Metallic nanowires and mesoscopic networks on a free surface of superfluid helium and charge-shuttling across the liquid–gas interface

Abstract

We investigate the motion of electrically charged metallic nano-and microparticles produced by laser ablation in He gas and injected into superfluid helium. In the presence of a vertical static electric field, the particles either perform a repetitive shuttle-like motion transporting the charge across the liquid-gas interface or become trapped under the free surface of liquid He and coalesce into long filaments and complex two-dimensional mesoscopic networks. A classical electrohydrodynamic model is used to describe the motion of charged microparticles in superfluid He. The resulting filaments and networks are analyzed using electron microscopy. It is demonstrated that each filament is in fact composed of a large number of nanowires with a characteristic diameter of order of 10 nm and extremely large aspect ratios.

Visualisation of quantised vortex reconnection as enabled by laser ablation

“…In this study, we demonstrated that the dense silicon nanoparticles are stabilised along the quantised vortex cores and move collectively with the quantised vortex. This finding clearly supports the hypothesis that the quantised vortex plays a major role in the formation of the semiconducting or metallic nanowires in superfluid 4 He [5,12,16,18,[25][26][27], although the intermediate process needs to be further studied. The laser ablation method can inject various nanoparticles, ranging from semiconductors [21] to metals [5,22], into superfluid 4 He.…”

“…A stunning example is the visualization of quantised vortex dynamics using frozen hydrogen particles [10,15]. However, although some reports have indicated that dense materials such as metallic or semiconducting nanowires are formed along the quantised vortex core [5,[16][17][18], the contribution of the quantised vortex remains controversial [5,12]. Herein, we provide direct experimental evidence of dense silicon nanoparticle attraction to the quantised vortex, and the stabilisation along the vortex core.…”

“…Quantised vortices are believed to play a major role in the interaction between superfluid helium and light impurities [2,[8][9][10][11]. However, the basic principle governing the interaction is still controversial for dense materials such as semiconductor and metal impurities [5,12]. Herein, we provide experimental evidence of the attraction of the dense silicon nanoparticles to the quantised vortex cores.…”

Dynamics of the Vortex-Particle Complexes Bound to the Free Surface of Superfluid Helium

“…The tracer particles are produced inside the cell and are trapped at the free surface by the technique developed in our recent studies [19][20][21]. A frequency-tripled pulsed diode-pumped solid-state (DPSS) laser (λ = 355 nm) with a pulse energy of 70 µJ is used to ablate a metal (Cu, Ba, Dy) target submerged in liquid He.…”

Dynamics of fine particles due to quantized vortices on the surface of superfluid $^4$He

“…trapped just below the surface of superfluid 4 He by Moroshkin et al They produce the particles by a laser ablation of a metallic target submerged in superfluid 4 He [1,2], and trap them just below the free surface by using a combination of surface tension and the applied static electric field. The particles are illuminated with the expanded beam of a cw laser, and their motions are tracked.…”