arXiv subjects

Sukla Pal

Publications and source records attributed to Sukla Pal.

At least 19 recordsLinked to original sources

arXiv2026

Dynamic scaling near the Kasteleyn transition in spin ice: critical relaxation of monopoles and strings following a field quench

We study dynamics in classical spin ice following a magnetic field quench to close to the Kasteleyn transition, using Monte Carlo simulations and dynamic scaling theory to characterize the relaxation of the magnetization and the density of magnetic monopoles. We have previously argued that this dynamics can be described in terms of seeding and growth of strings of flipped spins, and our results here demonstrate that a solvable stochastic model based on independent strings correctly describes the relaxation as well as the distribution of string lengths within the critical scaling regime near the transition. We also show how generalized scaling forms capture the behavior over a broader range of monopole densities and provide a clear understanding of the breakdown of the scaling picture further from the critical point.

cond-mat.stat-mech↗

arXiv2025

Dynamic scaling theory for a field quench near the Kasteleyn transition in spin ice

We present a dynamic scaling theory to describe relaxation dynamics following a magnetic-field quench near an unconventional phase transition in the magnetic material spin ice. Starting from a microscopic model, we derive an effective description for the critical dynamics in terms of the seeding and growth of string excitations, and use this to find scaling forms in terms of time, reduced temperature and monopole fugacity. We confirm the predictions of scaling theory using Monte Carlo simulations, which also show good quantitative agreement with analytical expressions valid in the limit of low monopole density. As well as being relevant for experiments in the spin ice materials, our results open the way for the study of dynamic critical properties in a family of unconventional classical phase transitions.

cond-mat.stat-mech↗

arXiv2023

Crossover from string to cluster dynamics following a field quench in spin ice

We investigate quench dynamics of spin ice after removal of a strong magnetic field along the [100] crystal direction, using Monte Carlo simulations and theoretical arguments. We show how the early-time relaxation of the magnetization can be understood in terms of nucleation and growth of strings of flipped spins, in agreement with an effective stochastic model that we introduce and solve analytically. We demonstrate a crossover at longer times to a regime dominated by approximately isotropic clusters, which we characterize in terms of their morphology, and present evidence for a percolation transition as a function of magnetization.

cond-mat.stat-mech↗

arXiv2022

Spectral analysis for compressible quantum fluids

Turbulent fluid dynamics typically involves excitations on many different length scales. Classical incompressible fluids can be cleanly represented in Fourier space enabling spectral analysis of energy cascades and other turbulence phenomena. In quantum fluids, additional phase information and singular behaviour near vortex cores thwarts the direct extension of standard spectral techniques. We develop a formal and numerical spectral analysis for $U(1)$ symmetry-breaking quantum fluids suitable for analyzing turbulent flows, with specific application to the Gross-Pitaevskii fluid. Our analysis builds naturally on the canonical approach to spectral analysis of velocity fields in compressible quantum fluids, and establishes a clear correspondence between energy spectral densities, power spectral densities, and autocorrelation functions, applicable to energy residing in velocity, quantum pressure, interaction, and potential energy of the fluid. Our formulation includes all quantum phase information and also enables arbitrary resolution spectral analysis, a valuable feature for numerical analysis. A central vortex in a trapped planar Bose-Einstein condensate provides an analytically tractable example with spectral features of interest in both the infrared and ultraviolet regimes. Sampled distributions modelling the dipole gas, plasma, and clustered regimes exhibit velocity correlation length increasing with vortex energy, consistent with known qualitative behaviour across the vortex clustering transition. The spectral analysis of compressible quantum fluids presented here offers a rigorous tool for analysing quantum features of superfluid turbulence in atomic or polariton condensates.

cond-mat.quant-gas↗

arXiv2021

Infinite dipolar droplet -- a simple theory for the macro-droplet regime

In this paper we develop a theory for an infinitely long droplet state of a zero temperature dipolar bosonic gas. The infinite droplet theory yields simpler equations to solve for the droplet state and its collective excitations. We explore the behavior of infinite droplets using numerical and variational solutions, and demonstrate that it can provide a quantitative description of large finite droplets of the type produced in experiments. We also consider the axial speed of sound and the thermodynamic limit of a dipolar droplet.

