C. Schank

Heavy-fermion superconductivity atT c =2K in the antiferromagnet UPd2Al3

UPd2Al3 is a new heavy-fermion superconductor with a recordTc of 2 K. In addition, it shows a transition to long-range antiferromagnetic order atTN=14 K. Its Sommerfeld coefficient is reduced from γp=210mJ/K2 mole in the paramagnetic to γ0=150mJ/K2 mole in the antiferromagnetic phase.

A new antiferromagnetic heavy Fermion compound : CePd2Al3

We report the first measurements of the electrical resistivity, the magnetic susceptibility and the specific heat of the new hexagonal compound CePd 2 Al 3 . The results indicate that CePd 2 Al 3 h is a new heavy fermion system with an electronic specific heat coefficient (γ) of 380 mJ/mol·K 2 and antiferromagnetic ordering below T N =2.8 K.

NMR and NQR Studies of Magnetism and Superconductivity in the Antiferromagnetic Heavy Fermion Superconductors UM2Al3 (M=Ni and Pd)

Both magnetic and superconducting characteristics of the new heavy fermion superconductors (HFS), UNi 2 Al 3 and UPd 2 Al 3 have been investigated extensively by means of 27 Al NMR and NQR. Systematic studies of the nuclear-spin-lattice relaxation time T 1 , the Knight shift and the spectrum of 27 Al have revealed different types of magnetic fluctuations and spin structure between these two compounds. UNi 2 Al 3 shows a band-type itinerant antiferromagnetic behavior, while UPd 2 Al 3 belongs to a heavy fermion antiferromagnet with an ordinary size of U-derived moment. In the superconducting state, the relaxation behavior in UPd 2 Al 3 is similar to those observed in the other HFS reported so far, providing an evidence for an unconventional anisotropic superconductivity with line of gap zeros on the Fermi surface as well. Knight shift has been found to decrease considerably below T c , showing that the pseudo spin is well defined, not affected by the impurity scattering.

d-Wave Superconductivity in Antiferromagnetic Heavy-Fermion Compound UPd2Al3 –Evidence from27Al NMR/NQR Studies–

The nuclear-spin-lattice relaxation rate, 27 (1/ T 1 ), of the high-quality polycrystalline UPd 2 Al 3 with a record T c =2 K and the narrowest Al NQR linewidth to date of 12 kHz has been measured in zero magnetic field by the NQR technique. 27 (1/ T 1 ) below T c has been found to obey the T 3 - law at least down to 0.18 K, giving strong evidence that the energy gap vanishes along lines on the Fermi surface. From the analysis of 27 Al Knight shift below T c , it is shown that the anisotropic residual Knight shift originates from the f -electron susceptibility in the antiferromagnetic state, whereas the isotropic reduction of the shift below T c is due to a singlet pairing nature of the superconductivity. Both the results of 27 (1/ T 1 ) and 27 Al Knight shift in UPd 2 Al 3 can be reproduced consistently by a d-wave pairing model characterized by lines of vanishing gap on the Fermi surface.

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.

4f-conduction electron hybridization in ternary CeTMAl compounds

Abstract We present an investigation of CeTMAl phase diagrams with TMRu, Pd, Pt and Au. Several new compounds have been characterized by measurements of the electrical resistivity ϱ ( T ), the do susceptibility χ ( T ) and, in some cases, the specific heat C ( T ). We find that in the compounds with TMRu, the hybridization strength between 4f and conduction electrons is strong, leading in most compounds to an intermediate valent (IV) state. By contrast, most of the investigated compounds with TMPd, Pt and Au order magnetically indicating a much weaker hybridization strength. However, some of the Pt and especially Pd compounds are very near to the crossover from the magnetic to the non-magnetic regime as deduced from a Kondo-type maximum in the resistivity and a large electronic specific heat at low temperatures.

Superconductivity and magnetism of the new heavy fermion superconductors UM2Al3(M=Ni,Pd)-27Al NMR study-

The magnetic and superconducting properties of the new heavy fermion superconductors (HFS), UNi 2 Al 3 and UPd 2 Al 3 have been investigated by 27 Al NMR. The magnetic ordering is unambiguously identified by a significant increase of 27 Al linewidth below T N =4.6 K and an enhancement of the nuclear-spin-lattice relaxation rate 27 (1/ T 1 ) around T N in UNi 2 Al 3 and by a gradual increase of the linewidth and a distinct drop of 27 (1/ T 1 ) below T N =14 K in UPd 2 Al 3 . Below T c =0.9 K in a magnetic field of 2.8 kOe, no anomalies of 1/ T 1 and Knight shift have been observed in UNi 2 Al 3 , whereas the superconductivity in UPd 2 Al 3 is well evidenced by a significant decrease of both 1/ T 1 and Knight shift below T c =1.8 K in 4.9 kOe. The behavior of 1/ T 1 in UPd 2 Al 3 , with no coherence peak just below T c , is well described down to 0.65 K by a model of gap zeros on lines at the Fermi surface, being quite similar to the behavior in HFS reported thus far.

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).

μ+SR studies of UM2Al3, M=Ni, Pd

Positive-muon spin rotation (μ+ SR) measurements have been carried out in the new heavy-fermion superconductors UM2Al3, M=Ni and Pd. In UNi2Al3 the observedμ+ frequencies in zero applied field indicate commensurate antiferromagnetic (AF) ordering of U moments ∼0.1μB/U atom. These moments coexist with superconductivity and have the highest values observed in an AF heavy-fermion superconductor. The absence of well-defined frequencies in zero-fieldμ+ SR in the AF state of UPd2Al3 suggests symmetricμ+ stopping sites. In this systemμ+ SR linewidths belowTc yield a preliminary value of ∼8000 Å for the London penetration depth.