Mitsuru Fukuchi

Hot Electrons in Si(100) Inversion Layer at Low Lattice Temperatures

The hot electron effect at low lattice temperatures 1≤ T ≤30 K is studied on the assumption that, in addition to the phonon scattering and some residual scattering independent of T , there is an unknown mechanism which limits the electron mobility such that µ -1 ( T e , T )=µ RES -1 +µ ph -1 ( T e , T )+µ ? -1 ( T e ), where T e is the electron temperature. µ ? -1 ( T e ) is determined by requiring that µ -1 ( T e , T ) reproduces the measured low field mobility. The field dependence of µ( T e , T ) is deduced from the usual energy balance consideration and it is concluded that the dependence can provide a crucial test for the existence of µ ? -1 ( T e ) for it should be noticeably weaker if there were no such unknown mechanism.

Numerical calculation of isomer shift on Eu151

Abstract On the isomer shift of the Mossbauer effect on Eu151, Brix et al., Shirley et al. and Nowik and Ofer have recently measured large values: -1.5 and -0.8 cm/sec for Eu2+-compounds and b.c.c. Eu metal relative to Eu3+- compounds, respectively. In order to clarify the origin of the phenomena, we have calculated first of all the energy band structure of b.c.c. metallic Eu by using Greens function method. We have obtained u nor Γ 1 (0)=+2.83 a H −3 2 , which leads to 2 Σoccck | ψk(0)|2=ξ×1.08×1026 cm-3, (ξ∼1), as the contribution of conduction electrons. This value is in good agreement with Brixs estimation from his and others experiment: +0.9 × 1026 cm-3. Furthermore, the difference between the isomer shifts for Eu3+ - and Eu2+- compounds is well understood by our present calculations of 5s wave functions in both crystals.

Phonon scattering by dislocations in LiF crystals

Abstract A theory is presented of the interaction between thermal phonons and a vibrating dislocation. An expression for the relaxation time of the phonon is obtained which is valid in an anisotropic medium. The relaxation time depends on the strength of the imaginary part of the effective mass of the vibrating dislocation. We have calculated numerically this factor for LiF and have found the mode dependence to be very strong. The slow transverse-mode component is about ten times larger than the other mode components. Hence, the slow transverse mode is scattered more strongly than other modes by vibrating dislocations in LiF. Agreement with experimental data is obtained.

Fermi surface and helical spin ordering in Eu metal

Abstract The band structure and the Fermi surface of the b.c.c. Eu metal have been calculated by the non-relativistic KKR method. The obtained Fermi surface is grossly similar to that of Andersen and Loucks. We should like, however, to point out essential differences. Our electron surface around H is shaped like a sphere with eight low mounds in eight directions near the HP -axes (called “bumpy sphere”). Our hole surface around P is shaped like a “rounded-off cube”, as was obtained by Andersen and Loucks, but the cross-section perpendicular to the HP -axis for the tetrahedrally located wing (or island) is shaped like a “truncated-triangle”, not like an ellipse. The helical spin ordering at low temperatures can be understood on the basis of the hole Fermi surface. The electron surface around H does not seem to concern the nesting. Some other phenomena are also considered briefly.

Breakdown properties of random systems with distributed conductances

The breakdown problem in a random system is investigated by numerical simulation for a network of distributed conductance The breakdown voltages are studied in the different conductance configurations. The mean breakdown strength shows anomalous size dependence given by ∝1/((ln L )) y for L (the linear dimension of the network). The exponent y depends upon a degree of non-uniformity of the system and gives an information on the critical event of the breakdown. For the case of a comparatively homogeneous network the micro-crack nucleation is the critical event of a breakdown. In such a random resistor network funnel defects act as the appropriate critical defects. On the other hand, in the case of strongly disordered system the critical event in a breakdown is attributed to growth of cracks.

Dynamics of an impurity hydrogen in magnesium

The dynamics of an impurity hydrogen in magnesium is investigated by using the pair potential technique. We have calculated the pair potential between hydrogen and magnesium, taking account of the non-linear screening effects of an impurity hydrogen. By use of it, we have calculated the energy profile for interstitial hydrogen and the force constants between hydrogen and magnesium. As the results of them, it is found that the minimum point of energy is too shallow to localize the interstitial hydrogen, and that the coupling between substitutional hydrogen and the nearest neighbor magnesium ion is very weak.

Mass and Line Tension of a Vibrating Dislocation

We have calculated the mass and line tension of a vibrating dislocation in LiF crystal. The results of our analysis were somewhat smaller than that predicted by the string model. They indicate that localized mode exists due to vibrating dislocation in LiF crystal.

Role of the Electron Fermi Surface in the Helical Spin Ordering of Rare Earth Metal Eu

Band structure and the detailed form of the Fermi surface of bcc Eu metal are calculated by the KKR method by using various exchange potentials of X α-type with α=2/3, 0.8, and 0.9. Already in 1976 and 1977, we have made a similar calculation with α=1 and have concluded that the electron Fermi surface is rather sphere-like on the contrary to the conclusion of Andersen and Loucks. Now in the present calculation, we confirm the fact that the previous conclusion is still kept valid even when the exchange potential is varied. Thus, we understand that the electron Fermi surface does not make practical contribution to the “nesting” phenomenon in the helical spin ordering of this metal.

Magnetization of a chain-like antiferromagnet

Abstract The temperature dependence of sublattice magnetizations in a chain-like antiferromagnet is investigated by the spin-wave theory considering kinematical interaction and dynamical interaction. For the latter the biquadratic terms are treated in the mean field approximation. The theory for zero-point spin reduction by Herbert and Ishikawa and Oguchi is extended to finite temperatures following Thermo-Field Dynamics approach by Takahashi. Numerical calculations for KCuF 3 show that the kinematical interaction plays an important role for the spontaneous magnetization, and when the effect of dynamical interaction is taken into account, the results obtained come nearer to the experimental ones.

Characteristic of a Microwave Strip Line Made from YBa2Cu3O7-x Superconductor on Alumina Substrate

Strip lines of high Tc (HTC) superconductor material are made on alumina substrates. Films with a sharp transition temperature of YBaCuO superconductor have been prepared by a printing method with buffer treatment. The attenuation of microwaves travelling on the HTC strip lines was examined by means of the time domain method at 77 K, and the value of the attenuation per meter was found to be 5.5 dB/m around 10 GHz.