arXiv subjects

Baowen Li

Publications and source records attributed to Baowen Li.

At least 145 records · Page 8Linked to original sources

arXiv2010

Berry-Phase induced Heat Pumping and its Impact on the Fluctuation Theorem

Applying adiabatic, cyclic two parameter modulations we investigate quantum heat transfer across an anharmonic molecular junction contacted with two heat baths. We demonstrate that the pumped heat typically exhibits a Berry phase effect in providing an additional geometric contribution to heat flux. Remarkably, a robust fractional quantized geometric phonon response is identified as well. The presence of this geometric phase contribution in turn causes a breakdown of the fluctuation theorem of the Gallavotti-Cohen type for quantum heat transfer. This can be restored only if (i) the geometric phase contribution vanishes and if (ii) the cyclic protocol preserves the detailed balance symmetry.

cond-mat.mes-hall↗

arXiv2010

Random matrix analysis of localization properties of Gene co-expression network

We analyze gene co-expression network under the random matrix theory framework. The nearest neighbor spacing distribution of the adjacency matrix of this network follows Gaussian orthogonal statistics of random matrix theory (RMT). Spectral rigidity test follows random matrix prediction for a certain range, and deviates after wards. Eigenvector analysis of the network using inverse participation ratio (IPR) suggests that the statistics of bulk of the eigenvalues of network is consistent with those of the real symmetric random matrix, whereas few eigenvalues are localized. Based on these IPR calculations, we can divide eigenvalues in three sets; (A) The non-degenerate part that follows RMT. (B) The non-degenerate part, at both ends and at intermediate eigenvalues, which deviate from RMT and expected to contain information about {\it important nodes} in the network. (C) The degenerate part with $zero$ eigenvalue, which fluctuates around RMT predicted value. We identify nodes corresponding to the dominant modes of the corresponding eigenvectors and analyze their structural properties.

q-bio.MN↗

arXiv2010

Energy carriers in the Fermi-Pasta-Ulam $β$ lattice: Solitons or Phonons?

We investigate anomalous energy transport processes in the Fermi-Pasta-Ulam $β$ lattice. They are determined by the maximum sound velocity of the relevant weakly damped energy carriers. That velocity can be numerically resolved by measuring the propagating fronts of the correlation functions of energy/momentum fluctuations at different times. The numerical results are compared with the predictions for solitons and effective (renormalized) phonons, respectively. Excellent agreement has been found for the prediction of effective long wavelength phonons, giving strong evidence that the energy carriers should be effective phonons rather than solitons.

cond-mat.stat-mech↗

arXiv2010

Ballistic thermal rectification in nanoscale three-terminal junctions

We study ballistic thermal transport in three-terminal atomic nanojunctions by the nonequilibrium Green's function method. We find that there is ballistic thermal rectification in asymmetric three-terminal structures because of the incoherent phonon scattering from the control terminal. With spin-phonon interaction, we also find the ballistic thermal rectification even in symmetric three-terminal paramagnetic structures.

cond-mat.mes-hall↗

arXiv2010

Violation of Fourier's Law and Anomalous Heat Diffusion in Silicon

We study heat conduction and diffusion in silicon nanowires (SiNWs) systematically by using non-equilibrium molecular dynamics. It is found that the thermal conductivity of SiNWs diverges with the length, even when the length is up to 1,100 nm which is much longer than the phonon mean free path. Moreover, an anomalous heat diffusion is observed which is believed to be responsible for the length dependent thermal conductivity. Our results provide strong evidence that Fourier's law of heat conduction is not valid in low dimensional nanostructures.

cond-mat.mtrl-sci↗

arXiv2010

Emergence and control of heat current from strict zero thermal bias

It is an ever-growing challenge to develop nano-devices for controlling energy transport. An open question is whether we can create and control heat current at {\it strict zero thermal bias}, and if yes, how to do it. In this paper, we demonstrate that a nonlinear asymmetric system, when pushed out of equilibrium, can produce heat current in the absence of a thermal bias. The emergence and control of heat current over a broad range of parameters are studied. Our results reveal the following three necessary conditions: non-equilibrium source, symmetry breaking, and nonlinearity. We also demonstrate that when heat baths are correlated, symmetry breaking is sufficient to generate heat current.

cond-mat.mes-hall↗

arXiv2010

Noise bridges dynamical correlation and topology in coupled oscillator networks

We study the relationship between dynamical properties and interaction patterns in complex oscillator networks in the presence of noise. A striking finding is that noise leads to a general, one-to-one correspondence between the dynamical correlation and the connections among oscillators for a variety of node dynamics and network structures. The universal finding enables an accurate prediction of the full network topology based solely on measuring the dynamical correlation. The power of the method for network inference is demonstrated by the high success rate in identifying links for distinct dynamics on both model and real-life networks. The method can have potential applications in various fields due to its generality, high accuracy and efficiency.

physics.data-an↗

arXiv2010

Elastic and non-linear stiffness of graphene: a simple approach

The recent experiment [Science \textbf{321}, 385 (2008)] on the Young's modulus and third-order elastic stiffness of graphene are well explained in a very simple approach, where the graphene is described by a simplified system and the force constant for the non-linear interaction is estimated from the Tersoff-Brenner potential.

cond-mat.mtrl-sci↗

arXiv2009

Phonon Hall Effect in Four-Terminal Junctions

Using an exact nonequilibrium Green's function formulism, the phonon Hall effect for paramagnetic dielectrics is studied in a four-terminal device setting. The temperature difference in the transverse direction of the heat current is calculated for two-dimensional models with the magnetic field perpendicular to the plane. We find a surprising result that the square lattice does not have the phonon Hall effect while a honeycomb lattice has. This can be explained by symmetry. The temperature difference changes sign if the magnetic field is sufficiently large.

cond-mat.mes-hall↗

arXiv2009

Thermal expansion in carbon nanotubes and graphene: nonequilibrium Green's function approach

The nonequilibrium Green's function method is applied to investigate the coefficient of thermal expansion (CTE) in single-walled carbon nanotubes (SWCNT) and graphene. It is found that atoms deviate about 1% from equilibrium positions at T=0 K, resulting from the interplay between quantum zero-point motion and nonlinear interaction. The CTE in SWCNT of different sizes is studied and analyzed in terms of the competition between various vibration modes. As a result of this competition, the axial CTE is positive in the whole temperature range, while the radial CTE is negative at low temperatures. In graphene, the CTE is very sensitive to the substrate. Without substrate, CTE has large negative region at low temperature and very small value at high temperature limit, and the value of CTE at T=300 K is $-6\times 10^{-6}$ K$^{-1}$ which is very close to recent experimental result, $-7\times 10^{-6}$ K$^{-1}$ (Nat. Nanotechnol. \textbf{10}, 1038 (2009)). A very weak substrate interaction (about 0.06% of the in-plane interaction) can largely reduce the negative CTE region and greatly enhance the value of CTE. If the substrate interaction is strong enough, the CTE will be positive in whole temperature range and the saturate value at high temperature reaches $2.0\times 10^{-5}$ K$^{-1}$.

cond-mat.mtrl-sci↗

arXiv2009

Reversal of Thermal Rectification in Quantum Systems

We study thermal transport in anisotropic Heisenberg spin chains using the quantum master equation. It is found that thermal rectification changes sign when the external homogeneous magnetic field is varied. This reversal also occurs when the magnetic field becomes inhomogeneous. Moreover, we can tune the reversal of rectification by temperatures of the heat baths, the anisotropy and size of the spin chains.

cond-mat.stat-mech↗

arXiv2009

Young's modulus of Graphene: a molecular dynamics study

The Young's modulus of graphene is investigated through the intrinsic thermal vibration in graphene which is `observed' by molecular dynamics, and the results agree quite well with the recent experiment [Science \textbf{321}, 385 (2008)]. This method is further applied to show that the Young's modulus of graphene: 1. increases with increasing size and saturation is reached after a threshold value of the size; 2. increases from 0.95 TPa to 1.1 TPa as temperature increases in the region [100, 500]K; 3. is insensitive to the isotopic disorder in the low disorder region ($< 5%$), and decreases gradually after further increasing the disorder percentage.

cond-mat.mtrl-sci↗

arXiv2009

Size dependent thermoelectric properties of silicon nanowires

By using first-principles tight-binding electronic structure calculation and Boltzmann transport equation, we investigate the size dependence of thermoelectric properties of silicon nanowires (SiNWs). With cross section area increasing, the electrical conductivity increases slowly, while the Seebeck coefficient reduces remarkably. This leads to a quick reduction of cooling power factor with diameter. Moreover, the figure of merit also decreases with transverse size. Our results demonstrate that in thermoelectric application, NW with small diameter is preferred. We also predict that isotopic doping can increase the value of ZT significantly. With 50% 29Si doping (28Si0.529Si0.5 NW), the ZT can be increased by 31%.

cond-mat.mtrl-sci↗

arXiv2009

Edge states induce boundary temperature jump in molecular dynamics simulation of heat conduction

We point out that the origin of the commonly occurred boundary temperature jump in the application of Nośe-Hoover heat bath in molecular dynamics is related to the edge modes, which are exponentially localized at the edge of the system. If heat baths are applied to these edge regions, the injected thermal energy will be localized thus leading to a boundary temperature jump. The jump can be eliminated by shifting the location of heat baths away from edge regions. Following this suggestion, a very good temperature profile is obtained without increasing any simulation time, and the accuracy of thermal conductivity calculated can be largely improved.

cond-mat.mtrl-sci↗

arXiv2009

Shuttling heat across 1D homogenous nonlinear lattices with a Brownian heat motor

We investigate directed thermal heat flux across 1D homogenous nonlinear lattices when no net thermal bias is present on average. A nonlinear lattice of Fermi-Pasta-Ulam-type or Lennard-Jones-type system is connected at both ends to thermal baths which are held at the same temperature on temporal average. We study two different modulations of the heat bath temperatures, namely: (i) a symmetric, harmonic ac-driving of temperature of one heat bath only and (ii) a harmonic mixing drive of temperature acting on both heat baths. While for case (i) an adiabatic result for the net heat transport can be derived in terms of the temperature dependent heat conductivity of the nonlinear lattice a similar such transport approach fails for the harmonic mixing case (ii). Then, for case (ii), not even the sign of the resulting Brownian motion induced heat flux can be predicted a priori. A non-vanishing heat flux (including a non-adiabatic reversal of flux) is detected which is the result of an induced dynamical symmetry breaking mechanism in conjunction with the nonlinearity of the lattice dynamics. Computer simulations demonstrate that the heat flux is robust against an increase of lattice sizes. The observed ratchet effect for such directed heat currents is quite sizable for our studied class of homogenous nonlinear lattice structures, thereby making this setup accessible for experimental implementation and verification.

cond-mat.stat-mech↗

arXiv2009

Thermal Rectification In Asymmetric Graphene Ribbons

In this paper, heat flux in graphene nano ribbons has been studied by using molecular dynamics simulations. It is found that the heat flux runs preferentially along the direction of decreasing width, which demonstrates significant thermal rectification effect in the asymmetric graphene ribbons. The dependence of rectification ratio on the vertex angle and the length are also discussed. Compared to the carbon nanotube based one-dimensional thermal rectifier, graphene nano ribbons have much higher rectification ratio even in large scale. Our results demonstrate that asymmetric graphene ribbon might be a promising structure for practical thermal (phononics) device.

cond-mat.mtrl-sci↗

arXiv2009

Carbon Nanocone: A Promising Thermal Rectifier

With molecular dynamics simulations, we demonstrate very obvious thermal rectification in large temperature range from 200 to 400 K in nanocone. We also observe that the rectification of nanocone does not depend on the length very sensitively, which is in stark contrast with the nanotube thermal rectifier in which the rectification decreases dramatically as the length increases. Our work demonstrates that carbon nanocone is a promising practical phononic device.

cond-mat.mes-hall↗

arXiv2009

Thermal conductance of graphene and dimerite

We investigate the phonon thermal conductance of graphene regarding the graphene sheet as the large-width limit of graphene strips in the ballistic limit. We find that the thermal conductance depends weakly on the direction angle $θ$ of the thermal flux periodically with period $π/3$. It is further shown that the nature of this directional dependence is the directional dependence of group velocities of the phonon modes in the graphene, originating from the $D_{6h}$ symmetry in the honeycomb structure. By breaking the $D_{6h}$ symmetry in graphene, we see more obvious anisotropic effect in the thermal conductance as demonstrated by dimerite.

cond-mat.mtrl-sci↗