cond-mat.quant-gas↗

arXiv2020

Variational theory for the ground state and collective excitations of an elongated dipolar condensate

We develop a variational theory for a dipolar condensate in an elongated (cigar shaped) confinement potential. Our formulation provides an effective one-dimensional extended meanfield theory for the ground state and its collective excitations. We apply our theory to investigate the properties of rotons in the system comparing the variational treatment to a full numerical solution. We consider the effect of quantum fluctuations on the scattering length at which the roton excitation softens to zero energy.

cond-mat.quant-gas↗

arXiv2020

FACt: FORTRAN toolbox for calculating fluctuations in atomic condensates

We develop a FORTRAN code to compute fluctuations in atomic condensates (FACt) by solving the Bogoliubov-de Gennes (BdG) equations for two component Bose-Einstein condensate (TBEC) in quasi two dimensions. The BdG equations are recast as matrix equations and solved self consistently. The code is suitable for handling quantum fluctuations as well as thermal fluctuations at temperatures below the critical point of Bose-Einstein condensation. The code is versatile, and the ground state density profile and low energy excitation modes obtained from the code can be easily adapted to compute different properties of TBECs -- ground state energy, overlap integral, quasi particle amplitudes of BdG spectrum, dispersion relation and structure factor and other related experimental observables.

cond-mat.quant-gas↗

arXiv2020

Excitations and number fluctuations in an elongated dipolar Bose-Einstein condensate

We study the properties of a magnetic dipolar Bose-Einstein condensate (BEC) in an elongated (cigar shaped) confining potential in the beyond quasi-one-dimensional (quasi-1D) regime. In this system the dipole-dipole interactions (DDIs) develop a momentum-dependence related to the transverse confinement and the polarization direction of the dipoles. This leads to density fluctuations being enhanced or suppressed at a length scale related to the transverse confinement length, with local atom number measurements being a practical method to observe these effects in experiments. We use meanfield theory to describe the ground state, excitations and the local number fluctuations. Quantitative predictions are presented based on full numerical solutions and a simplified variational approach that we develop. In addition to the well-known roton excitation, occurring when the dipoles are polarized along a tightly confined direction, we find an "anti-roton" effect for the case of dipoles polarized along the long axis: a nearly non-interacting ground state that experiences strongly repulsive interactions with excitations of sufficiently short wavelength.

cond-mat.quant-gas↗

arXiv2020

Supersolid phase of the extended Bose-Hubbard model with an artificial gauge field

We examine the zero and finite temperature phase diagrams of soft-core bosons of the extended Bose-Hubbard model on a square optical lattice. To study various quantum phases and their transitions we employ single-site and cluster Gutzwiller mean-field theory. We have observed that the Mott insulator phase vanishes above a critical value of nearest-neighbour interaction and the supersolid phase occupies a larger region in the phase diagram. We show that the presence of artificial gauge field enlarges the domain of supersolid phase. The finite temperature destroys the crystalline structure of the supersolid phase and thereby favours normal fluid to superfluid phase transition. The presence of an envelope harmonic potential demonstrates coexistence of different phases and at $z~k_{B}T\geqslant V$, thermal energy comparable and higher to the long-range interaction energy, the supersolidity of the system is destroyed.

cond-mat.quant-gas↗

arXiv2019

Quantum Hall states for $α= 1/3$ in optical lattices

We examine the quantum Hall (QH) states of the optical lattices with square geometry using Bose-Hubbard model (BHM) in presence of artificial gauge field. In particular, we focus on the QH states for the flux value of $α= 1/3$. For this, we use cluster Gutzwiller mean-field (CGMF) theory with cluster sizes of $3\times 2$ and $3\times 3$. We obtain QH states at fillings $ν= 1/2, 1, 3/2, 2, 5/2$ with the cluster size $3\times 2$ and $ν= 1/3, 2/3, 1, 4/3, 5/3, 2, 7/3, 8/3$ with $3\times 3$ cluster. Our results show that the geometry of the QH states are sensitive to the cluster sizes. For all the values of $ν$, the competing superfluid (SF) state is the ground state and QH state is the metastable state.

