Physical Chemistry Chemical Physics

Capture of Xe and Ar atoms by quantized vortices in 4 He nanodroplets

François Coppens, Francesco Ancilotto, M. Barranco, Nadine Halberstadt, Martí Pi

Published Jan 1, 2017• 32 citations

Abstract

He droplet hosting a 6-vortex array whose cores are filled with Ar atoms. As observed in recent experiments, we find that doping adds substantial rigidity to the system, such that the doped vortex array remains stable, even at low values of the angular velocities where the undoped vortices would otherwise be pushed towards the droplet surface and be expelled.

DOI: 10.1039/c7cp03307a

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Physical Chemistry Chemical Physics

Capture of Xe and Ar atoms by quantized vortices in 4 He nanodroplets

François Coppens, Francesco Ancilotto, M. Barranco, Nadine Halberstadt, Martí Pi

Published Jan 1, 2017• 32 citations

Publisher

Abstract

DOI: 10.1039/c7cp03307a

Related papers

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Martí Pi, José María Escartín, Francesco Ancilotto +1 more

Within density functional theory, we have studied the interplay between vortex arrays and capillary waves in spinning prolate $^{4}\mathrm{He}$ droplets made of several thousand helium atoms. Surface capillary waves are ubiquitous in prolate superfluid $^{4}\mathrm{He}$ droplets, and depending on the size and angular momentum of the droplet, they may coexist with vortex arrays. We have found that the equilibrium configuration of small prolate droplets is vortex free, evolving towards vortex hosting as the droplet size increases. This result is in agreement with a recent experiment [O'Connell et al., Phys. Rev. Lett. 124, 215301 (2020)] that disclosed that vortex arrays and capillary waves coexist in the equilibrium configuration of very large drops. In contrast to viscous droplets executing rigid-body rotation, the stability phase diagram of spinning $^{4}\mathrm{He}$ droplets cannot be universally described in terms of dimensionless angular momentum and angular velocity variables: Instead, the rotational properties of superfluid helium droplets display a clear dependence on the droplet size and the number of vortices they host.Within density functional theory, we have studied the interplay between vortex arrays and capillary waves in spinning prolate $^{4}\mathrm{He}$ droplets made of several thousand helium atoms. Surface capillary waves are ubiquitous in prolate superfluid $^{4}\mathrm{He}$ droplets, and depending on the size and angular momentum of the droplet, they may coexist with vortex arrays. We have found that the equilibrium configuration of small prolate droplets is vortex free, evolving towards vortex hosting as the droplet size increases. This result is in agreement with a recent experiment [O'Connell et al., Phys. Rev. Lett. 124, 215301 (2020)] that disclosed that vortex arrays and capillary waves coexist in the equilibrium configuration of very large drops. In contrast to viscous droplets executing rigid-body rotation, the stability phase diagram of spinning $^{4}\mathrm{He}$ droplets cannot be universally described in terms of dimensionless angular momentum and angular velocity variables: Instead, the rotational properties of superfluid helium droplets display a clear dependence on the droplet size and the number of vortices they host.

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\mathrm{dopant}+\mathrm{vortex}{+}^{4}{\mathrm{He}}_{{N}_{4}}

complex, which in a previous work [F. Dalfovo et al., Phys. Rev. Lett. 85, 1028 (2000)] was found to be energetically stable below a critical size

{N}_{\mathrm{cr}}

, is robust against the addition of

{}^{3}\mathrm{He}

. While

{}^{3}\mathrm{He}

atoms are distributed along the vortex line and on the surface of the

{}^{4}\mathrm{He}

drop, the impurity is mostly coated by

{}^{4}\mathrm{He}

atoms. Results for

{N}_{4}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}500

and a number of

{}^{3}\mathrm{He}

atoms ranging from 0 to 100 are presented, and the binding energy of the dopant to the vortex line is determined.

We present a diffusion Monte Carlo study of a vortex line excitation attached to the center of a

^{4}\mathrm{He}

droplet at zero temperature. The vortex energy is estimated for droplets of increasing number of atoms, from

N=70

up to 300, showing a monotonous increase with

N

. The evolution of the core radius and its associated energy, the core energy, is also studied as a function of

N

. The core radius is $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ in the center and increases when approaching the droplet surface; the core energy per unit volume stabilizes at a value $2.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}{\ensuremath{\sigma}}^{\ensuremath{-}3}$ $(\ensuremath{\sigma}=2.556\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})$ for $N\ensuremath{\ge}200$.

Within density functional theory, we have studied the interplay between vortex arrays and capillary waves in spinning prolate

^{4}\mathrm{He}

droplets made of several thousand helium atoms. Surface capillary waves are ubiquitous in prolate superfluid

^{4}\mathrm{He}

droplets, and depending on the size and angular momentum of the droplet, they may coexist with vortex arrays. We have found that the equilibrium configuration of small prolate droplets is vortex free, evolving towards vortex hosting as the droplet size increases. This result is in agreement with a recent experiment [O'Connell et al., Phys. Rev. Lett. 124, 215301 (2020)] that disclosed that vortex arrays and capillary waves coexist in the equilibrium configuration of very large drops. In contrast to viscous droplets executing rigid-body rotation, the stability phase diagram of spinning

^{4}\mathrm{He}

droplets cannot be universally described in terms of dimensionless angular momentum and angular velocity variables: Instead, the rotational properties of superfluid helium droplets display a clear dependence on the droplet size and the number of vortices they host.