Heavy fermions: Typical phenomena and recent developments

A survey is given of typical phenomena, new materials and recent developments in heavy-fermion physics. In particular, the following topics are addressed: (i) YbNiAl, a new heavy-fermion local-moment antiferromagnet (LMM) with Néel temperature T_n = 3 K, (ii) non-Fermi-liquid behavior at the magnetic instability in two heavy-fermion systems with intact f-ion sublattice, i.e. orthorhombic CePt(Si_1–xGe_x) and tetragonal U(Cu_4+xAl_8–x), (iii) the low-temperature properties of the anisotropic Rondo insulator CeNiSn, and (iv) some of the most unusual observations made on low-carrier-density rare-earth systems like Sm₃Te₄ and Sm₃Se₄. While the exotic symmetry-broken (superconducting and magnetic) ground states of heavy-fermion metals are discussed in several other contributions to this volume, we focus in the remainder of this paper on the relationship between LMM ordering and heavy-fermion superconductivity: Firstly, the LMM ordered compound CeCu₂Ge₂ (T_n = 4.1K) is addressed which was recently found to become a non-magnetic heavy-fermion superconductor under high hydrostatic pressure, p 70 kbar (D. Jaccard et al., Phys. Lett. A163,475 (1992)). Point-contact spectroscopy is used to investigate in more detail the high-pressure superconducting phase of CeCu₂Ge₂. Secondly, we summarize high-pressure results on UPd₂Al₃, the first compound to show homogeneous coexistence between LMM ordering and heavy-fermion superconductivity.