arXiv subjects

Chi-Ho Cheng

Publications and source records attributed to Chi-Ho Cheng.

At least 19 recordsLinked to original sources

arXiv2024

Coexistence of distinct nonuniform nonequilibrium steady states in Ehrenfest multiurn model on a ring

The recently proposed Ehrenfest M-urn model with interactions on a ring is considered as a paradigm model which can exhibit a variety of distinct nonequilibrium steady states. Unlike the previous three-urn model on a ring which consists of a uniform steady state and a nonuniform nonequilibrium steady state, it is found that for even M>=4, an additional nonequilibrium steady state can coexist with the original ones. Detailed analysis reveals that this additional nonequilibrium steady state emerged via a pitchfork bifurcation which cannot occur if M is odd. Properties of this nonequilibrium steady state, such as stability, and steady-state flux are derived analytically for the four-urn case. The full phase diagram with the phase boundaries is also derived explicitly. The associated thermodynamic stability is also analyzed, confirming its stability. These theoretical results are also explicitly verified by direct Monte Carlo simulations for the three-urn and four-urn ring models.

cond-mat.stat-mech↗

arXiv2024

Non-equilibrium Dynamics and Phase Transitions in Potts model and Interacting Ehrenfest urn model

We show that the recently proposed interacting Ehrenfest M-urn model at equilibrium can be exactly mapped to a mean-field M-state Potts model. By exploiting this correspondence, we show that the M-state Potts model with M >= 3, with transition rates motivated by the non-equilibrium urn model, can exhibit rich non-equilibrium spin dynamics such as non-equilibrium steady states and non-equilibrium periodic states. Monte Carlo simulations of the 3-state Potts model are performed to demonstrate explicitly the first-order transitions for the equilibrium and non-equilibrium steady states, as well as the far-from-equilibrium periodic states.

cond-mat.stat-mech↗

arXiv2023

Theory of Non-equilibrium Asymptotic State Thermodynamics: Interacting Ehrenfest Urn Ring as an Example

A generalized class of non-equilibrium state, called non-equilibrium asymptotic state (NEAS), is proposed. The NEAS is constructed within the framework of the Fokker-Planck equations in thermodynamic limit. Besides the usual equilibrium state and non-equilibrium steady state (NESS), the class of NEAS could also cover non-equilibrium periodic state (NEPS) in which its dynamics shows periodicity, non-equilibrium quasi-periodic state (NEQPS), and non-equilibrium chaotic state (NECS) in which its dynamics becomes chaotic. Based on the theory of NEAS thermodynamics, the corresponding thermodynamics of different NEAS could also be determined. Finally the interacting Ehrenfest urn ring model is used as an example to illustrate how different kinds of NEAS (equilibrium state, uniform NESS, non-uniform NESS, NEPS) in three-urn case are identified in our framework. In particular, the thermodynamics of NEPS and its phase transitions to other types of NEAS are studied.

cond-mat.stat-mech↗

arXiv2021

Analytical Studies of the Magnetic Domain Wall Structure in the presence of Non-uniform Exchange Bias

The pinning phenomena of the domain wall in the presence of exchange bias is studied analytically. The analytic solution of the domain wall spin configuration is presented. Unlike the traditional solution which is symmetric, our new solution could exhibit the asymmetry of the domain wall spin profile. Using the solution, the domain wall position, its width, its stability, and the depinning field are discussed analytically.

cond-mat.mes-hall↗

arXiv2021

Non-equilibrium thermodynamics and Phase transition of Ehrenfest urns with interactions

Ehrenfest urns with interaction that are connected in a ring is considered as a paradigm model for non-equilibrium thermodynamics and is shown to exhibit two distinct non-equilibrium steady states (NESS) of uniform and non-uniform particle distributions. As the inter-particle attraction varies, a first order non-equilibrium phase transition occurs between these two NESSs characterized by a coexistence regime. The phase boundaries, the NESS particle distributions near saddle points and the associated particle fluxes, average urn population fractions, and the relaxational dynamics to the NESSs are obtained analytically and verified numerically. A generalized non-equilibrium thermodynamics law is also obtained, which explicitly identifies the heat, work, energy and entropy of the system.

