In the antiferromagnetic (AF) heavy-fermion system CePdAl the magnetic Ce ions form a network of equilateral triangles in the (001) plane, similar to the kagomé lattice, with one third of the Ce moments not participating in the long-range order. The Néel temperature TN = 2.7 K is reduced upon replacing Pd by Ni in CePd1−xNixAl, with TN → 0 for x = 0.144, where the specific heat C exhibits a C/T ∝ − log T dependence. Within the Hertz-Millis-Moriya model of quantum criticality, this behavior might indicate 2D critical antiferromagnetic fluctuations arising from the decoupling of 3D magnetic order by frustration. On the other hand, the simultaneous presence of Kondo effect and geometric frustration might entail a new route to quantum criticality.
To resolve the discrepancies of the superconducting order parameter in quasi-two-dimensional NbSe 2 , comprehensive specific-heat measurements have been carried out. By analyzing both the zero-field and mixed-state data with magnetic fields perpendicular ͑H Ќ c͒ to and parallel ͑H ʈ c͒ to the c axis of the crystal and using the two-gap model, we conclude that ͑1͒ more than one energy scale of the order parameter is required for superconducting NbSe 2 due to the thermodynamic consistency; ͑2͒ ⌬ L = 1.26 meV and ⌬ S = 0.73 meV are obtained; ͑3͒ N S ͑0͒ / N͑0͒ = 11% -20%; ͑4͒ the observation of the kink in ␥͑H͒ curve suggests that the two-gap scenario is more favorable than the anisotropic s-wave model to describe the gap structure of NbSe 2 ; and ͑5͒ ⌬ S is more isotropic and has a three-dimensional-like feature and is located either on the Se or the bonding Nb Fermi sheets.
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