Transport Properties of the Two-Dimensional Wigner Solid on Liquid Helium in the Presence of?a?High-Frequency Damaging Electric Field

Experimental studies of transport properties of the two-dimensional (2D) Wigner solid (WS) over a liquid helium surface are performed in the presence of an additional (damaging) high frequency electric field. Surface electrons are in the linear transport regime with regard to the driving electric field created by a potential of a small amplitude (about 1 mV) whose frequency varies in the range 3?C8 MHz. The damaging potential applied simultaneously has substantially higher amplitudes (30?C300 mV) and frequency 36 MHz. The evolution of resonance spectra of the coupled phonon-ripplon system, electron resistivity, and the effective mass of surface dimples caused by an increase in the damaging electric field amplitude is observed. At a certain damaging potential of about 300 mV the major electron-ripplon resonance is shown to disappear, which is accompanied by a sharp decrease in the dimple effective mass, and electron resistivity. Experimental data are explained by a theoretical model of high-frequency WS decoupling from surface dimples caused by the breakdown of the balance of forces applied to the WS.     

Mobility of Electrons at Liquid Helium Surface under Overheating

Mobility of surface electrons (SE) on liquid helium at low temperatures (T≃0.52 K) is studied as a function of the driving electric field E _∥ in the range 1–25 mV/cm. The experimental conditions correspond approximately to effective electron temperatures T _e ≃1–12 K. The measurements are performed for SE with the surface electron density n _s =1.46×10⁸ cm⁻² at different holding electric fields E _⊥ =200–1400 V/cm. The mobility is observed to be an increasing function of the driving field. The function depends strongly on the holding electric field applied. The experimental results are in reasonable agreement with theoretical curves calculated using the force-balance equation method expressing the mobility in terms of the dynamical structure factor of SE.     

Nonlinear Features of Phonon–Ripplon Modes in the Electron Crystal Over Liquid Helium

The resonance spectra of coupled phonon–ripplon oscillations in two-dimensional electron crystals over liquid helium are measured at different driving electric potentials. The crystals with surface electron densities n _s = (3.2 − 12) × 10⁸ cm⁻² are studied at holding electric fields E _⊥ = 590−1180 V/cm at temperature T≈ 80 mK. It is found that an increase of the driving potential leads to a change of resonance curves: the curves become more flat, asymmetric, and splintered depending on electron density and holding potential. The data obtained are used to estimate the electron effective mass in the crystal. It is shown for the first time that the effective electron mass in the crystal increases as the driving field increases.     

Coupled Phonon-Ripplon Modes in the Electron Crystal at Different Driving Fields

Coupled phonon-ripplon oscillations in a two-dimensional electron crystal over liquid helium with surface electron density n _s =1.2×10⁹ cm⁻² at the temperature T=83 mK are studied in a Corbino experimental cell. The measurements are performed in the frequency interval where resonances of the coupled oscillations are observed and at different driving voltages V _∥ <10 mV at which nonlinear features in the crystal conductivity start to appear. A special attention is paid to a relatively narrow frequency interval ω/2π≃3–5 MHz. In this interval the jumps in the oscillation spectrum are observed. From the data obtained, the mobility and electron effective mass are calculated as functions of driving electric field. The electron effective mass in the crystal and dissipative losses are found to increase with the driving field increase. A possible reason for that can be an anharmonicity of the electron-ripplon interaction, which become noticeable if the electron crystal velocity along the surface is high enough.     

Influence of Hatch Strategy on Crystallographic Texture Evolution,Mechanical Anisotropy of Laser Beam Powder Bed Fused S316L Steel

The correlations between process conditions, microstructure, and mechanical properties of additively manufactured components are not fully understood yet. In this contribution, three different hatch strategies are used to fabricate rod-like samples from S316L stainless steel, which are further investigated using synchrotron diffraction, optical microscopy, and tensile tests. The results indicate the presence of ⟨110⟩ biaxial and fiber textures, whose sharpness depends on the applied hatch strategy. Mechanical tests reveal a strong correlation of the samples’ response to the observed anisotropy in the plane perpendicular to the build direction. Even though the average yield and ultimate tensile strengths of around 475 and 500 MPa, respectively, do not differ significantly, the stress–strain behavior can be correlated with the observed in-plane anisotropy. Particularly, twinning-induced plasticity, a distinct increase of the work hardening rate at larger strains and elliptical necking are observed in some samples with biaxial (Goss) texture. These findings indicate that texture design by means of applying dedicated hatch strategies can be used to effectively tune the multiaxial deformation behavior of components produced by laser powder bed fusion.