arXiv subjects

Chandradip Khamrai

Publications and source records attributed to Chandradip Khamrai.

3 recordsLinked to original sources

arXiv2026

Phase ordering kinetics in Light-Heavy-Vacancy model: unusual coarsening dynamics

We study a one dimensional lattice model of coupled driven system where two kinds of hardcore particle species, `light' and `heavy', move on a fluctuating landscape. Light particles prefer to move upward along the local height gradient of the landscape, and heavy particles prefer to move downhill. In addition, these particle species also exert bias on the local height profile. The unoccupied or vacant parts of the landscape experience no bias and undergo symmetric height fluctuations. In an earlier work, we had derived a phase diagram of the system consisting of different kinds of ordered and disordered phases. In the ordered phase, one or both particle species phase-separate, while the landscape forms a large hill or deep valley. Here we study coarsening by monitoring the development of long-range order in the particles and landscape from an initially disordered state. Unlike conventional phase-ordering systems, where coarsening proceeds through the formation and merger of ordered domains, here we find that domains formed at early times become unsustainable at later times. Instead of merging together, these early domains disintegrate and new domains emerge which finally give rise to large scale ordered structure in the long time limit, resulting a highly unusual coarsening behavior. For particle coarsening, the characteristic length scale grows with two distinctly different power law exponents at early and late times. The landscape coarsening is even more dramatic where the length scale decreases for brief time-intervals, instead of increasing continuously. The height fluctuations of the landscape shows periodic oscillations with time during the coarsening phase. Using linear hydrodynamics we explain that this is caused by three normal modes which move through the system like travelling waves. We calculate the propagation velocities of these modes within mean field approximation.

cond-mat.stat-mech↗

arXiv2026

A Novel Mechanism of Ordering in a Coupled Driven System: Vacancy Induced Phase Separation

We study a coupled driven system where two different species of particles, along with some vacancies or holes, move on a landscape whose shape fluctuates with time. The movement of the particles is guided by the local shape of the landscape, and this shape is also affected by the presence of different particle species. When a particle species push the landscape in the same (opposite) direction of its own motion, it is called an aligned (a reverse) bias. Aligned bias promotes ordering while reverse bias destroys it. In absence of vacancies, the system reduces to previously studied LH model with different kinds of ordered and disordered phases which could be explained as a competition or cooperation between aligned bias and reverse bias. This interplay is expected to remain unaffected even when vacancies are present since vacancies do not impart any kind of bias on the landscape. However, we find presence of vacancies effectively weakens the reverse bias and this significantly changes the outcome of the competition between the two bias types. As a result novel ordered phases emerge which were not seen before. We analytically calculate the new phase boundaries within mean field approximation. We show even when aligned bias is weaker than reverse bias, it is possible to find long range order in the system. We discover two new phases where particle species showing weak aligned bias phase separate and the other species with strong reverse bias stays mixed with the vacancies. We call these phases finite current with partial phase separation (FPPS) and vacancy induced phase separation (VIPS). The landscape beneath the phase separated species takes the form of a macroscopic hill or valley in FPPS phase. But in VIPS phase it has the shape like a plateau whose height scales as square root of system size. The landscape in the remaining part of the system is disordered in both these phases.

cond-mat.stat-mech↗

arXiv2024

Effect of relative timescale on a system of particles sliding on a fluctuating energy landscape: Exact derivation of product measure condition

We consider a system of hardcore particles advected by a fluctuating potential energy landscape, whose dynamics is in turn affected by the particles. Earlier studies have shown that as a result of two-way coupling between the landscape and the particles, the system shows an interesting phase diagram as the coupling parameters are varied. The phase diagram consists of various different kinds of ordered phases and a disordered phase. We introduce a relative timescale $ω$ between the particle and landscape dynamics, and study its effect on the steady state properties. We find there exists a critical value $ω= ω_{c}$ when all configurations of the system are equally likely in the steady state. We prove this result exactly in a discrete lattice system and obtain an exact expression for $ω_c$ in terms of the coupling parameters of the system. We show that $ω_c$ is finite in the disordered phase, diverges at the boundary between the ordered and disordered phase, and is undefined in the ordered phase. We also derive $ω_c$ from a coarse-grained level description of the system using linear hydrodynamics. We start with the assumption that there is a specific value $ω^\ast$ of the relative timescale when correlations in the system vanish, and mean-field theory gives exact expressions for the current Jacobian matrix $A$ and compressibility matrix $K$. Our exact calculations show that Onsager-type current symmetry relation $AK = KA^{T}$ can be satisfied if and only if $ω^\ast = ω_c$ . Our coarse-grained model calculations can be easily generalized to other coupled systems.

cond-mat.stat-mech↗