Abstract. -CeIrIn 5 is a member of a new family of heavy-fermion compounds and has a Sommerfeld specific heat coefficient of 720 mJ/mol-K 2 . It exhibits a bulk, thermodynamic transition to a superconducting state at T c =0.40 K, below which the specific heat decreases as T 2 to a small residual T-linear value. Surprisingly, the electrical resistivity drops below instrumental resolution at a much higher temperature T 0 =1.2 K.These behaviors are highly reproducible and field-dependent studies indicate that T 0 and T c arise from the same underlying electronic structure. The layered crystal structure of suggest that heavy-fermion superconductivity might be found in structurally-related materials.Experimental and theoretical study of the superconductivity in these heavyfermion materials has formed a substantial basis for understanding more broadly classes of unconventional superconductors, including the high-T c cuprates, in which the electronpairing interaction responsible for superconductivity may be mediated by spin fluctuations [1]. In spite of progress, the heavy-fermion problem and heavy-fermion superconductivity in particular remain challenges to experiment and theory [6]. Though heavy-fermion behavior has been found in several structure types, it appears that, like conventional BCS superconductivity, heavy-fermion superconductivity may be favored by particular crystallographic structures. Because of the limited number of examples, we know very little about relationships that should exist between the structure and properties of these materials. Any predictive understanding of how superconductivity can emerge in the highly correlated ground state has to be able to explain why it appears in one crystal structure and not another. This makes the discovery of a new prototype structure for heavy-fermion superconductivity of special interest. Here, we report a new ambientpressure Ce-based heavy-fermion superconductor that is isostructural to CeRhIn 5 , suggesting that this structure, like the ThCr 2 Si 2 structure, may be particularly favorable for superconductivity. Unlike CeCu 2 Si 2 , this new compound grows easily and reproducibly as large, very pure single crystals, opening the possibility for unprecedented study. Thermodynamic and transport properties of CeIrIn 5 at low temperatures are summarized in Fig. 2. Above 0.4 K, the specific heat divided by temperature C/T≡ γ=720 mJ/mole-K 2 and is nearly temperature independent. At T c =0.40 K, there is a jump in C/T
We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn5 at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and NQR measurements confirm the presence of bulk superconductivity. This work places new constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn5.
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