cond-mat.quant-gas↗

arXiv2019

Quantum phases of tilted dipolar bosons in two-dimensional optical lattice

We consider a minimal model to describe the quantum phases of ultracold dipolar bosons in two-dimensional (2D) square optical lattices. The model is a variation of the extended Bose-Hubbard model and apt to study the quantum phases arising from the variation in the tilt angle $θ$ of the dipolar bosons. At low tilt angles $0^{\circ}\leqslantθ\apprle25^{\circ}$, the ground state of the system are phases with checkerboard order, which could be either checkerboard supersolid or checkerboard density wave. For high tilt angles $55^{\circ}\apprgeθ\apprge35^{\circ}$, phases with striped order of supersolid or density wave are preferred. In the intermediate domain $25^{\circ}\apprleθ\apprle35^{\circ}$ an emulsion or SF phase intervenes the transition between the checkerboard and striped phases. The attractive interaction dominates for $θ\apprge55^{\circ}$, which renders the system unstable and there is a density collapse. For our studies we use Gutzwiller mean-field theory to obtain the quantum phases and the phase boundaries. In addition, we calculate the phase boundaries between an incompressible and a compressible phase of the system by considering second order perturbation analysis of the mean-field theory. The analytical results, where applicable, are in excellent agreement with the numerical results.

cond-mat.quant-gas↗

arXiv2019

Enhancement of the Bose glass phase in the presence of an artificial gauge field

We examine the effects of an artificial gauge field and finite temperature in a two-dimensional disordered Bose-Hubbard model. The disorder considered is diagonal and quenched in nature. A signature of disorder in the Bose-Hubbard model is the Bose glass phase. Our work shows that the introduction of an artificial gauge field enhances the domain of the Bose glass phase in the phase diagram. Most importantly, the size of the domain can be tuned with the strength of the artificial gauge field. The introduction of the finite temperature effects is essential to relate theoretical results with the experimental realizations. For our studies we use the single site and cluster Gutzwiller mean-field theories. The results from the latter are more reliable as it better describes the correlation effects. Our results show that the Bose glass phase has a larger domain with the latter method.

cond-mat.quant-gas↗

arXiv2018

Bosonic quantum Hall states in single-layer two-dimensional optical lattices

Quantum Hall (QH) states of 2D single layer optical lattices are examined using Bose-Hubbard model (BHM) in presence of artificial gauge field. We study the QH states of both the homogeneous and inhomogeneous systems. For the homogeneous case we use cluster Gutzwiller mean field (CGMF) theory with cluster sizes ranging from $2\times 2$ to $5\times 5$. We, then, consider the inhomogeneous case, which is relevant to experimental realization. In this case, we use CGMF and exact diagonalization (ED). The ED studies are using lattice sizes ranging from $3\times 3$ to $4\times 12$. Our results show that the geometry of the QH states are sensitive to the magnetic flux $α$ and cluster sizes. For homogeneous system, among various combinations of $1/5\leqslant α\leqslant 1/2$ and filling factor $ν$, only the QH state of $α=1/4$ with $ν=1/2$, $1$, $3/2$ and $2$ occur as ground states. For other combinations, the competing superfluid (SF) state is the ground state and QH state is metastable. For BHM with envelope potential all the QH states observed in homogeneous system exist for box potentials, but none for the harmonic potential. The QH states also persist for very shallow Gaussian envelope potential. As a possible experimental signature we study the two point correlations of the QH and SF states.

