Dynamics and hysteresis of the contact line between liquid hydrogen and cesium substrates

We have measured both the hysteresis and the dynamics of the edge of a liquid hydrogen meniscus on several solid cesium substrates. We find that the dynamics of the contact line is thermally activated. For all substrates, we find that the activation energy is of the order of the hysteresis. We show that the pinning of the contact line on mesoscopic defects of the Cs substrate is likely to control both the hysteresis and the dynamics of the contact line at low velocity, close to the depinning threshold. Such a mechanism could be relevant also for simple room-temperature systems.     

Asymmetric wetting hysteresis on chemical defects

Using the Wilhelmy plate technique, the role of chemical defects in hysteretic wetting behavior was investigated. The wetting and dewetting work differ significantly, depending on the defect energy (i.e., high or low energy with respect to the matrix). For one, or an array of high-energy defects, advancing measurements departed from equilibrium theory, while the receding data were in close agreement. Conversely for low-energy defects, only the receding measurements showed significant departure from theory. We propose that distinct wetting mechanisms for high- and low-energy defects explain the phenomenon of asymmetric hysteresis, where the advancing or receding contact angle deviates more strongly from the equilibrium angle.     

Neutralisation of fast helium ions by cesium

The absolute cross-section for charge-exchange in cesium vapor has been measured for 5 to 25 keV He⁺ ions. The proportion of He¹ metastable triplet in the post charge-exchange beam has been estimated.     

Helium wetting: Theme and variations on inhomogeneous helium

The surprising discovery, in 1991, that liquid helium does not wet a cesium surface at low temperature has triggered an important activity both theoretical and experimental: helium has become a model system for the study of wetting transitions. After summarizing the main theme of helium wetting, I will focus on more recent studies, such as the structure and excitations of helium interfaces, experiments on the capillary rise, the “surfactant effect” of helium-3 impurities on liquid helium-4 and the “quantum prewetting transition” of pure helium-3. Unexpected consequences on the phase separation of³He?⁴He mixtures in restricted geometry will be drawn.     

Electrical resistivity of liquid cesium

The temperature dependences of liquid cesium resistivity are calculated using smooth nonlocal model pseudopotentials (SNMP). The calculations were performed for temperatures of 35, 150, 280, 310, 470, and 630°C, both with temperature-dependent SNMP parameter variations and without them. The SNMP parameters of liquid cesium were determined based only on the experimental values of free ion terms without applying any methods of adjustment to the electrical resistivity of cesium. Application of SNMP makes it possible to substantially improve the similarity of the temperature dependences for calculated and experimentally obtained electrical resistivities of liquid cesium as compared to the calculations based on local model potentials.     

Hydrogen and helium films as model systems of wetting

Optical experiments on the wetting properties of liquid ⁴He and molecular hydrogen are reviewed. Hydrogen films on noble metal surfaces serve as model systems for studying triple point wetting, a continuous transition between wetting and non-wetting. By means of optically excited surface plasmons, the adsorbed film thickness for temperatures around, and far below, the bulk melting temperature is measured, and the physical mechanisms responsible for the transition are elucidated. Possible applications for other experiments in pure and applied research are discussed. Thin films and droplets of liquid helium are studied on cesium surfaces, on which there is a first order wetting transition. Our studies concentrate on dynamical observations via surface plasmon microscopy, which provide insight into the morphology of liquid helium droplets spreading at different temperatures. Features corresponding to pinning forces, the prewetting line, and the Kosterlitz-Thouless transition are clearly observed.     

Electron bound states on liquid helium

Using an exactly soluble model of image potential which has the form -Ze²/ (z+β), we have calculated the energy levels of electrons trapped on the surface of liquid helium as a function of the parameter β. Our results show that the experimental values of Grimes et al can be fit very well by locating the effective liquid helium-vacuum interface at β = 1.01 Å.     

Parity violation in helium and cesium and the effect of electron-electron interaction

We investigate the parity violating effect in helium and cesium atoms due to the exchange of a Z⁰-meson between atomic electrons. It is found that this effect is negligible for both atoms in comparison with the contribution from the electron-nucleus interactions, if we take the neutral-current coupling between electrons as predicted by the SU (2) × U (1) theory and sin²θ_W ≈ 0.3.     

超导重力仪用液氦恒温器研制

介绍了一套超导重力仪用液氦恒温器,包括技术指标要求、总体结构、关键技术、试验步骤及结果.恒温器液氦消耗量为0.8L/h,真空腔体内部温度稳定度为±5mK,低温下真空腔体真空度优于5×10-4pa,各参数均优于技术指标要求,完全满足超导重力仪工作环境要求.表明该设计方案是合理的,试验流程是正确的.     

Variational methods for the ground state of liquid helium4

Assuming a Bijl-Jastrow-type wave function for the ground state of liquid He⁴, one can express the energy as a functional of the pair distribution functiong(r) when use is made of one of several “cluster approximations” known from the theory of classical fluids. The applicability of these approximations, and especially an integrodifferential equation forg(r) derived byAbe andHiroike, are discussed. It is shown that both the HNC and the PY approximations, when used consistently, yield the phonon behaviour of the liquid-structure factorS(k) for smallk. In the HNC approximation the energy as a function of density is calculated by a variational procedure. The velocity of sound following from \(\mathop {\lim }\limits_{k \to 0} \) S(k) is in good agreement with experiments and, at the equilibrium density, also with that calculated from the energy-versus-density curve. In the PY approximation a minimum of the energy expectation value does not exist without further restrictions on the trial wave function.     

Surface tension of liquid helium

We calculated the surface tension of liquid helium using a relation between the condensate fraction and surface tension. The paired-phonon model for the condensate fraction results in calculated surface tension in excellent agreement with experiment at low temperatures.     

Self-consistent Debye-Waller factors of the electron solid on liquid helium

Based on the self-consistent field formalism we propose a shear-mode self-consistency for the high-frequency Debye-Waller factors (HFDWF) of the electron solid bound on a free surface of liquid helium. Our results are qualitatively in agreement with the empirical DW factor determined by Fisher, Halperin, and Platzman with the experiment of Grimes and Adams. We also report the analysis of the HFDWF according to the Lindemann law.     

Properties of surface state electrons on liquid helium

Electrons on the surface of liquid helium form a two-dimensional system that is of great interest for its own unique properties as well as being a probe of the helium surface. The spectroscopic evidence for the hydrogenic nature of the surface state is compared with predictions. Measurements of the electron mobility parallel to the surface in low and high electric fields are compared with theory. The lifetime in the surface state is discussed as well as the effect of the electron on the liquid surface. The possibility that the electrons crystallize to form a two-dimensional lattice and the properties of this lattice are also analyzed.