Impurity States in Kondo Insulators

  • P. Schlottmann
Chapter

Abstract

Kondo insulators are compounds with small-gap semiconductor properties. A Mondo hole is the charge neutral substitution of a rare earth or actinide atom by a nonmagnetic analog. Kondo holes break the translational invariance and give rise to boundstates in the gap, which pin the Fermi level and determine the magnetic, thermal and transport properties. A finite concentration of Kondo holes generates an impurity hand inside the gap of the semiconductor. For small concentration, c, the height and width of the impurity band in the density of states are proportional to √c. We consider arbitrary clusters of Kondo holes embedded into the symmetric non-degenerate Anderson lattice with nearest-neighbor tight-binding conduction band on a simple cubic lattice. Properties of boundstates at the Fermi level are related to the connectivity of the cluster. The impurity band undergoes an insulator-metal transition, which is reduced to the classical site percolation of Kondo holes with first, second and fourth nearest-neighbor bonds. The critical percolation concentration is estimated at c cr = 0.10. Of great interest are also the consequences of doping, ligand defects and the effect of Mondo holes on magnetic instabilities. Within a KotliarRuckenstein mean-field approximation the Mondo insulator is unstable to long-range antiferromagnetism for U > U c and to ferromagnetism in sufficiently large fields. The paramagnetic-antiferromagnetic phase boundary is re-entrant as a. function of the concentration of Kondo holes.

Keywords

Spectral Weight Impurity Band Impurity Site Kondo Lattice Magnetic Instability 
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Copyright information

© Springer Science+Business Media New York 1998

Authors and Affiliations

  • P. Schlottmann
    • 1
  1. 1.Department of PhysicsFlorida State UniversityTallahasseeUSA

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