cond-mat.quant-gas↗

arXiv2017

Collective modes in multicomponent condensates with anisotropy

We report the effects of anisotropy in the confining potential on two component Bose-Einstein condensates (TBECs) through the properties of the low energy quasiparticle excitations. Starting from generalized Gross Pitaevskii equation, we obtain the Bogoliubov de-Gennes (BdG) equation for TBECs using the Hartree-Fock-Bogoliubov (HFB) theory. Based on this theory, we present the influence of radial anisotropy on TBECs in the immiscible or the phase-separated domain. In particular, the TBECs of $^{85}$Rb~-$^{87}$Rb and $^{133}$Cs~-$^{87}$Rb TBECs are chosen as specific examples of the two possible interface geometries, shell-structured and side by side, in the immiscible domain. We also show that the dispersion relation for the TBEC shell-structured interface has two branches, and anisotropy modifies the energy scale and structure of the two branches.

cond-mat.quant-gas↗

arXiv2017

Dynamics of binary Bose-Einstein condensate via Ehrenfest like equations: Appearance of almost shape invariant states

We derive Ehrenfest like equations for the coupled Gross Pitaevskii equations (CGPE) which describe the dynamics of the binary Bose-Einstein condensate (BBEC) both in the free particle regime and in the regime where condensate is well trapped. Instead of traditional variational technique, we propose a new Ehrenfest based approach to explore so far unrevealed dynamics for CGPE and illustrate the possibility of almost shape invariant states in both the regimes. In absence of trapping potential, when all the interactions present in the system are attractive, it is possible for an initially mixed Gaussian state to propagate with almost no change in width if the proper initial condition is satisfied. Even for repulsive intra-atomic and attractive inter-atomic interaction ($g_{αβ}$) one can tune $|g_{αβ}|$ such that the width of the propagating wave packet remains bounded within almost about $10\%$. We also discuss the dynamics of the initially phase separated condensate and have shown the breakdown of Gaussian nature of the wave packets due to collisions. However, when BEC is trapped in simple harmonic oscillator(SHO) potential, for $g_{αβ}>0$, it is possible for an initially overlapping state to retain its initial shape if $g_{αβ}$ is less than a critical value ($g_{αβ}^c$). If $g_{αβ}$ exceeds $g_{αβ}^c$, an overlapping state can become phase separated while keeping its shape unchanged.

cond-mat.quant-gas↗

arXiv2016

Bifurcations, stability, and mode evolution in segregated condensate mixtures

We present new features of low energy Bogoliubov quasiparticle excitations of a two component Bose-Einstein condensate (TBEC) in quasi-2D geometry at zero temperature using Hartree-Fock-Bogoliubov (HFB). We, in particular, consider the TBECs of $^{133}$Cs~-$^{87}$Rb and $^{85}$Rb~-$^{87}$Rb, and show specific features in the low energy excitation spectrum as a function of the interaction strength. For $^{85}$Rb~-$^{87}$Rb TBEC, the appearance of a new zero energy mode is observed. Whereas for $^{133}$Cs~-$^{87}$Rb TBEC we report a bifurcation of the softened Kohn mode at the point of transition from miscible to immiscible domain. The lower energy mode, after the bifurcation, goes soft and becomes a new Goldstone mode of the system.

cond-mat.quant-gas↗

arXiv2016

Large compact clusters and fast dynamics in coupled nonequilibrium systems

We demonstrate particle clustering on macroscopic scales in a coupled nonequilibrium system where two species of particles are advected by a fluctuating landscape and modify the landscape in the process. The phase diagram generated by varying the particle-landscape coupling, valid for all particle density and in both one and two dimensions, shows novel nonequilibrium phases. While particle species are completely phase separated, the landscape develops macroscopically ordered regions coexisting with a disordered region, resulting in coarsening and steady state dynamics on time scales which grow algebraically with size, not seen earlier in systems with pure domains.

cond-mat.stat-mech↗

arXiv2015

Stability and The Existence of Coherent Structure in Demixed State of Binary BEC

From a linear stability analysis of the Gross Pitaevskii equation for binary Bose Einstein condensates, it is found that the uniform state becomes unstable to a periodic perturbation of wave number k if k exceeds a critical value kc. However we find that a stationary spatially periodic state does not exist. We show the existence of pulse type solutions, when the pulse structure for one condensate is strongly influenced by the presence of the other condensate.

cond-mat.quant-gas↗