Induced-moment magnetic form factor of the heavy-fermion superconductors UPt3, UBe13, and CeCu2Si2.

Abstract

15 SEPTEMBER 1986 VOLUME 34, NUMBER 6 PHYSICAL REVIE% B Induced-moment magnetic form factor of the heavy-fermion superconductors UPt3, UBet3, and CeCuzstz Ames Laboratory and Department C. Stassis of Physics, iowa State University, Ames', owa 50011 J. Arthur' Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 C. F. Majkrzak and J. D. Axe arookhaven Nationa/ Laboratory, B. Batlogg ATcfc T Be// Laboratories, Upton, New York and J. Remeika Murray Hill, New Jersey 07974 Z. Fisk and J. L. Smith Los A/amos Natt'ona/ Laboratories, Los Alamos, New Mexico 87545 A. S. Edelstein Nava/ Research Laboratory, Washington, (Received 12 May 1986) D. C. 20375 Polarized neutron scattering techniques have been used to study the spatial distribution and induced in single crystals of UPt3, UBe», and temperature dependence of the magnetization CeCu2si2 by an externally applied magnetic field. We find that (a) the induced magnetization in the normal low-temperature state is predominantly of f-electronic character and that (b) the gen- eralized electronic susceptibility X((},0) (where Q is a reciprocal-lattice vector), obtained by mea- surements with H H in particular, the magnetic susceptibility follows a Curie-Weiss law. At low temperatures, on the other hand, their properties are characteristic of a highly corre- lated electromc Fermi liquid; in particular, their magnetic susceptibility is Pauli-like. Among these systems, those that become superconduct- ing (i.e. , CeCu2Siz, UBe~3, and UPt3) are of particular in- and the entropy change in terest. The values of H, passing through T, have been found to be consistent with the normal-state y, indicating that the heavy electrons are in these systems. responsible for the superconductivity This observation and the unusual superconducting-state properties of these systems have raised important ques- tions regarding the nature of their supercondueting state. f JT, In particular, it has been suggested by analogy to He, that these systems are odd-parity superconductors. Actu- ally, a polar state has been suggested for the superconduct- Both a polar and an Anderson- ing phase of UPt3. Brinkman-Morel (ABM) state5 have been proposed for UBe~3, and an ABM state for CeCuzSi2. However, it has also been argued '0 that these systems, in particular, CeCu2Si2, may be conventional s-wave superconductors. Information about the nature of the superconducting electrons and the superconducting state can be obtained by neutron scattering studies of the spatial distribution and temperature dependence of the magnetization induced by an externally applied magnetic field. The measurements can, in principle, determine the temperature dependence of the spin susceptibility below T„and thus provide informa- tion about the nature of the superconducting state. In fact, measurements by Shull and Wedgwood on V3Si sho~ed that the d electrons are responsible for the super- conductivity, and that the spin susceptibility below T, has a temperature dependence consistent with s-wave super- We were thus motivated to undertake conductivity. ' similar studies on the heavy-electron superconductors, and in this Rapid Communication ~e present the results ob- on UBe~ 3, UPt3, and tained from our experiments CeCu2Si2. 1986 The American Physical Society