Spin fluctuations and superconductivity in UPt3 (invited)

Abstract

Of the three known high effective mass (‘‘heavy fermion’’) superconductors, UPt₃ has quite different properties from the rather similar CeCu₂Si₂ and UBe₁₃. In particular, UPt₃ has a much different temperature dependence of its resistivity below 300 K, a much lower initial slope of the superconducting critical field, H^’_c2(T_c), a much greater dependence of the superconducting transition temperature, T_c, on lattice perfection (proportional to resistivity ratio), and a much different temperature dependence of the low temperature normal state specific heat, C_n. This temperature dependence of C_n in fact includes a T₃ ln T term for UPt₃, compared to approximately a T⁻² dependence for UBe₁₃ and CeCu₂Si₂ at low temperatures. The presence of a T₃ ln T term in C_n for UPt₃, coupled with the extreme dependence of T_c on lattice perfection, has led to speculation that the pairing of the superconducting electrons in UPt₃ may not be between opposite spins, but between parallel spins, i.e., p‐wave instead of s‐wave pairing. Recently, further experimental and theoretical evidence has been found supporting this speculation that UPt₃ may be a p‐wave superconductor. The present work surveys the properties of UPt₃, including new results on the spin fluctuation behavior in the normal state of UPt₃.