Strong Correlations in Solids: A Survey of Experimental Facts

Abstract

Low‐temperature physical properties of d‐ and f‐electron transition‐metal intermetallics are often dominated by strong interactions among the conduction electrons. New developments started with considerations of the stability of magnetic moments in a metallic matrix, first as impurities and later as residing on regular lattice sites of compounds. A special case are compounds where these interactions provoke a transfer of magnetic degrees of freedom to the subsystem of the conduction electrons, resulting in extreme enhancements of the effective mass of these charge carriers and to quantum‐critical behaviour.. Of particular interest is the onset of superconductivity in this type of compounds, with strong indications of unconventional superconducting phases in the vicinity of magnetic order. Evidence for unconventional superconductivity is also obtained from studies of systems close to a metal‐insulator transition. Examples are oxide materials, most spectacularly the Cu oxides exhibiting high‐Tc superconduct...