arXiv subjects

Massimo Boninsegni

Publications and source records attributed to Massimo Boninsegni.

At least 19 recordsLinked to original sources

arXiv2026

Bound state of a He-3 atom at free He-4 surfaces

Quantum Monte Carlo simulations confirm the existence of a bound state of a single He-3 atom at a free superfluid He-4 surface in three dimensions, localized within a ~10-A thick low-density He-4 surface layer, with a binding energy of approximately 4 K with respect to vacuum. As the temperature is raised above ~ 1 K the He-3 atom leaves the surface to dissolve into the superfluid. The situation is entirely different in two dimensions, as the He-3 atom is excluded from the superfluid and no surface bound state exists. Results are also presented for the a He-3 atom binding to nanoscale size He-4 clusters adsorbed on weak substrates, a physical system that may allow for the observation of some of the physics predicted for extended surfaces. It is shown that a He-3 bound state localized at the perimeter of sufficiently small (a few tens of atoms) clusters exists not just on Cs, as previously reported, but on all alkali substrates.

cond-mat.stat-mech↗

arXiv2026

Ground state correlations in the one-dimensional Fermi one-component plasma

Structural and dynamic correlations in the ground state of the one-dimensional Fermi one-component plasma are studied by Quantum Monte Carlo simulations. Results are presented for the pair correlation function, static structure factor, the one-particle density matrix and the momentum distribution, for the cases of full, partial and no polarization. {Within the precision of the calculation, the results conform to the fundamental scaling prediction of the Tomonaga-Luttinger Liquid Theory}. Evidence is reported of density correlations slowly decaying with distance, with the concurrent emergence of quasi-crystalline order even in the weakly correlated regime. Effects of quantum statistics in the momentum distribution are discussed.

cond-mat.str-el↗

arXiv2026

Monte Carlo study of the superfluid phase of $^4$He

Detailed numerical results obtained with state-of-the-art Quantum Monte Carlo (QMC) simulations are presented for the superfluid phase of $^4$He at saturated vapor pressure. The aim of this contribution is that of providing reliable, up-to-date estimates for this archetypal superfluid, reflecting the methodological progress that has taken place over the past two decades. We simulate a system comprising 2,048 helium atoms, i.e., an order of magnitude greater in size than those for which results currently regarded as standard references were originally obtained. We offer revised estimates for energetic and structural properties, as well as for the ground state condensate fraction.

cond-mat.stat-mech↗

arXiv2026

Bose one-component plasma in 2D: a Monte Carlo study

The low-temperature properties of a 2D Bose fluid of charged particles interacting through a 1/r potential, moving in the presence of a uniform neutralizing background, is studied by Quantum Monte Carlo simulations. We make use of the Modified Periodic Coulomb potential formalism to account for the long-range character of the interaction, and explore a range of density corresponding to average interparticle separation $1 \le r_s\le 80$. We report numerical results based on simulations of system comprising up to 2304 particles. We find a superfluid ground state for $r_s$ as large as 70, i.e., significantly above the most recent numerical estimate of the Wigner crystallization threshold, which we estimate at $r_W \approx 71$. Furthermore, no thermally re-entrant crystalline phase nor any evidence of metastable bubbles is observed near the transition, in contrast with a previous theoretical study in which quantum statistics was neglected. The computed superfluid transition temperature depends remarkably weakly on density.

cond-mat.stat-mech↗

arXiv2025

Isotopic separation in mixed clusters of molecular hydrogen

We investigate mixed (50/50) clusters of parahydrogen and orthodeuterium at low temperature, by means of Quantum Monte Carlo simulations. Our results provide evidence of liquid-like behavior and partial isotopic separation in a cluster of 640 molecules, at temperature T=10 K. As the temperature is lowered below ~ 6 K, crystallization occurs, with no indication that the liquid phase is more resilient at low temperature in a mixed cluster. Isotopic separation is therefore predicted to take place at low temperature only through the slow process of molecular self-diffusion in a crystalline matrix.

cond-mat.mes-hall↗

arXiv2025

Momentum distribution of He-3 in one dimension

The one-particle density matrix of a one-dimensional system of fermions featuring a hard-core repulsive interaction at short distances can be computed (numerically) exactly by means of the continuous-space Worm Algorithm, without any sign instability. We present here results for this quantity, and the related momentum distribution, for a helium-three fluid. It is shown that effects of quantum statistics are observable in the fully polarized system, but are suppressed in the unpolarized one, atoms being essentially distinguishable in the latter case.

