M. Hunt

Heavy quasiparticles in CeCu6 studied using magnetic quantum oscillations

Angle resolved measurements of the de Haas-van Alphen effect are reported in the heavy-fermion compound CeCu6. The experiments confirm the presence at low temperature of a sharply defined Fermi surface resulting from the existence of heavy long-lived charged fermion quasiparticles. LMTO electronic structure calculations have been performed within the local density approximation, in which the f electrons are included as either band or core states, but in neither case are the results in satisfactory agreement with experiment. The measured effective masses, which are in the range 6-80 me, are found to be magnetic field dependent in a manner which closely resembles that of the linear specific heat coefficient. The authors deduce that, in zero applied field, the mass renormalization in CeCu6 is greater than 200.

Magnetic oscillation phenomena in the heavy fermion superconductor CeCu2Si2

Abstract Measurements of the magnetisation of single crystals of CeCu2Si2 at ∼20MK and ∼13T clearly demonstrate oscillations periodic in 1B (the de Haas van Alphen effect). This is direct evidence for the existence of long lived charged quasiparticles in a Fermi Liquid like environment. We provide details of quasiparticle masses and the variation of the dHvA frequencies as a function of crystal orientation.

Variation of quasiparticle mass with magnetic field in CeCu6

Abstract New measurements of quasiparticle effective masses in the heavy fermion compound CeCu6 are presented. The masses, which are determined from de Haas-van Alphen effect measurements with higher precision than previously reported in this compound, reveal a variation with magnetic field which is in qualitative agreement with that of the low temperature linear specific heat coefficient, thereby supporting a Fermi liquid description of CeCu6 at low temperatures. The results are used to derive zero-field values for the quasiparticle masses of the orbits involved.

Phase diagram of CeCu2Si2 in the B-T plane

Abstract A combination dHvA and resistivity measurements investigations on a single crystal of the heavy fermion superconductor CeCu2Si2 has revealed a hitherto hidden complexity in the B-T phase diagram. As well as the superconducting-normal phase boundary, with T c =0.72K and B Cc2 =1.5T, a double magnetic transition is observed which, depending on the orientation, occurs between 7.2T and 2.8T at 20mK, and which near the c axis accompanies a possible third transition. In the c-direction at least, the two transitions merge and then vanish as the temperature rises to 470mK so revealing an occlusion in the B-T phase plane. The nature of the phase transitions is not revealed by these experiments but a minor reconstruction of the Fermi surface and a change in quasiparticle mass is seen to occur across the occlusion

Phase transitions in CeCu2Si2

We report the first measurements of the de Haas-van Alphen effect in the heavy-fermion superconductor CeCu 2 2Si 2 . In addition to providing information on the quasiparticle band structure and effective masses, the measurements reveal a complex phase diagram in the B-T plane. By observing magnetic oscillations on either side of a magnetic phase transition, we detect in one instance a minor modification of the Fermi surface, although the nature of the magnetic or other ordering is not determined. We conclude that the superconducting state in CeCu 2 Si 2 formes out of a fully developed coherent Fermi liquid.

Evidence for the Anderson lattice model from dHVA studies in CeCu6

Abstract We have studied the harmonic content of the de Haas-van Alphen effect oscillations in the heavy-fermion metal CeCu 6 . Attempts to interpret the measurements according to the conventional Lifshitz-Kosevich theory are found to fail. The results however are found to be consistent with an alternative theoretical approach based on the Anderson lattice model.