Kondo-Lattice Metals and Semiconductors with Compensated Magnetic Moments: a Brief Overview

Abstract

The heavy-fermion systems have been studied intensively during the two last decades. The interest started with the discovery [1] that the metallic system CeCu2Si2 with the heavy quasiparticles of mass m* 103 m0, where m0 is the free-electron mass, are superconductors below the temperature TS 1 K. The interest in those systems was also stimulated by two further findings. First [2], some of those systems such as Ce3 Bi4 Pt3 or YbB 12 are insulating at temperature T = 0 K, but become heavy-fermion metals with increasing temperature. They are called the Kondo insulators. Second [3], several metallic systems exhibit strong deviations from the Fermi-liquid behavior at T < 1 K. Namely, one encounters the behavior of the linear-specific-heat coefficient y(T) ≡ C(T)/T ln(T0/T), the dependence for the magnetic susceptibility x(T) ~ x0(1 — αvT), and the resistivity behavior p p0 -lAl', where T0, x0, α, po, and A' are constants. These temperature dependences are commonly termed a non-Fermi liquid behavior (strictly, they should be called a non-Landau behavior of fermionic liquids). One should recognize at the outset a fundamental significance of those results. First, the electrons, almost as heavy as the nucleons, should be regarded as being very close to the Mott localization point (at which the electrons in the localized or atomic states acquire infinite effective mass for translational motion throughout the system). The fact that they are almost localized (i.e. have large density of states at the Fermi level) means that they have well defined magnetic