arXiv subjects

Marek Napiórkowski

Publications and source records attributed to Marek Napiórkowski.

13 recordsLinked to original sources

arXiv2025

Thermal Casimir effect in the spin-orbit coupled Bose gas

We study the thermal Casimir effect in ideal Bose gases with spin-orbit (S-O) coupling of Rashba type below the critical temperature for Bose-Einstein condensation. In contrast to the standard situation involving no S-O coupling, the system exhibits long-ranged Casimir forces both in two and three dimensions ($d=2$ and $d=3$). We identify the relevant scaling variable involving the ratio $D/\nu$ of the separation between the confining walls $D$ and the S-O coupling magnitude $\nu$. We derive and discuss the corresponding scaling functions for the Casimir energy. In all the considered cases the resulting Casimir force is attractive and the S-O coupling $\nu$ has impact on its magnitude. In $d=3$ the exponent governing the decay of the Casimir force becomes modified by the presence of the S-O coupling, and its value depends on the orientation of the confining walls relative to the plane defined by the Rashba coupling. In $d=2$ the obtained Casimir force displays singular behavior in the limit of vanishing $\nu$

cond-mat.quant-gas↗

arXiv2024

Spin-orbit coupled mean-field Bose gas at finite temperature

We consider the spin-orbit coupled Bose gas with repulsive mean-field interparticle interactions. We analyze the phase diagram of the system varying the temperature $T>0$, the chemical potentials, as well as interparticle and spin-orbit interaction couplings. Our results indicate that, for Rashba- and Weyl-type spin-orbit couplings, condensates featuring ordering wavevector $\vec{Q}\neq \vec{0}$ are fragile with respect to thermal fluctuations and, at $T>0$, the only stable thermodynamic phases involving the Bose-Einstein condensate (BEC) are those of uniform type with $\vec{Q}=\vec{0}$. On the other hand, presence of the spin-orbit coupling stabilizes the $\vec{Q}=\vec{0}$ BEC state at any dimensionality $d>1$ and modifies either the order or the universality class of the corresponding phase transition. We emphasize the singular nature of the limit of vanishing spin-orbit interaction coupling $v$, sizable shifts of the phase boundaries upon varying $v$, as well as the role of the relative magnitudes of the interparticle interaction couplings for the character of the condensation transition.

cond-mat.quant-gas↗

arXiv2024

Fully polarized Fermi systems at finite temperature

We propose a simple model of an interacting, fully spin--polarized Fermi gas in dimensions $d=2$ and $d=3$, and derive the approximate expression for the energy spectrum and the corresponding formula for the Helmholtz free energy. We analyze the thermodynamics of the system and find the lines of first--order phase transitions between the low and high density phases terminating at critical points. The properties of the corresponding phase diagrams are qualitatively different for $d=2$ and $3$, and sensitively depend on the interparticle attraction, which marks a departure from the standard van der Waals theory. The differences originate from the Pauli exclusion principle and are embeded in the fermionic nature of the system under study.

cond-mat.quant-gas↗

arXiv2023

First-order, continuous, and multicritical Bose-Einstein condensation in Bose mixtures

We address the possibility of realizing Bose-Einstein condensation as a first-order phase transition by admixture of particles of different species. To this aim we perform a comprehensive analysis of phase diagrams of two-component mixtures of bosons at finite temperatures. As a prototype model, we analyze a binary mixture of Bose particles interacting via an infinite-range (Kac-scaled) two-body potential. We obtain a rich phase diagram, where the transition between the normal and Bose-Einstein condensed phases may be either continuous or first-order. The phase diagram hosts lines of triple points, tricritical points, as well as quadruple points. We address the structure of the phase diagram depending on the relative magnitudes of the inter- and intra-species interaction couplings. In addition, even for purely repulsive interactions, we identify a first-order liquid-gas type transition between non-condensed phases characterized by different particle concentrations. In the obtained phase diagram, a surface of such first-order transitions terminates with a line of critical points.

cond-mat.quant-gas↗

arXiv2022

Variance of the Casimir force in an ideal Bose gas

We consider an ideal Bose gas enclosed in a $d$-dimensional slab of thickness $D$. Using the grand canonical ensemble we calculate the variance of the thermal Casimir force acting on the slab's walls. The variance evaluated per unit wall area is shown to decay like $ Δ_{var}/D$ for large $D$. The amplitude $ Δ_{var}$ is a non-universal function of two scaling variables $λ/ ξ$ and $D/ ξ$, where $λ$ is the thermal de Broglie wavelength and $ξ$ is the bulk correlation length. It can be expressed via the bulk pressure, the Casimir force per unit wall area, and its derivative with respect to chemical potential. For thermodynamic states corresponding to the presence of the Bose-Einstein condensate the amplitude $ Δ_{var}$ retains its non-universal character while the ratio of the mean standard deviation and the Casimir force takes the scaling form $(D/L)^{\frac{d-1}{2}}\, (D/λ)^{d/2}$, where $L$ is the linear size of the wall.

cond-mat.stat-mech↗

arXiv2021

Casimir forces for the ideal Bose gas in anisotropic optical lattices: the effect of alternating sign upon varying dimensionality

We analyze the thermodynamic Casimir effect occurring in a gas of non-interacting bosons confined by two parallel walls with a strongly anisotropic dispersion inherited from an underlying lattice. In the direction perpendicular to the confining walls the standard quadratic dispersion is replaced by the term $|{\bf p}|^α$ with $α\geq 2$ treated as a parameter. We derive a closed, analytical expression for the Casimir force depending on the dimensionality $d$ and the exponent $α$, and analyze it for thermodynamic states in which the Bose-Einstein condensate is present. For $α\in\{4,6,8,\dots\}$ the exponent governing the decay of the Casimir force with increasing distance between the walls becomes modified and the Casimir amplitude $Δ_α(d)$ exhibits oscillations of sign as a function of $d$. Otherwise we find that $Δ_α(d)$ features singularities when viewed as a function of $d$ and $α$. Recovering the known previous results for the isotropic limit $α=2$ turns out to occur via a cancellation of singular terms.

cond-mat.quant-gas↗

arXiv2016

Continuous and discontinuous morphological transitions between capillary bridges on a beaded chain pulled out from a liquid

We describe theoretically and validate experimentally the mechanism of formation of capillary bridges during pulling a beaded chain out from a liquid with a planar surface. There are two types of capillary bridges present in this system, namely the sphere-planar liquid surface bridge initially formed between the spherical bead leaving the liquid bath and the original bulk planar liquid surface, and the sphere-sphere capillary bridge formed between neighbouring beads in the part of the chain above the liquid surface. During pulling the chain out of the liquid, the sphere-planar liquid surface bridge transforms into the sphere-sphere bridge. We show that for monodisperse spherical beads comprising the chain, this morphological phase transition can be either continuous or discontinuous. The transition is continuous when the diameter of the spherical beads is larger than the capillary length. Otherwise, the transition is discontinuous, likewise the capillary force acting on the chain.

cond-mat.soft↗

arXiv2016

Lateral critical Casimir force in two-dimensional inhomogeneous Ising strip. Exact results

We consider two-dimensional Ising strip bounded by two planar, inhomogeneous walls. The inhomogeneity of each wall is modeled by a magnetic field acting on surface spins. It is equal to $+h_1$ except for a group of $N_1$ sites where it is equal to $-h_1$. The inhomogeneities of the upper and lower wall are shifted with respect to each other by a lateral distance $L$. Using exact diagonalization of the transfer matrix, we study both the lateral and normal critical Casimir forces as well as magnetization profiles for a wide range of temperatures and system parameters. The lateral critical Casimir force tends to reduce the shift between the inhomogeneities, and the excess normal force is attractive. Upon increasing the shift $L$ we observe, depending on the temperature, three different scenarios of breaking of the capillary bridge of negative magnetization connecting the inhomogeneities of the walls across the strip. As long as there exists a capillary bridge in the system, the magnitude of the excess total critical Casimir force is almost constant, with its direction depending on $L$. By investigating the bridge morphologies we have found a relation between the point at which the bridge breaks and the inflection point of the force. We provide a simple argument that some of the properties reported here should also hold for a whole range of different models of the strip with the same type of inhomogeneity.

cond-mat.stat-mech↗

arXiv2015

Quantum wetting transitions in two dimensions: an alternative path to non-universal interfacial singularities

We consider two-dimensional ($d=2$) systems with short-ranged microscopic interactions, where interface unbinding (wetting) transitions occur in the limit of vanishing temperature $T$. For $T=0$ the transition is characterized by non-universal critical properties analogous to those established for thermal wetting transitions in $d=3$, albeit with a redefined capillary parameter $\tildeω$. Within a functional renormalization-group treatment of an effective interfacial model, we compute the finite temperature phase diagram, exhibiting a line of interface unbinding transitions, terminating at $T=0$ with an interfacial quantum critical point. At finite $T$ we identify distinct scaling regimes, reflecting the interplay between quantum and thermal interfacial fluctuations. A crossover line marking the onset of the quantum critical regime is described by the $d=3$ interfacial correlation-length exponent $ν_{||}$. This opens a new way to investigate the non-universal character of $ν_{||}$ without penetrating the true critical regime. On the other hand, the emergent interfacial quantum critical regime shows no signatures of non-universality.

cond-mat.stat-mech↗

arXiv2014

Lateral critical Casimir force in 2D Ising strip with inhomogeneous walls

We analyze the lateral critical Casimir force acting between two planar, chemically inhomogeneous walls confining an infinite 2D Ising strip of width $M$. The inhomogeneity of each of the walls has size $N_1$; they are shifted by the distance $L$ along the strip. Using the exact diagonalization of the transfer matrix, we calculate the lateral critical Casimir force and discuss its properties, in particular its scaling close to the 2D bulk critical point, as a function of temperature, surface magnetic field, and the geometric parameters $M$, $N_1$, $L$. We determine the magnetization profiles which display the formation of the bridge joining the inhomogeneities on the walls and establish the relation between the characteristic properties of the lateral Casimir force and magnetization morphologies. We check numerically that breaking of the bridge is related to the inflection point of the lateral force.

cond-mat.stat-mech↗

arXiv2013

The influence of van der Waals forces on droplet morphological transitions and solvation forces in nanochannels

The morphological phase transition between a sessile and lenticular shapes of a droplet placed in a nanochannel is observed upon increasing the droplet volume. The phase diagram for this system is discussed within the macro- and mesoscopic approaches. On the mesoscopic level, the van der Waals forces are taken into account via the effective interface potential acting between the channel walls and the droplet. We discuss the contact angle dependence on the droplet volume and the distance between the walls; this angle turns out to be smaller than the macroscopic Young's angle. The droplet presence induces the solvation force acting between the channel walls. It can be both attractive and repulsive, depending on the width of the channel.

cond-mat.soft↗

arXiv2012

The bulk correlation length and the range of thermodynamic Casimir forces at Bose-Einstein condensation

The relation between the bulk correlation length and the decay length of thermodynamic Casimir forces is investigated microscopically in two three-dimensional systems undergoing Bose-Einstein condensation: the perfect Bose gas and the imperfect mean-field Bose gas. For each of these systems, both lengths diverge upon approaching the corresponding condensation point from the one-phase side, and are proportional to each other. We determine the proportionality factors and discuss their dependence on the boundary conditions. The values of the corresponding critical exponents for the decay length and the correlation length are the same, equal to 1/2 for the perfect gas, and 1 for the imperfect gas.

cond-mat.stat-mech↗

arXiv2009

Properties of the solvation force of a two-dimensional Ising strip in scaling regimes

We consider d=2 Ising strip with surface fields acting on boundary spins. Using the properties of the transfer matrix spectrum we identify two pseudotransition temperatures and show that they satisfy similar scaling relations as expected for real transition temperatures in strips with d>2. The solvation force between the boundaries of the strip is analysed as a function of temperature, surface fields and the width of the strip. For large widths the solvation force can be described by scaling functions in three different regimes: in the vicinity of the critical wetting temperature of 2D semi-infinite system, in the vicinity of the bulk critical temperature, and in the regime of weak surface fields where the critical wetting temperature tends towards the bulk critical temperature. The properties of the relevant scaling functions are discussed.

cond-mat.stat-mech↗