cond-mat.other↗

arXiv2024

Liquid-liquid transition in a Bose fluid near collapse

Discovering novel emergent behavior in quantum many-body systems is a main objective of contemporary research. In this paper, we explore the effects on phases and phase transitions of the proximity to a Ruelle-Fisher instability, marking the transition to a collapsed state. To accomplish this, we study by quantum Monte Carlo simulations a two-dimensional system of soft-core bosons interacting through an isotropic finite-ranged attraction, with a parameter $η$ describing its strength. If $η$ exceeds a characteristic value $η_c$, the thermodynamic limit is lost, as the system becomes unstable against collapse. We investigate the phase diagram of the model for $η\lesssimη_c$, finding -- in addition to a liquid-vapor transition -- a first-order transition between two liquid phases. Upon cooling, the high-density liquid turns superfluid, possibly above the vapor-liquid-liquid triple temperature. As $η$ approaches $η_c$, the stability region of the high-density liquid is shifted to increasingly higher densities, a behavior at variance with distinguishable quantum or classical particles. Finally, for $η$ larger than $η_c$ our simulations yield evidence of collapse of the low-temperature fluid for any density; the collapsed system forms a circular cluster whose radius is insensitive to the number of particles.

cond-mat.stat-mech↗

arXiv2024

He-4 monolayer on Graphene: a Quantum Monte Carlo study

We revisit the problem of adsorption of a single He-4 layer on graphene, focusing on the commensurate C1/3 crystalline phase, specifically on whether it may possess a nonzero superfluid response, and on the existence of superfluid phases, either (metastable) liquid or vacancy-doped crystalline. We make use of canonical Quantum Monte Carlo simulations at zero and finite temperature, based on a realistic microscopic model of the system. Our results confirm the absence of any superfluid response in the commensurate crystal, and that no thermodynamically stable uniform phase exists at lower coverage. No evidence of a possibly long-lived, metastable superfluid phase at C1/3 coverage is found. Altogether, the results of ground-state projection methods and finite-temperature simulations are entirely consistent.

cond-mat.str-el↗

arXiv2024

Quantum Monte Carlo study of thin parahydrogen films on graphite

The low-temperature properties of one and two layers of parahydrogen adsorbed on graphite are investigated theoretically through Quantum Monte Carlo simulations. We adopt a microscopic model that explicitly includes the corrugation of the substrate. We study the phase diagram of a monolayer up to second layer promotion, and the possible occurrence of superfluidity in the second layer. We obtain results down to a temperature as low as 8 mK. We find second-layer promotion to occur at a considerably greater coverage than obtained in previous calculations and estimated experimentally; moreover, we find no evidence of a possible finite superfluid response in the second layer, disproving recent theoretical predictions.

cond-mat.other↗

arXiv2024

Superclimbing modes in transverse quantum fluids: signature statistical and dynamical features

Superclimbing modes are hallmark degrees of freedom of transverse quantum fluids describing wide superfluid one-dimensional interfaces and/or edges with negligible Peierls barrier. We report the first direct numeric evidence of quantum shape fluctuations -- caused by superclimbing modes -- in simple lattice models, as well as at the free edge of an incomplete solid monolayer of $^4$He adsorbed on graphite. Our data unambiguously reveals the defining feature of the superclimbing modes -- canonical conjugation of the edge displacement field to the field of superfluid phase -- and its unexpected implication, i.e., that superfluid stiffness can be inferred from density snapshots.

cond-mat.other↗

arXiv2024

Thermocrystallization of lattice dipolar bosons coupled to a high-finesse cavity

Investigating finite temperature effects on quantum phases is key to their experimental realization. Finite temperature, and the interplay between quantum and thermal fluctuations can undermine properties and/or key features of quantum systems but they can also bring upon interesting phenomena. In this paper, we present a comprehensive investigation of the finite temperature phase diagram of two-dimensional lattice dipolar bosons coupled to a high-finesse optical cavity. Interestingly, we observe that checkerboard density-density correlations are enhanced at finite temperature. Indeed, we found that finite temperature drives a superfluid ground state into a normal state which will then develop checkerboard order at higher temperatures. We show that this effect is solely due to the cavity-mediated interactions. We also confirm that the supersolid checkerboard phase survives for a wide range of filling factors up to temperature scale of the order of half hopping amplitude, while the checkerboard diagonal order can survive up to temperatures of a few hopping amplitudes.

