Peculiarity of high-Tc oxide superconductors

We calculate Tc map in region of weak electron–phonon coupling based on simple phonon spectrum. By using linear-response method and density functional theory, we calculate phonon spectra and Eliashberg functions of simple metals under pressure. Based on the evolutions of superconducting parameters of simple metals on the Tc map with increasing pressure, we find that there are two different responses to pressure for simple metals: (1) enhancing electron–phonon interaction k such as for La and Li, (2) increasing phonon frequency such as for Pb, Pt. The k threshold effect is found, which origins from the competition between electron–phonon interaction and electron–electron Coulomb interaction and is the reason why Tc of most superconductors of simple metals are higher than 0.1 K.

Tc map and superconductivity of simple metals at high pressure

The local plasticity characterizing the area around the crack tip affects the elastic strain field area due to the boundary interaction between the two zones. Its effects on the SIF and on the Paris’ Law are known, hence it must be considered in the crack growth monitoring and the fatigue limit estimation. Among the different approaches developed, those focusing their attention on the interaction between the elastic stress field and the plastic area seems to be more promising in the evaluation of the crack growth behaviour. In this work, an experimental approach was adopted to identify the plastic zone around the crack. In particular the Thermal Signal Analysis was employed and the thermal footprint was compared with shape and size of the plastic zone predicted through the application of Digital Image Correlation (DIC) in combination with two theoretical models: Westergaard’s model for the stress distribution around the crack tip and the more recent Christopher–James–Patterson (CJP) model

Investigation of the plastic zone around the crack tip in small-scale pure Titanium specimens by means of Thermal Signal Analysis and Digital Image Correlation

Recently a new method of residual stress measurement, TERSA, was described1and it was suggested that there was a contribution to the effects reported from the stress dependence of specific heat. In this paper, experimental and theoretical evidence is presented demonstrating that the magnitude of the change of specific heat with stress is too small to make a significant contribution to the change in temperature resulting from a stress increment applied to a laser irradiated object.

Stress dependence of specific heat: observations on the TERSA technique

The superconducting transition temperature and the superconducting energy gap of alkali intercalated fullerenes have been investigated by considering the Eliashberg equations based on the strong coupling theory of superconductivity incorporating the frequency dependence of the gap in a limited way. The present treatment reduces to an energy dependent electron-phonon interaction in the BCS theory. It has been also inferred that the intermolecular vibrations play an important role in explaining the superconductivity mechanism in alkali-intercalated fullerenes.

Electron-phonon interaction, superconducting transition temperature and energy gap of alkali intercalated fullerenes

Analytic solution to the Eliashberg equation for the superconducting critical temperatures

Conoscopic interferometry is a promising detection technique for ultrafast acoustics. By focusing a probe beam through a birefringent crystal before passing it through a polarizer, conoscopic interferences sculpt the spatial proﬁle of the beam. The use of these patterns for acoustic wave detection revealed a higher detection sensitivity over existing techniques, such as reﬂectometry and beam distortion detection. However, the physical origin of the increased sensitivity is unknown. In this work, we present a model, describing the sensitivity behaviour of conoscopic interferometry with respect to the quarter-wave plate orientation and the diaphragm aperture, which is validated experimentally. Using the model, we optimize the detection sensitivity of conoscopic interferometry. We obtain a maximal sensitivity of detection when placing the diaphragm edge on the dark fringes of the conoscopic interference patterns. In the conﬁgurations studied in this work, conoscopic interferometry can be 8x more sensitive to acoustic waves than beam distortion detection.

Conoscopic interferometry for optimal acoustic pulse detection in ultrafast acoustics

https://doi.org/10.1016/j.pacs.2023.100470

Zi-Fang Zhou

Papers

Analytic solution to the Eliashberg equation for the superconducting critical temperatures

Conoscopic interferometry for optimal acoustic pulse detection in ultrafast acoustics

Experimental and numerical study of Conoscopic Interferometry sensitivity for optimal acoustic pulse detection in ultrafast acoustics