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The formation of the pseudogap in CeNiSn has been investigated by means of resistivity and specific-heat measurements in high magnetic fields. When the field is raised from 0 to 12 T along the orthorhombic a axis, the semiconductorlike behavior in the resistivity below 6 K disappears and the linear electronic term in the specific heat increases from 57 to 100 mJ/${\mathrm{K}}^{2}$ mol. However, no significant effect was observed for fields along the b and c axes up to 15 T. These results suggest an anisotropic suppression of the pseudogap, which can be interpreted as a result of strong spin polarization of the renormalized narrow band.

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).

Magnetic phase diagrams have been explored in heavy-fermion (HF) compounds by controlled changes of the stoichiometry (UCu4+xAl8−x), dopant concentration (Ce(Cu1−xNix)2Ge2) and magnetic field (CeCu2Si2). The results demonstr competition (i) between Kondo and RKKY interactions in the former two compounds and (ii) between HF superconductivity and some cooperative state, presumably HF band magnetism, in the latter.

Substitution of Th replacing Ce in Ce1-xThxCu2.2Si2 results in pronounced pair breaking, as usually observed for non-magnetic impurities. In contrast to La- and Y-doping, Th-substitution leaves the coherent normal Fermi liquid state almost unaffected, up to a concentration as high as 6 at%. The “critical” Th-concentration (Tc→0) is extrapolated to be approximately 20 at%.

The specific heat of Yb 4 As 3 , a mixed-valence system, has been measured down to 100 mK in magnetic fields up to 4 T. at low temperature a nuclear contribution in the specific heat is seen. The Sommerfeld coefficient λ is ∼ 150 mJ/K 2 mole at zero field. The magnetic field opens up a gap at low temperatures.

Progressive substitution of Cu for Al in UCu 4+ x Al 8 −x yields as increasing compression of the unit cell. This results in a reduction of the Neel temperature from ifT N = 42 K for x = 0 to ifT N = 15 K for x = 1.0. No magnetic ordering is found for x ⩾ 1.5. Rather the T -dependence of the resistivity shows a maximum in the range 6 to 15 K and indicates the formation of a Kondo-lattice state. The latter is characterized by heavy fermions (γ( T a0)≅0.8 J/K 2 mol for x = 1.75).

We review (i) an itinerant antiferromagnetic phase transition below 4 K in Ni-rich Ce(Cu 1− x Ni x ) 2 Ge 2 systems, (ii) the coincidence at T = 0.63 K of both a structural lattice instability in “as-grown” (non-superconducting) CeCu 2 Si 2 single crystals and bulk superconductivity in annealed ones as well as (iii) antiferromagnetic and superconducting transitions at T N = 4.6 K and T c = 1 K, respectively, in the heavy-fermion compound UNi 2 Al 3 .

Specific heat measurements were carried out down to 80 mK in magnetic fields up to 8 T on Sm3Te4. Two sharp antiferromagnetic phase transitions were observed at 0.7 and 0.9 K. At 1.4 K, the specific heat shows a broad peak which can be fitted by the impurity Kondo model for S = 1 2 . Heavy-fermion character at low temperature was established with a large γ-value, 0.6 J/K2 mol Sm3+.

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.

We report measurements of the upper critical magnetic field,Bc2(T), on single crystal and polycrystalline samples of the heavy-fermion superconductors CeCu2Si2, UPt3 and UBe13. Comparison is made with experimental results for a “conventional” superconductor (CeRu3Si2) and with results of the weak-coupling theory applied to both ans-wave superconductor in the “dirty-limit” and ap-wave superconductor. New anomalies are discovered to add to the unusualBc2(T) behavior.

Specific heat and thermal conductivity in the superconducting state of the Kondo-lattice system CeCu2Si2 and the paramagnon system UPt3 point to substantial mass anisotropies at the Fermi surface (FS): while in CeCu2Si2 bare band electrons at certain portions of the FS seem to remain normal, in UPt3 heavier fermions seem to stay normal and Cooper pairs are formed by somewhat less heavy ones. The upper critical field of UPt3 shows no influence of Pauli limiting and can reasonably well be explained with S = 0 as well as S = 1 pairing. CeCu2Si2 is strongly Pauli limited, independent of orientation. This substantiates recent Josephson experiments which show that CeCu2Si2 is a singlet superconductor.

We report measurements of Tc and ΔC for Ce1−xMxCu2.22Si2 (M = La, Y, Gd) and U1−xMxBe13 (M: Th, La, Y). “Diamagnetic” pair breaking by nonmagnetic dopants is observed which implies an anisotropic nature of both the superconducting order parameter and the impurity-scattering mechanism. Gd impurities in CeCu2.2Si2 give rise to additional “paramagnetic” pair breaking.

The present status concerning lower and upper critical magnetic fields, Bc1(T) and Bc2(T), and specific heats, CS(T), of heavy-fermion superconductors is reviewed. For CeCu2Si2, the data near Tc are found to be in full accord with GL theory. Yet, a surprising enhancement of the elastic mean free path over that in the normal state is inferred. Structure in both Bc1(T) and Bc2(T) of UBe13 appears related to a bump in the normal-state specific heat (B = 0) around T = 0.5 Tc. This may be a precursor to the lower of the two calorimetric transitions in U0.97Th0.03Be13 which are confirmed by new Bc1(T)‖ results.

Measurements are reported on the electrical resistivity, susceptibility, dc-Meissner effect and specific heat of the tetragonal U-compound URu2Si2. At T N ≃17 K, an antiferromagnetic phase transition is observed. This magnetically ordered state appears to coexist with superconductivity, which is found below T c ≃1.5 K. An analysis of the upper critical field data reveals rather unusual properties of both the normal-and the superconducting state. The effective mass of the quasiparticles at low temperatures is substantially enhanced (m*≃50 m 0), though the measured low-temperature specific heat coefficient γ does not exceed 65 mJ/K2mol.

Non-magnetic La and Y impurities in CeCu 2.2 Si 2 give rise to a “diamagnetic” pair-breaking effect and, in addition, Gd causes “paramagnetic” pair breaking. In dilute (0 1-x La x Cu 2.2 Si 2 alloys an “alloying-induced depression of incoherent scattering” is observed and related to the formation of antiferromagnetic order at several K.