cond-mat.stat-mech↗

arXiv2021

Phase Transitions in Ehrenfest Urns Model with Interactions: Coexistence of uniform and non-uniform states

A model based on the classic non-interacting Ehrenfest urn model with two-urns is generalized to $M$ urns with the introduction of interactions for particles within the same urn. As the inter-particle interaction strength is varied, phases of different levels of non-uniformity emerge and their stabilities are calculated analytically. In particular, coexistence of locally stable uniform and non-uniform phases connected by first-order transition occurs. The phase transition threshold and energy barrier can be derived exactly together with the phase diagram obtained analytically. These analytic results are further confirmed by Monte Carlo simulations.

cond-mat.stat-mech↗

arXiv2019

Theory of thermalization in an isolated Bose-Einstein condensate

Thermalization in an isolated oscillating Bose-Einstein condensate in a disordered trap is investigated. We show Shannon entropy in $x$ or $p$ representation is the eligible one to describe the thermalization. Besides, we show that multiple scattering with the disorder generates more and more incoherent thermal particles and condensed and thermal particles act as mutual heat bath that results in the thermalization of the whole system. We also demonstrate that Loschmidt's paradox can be resolved in the present system.

cond-mat.quant-gas↗

arXiv2017

Ehrenfest urn model with interaction

We studied the Ehrenfest urn model in which particles in the same urn interact with each other. Depending on the nature of interaction, the system undergoes a first-order or second-order phase transition. The relaxation time to the equilibrium state, the Poincare cycles of the equilibrium state and the most far-from-equilibrium state, and the duration time of the states during first-order phase transition are calculated. It was shown that the scaling behavior of the Poincare cycles could be served as an indication to the nature of phase transition, and the ratio of duration time of the states could be a strong evidence of the metastability during first-order phase transition.

cond-mat.stat-mech↗

arXiv2017

SU(N) Fermi liquid at finite temperature

We consider the thermodynamic potential $Ω$ of an N component Fermi gas with a short range interaction obeying SU(N) symmetry. We analyze especially the part of $Ω$ that depends on the temperature T non-analytically for small T . We examine the temperature range where one can observe this $T^4 ln T$ contribution and discuss how it can be extracted experimentally.

cond-mat.quant-gas↗

arXiv2012

Spectrum of the Vortex Bound States of the Dirac and Schrodinger Hamiltonian in the presence of Superconducting Gaps

We investigate the vortex bound states both Schrodinger and Dirac Hamiltonian with the s-wave superconducting pairing gap by solving the mean-field Bogoliubov-de-Gennes equations. The exact vortex bound states spectrum is numerically determined by the integration method, and also accompanied by the quasi-classical analysis. It is found that the bound state energies is proportional to the vortex angular momentum when the chemical potential is large enough. By applying the external magnetic field, the vortex bound state energies of the Dirac Hamiltonian are almost unchanged; whereas the energy shift of the Schrodinger Hamiltonian is proportional to the magnetic field. These qualitative differences may serve as an indirect evidence of the existence of Majorana fermions in which the zero mode exists in the case of the Dirac Hamiltonian only.

cond-mat.str-el↗

arXiv2009

Thermodynamics of the System of Distinguishable Particles

The issue of the thermodynamics of a system of distinguishable particles is discussed in this paper. In constructing the statistical mechanics of distinguishable particles from the definition of Boltzmann entropy, it is found that the entropy is not extensive. The inextensivity leads to the so-called Gibbs paradox in which the mixing entropy of two identical classical gases increases. Lots of literature from different points of view were created to resolve the paradox. In this paper, starting from the Boltzmann entropy, we present the thermodynamics of the system of distinguishable particles. A straightforward way to get the corrected Boltzmann counting is shown. The corrected Boltzmann counting factor can be justified in classical statistical mechanics.

physics.chem-ph↗

arXiv2006

Trapped Resonant Fermions above Superfluid Transition Temperature

We investigate trapped resonant fermions with unequal populations within the local density approximation above the superfluid transition temperature. By tuning the attractive interaction between fermions via Feshbach resonance, the system evolves from weakly interacting fermi gas to strongly interacting fermi gas, and finally becomes bose-fermi mixture. The density profiles of fermions are examined and compared with experiments. We also point out the simple relationships between the local density, the axial density, and the gas pressure within the local density approximation.

cond-mat.supr-con↗

arXiv2006

Pairing Symmetry in the Anisotropic Fermi Superfluid under p-wave Feshbach Resonance

The anisotropic Fermi superfluid of ultra-cold Fermi atoms under the p-wave Feshbach resonance is studied theoretically. The pairing symmetry of the ground state is determined by the strength of the atom-atom magnetic dipole interaction. It is $k_z$ for a strong dipole interaction; while it becomes $k_z - i βk_y$, up to a rotation about z, for a weak one (Here $β$ < 1 is a numerical coefficient). By changing the external magnetic field or the atomic gas density, a phase transition between these two states can be driven. We discuss how the pairing symmetry of the ground state can be determined in the time-of-flight experiments.

cond-mat.other↗

arXiv2005

Boundary Condition of Polyelectrolyte Adsorption

The modification of the boundary condition for polyelectrolyte adsorption on charged surface with short-ranged interaction is investigated under two regimes. For weakly charged Gaussian polymer in which the short-ranged attraction dominates, the boundary condition is the same as that of the neutral polymer adsorption. For highly charged polymer (compressed state) in which the electrostatic interaction dominates, the linear relationship (electrostatic boundary condition) between the surface monomer density and the surface charge density needs to be modified.

cond-mat.soft↗

arXiv2005

Low-energy Effective Theory for Spin Dynamics of Fluctuating Stripes

We derive an effective Hamiltonian for spin dynamics of fluctuating smectic stripes from the t-J model in the weak coupling limit t >> J. Besides the modulation of spin magnitude, the high energy hopping term would induce a low-energy anti-ferromagnetic interaction between two neighboring ``blocks of spins". Based on the effective Hamiltonian, we applied the linear spin-wave theory and found that the spin-wave velocity is almost isotropic for La_{2-x}Sr_x CuO_4 unless the structural effect is considered. The intensity of the second harmonic mode is found to be about 10% to that of the fundamental mode.

cond-mat.supr-con↗

arXiv2005

Anisotropic Fermi Superfluid via p-wave Feshbach Resonance

We investigate theoretically Fermionic superfluidity induced by Feshbach resonance in the orbital p-wave channel. We show that, due to the dipole interaction, the pairing is extremely anisotropic. When this dipole interaction is relatively strong, the pairing has symmetry $k_z$. When it is relatively weak, it is of symmetry $k_z + i βk_y$ (up to a rotation about $\hat z$, here $β< 1$). A phase transition between these two states can occur under a change in the magnetic field or the density of the gas.

cond-mat.other↗

arXiv2005

Conformational Properties of an Adsorbed Charged Polymer

The behavior of a strongly charged polymer adsorbed on an oppositely charged surface of low-dielectric constant is formulated by the functional integral method. By separating the translational, conformational, and fluctuational degrees of freedom, the scaling behaviors for both the height of the polymer and the thickness of the diffusion layer are determined. Unlike the results predicted by scaling theory, we identified the continuous crossover from the weak compression to the compression regime. All teh analytical results are found to be consistent with Monte-Carlo simulations. Finally, an alternative (operational) definition of a charged polymer adsorption is proposed.

cond-mat.soft↗

arXiv2004

Scaling Theory of Polyelectrolyte Adsorption on Repulsive Charged Surface

We studied polyelectrolyte adsorption on a repulsive charged surface by scaling analysis. At low ionic strength and low surface charge density in which a single polyelectrolyte is able to be adsorbed onto the surface, different regimes in the phase diagram are identified. The possibility of multi-layer structure formed by polyelectrolytes of like charge is also investigated.

cond-mat.soft↗