arXiv subjects

M. Boninsegni

Publications and source records attributed to M. Boninsegni.

At least 19 recordsLinked to original sources

arXiv2025

Exchange-driven self-diffusion of nanoscale crystalline parahydrogen clusters on graphite

Computer simulations yield evidence of superfluid behavior of nanoscale size clusters of parahydrogen adsorbed on a graphite substrate at low temperature ($T\lesssim 0.25 \text{ K}$). Clusters with a number of molecules between 7 and 12 display concurrent superfluidity and crystalline order, reflecting the corrugation of the substrate. Remarkably, it is found that specific clusters with a number of molecules ranging between 7 and 12 self-diffuse on the surface like free particles, despite the strong pinning effect of the substrate. This effect is underlain by coordinated quantum-mechanical exchanges of groups of identical molecules, i.e., it has no classical counterpart.

cond-mat.other↗

arXiv2025

Superfluidity of quasi-2D He-4 droplets on graphite

The superfluid response of nanoscale size quasi-2D He-4 droplets adsorbed on a graphite substrate is investigated by computer simulations. It is found that clusters comprising as few as 7 atoms are stable at temperatures lower than < 0.15 K. Clusters of ~20 atoms or less are liquid-like and ~100% superfluid. As the size is increased, the central region crystallizes, forming the commensurate C_1/3 phase, with a surface sliver of superfluidity evolving into a perimetral 1D Luttinger liquid with increasing cluster size. The relevance to quasi-2D molecular spectroscopy and to transverse quantum superfluidity is discussed.

cond-mat.other↗

arXiv2023

Comment on "Absence of Off-Diagonal Long- Range Order in hcp $^4$He Dislocation Cores"

We contend that the arguments provided in Phys. Rev. Lett. 130, 016001 (2023), purporting to show the absence of off-diagonal long-range order in hcp $^4$He dislocation cores are misleading and incorrect. In particular, the one-body density matrix averaged over the whole crystalline sample provides no useful information on the possible superfluid behavior inside the quasi-one-dimensional core of a dislocation in the crystal.

cond-mat.other↗

arXiv2023

Zero-Point Motion of Liquid and Solid Hydrogen

We present an inelastic neutron scattering study of liquid and solid hydrogen carried out using the wide Angular Range Chopper Spectrometer at Oak Ridge National Laboratory. From the observed dynamic structure factor, we obtained empirical estimates of the molecular mean-squared displacement and average translational kinetic energy. We find that the former quantity increases with temperature, indicating that a combination of thermal and quantum effects is important near the liquid-solid phase transition, contrary to previous measurements. We also find that the kinetic energy drops dramatically upon melting of the crystals, a consequence of the large increase in molar volume together with the Heisenberg indeterminacy principle. Our results are compared with quantum Monte Carlo simulations based on different model potentials. In general, there is good agreement between our findings and theoretical predictions based on the Silvera-Goldman and Buck potentials.

cond-mat.other↗

arXiv2017

Kinetic energy and momentum distribution of isotopic liquid helium mixtures

The momentum distribution and atomic kinetic energy of the two isotopes of helium in a liquid mixture at temperature T=2 K are computed by quantum Monte Carlo simulations. Quantum statistics is fully included for He-4, whereas He-3 atoms are treated as distinguishable. Comparison of theoretical estimates with a collection of the most recent experimental measurements shows reasonable agreement for the energetics of He-4 and pure He-3. On the other hand, a significant discrepancy (already observed in previous works) is reported between computed and measured values of the He-3 kinetic energy in the mixture, in the limit of low He-3 concentration. We assess quantitatively the importance of Fermi statistics and find it to be negligible for a He-3 concentration less than approximately 20%. Our results for the momentum distributions lend support to what already hypothesized by other authors, namely that the discrepancy is likely due to underestimation of the He-3 kinetic energy contribution associated with the tail of the experimentally measured momentum distribution.

