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Baowen Li

Publications and source records attributed to Baowen Li.

At least 199 records · Page 11Linked to original sources
arXiv2005

Thermal Conductivity of Nanotubes Revisited: Effects of Chirality, Isotope Impurity, Tube Length, and Temperature

We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality, isotope impurity, tube length and temperature by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also found that the tube length dependence of thermal conductivity is different for nanotubes of different radius at different temperatures.

cond-mat.mes-hall↗
arXiv2005

Interface thermal resistance between dissimilar anharmonic lattice

We study interface thermal resistance (ITR) in a system consisting of two dissimilar anharmonic lattices exemplified by Fermi-Pasta-Ulam (FPU) model and Frenkel-Kontorova (FK) model. It is found that the ITR is asymmetric, namely, it depends on how the temperature gradient is applied. The dependence of the ITR on the coupling constant, temperature, temperature difference, and system size are studied. Possible applications in nanoscale heat management and control are discussed.

cond-mat.dis-nn↗
arXiv2005

Uniform semiclassical approach to fidelity decay in the deep Lyapunov regime

We use the uniform semiclassical approximation in order to derive the fidelity decay in the regime of large perturbations. Numerical computations are presented which agree with our theoretical predictions. Moreover, our theory allows to explain previous findings, such as the deviation from the Lyapunov decay rate in cases where the classical finite-time instability is non-uniform in phase space.

quant-ph↗
arXiv2005

Modification to the pre-factor of the semiclassical propagator

We modify the pre-factor of the semiclassical propagator to improve its efficiency in practical implementations. The new pre-factor represents the smooth portion of an orbit's contribution, and leads to fast convergence in numerical calculations. As an illustration of the accuracy and efficiency of the resultant propagator, we numerically calculate overlaps between quantum and semiclassical wave functions, as well as low-lying spectrum density in a 10-dimensional system contains unstable classical orbits. This sheds light on applying semiclassical propagator to high dimensional systems.

cond-mat.other↗
arXiv2005

Fidelity of a Bose-Einstein Condensate

We investigate fidelity, the Loschmidt echo, for a Bose-Einstein Condensate. It is found that the fidelity decays with time in various ways (exponential, Gaussian, and power-law), depending on the choice of initial coherent state as well as the parameters that determine properties of the underlying classical dynamics. Moreover, high fidelity is found for initial states lying in the regular region of a mixed-type phase space. A possible experimental scheme is suggested.

cond-mat.mes-hall↗
arXiv2004

Uniform Semiclassical Approach to Fidelity Decay: from Weak to Strong Perturbation

We study fidelity decay by a uniform semiclassical approach, in the three perturbation regimes, namely, the perturbative regime, the Fermi-golden-rule (FGR) regime, and the Lyapunov regime. A semiclassical expression is derived for fidelity of initial Gaussian wave packets with width of the order $\sqrt{\hbar}$ ($\hbar$ being the effective Planck constant). Short time decay of fidelity of initial Gaussian wave packets is also studied, with respect to two time scales introduced in the semiclassical approach. In the perturbative regime, it is confirmed numerically that fidelity has the FGR decay before the Gaussian decay sets in. An explanation is suggested to a non-FGR decay in the FGR regime, which has been observed in a system with weak chaos in the classical limit, by using the Levy distribution as an approximation for the distribution of action difference. In the Lyapunov regime, it is shown that the average of the logarithm of fidelity may have roughly the Lyapunov decay within some time interval, in systems possessing large fluctuation of the finite-time Lyapunov exponent in the classical limit.

quant-ph↗
arXiv2004

Thermal diode: Rectification of heat flux

By coupling two nonlinear one dimensional lattices, we demonstrate a thermal diode model that works in a wide range of system parameters. We provide numerical and analytical evidence for the underlying mechanism which allows heat flux in one direction while the system acts like an insulator when the temperature gradient is reversed. The possible experimental realization in nano scale systems is briefly discussed.

cond-mat.dis-nn↗
arXiv2004

Anomalous heat conduction and anomalous diffusion in nonlinear lattices, single walled nanotubes, and billiard gas channels

We study anomalous heat conduction and anomalous diffusion in low dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is $σ^2(t)\equiv <Δx^2> =2Dt^α (0<α\le 2)$, then the thermal conductivity can be expressed in terms of the system size $L$ as $κ= cL^β$ with $β=2-2/α$. This result predicts that a normal diffusion ($α=1$) implies a normal heat conduction obeying the Fourier law ($β=0$), a superdiffusion ($α>1$) implies an anomalous heat conduction with a divergent thermal conductivity ($β>0$), and more interestingly, a subdiffusion ($α<1$) implies an anomalous heat conduction with a convergent thermal conductivity ($β<0$), consequently, the system is a thermal insulator in the thermodynamic limit. Existing numerical data support our theoretical prediction.

cond-mat.stat-mech↗
arXiv2004

Universal decay of classical Loschmidt echo of neutrally stable but mixing dynamics

We provide analytical and numerical evidence that classical mixing systems which lack exponential sensitivity on initial conditions, exhibit universal decay of Loschmidt echo which turns out to be a function of a single scaled time variable delta^(2/5)t, where delta is the strength of perturbation. The role of dynamical instability and entropy production is discussed.

nlin.CD↗
arXiv2004

Mode-coupling theory and molecular dynamics simulation for heat conduction in a chain with transverse motions

