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Joyjit Kundu

Publications and source records attributed to Joyjit Kundu.

22 records · Page 2Linked to original sources

arXiv2014

Asymptotic Behavior of the Isotropic-Nematic and Nematic-Columnar Phase Boundaries for the System of Hard Rectangles on a Square lattice

A system of hard rectangles of size $m\times mk$ on a square lattice undergoes three entropy driven phase transitions with increasing density for large enough aspect ratio $k$: first from a low density isotropic to an intermediate density nematic phase, second from the nematic to a columnar phase, and third from the columnar to a high density sublattice phase. In this paper we show, from extensive Monte Carlo simulations of systems with $m=1,2$ and $3$, that the transition density for the isotropic-nematic transition is $\approx A_1/k$ when $k \gg 1$, where $A_1$ is independent of $m$. We estimate $A_1=4.80\pm 0.05$. Within a Bethe approximation, we obtain $A_1=2$ and the virial expansion truncated at second virial coefficient gives $A_1=1$. The critical density for the nematic-columnar transition when $m=2$ is numerically shown to tend to a value less than the full packing density as $k^{-1}$ when $k\to \infty$. We find that the critical Binder cumulant for this transition is non-universal and decreases as $k^{-1}$ for $k \gg 1$. However, the transition is shown to be in the Ising universality class.

cond-mat.stat-mech↗

arXiv2014

Phase transitions in a system of hard rectangles on the square lattice

The phase diagram of a system of monodispersed hard rectangles of size $m\times m k$ on a square lattice is numerically determined for $m=2,3$ and aspect ratio $k= 1,2,\ldots, 7$. We show the existence of a disordered phase, a nematic phase with orientational order, a columnar phase with orientational and partial translational order, and a solid-like phase with sublattice order, but no orientational order. The asymptotic behavior of the phase boundaries for large $k$ are determined using a combination of entropic arguments and a Bethe approximation. This allows us to generalize the phase diagram to larger $m$ and $k$, showing that for $k \geq 7 $, the system undergoes three entropy driven phase transitions with increasing density. The nature of the different phase transitions are established and the critical exponents for the continuous transitions are determined using finite size scaling.

cond-mat.stat-mech↗

arXiv2013

Re-entrant Disordered Phase in a System of Repulsive Rods on a Bethe-like Lattice

We solve exactly a model of monodispersed rigid rods of length $k$ with repulsive interactions on the random locally tree like layered lattice. For $k\geq 4$ we show that with increasing density, the system undergoes two phase transitions: first from a low density disordered phase to an intermediate density nematic phase and second from the nematic phase to a high density re-entrant disordered phase. When the coordination number is $4$, both the phase transitions are continuous and in the mean field Ising universality class. For even coordination number larger than $4$, the first transition is discontinuous while the nature of the second transition depends on the rod length $k$ and the interaction parameters.

cond-mat.stat-mech↗

arXiv2013

The nematic-disordered phase transition in systems of long rigid rods on two dimensional lattices

We study the phase transition from a nematic phase to a high-density disordered phase in systems of long rigid rods of length $k$ on the square and triangular lattices. We use an efficient Monte Carlo scheme that partly overcomes the problem of very large relaxation times of nearly jammed configurations. The existence of a continuous transition is observed on both lattices for $k=7$. We study correlations in the high-density disordered phase, and we find evidence of a crossover length scale $ξ^* \gtrsim 1400$, on the square lattice. For distances smaller than $ξ^*$, correlations appear to decay algebraically. Our best estimates of the critical exponents differ from those of the Ising model, but we cannot rule out a crossover to Ising universality class at length scales $\gg ξ^*$. On the triangular lattice, the critical exponents are consistent with those of the two dimensional three-state Potts universality class.

cond-mat.stat-mech↗