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Anomalously enhanced plasma diffusion transverse to a magnetic field in n-Ge
ii
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN THE J. PHYS. CHEM. SOLIDS Vol. 34, No. 8
With the magnetic interactions previously considered, it is shown that the magnetic structure of MnCr2S4 at H ~ 105 kOe cannot be fully described neither by magnetization curves nor by neutron diffraction. Received 30 October 1979 6.
THE ABSORPTION EDGES OF GeS AND URBACH’S RULE J.D. Wiley and D. Thomas, Dept. of Electrical and Computer Engineering, University of Wisconsin, Madison, WI 53706, U.S.A.; E. SchOnherr and A. Breitschwerdt, Max-PlanckInstitut für Festkoperforschung, Stuttgart, Federal Republic of Germany.
The low-energy absorption tail of the E II a exciton in GeS obeys Urbach’s rule over at least three orders of magnitude in absorption coefficient for 4.2 ~ T ~ 240 K. The E II b polarization (for which no exciton is observed) does not obey Urbach’s rule. The E I! a Urbach edge is caused by interactions between the excitons and a 8.7 meV rigid-layer vibrational mode. Our results are consistent with Sumi and Toyazawa’s theory of the Urbach edge, and inconsistent with the models of Dow and Redfield,and Skettrup. The absorption edge of GeS is confirmed as a direct edge.
7.
Received 21 August 1979 Revised 13 December 1979 ON THE DIELECTRIC THEORY OF A CRYSTALLINE SLAB OF POINT MOLECULES J. Grindlay, Physics Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1
We discuss the dielectric response of a crystalline slab of point molecules to an incident plane electromagnetic wave. The slab is assumed to be made up of nonpolar, polarizable molecules (a) lying at points of a simple cubic lattice and (b) interacting only via the electromagnetic field. Expressions for the dispersion relations, polarization and electric fields and the transmission coefficient are derived. Conditions under which a point dielectric equation of state holds are obtained. This simple system exhibits three resonances near the transverse optic frequency. Received 5 September 1979 8.
THE ELECTROMAGNETIC FIELD IN A CRYSTALLINE SLAB A. Redlack and J. Grindlay, Physics Department, University of Waterloo, Waterloo, Ontario, Canada.
The vector and scalar potentials of a crystalline slab of oscillating point charges are partitioned into four types of terms; three with at least part of the periodicity of the orthorhombic lattice, average to zero through the unit cell and the fourth, with no lattice periodicity, is related to the macroscopic field. The general behaviour of the periodic terms is easily described but a complete description of the properties of the remainder isobtained only under special conditions. The results are used to derive explicit expressions for both the microscopic and macroscopic fields in the slab. A comparison is made with the infinite and semi-infinite crystal fields. Received 13 December 1979 9.
ANOMALOUSLY ENHANCED PLASMA DIFFUSION TRANSVERSE TO A MAGNETIC FIELD IN n-Ge W. Schneider and R. Schlitzer, Institut für Angewandte Physik II der Universitat, D-6900 Heidelberg, Federal Republic of Germany.
From the broadening of a narrow plasma sheet drifting along E~x B, we measured the transverse diffusion coefficient D1 in n-Ge. Contrary to the classical theory, D1 increases with the electric field E~,increases with the magnetic field B up to ji~B~ 1, and decreases proportional to 1/B in higher magnetic fIelds. The transverse drift velocity v1 measured simultaneously shows a classical behavior over the whole field ranges of were 1 andB = 0.1—2.3 T, which E~ = 3—llOVcm used in our experiment. The results correspond to those gained previously in n-InSb. However, whereas in InSb plasma instabilities were observed together with the anomalous diffusion, no instabilities could be found in Ge. Various ways to arrive at an explanation of the anomalous effect are discussed and possible applications are indicated. Received 2 August 1979 Revised 14 December 1979 10.
REORDERING KINETICS OF DISORDERED Al 5 COMPOUNDS David Dew-Hughes, Brookhaven National Laboratory, Upton, NY 11973, U.S.A.
The study of reordering in Al 5 compounds gives valuable information about atomic processes in this structure. This information is relevant to diffusion and solid-state compound growth, as well as to recovery from radiation damage. It also offers further valuable insight into the nature of radiation damage in these materials, complementing the results obtained by X-ray studies, electron microscopy, and the measurement of superconducting and normal-state properties. The
ABSTRACTS OF ARTICLES TO BE PUBLISHED IN THE J. PHYS. CHEM. SOLIDS Vol. 34, No. 8
With the magnetic interactions previously considered, it is shown that the magnetic structure of MnCr2S4 at H ~ 105 kOe cannot be fully described neither by magnetization curves nor by neutron diffraction. Received 30 October 1979 6.
THE ABSORPTION EDGES OF GeS AND URBACH’S RULE J.D. Wiley and D. Thomas, Dept. of Electrical and Computer Engineering, University of Wisconsin, Madison, WI 53706, U.S.A.; E. SchOnherr and A. Breitschwerdt, Max-PlanckInstitut für Festkoperforschung, Stuttgart, Federal Republic of Germany.
The low-energy absorption tail of the E II a exciton in GeS obeys Urbach’s rule over at least three orders of magnitude in absorption coefficient for 4.2 ~ T ~ 240 K. The E II b polarization (for which no exciton is observed) does not obey Urbach’s rule. The E I! a Urbach edge is caused by interactions between the excitons and a 8.7 meV rigid-layer vibrational mode. Our results are consistent with Sumi and Toyazawa’s theory of the Urbach edge, and inconsistent with the models of Dow and Redfield,and Skettrup. The absorption edge of GeS is confirmed as a direct edge.
7.
Received 21 August 1979 Revised 13 December 1979 ON THE DIELECTRIC THEORY OF A CRYSTALLINE SLAB OF POINT MOLECULES J. Grindlay, Physics Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1
We discuss the dielectric response of a crystalline slab of point molecules to an incident plane electromagnetic wave. The slab is assumed to be made up of nonpolar, polarizable molecules (a) lying at points of a simple cubic lattice and (b) interacting only via the electromagnetic field. Expressions for the dispersion relations, polarization and electric fields and the transmission coefficient are derived. Conditions under which a point dielectric equation of state holds are obtained. This simple system exhibits three resonances near the transverse optic frequency. Received 5 September 1979 8.
THE ELECTROMAGNETIC FIELD IN A CRYSTALLINE SLAB A. Redlack and J. Grindlay, Physics Department, University of Waterloo, Waterloo, Ontario, Canada.
The vector and scalar potentials of a crystalline slab of oscillating point charges are partitioned into four types of terms; three with at least part of the periodicity of the orthorhombic lattice, average to zero through the unit cell and the fourth, with no lattice periodicity, is related to the macroscopic field. The general behaviour of the periodic terms is easily described but a complete description of the properties of the remainder isobtained only under special conditions. The results are used to derive explicit expressions for both the microscopic and macroscopic fields in the slab. A comparison is made with the infinite and semi-infinite crystal fields. Received 13 December 1979 9.
ANOMALOUSLY ENHANCED PLASMA DIFFUSION TRANSVERSE TO A MAGNETIC FIELD IN n-Ge W. Schneider and R. Schlitzer, Institut für Angewandte Physik II der Universitat, D-6900 Heidelberg, Federal Republic of Germany.
From the broadening of a narrow plasma sheet drifting along E~x B, we measured the transverse diffusion coefficient D1 in n-Ge. Contrary to the classical theory, D1 increases with the electric field E~,increases with the magnetic field B up to ji~B~ 1, and decreases proportional to 1/B in higher magnetic fIelds. The transverse drift velocity v1 measured simultaneously shows a classical behavior over the whole field ranges of were 1 andB = 0.1—2.3 T, which E~ = 3—llOVcm used in our experiment. The results correspond to those gained previously in n-InSb. However, whereas in InSb plasma instabilities were observed together with the anomalous diffusion, no instabilities could be found in Ge. Various ways to arrive at an explanation of the anomalous effect are discussed and possible applications are indicated. Received 2 August 1979 Revised 14 December 1979 10.
REORDERING KINETICS OF DISORDERED Al 5 COMPOUNDS David Dew-Hughes, Brookhaven National Laboratory, Upton, NY 11973, U.S.A.
The study of reordering in Al 5 compounds gives valuable information about atomic processes in this structure. This information is relevant to diffusion and solid-state compound growth, as well as to recovery from radiation damage. It also offers further valuable insight into the nature of radiation damage in these materials, complementing the results obtained by X-ray studies, electron microscopy, and the measurement of superconducting and normal-state properties. The