ISSN:0370-1972    

DOI:10.1002/pssb.2221370150

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221370151

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe Green function approach to the Heisenberg ferromagnet is confronted with the difficulties connected with the commutation rules of spin operators. Recently, Baryakhtar, Krivoruchko, and Yablonskii (BKY) proposed a new diagram technique for Green functions containing spin operators based on the corresponding technique by Izyumov and Kassan‐Ogly. The new approach is compared with that proposed earlier by Haberlandt and Kühnel. Calculating some crucial terms it is shown why the diagrams of BKY do not represent the corresponding analytical terms properly if kinematic interaction due to the peculiar commutation relations is involved. The results for the low temperature spin wave energy and magnetization are discuss

ISSN:0370-1972    

DOI:10.1002/pssb.2221370110

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221370152

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221370153

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe three‐spin interaction in the form of a box product, σ1× σ2· σ3, is investigated including additional interaction terms in the Hamiltonian in the forms\documentclass{article}\pagestyle{empty}\begin{document}$ \sum\limits_i {\sigma _{iz},} \sum\limits_{ij} {\sigma _{iz} \sigma _{jz}} $\end{document}, and πiσiz. With the relative strengths considered as parameters, the thermodynamic properties are evaluated as a function of temperature and show considerable variety. Both second‐ and first‐order phase transitio

ISSN:0370-1972    

DOI:10.1002/pssb.2221370111

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

ISSN:0370-1972    

DOI:10.1002/pssb.2221370154

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractBased on theoretical grounds some serious objections against Levin's modifications are discussed and an alternate approach to calculate the ionic gapEcis presented. An attempt is made to see the validity of the theory in a wide range of structures. Calculated data show that the number of d‐electrons taking part in the bond formation depends on the ionicity which is in accordance with the earlier prediction

ISSN:0370-1972    

DOI:10.1002/pssb.2221370112

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA generalisation of Gell‐Mann‐Brueckner's formula is derived for two‐component systems of charged particles with any mass ratio and multi‐valley degeneracy. Higher orderrs‐contribution are determined in the random phase approximation. Numerical values are given especially for hydrogen plasmas and for optically excited electron—hole plasmas in

ISSN:0370-1972    

DOI:10.1002/pssb.2221370113

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe frequency spectrum of polar interface modes of superlattices is derived with regard of bulk spatial dispersion. The results are applied to free carrier excitations of superlattices. Dispersion relations are given for intra‐ and intersubband interface plasmon modes. It is shown that collective electronic excitations of superlattices considered in previous papers are limiting cases of interface plasmon modes. Experimental data on plasmon dispersion can be understood in terms of interface plasmon modes if carrier confinement is taken into accoun

ISSN:0370-1972    

DOI:10.1002/pssb.2221370114

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY