On Magnetic Impurities in Gapless Fermi Systems

L.S. Borkowski Institute of Physics, A. Mickiewicz University, Matejki 48/49, 60-769 Poznań, Poland

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In ordinary metals, antiferromagnetic exchange between conduction electrons and a magnetic impurity leads to screening of the impurity spin below the Kondo temperature, TK. In systems such as semimetals, small-gap semiconductors and unconventional superconductors, a reduction in available conduction states near the chemical potential can greatly depress TK. The behavior of an Anderson impurity in a model with a power-law density of states, ρ(ε) ∝ |ε|r, r>0, for |ε|<Δp, where Δp is small compared to the bandwidth, is studied using the non-crossing approximation. The transition from the Kondo singlet to the magnetic ground state can be seen in the behavior of the impurity magnetic susceptibility χ. The product Tχ saturates at a finite value at low temperature for coupling smaller than the critical one. For sufficiently large coupling Tχ → 0, as T → 0, indicating a complete screening of the impurity spin.

DOI: 10.12693/APhysPolA.91.359 PACS numbers: 75.20.Hr, 72.15.Qm, 74.70.Tx