Positive magnetoconductance of hopping conduction due to correlation effect

The correlation effect is investigated on the hopping conduction in a magnetic field which is observed in strongly Anderson-localized regime. We calculate the electronic states in the Hubbard model with disordered on-site energies and suggest a new mechanism of the positive magnetoconductance: Zeeman effect increases the number of the high spin states in which the orbitals at the Fermi level are more extended owing to the weaker correlation effect than in the low spin states. The mechanism can explain the magnetoconductance independent of the direction of the magnetic field which was observed in a Cu-particles film. The positive magnetoconductance should be also observable in an array of quantum dots.