cond-mat.quant-gas↗

arXiv2023

Phase diagram of muonium hydride: when dimensionality matters

We carry out a theoretical investigation of the low-temperature phase diagram of muonium hydride in two dimensions, using numerical simulations. It is shown that the phase diagram of this substance is qualitatively different in two and three dimensions. Specifically, while in three dimensions it has been shown to be essentially identical to that of parahydrogen, i.e., only displaying a single (crystalline) phase, in two dimensions it is very similar to that of He-4, with an equilibrium liquid phase that turns superfluid at a temperature as high as ~ 2.2 K, and that crystallizes under applied pressure. To our knowledge, this is the first well-described case of a condensed matter system whose phase diagram is drastically altered by dimensional reduction.

cond-mat.stat-mech↗

arXiv2023

The solid phase of He-4: A Monte Carlo simulation study

The thermodynamics of solid (hcp) He-4 is studied theoretically by means of unbiased Monte Carlo simulations at finite temperature, in a wide range of density. This study complements and extends previous theoretical work, mainly by obtaining results at significantly lower temperatures (down to 60 mK) and for systems of greater size, by including in full the effect of quantum statistics, and by comparing estimates yielded by different pair potentials. All the main thermodynamic properties of the crystal, e.g., the kinetic energy per atom, are predicted to be essentially independent of temperature below 1 K. Quantum-mechanical exchanges are virtually non-existent in this system, even at the lowest temperature considered. However, effects of quantum statistics are detectable in the momentum distribution. Comparison with available measurements shows general agreement within the experimental uncertainties.

cond-mat.other↗

arXiv2023

Superconducting transition temperature of the Bose one-component plasma

We present results of first principle numerical simulations of the Bose one-component plasma, i.e., a Bose gas with pairwise Coulomb interactions among particles and a uniform neutralizing background. We compute the superconducting transition temperature for a wide range of densities, in two and three dimensions, for both continuous and lattice versions of the model. Our results are of direct relevance to quantitative studies of bipolaron mechanisms of (high-temperature) superconductivity.

cond-mat.quant-gas↗

arXiv2023

Uniaxial modulation and the Berezinskii-Kosterlitz-Thouless transition

We present a theoretical study of the Berezinskii-Kosterlitz-Thouless transition of a two-dimensional superfluid in the presence of an externally imposed density modulation along a single axis. The subject is investigated in the context of the $|ψ|^4$ classical field theory, by means of analytical and numerical techniques. We show that, as the amplitude of the modulation increases, the physics of the system approaches that of the anisotropic $x$-$y$ model, with a suppressed superfluid transition temperature and an anisotropic response, but with no dimensional crossover.

cond-mat.stat-mech↗

arXiv2022

Microscopic pair potentials and the physical properties of the condensed phase of parahydrogen

Equilibrium physical properties of the solid and liquid phases of parahydrogen, computed by first principle computer simulations, are compared for different choices of pairwise, spherically symmetric intermolecular potentials. The most recent ab initio potential [Patkowski et al., J. Chem. Phys., 2008, 129, 094304], which has a stiffer repulsive core than the commonly used Silvera-Goldman, yields results for structural quantities in better agreement with the most recent experimental measurements, while possibly overestimating the kinetic energy per molecule by as much as 10%. Altogether, the comparison between theory and the available experimental evidence suggests that the potential of Patkowski et al. may be a better choice for simulations of condensed phases of parahydrogen at moderate pressure.

cond-mat.other↗

arXiv2022

Superfluid transition of the second layer of He-4 on graphite: does substrate corrugation matter?

The second layer of He-4 adsorbed on a graphite substrate is studied by Quantum Monte Carlo simulations. We make use of a microscopic model of the substrate fully accounting for its corrugation, and compare the results to those obtained with a smooth substrate. The only effect of corrugation is a ~20% reduction of the value of the superfluid fraction of the top layer, in the limit of zero temperature. No evidence of any commensurate (7/12) crystalline and/or "supersolid" phase is found; the superfluid transition temperature is estimated to be ~ 0.75 K. We discuss the implication of these findings on the interpretation of recent experiments.

cond-mat.stat-mech↗

arXiv2022

Thin He-4 films on alkali substrates: where do He-3 atoms bind?

The possible occurrence of bound states of He-3 atoms in the vicinity of a weakly attractive substrate coated with a thin superfluid He-4film is investigated by first principle computer simulations. No evidence is seen of such bound states, even in the case of the weakest substrate, i.e., Cs; a single He-3 atom always binds to the free He-4 surface, regardless of the thickness of the He-4 film. A comparison of He-4 density profiles computed in this work with those yielded by the Density Functional approach that led to the prediction of He-3 bound states near the substrate, shows that the latter may not have afforded a sufficiently accurate structural description of the adsorbed He-4 film.

cond-mat.stat-mech↗