cond-mat.other↗

arXiv2012

Role of Bose Statistics in Crystallization and Quantum Jamming

Indistinguishability of particles is a major factor destabilizing crystalline order in Bose systems. We describe this effect in terms of damped quasi-particle modes and in the dual language of Feynman paths, and illustrate it by first-principle simulations of dipolar bosons and bulk condensed helium-four. The first major implication is that, contrary to conventional wisdom, zero-point motion alone cannot prevent helium-four crystallization at low temperature, at saturated vapour pressure. Secondly, Bose statistics leads to quantum jamming at finite temperature, dramatically enhancing the metastability of superfluid glasses. Only studies of indistinguishable particles can reliably address these issues.

cond-mat.stat-mech↗

arXiv2011

Phase diagram of soft-core bosons in two dimensions

The low temperature phase diagram of Bose soft disks in two dimensions is studied by numerical simulations. It is shown that a supersolid cluster phase exists, within a range of the model parameters, analogous to that recently observed for a system of aligned dipoles interacting via a softened potential at short distance. These findings indicate that a long-range tail of the interaction is unneeded to obtain such a phase, and that the soft-core repulsive interaction is the minimal model for supersolidity.

cond-mat.quant-gas↗

arXiv2010

A superfluid-droplet crystal and a free-space supersolid in a dipole-blockaded gas

A novel supersolid phase is predicted for an ensemble of Rydberg atoms in the dipole-blockade regime, interacting via a repulsive dipolar potential "softened" at short distances. Using exact numerical techniques, we study the low temperature phase diagram of this system, and observe an intriguing phase consisting of a crystal of mesoscopic superfluid droplets. At low temperature, phase coherence throughout the whole system, and the ensuing bulk superfluidity, are established through tunnelling of identical particles between neighbouring droplets.

cond-mat.quant-gas↗

arXiv2010

Strongly correlated gases of Rydberg-dressed atoms: quantum and classical dynamics

We discuss techniques to generate long-range interactions in a gas of groundstate alkali atoms, by weakly admixing excited Rydberg states with laser light. This provides a tool to engineer strongly correlated phases with reduced decoherence from inelastic collisions and spontaneous emission. As an illustration, we discuss the quantum phases of dressed atoms with dipole-dipole interactions confined in a harmonic potential, as relevant to experiments. We show that residual spontaneous emission from the Rydberg state acts as a heating mechanism, leading to a quantum-classical crossover.

cond-mat.quant-gas↗

arXiv2009

Mesoscopic phases of dipolar ensembles with polar molecules and Rydberg atoms

We discuss the realization of mesoscopic phases of dipolar gases relevant to current experiments with cold polar molecules and Rydberg atoms confined to two dimensions. We predict the existence of superfluid clusters, mesoscopic supersolids, and crystals for a small number of trapped particles, with no counterpart in the homogeneous situation. For certain strengths of the dipole-dipole interactions, the stabilization of purely {\it non-classical crystals} by quantum fluctuations is possible. We propose a magnification scheme to detect the spatial structure of these crystalline phases.

cond-mat.quant-gas↗

arXiv2008

Phase diagram of 4He adsorbed on graphite

We present results of a theoretical study of 4He films adsorbed on graphite, based on the continuous space worm algorithm. In the first layer, we find a domain-wall phase and a (7/16) registered structure between the commensurate (1/3) and the incommensurate solid phases. For the second layer, we find only superfluid and incommensurate solid phases. The commensurate phase found in previous simulation work is only observed if first layer particles are kept fixed; it disappears upon explicitly including their zero-point fluctuations. No evidence of any "supersolid" phase is found.

cond-mat.stat-mech↗

arXiv2008

Local stress and superfluid properties of solid Helium-4

More than half a century ago Penrose asked: are the superfluid and solid state of matter mutually exclusive or do there exist "supersolid" materials where the atoms form a regular lattice and simultaneously flow without friction? Recent experiments provide evidence that supersolid behavior indeed exists in Helium-4 -- the most quantum material known in Nature. In this paper we show that large local strain in the vicinity of crystalline defects is the origin of supersolidity in Helium-4. Although ideal crystals of Helium-4 are not supersolid, the gap for vacancy creation closes when applying a moderate stress. While a homogeneous system simply becomes unstable at this point, the stressed core of crystalline defects (dislocations and grain boundaries) undergoes a radical transformation and can become superfluid.

