Wataru Sasaki

Magnetic field dependence of the specific heat of heavily phosphorus doped silicon

Abstract The specific heat of phosphorus doped silicon was measured at temperatures 0.1 T K in external magnetic fields 0 ≦ H ext ≦ 38 kOe . The phosphorus concentration of the samples ranges from 5.3 × 10 17 to 8.9 × 10 18 cm −3 . The magnetic field dependence of the specific heat was observed in the just metallic samples as well as the non-metallic ones. The metal—non-metal transition is discussed on the basis of the Anderson localized states with correlations.

Anomalous magnetoresistance in heavily antimony doped germanium

Abstract Anomalous magnetoresistance in heavily antimony doped germanium is studied down to 5 mK. The experimental results is reasonably interpreted within a framework of s-d interaction with a negative exchange constant. Electrons localized in a sense of Anderson are suggested to play a role of d electrons when Coulomb correlation is introduced.

Two-dimensional electrons on the helium film-solid neon system

Abstract Two-dimensional electrons on thin films of helium adsorbed on solid neons are studied. It is shown that electrons are stably trapped on the film, moving with high mobility. When the film is thin, the electron mobility is governed by gas atom scattering and surface roughness scattering. At a moderate film thickness, a decrease of the mobility was observed, which may be interpreted in terms of a “polaron”, an electron with surface deformation.

Variable range hopping conduction in the lowest temperature region

Abstract Experiment on doped semiconductor indicates that there exists a temperature region of hopping conduction where the resistivity varies as T-2, deviating from the Mott formula exp [ (T 1 T ) 1 4 ] . A new version of the variable range hopping is proposed taking into account the effect of random nature of the system on the correlation of the energy levels of localized states, and is shown to lead to T-2 dependence of the resistivity in the lowest temperature region.

Escape rate of two-dimensional electrons on a liquid helium surface around 1 K

Electron escape from a two-dimensional surface state on liquid helium to three-dimensional free space is studied. A thermal-activation-type temperature dependence of the escape rate is observed at 1.1>T>0.9 K for the first time. The mechanism of electron escape is discussed.

Electron localization and interaction in two-dimensional magnetic films

Abstract Temperature and magnetic field dependence of conductivity was studied in Ni, Mn and Cu-Mn films. The results are consistent with the recent theories of the Anderson localization and the Coulomb interaction between electrons in two dimensional disordered metals when the spin scattering time is taken into account.

Two-dimensional random array of Josephson-coupled fine particles

Abstract Temperature and magnetic field dependence of resistivity of two-dimensional Josephson coupled random array of tin particles is measured. Sample consists of Sn particles of 300A in diameter which are randomly distributed on substrate and coupled to each other through thin oxide layers. Variety of temperature and magnetic field dependence is observed, depending on the degree of oxidation.

Variable range hopping in Si:P at very low temperature

Abstract The resistivity of doped semiconductor Si: P in the intermidiate concentration range was measured in low temperature region down to 10 mK. In the lowest temperatures Motts formula for the variable range hopping is shown to be not applicable and T -n -like temperature dependence of resistivity is confirmed. The Importance of the level correlation in the random system is discussed.

Comment on “variable range hopping in Si:P at very low temperature” surface conduction in Si:P

Abstract The electrical resistivity of doped semiconductor Si:P in the intermediate concentration range was measured under various surface conditions. The surface treatments are shown to have a great influence upon the low temperature electrical conduction, and T -2 -like temperature dependence of resistivity is attributed to the surface layer electrical conduction.

Anisotropic magnetoconductance in metallic doped Ge:Sb

Abstract The dependence of magnetoconductance on the direction of a magnetic field is measured in four valley and stressed single valley lightly metallic Ge:Sb, and is analyzed on the basis of the localization and the interaction theories of dirty metal. Positive magnetoconductance is described fairly well by the localization theory in its anisotropy. The theory is consistent with the experiment also in its magnitude in single valley case but is too large in four valley case. Negative magnetoconductance is analyzed as a sum of the components of orbital and g-factor anisotropy. The latter contribution is found to be dominant, though its magnitude is larger than the interaction theory both in four and single valley cases.