R. Modler

New observations concerning magnetism and superconductivity in heavy-fermion metals

Abstract Ce-based heavy-fermion superconductors (HFSC) exhibit magnetic phase diagrams differing from those of both the ideal Kondo lattice and substitutional alloys with intact Ce sublattice. While for the Ce-based HFSC (with well localized 4f shell) superconductivity and antiferromagnetic order seem to compete with each other, both phenomena typically coexist for U-based HFSC (with less localized 5f shell).

UPd2Al3-a new heavy-fermion superconductor with Tc = 2K

Abstract We report measurements on polycrystalline and, for the first time, single-crystalline samples of UPd2Al3, a new heavy-fermion superconductor (HFS) with a record-Tc of 2K and an antiferromagnetic transition at TN = 14K.

Ground state properties of UNi2Al3 and UPd2Al3

Abstract We present a status report on our investigation of the two new heavy fermion superconductors UNi 2 Al 3 and UPd 2 Al 3 . We discuss in particular the magnetic phase diagram, crystal field effects and the properties of the superconducting state.

Phase transitions in the heavy Fermi-liquid state: CeCu2Si2, UNi2Al3 and UPd2Al3

Abstract We discuss the superconducting and other phase transitions in CeCu 2 Si 2 and UT 2 Al 3 (T: Ni,Pd). For CeCu 2 Si 2 , a novel lattice instability is found to limit the highest T c attainable by appropriate heat treatment. In the UT 2 Al 3 homologs, antiferromagnetism develops at T N = 4.6K (14K) and possibly coexists with heavy-fermion superconductivity below T c = 1K (2K) for T = Ni(Pd).

Experimental evidence for a generalized FFLO state in clean type-II superconductors with short coherence length and enhanced Pauli susceptibility

Abstract We report an investigation of the magnetic and dilatometric properties of single crystals of the superconductors UPd 2 Al 3 and CeRu 2 , both compounds exhibiting enhanced spin susceptibilities. Our results suggest for both systems a first-order transition between weak and strong pinning at T T c , somewhat below H c2 ( T ). We argue that these observations are compatible with a staggered order parameter due to the formation of a “generalized Fulde-Ferrell-Larkin-Ovchinnikov state”.

The effect of composition on the occurrence of a second phase transition in the vicinity of Tc in CeCu2Si2

We report on measurements of the thermal expansion and specific heat on a series of polycrystalline CeCu 2 Si 2 samples with small variations in the stoichiometry. The occurrence of superconductivity and/or the surrounding phase labeled »A«, were found to be most sensitively controlled by the Ce:Cu:Si composition

Thermal expansion, magnetostriction and elastic constants of UPd2Al3

Abstract We report thermal-expansion, magnetostriction and ultrasound measurements on monocrystalline samples of the hexagonal heavy fermion compound UPd2Al3. At high magnetic fields anomalies are found within the superconducting phase. The absolute values of the elastic constants were determined using ultrasound techniques.

Is UPd2Al3 a Fulde-Ferrell superconductor?

Abstract We report dilatation and vibrating-reed experiments on monocrystalline UPd 2 Al 3 . Anomalies found at high fields near T c may reflect the transition to the Fulde-Ferrell-Larkin-Ovchinnikov superconducting state. We discuss possible effects due to the pinning of flux lines.

Anomalous pinning in superconductors with strong Pauli paramagnetism

Abstract The results of the magnetization, magnetostriction and AC-susceptibility experiments are presented for both the antiferromagnetic heavy-Fermion superconductor UPd 2 Al 3 and the valence fluctuation compound CeRu 2 . For ( H > 10 kOe). These results are discussed on the basis of a generalized Fulde-Ferrell-Larkin-Ovchinnikov superconducting state.

Thermal expansion of the heavy-fermion superconductor UNi2Al3

We have investigated the superconducting and the antiferromagnetic transition of polycrystalline UNi2Al3 by means of high-resolution dilatometry. At Tc = 0.95 K and TN = 4.6 K the thermal-expansion coefficient α shows second-order phase-transition anomalies of negative sign. Investigations of the antiferromagnetic transition under magnetic fields in dicate a complex magnetic phase diagram reminiscent of that of the Pd homolog.