-dimensional (1D) $t-J$ model. With the open boundary condition of the wave functions at the impurity sites, the model can be exactly solved via Bethe ansatz for a class of $J_{R,L}$ (Kondo coupling constants) and $V_{L,R}$ (impurity potentials) parametrized by a single parameter $c$. The integrable value of $J_{L,R}$ runs from negative infinity to positive infinity, which allows us to study both the ferromagnetic Kondo problem and antiferromagnetic Kondo problem in a strongly correlated electron system. Generally, there is a residual entropy for the ground state, which indicates a typical non-Fermi liquid behavior.

cond-mat.str-el↗