Heavy-fermion superconductor

On the other hand, recent measurements on UBcis have shown this intermetallic to be a very special species of superconductor with a large density of electronic states at Ep ( 1000 mJ/mol K ). Such results will certainly motivate both theoreticians and experimentalists and the so called heavy-fermion superconductors family is already developing . ... 

ADP atomic displacement parameters HFSC heavy-fermion superconductor... 

The situation improves for the 5f elemental metals due to the greater delocalization of the 5f as compared to the 4f electrons. In fact, the equilibrium lattice constants of the 5f elemental metals are well reproduced even with the f electrons treated as band states, as long as spin polarization is taken into account (12). The spin polarization "turns on" at Am, and correlates with an inferred localization of the f electrons. Even for such strongly correlated metals as the heavy fermion superconductors UPt3 and UBe-ia, the equilibrium lattice constant and bulk modulus are well-given oy LDA f band calculations 0M4). 

In Table 1 are shown the characteristics of the superconductivity in the heavy fermion superconductors, high-7) superconductors, Sr2Ru04 and YNi2B2C, which were obtained by NMR measurements. Discussion of each system is given below. 

Frequently, NMR has been applied for the study of simple superconducting intermetallic compounds. We refer to the review of MacLaughlin (1976) for a general introduction. Occasionally, NMR has also been applied to tackle more complicated systems, like heavy-fermion superconductors (sect. 5.5.1) or systems, where the eventual coexistence between magnetism and superconductivity was of interest (sect. 5.4.1). NMR has made important contributions to a better understanding of the high-Tj, oxide compounds, as well. The latter, growing, field of activity has to be covered in a future volume of this Handbook. 

Properties and microscopic parameters characterizing the normal and superconducting states of polycrystalline heavy-fermion superconductors T, from speciflc-heat measurements B and, slopes of upper and lower critical-field curves at T p , normal-state (T — 0) resistivity 1, total mean free path I, Ginzburg-Landau coherence length A, London penetration depth k, Ginzburg-Landau parameter 0) B, , B j(T—>0). The other... 

In the 4f- and 5f-based heavy fermion superconductors the spin-orbit interaction is strong. As a consequence classification according to physical pair spins cannot be used. If their high-temperature crystal stractures, however, have an inversion center then classification according to parity is still possible. We note here that recently the first example of a HF superconductor (CePtsSi) which lacks inversion symmetry was discovered (Bauer et al., 2004) and its theoretical implications were discussed by Frigeri et al. (2004). 

The discovery of superconductivity in CeCu2Si2 by Steglich et al. (1979) initiated the rapid development of heavy fermion physics. For nearly two decades, this material was the only Ce-based heavy-fermion superconductor at ambient pressure. Only recently, superconductivity at ambient pressure was found in the new class of heavy-fermion materials Ce MmIn3 2iH where M stands for the transition metal ion Co, Ir or Rh and m = I while n = 1 or n = 2 (Thompson et al., 2001). Typical examples are CeColus (Petrovic et al., 2001b) and Celrins (Petrovic et al., 2001a). 

---