cond-mat.stat-mech↗

arXiv2008

Phase diagram of anisotropic boson t-J model

We have studied by Quantum Monte Carlo simulations the low temperature phase diagram of a mixture of isotopic, hard core bosons, described by the t-Jz-Jperp model, with Jperp=a Jz. Coexistence of superfluid hole-rich and insulating, antiferromagnetically ordered hole-free phases is observed at sufficiently low hole density, for any a < 1. A two-component checkerboard supersolid phase is not observed. The experimental relevance and possible broader implications of these findings are discussed.

cond-mat.stat-mech↗

arXiv2007

Superfluidity of Grain Boundaries in Solid Helium-4

By large-scale quantum Monte Carlo simulations we show that grain boundaries in Helium-4 crystals are generically superfluid at low temperature, with a transition temperature of the order of ~0.5K at the melting pressure; insulating grain boundaries are found only for special orientations of the grains. We also find that close vicinity to the melting line is not a necessary condition for superfluid grain boundaries, and a grain boundary in direct contact with the superfluid liquid at the melting curve is found to be mechanically stable and the grain boundary superfluidity observed by Sasaki et al. [Science 313, 1098 (2006)] is not just a crack filled with superfluid.

cond-mat.stat-mech↗

arXiv2007

Luttinger Liquid in the Core of Screw Dislocation in Helium-4

On the basis of first-principle Monte Carlo simulations we find that the screw dislocation along the hexagonal axis of an hcp He4 crystal features a superfluid core. This is the first example of a regular quasi-one-dimensional supersolid, and one of the cleanest cases of a regular Luttinger-liquid system. In contrast, the same type of screw dislocation in solid Hydrogen is insulating.

cond-mat.other↗

arXiv2006

Worm Algorithm and Diagrammatic Monte Carlo: A New Approach to Continuous-Space Path Integral Monte Carlo Simulations

A detailed description is provided of a new Worm Algorithm, enabling the accurate computation of thermodynamic properties of quantum many-body systems in continuous space, at finite temperature. The algorithm is formulated within the general Path Integral Monte Carlo (PIMC) scheme, but also allows one to perform quantum simulations in the grand canonical ensemble, as well as to compute off-diagonal imaginary-time correlation functions, such as the Matsubara Green function, simultaneously with diagonal observables. Another important innovation consists of the expansion of the attractive part of the pairwise potential energy into elementary (diagrammatic) contributions, which are then statistically sampled. This affords a complete microscopic account of the long-range part of the potential energy, while keeping the computational complexity of all updates independent of the size of the simulated system. The computational scheme allows for efficient calculations of the superfluid fraction and off-diagonal correlations in space-time, for system sizes which are orders of magnitude larger than those accessible to conventional PIMC. We present illustrative results for the superfluid transition in bulk liquid helium-four in two and three dimensions, as well as the calculation of the chemical potential of solid helium-four.

physics.comp-ph↗

arXiv2006

Superglass Phase of Helium-four

We study different solid phases of Helium-four, by means of Path Integral Monte Carlo simulations based on a recently developed "worm" algorithm. Our study includes simulations that start off from a high-T gas phase, which is then "quenched" down to T=0.2 K. The low-T properties of the system crucially depend on the initial state. While an ideal hcp crystal is a clear-cut insulator, the disordered system freezes into a "superglass", i.e., a metastable amorphous solid featuring off-diagonal long-range order and superfluidity.

cond-mat.stat-mech↗

arXiv2006

Worm Algorithm for Continuous-space Path Integral Monte Carlo Simulations

We present a new approach to path integral Monte Carlo (PIMC) simulations based on the worm algorithm, originally developed for lattice models and extended here to continuous-space many-body systems. The scheme allows for efficient computation of thermodynamic properties, including winding numbers and off-diagonal correlations, for systems of much greater size than that accessible to conventional PIMC. As an illustrative application of the method, we simulate the superfluid transition of Helium-four in two dimensions.

cond-mat.stat-mech↗