We study heat conduction in a one-dimensional chain of particles with longitudinal as well as transverse motions. The particles are connected by two-dimensional harmonic springs together with bending angle interactions. The problem is analyzed by mode-coupling theory and compared with molecular dynamics. We find very good, quantitative agreement for the damping of modes between a full mode-coupling theory and molecular dynamics result, and a simplified mode-coupling theory gives qualitative description of the damping. The theories predict generically that thermal conductance diverges as N^{1/3} as the size N increases for systems terminated with heat baths at the ends. The N^{2/5} dependence is also observed in molecular dynamics which we attribute to crossover effect.

cond-mat.stat-mech↗
arXiv2004

Thermal conduction of carbon nanotubes using molecular dynamics

The heat flux autocorrelation functions of carbon nanotubes (CNTs) with different radius and lengths is calculated using equilibrium molecular dynamics. The thermal conductance of CNTs is also calculated using the Green-Kubo relation from the linear response theory. By pointing out the ambiguity in the cross section definition of single wall CNTs, we use the thermal conductance instead of conductivity in calculations and discussions. We find that the thermal conductance of CNTs diverges with the CNT length. After the analysis of vibrational density of states, it can be concluded that more low frequency vibration modes exist in longer CNTs, and they effectively contribute to the divergence of thermal conductance.

cond-mat.mtrl-sci↗
arXiv2003

Crossover of quantum Loschmidt echo from golden rule decay to perturbation-independent decay

We study the crossover of the quantum Loschmidt echo (or fidelity) from the golden rule regime to the perturbation-independent exponential decay regime by using the kicked top model. It is shown that the deviation of the perturbation-independent decay of the averaged fidelity from the Lyapunov decay results from quantum fluctuations in individual fidelity, which are caused by the coherence in the initial coherent states. With an averaging procedure suppressing the quantum fluctuations effectively, the perturbation-independent decay is found to be close to the Lyapunov decay. We also show that the Fourier transform of the fidelity is determined directly by the initial state and the eigenstates of the Floquet operators of the two classically chaotic systems concerned. The absolute value part and the phase part of the Fourier transform of the fidelity are found to be divided into several correlated parts, which is a manifestation of the coherence of the initial coherent state. In the whole crossover region, some important properties of the fidelity, such as the exponent of its exponential decay and the short initial time within which the fidelity almost does not change, are found to be closely related to properties of the central part of its Fourier transform.

nlin.CD↗
arXiv2003

Intriguing Heat Conduction of a Polymer Chain

We study heat conduction in a one-dimensional chain of particles with longitudinal as well as transverse motions. The particles are connected by two-dimensional harmonic springs together with bending angle interactions. Using equilibrium and nonequilibrium molecular dynamics, three types of thermal conducting behaviors are found: a logarithmic divergence with system sizes for large transverse coupling, 1/3 power-law at intermediate coupling, and 2/5 power-law at low temperatures and weak coupling. The results are consistent with a simple mode-coupling analysis of the same model. The 1/3 power-law divergence should be a generic feature for models with transverse motions.

cond-mat.stat-mech↗
arXiv2003

Fourier law in the alternate mass hard-core potential chain

We study energy transport in a one-dimensional model of elastically colliding particles with alternate masses $m$ and $M$. In order to prevent total momentum conservation we confine particles with mass $M$ inside a cell of finite size. We provide convincing numerical evidence for the validity of Fourier law of heat conduction in spite of the lack of exponential dynamical instability. Comparison with previous results on similar models shows the relevance of the role played by total momentum conservation.

cond-mat.stat-mech↗
arXiv2003

Electronic Transport in Hybrid Mesoscopic Structures: A Nonequilibrium Green Function Approach

We present a unified transport theory of hybrid structures, in which a confined normal state ($N$) sample is sandwiched between two leads each of which can be either a ferromagnet ($F$) or a superconductor ($S$) via tunnel barriers. By introducing a four-dimensional Nambu-spinor space, a general current formula is derived within the Keldysh nonequilibrium Green function formalism, which can be applied to various kinds of hybrid mesoscopic systems with strong correlations even in the nonequilibrium situation. Such a formula is gauge invariant. We also demonstrate analytically for some quantities, such as the difference between chemical potentials, superconductor order parameter phases and ferromagnetic magnetization orientations, that only their relative value appears explicitly in the current expression. When applied to specific structures, the formula becomes of the Meir-Wingreen-type favoring strong correlation effects, and reduces to the Landauer-Büttiker-type in noninteracting systems such as the double-barrier resonant structures, which we study in detail beyond the wide-band approximation.

cond-mat.mes-hall↗
arXiv2003

Anomalous heat conduction and anomalous diffusion in one dimensional systems

We establish a connection between anomalous heat conduction and anomalous diffusion in one dimensional systems. It is shown that if the mean square of the displacement of the particle is $<Δx^2> =2Dt^α (0<α\le 2)$, then the thermal conductivity can be expressed in terms of the system size $L$ as $κ= cL^β$ with $β=2-2/α$. This result predicts that a normal diffusion ($α=1$) implies a normal heat conduction obeying the Fourier law ($β=0$), a superdiffusion ($α>1$) implies an anomalous heat conduction with a divergent thermal conductivity ($β>0$), and more interestingly, a subdiffusion ($α<1$) implies an anomalous heat conduction with a convergent thermal conductivity ($β<0$), consequently, the system is a thermal insulator in the thermodynamic limit. Existing numerical data support our results.

cond-mat.stat-mech↗
arXiv2003

Electron transport in interacting hybrid mesoscopic systems

A unified theory for the current through a nanoscale region of interacting electrons connected to two leads which can be either ferromagnet or superconductor is presented, yielding Meir-Wingreen-type formulas when applied to specific circumstances. In such a formulation, the requirement of gauge invariance for the current is satisfied automatically. Moreover, one can judge unambiguously what quantities can be measured in the transport experiment.

cond-mat.mes-hall↗