Ellipsometric measurements of the dielectric constant of undoped Ge were performed between 1.25 and 5.6 eV in the temperature range of 100 to 850 K. The dependence of the ${E}_{1}$, ${E}_{1}+{\ensuremath{\Delta}}_{1}$, ${E}_{0}^{\ensuremath{'}}$, and ${E}_{2}$ critical energies on temperature was obtained. It can be represented either with Varshni's empirical formula or with an expression proportional to the Bose-Einstein statistical factor of an average phonon. Broadening parameters, amplitudes, and phase angles for the corresponding critical points were also obtained. A decrease of the excitonic interaction with increasing temperature was found. The results are discussed in the light of recent calculations of the effect of temperature on the band structure of Ge containing Debye-Waller and self-energy contributions.

Temperature dependence of the dielectric function of germanium

Characterization of epitaxial semiconductor growth by reflectance anisotropy spectroscopy and ellipsometry

Thermoacoustic prime movers and refrigerators: Thermally powered engines without moving components

Transport measurements of critical current density, Jct, in monocore powder-in-tube MgB2 strands have been carried out at temperatures, T, of from 4.2 to 40 K, and in transverse fields, B, of up to 14 T. Processing methods used were conventional continuous tube forming/filling (CTFF) and internal magnesium diffusion (IMD). Strands with several powder compositions were measured, including binary (undoped) MgB2, 2% carbon doped MgB2, and 3% carbon doped MgB2. Magnetization loops (M–B) were also measured, and magnetic critical current density, Jcm, values extracted from them. The transport, Jct(B) and magnetic, Jcm(B), critical current densities were compared. Also studied was the influence of doping on the resistively measured irreversibility field, Birr, and upper critical field, Bc2. Critical current densities, Jct, and n-values were extracted from transport measurements and were found to be universally related (for all B and T) according to in which m = 0.52 ± 0.11. Likewise n was found to be related to B according to n ∝ B−p with a T-dependent p in the range of about 0.08–0.21. Further analysis of the field (B) and temperature (T) dependences of n-value resulted in an expression that enabled n(B,T), for all B and T, to be estimated for a given strand based on the results of transport Jct(B) measurements made at one arbitrarily chosen temperature.

https://iopscience.iop.org/article/10.1088/0953-2048/25/2/025001/pdf

Critical current densities and n-values of MgB 2 strands over a wide range of temperatures and fields

Impact of acoustic impedance and flow resistance on the power output capacity of the regenerators in travelling-wave thermoacoustic engines

The influence of the external current on the magnetization of non-ideal type II superconductors is explained. It is shown how in the mixed state the external current brings about a particular state of the critical distribution of flux threads allowing a finite total transport current. In the case where the external current is perpendicular to the external magnetic field, the reduction of the magnetization due to the external current and its dependence on the history of the application of current and field are explained quantitatively in Nb-Zr(25%) alloy. The transverve paramagnetic effect observed by LeBlanc is also discussed.

Effect of External Current on the Magnetization of Non-Ideal Type II Superconductors

Experimental study on thermally actuated pressure wave generator for space cryocooler

Experimental results on V-M type pulse tube refrigerator

https://www.jstage.jst.go.jp/article/jcsj/40/11/40_11_455/_pdf

Hisayasu Kobayashi

Papers

Effect of External Current on the Magnetization of Non-Ideal Type II Superconductors

Experimental study on thermally actuated pressure wave generator for space cryocooler

Experimental results on V-M type pulse tube refrigerator

Fibrous structure and critical current density of MgB2 superconducting wire

Recovery heat flux from silent and noisy film boiling states in saturated liquid He II