We report the observation of heavy-fermion superconductivity in CeCoIn 5 at T c = 2.3 K. When compared to the pressure-induced T c of its cubic relative CeIn 3 (T c ∼ 200 mK), the T c of CeCoIn 5 is remarkably high. We suggest that this difference may arise from magnetically mediated superconductivity in the layered crystal structure of CeCoIn 5. Superconductivity is distinct in the correlation often evident between structure and properties: certain crystal structures or substructures favour superconductivity [1]. In particular, what underlies this relationship in the high-T c cuprates and heavy-fermion materials, which border so closely on magnetically ordered phases, is of essential interest both fundamentally and in the search for new superconducting materials [2, 3]. For example, fully half of the known heavyfermion superconductors crystallize in the tetragonal ThCr 2 Si 2 structure, which is also the structure type of the La 2 CuO 4 family of high-T c superconductors [4]. For the cuprates, there is no consensus on the origin of the superconductivity, but their quasi-2D structure and proximity to magnetic order have been shown to be particularly favourable for an unconventional form of superconductivity in which a pairwise-attractive interaction among quasiparticles is mediated by magnetic correlations [5]. Here, we report the discovery of a possible heavy-fermion analogue of the cuprates, a new layered superconductor CeCoIn 5 , with the highest known ambient-pressure superconducting transition temperature T c in the class of heavy-fermion materials. Heavy-fermion superconductors are materials in which superconductivity emerges out of a normal state with strong electronic correlations. The presence of an appropriate magnetic ion-in this case Ce-enhances the effective mass m * of conduction electrons by several orders of magnitude [6]. In the more than twenty years since the first heavy-fermion superconductor was discovered (CeCu 2 Si 2) [7], only one other Ce-based material has been found that unambiguously shows superconductivity at ambient pressure: CeIrIn 5 [8]. Both of these materials exhibit rather complex phenomena and/or metallurgy, making their study challenging. The ground state of CeCu 2 Si 2 can be either antiferromagnetic or superconducting depending on very small changes in unit-cell volume or composition [9]; CeIrIn 5 shows zero resistivity near 1 K but does not produce a thermodynamic signature of superconductivity until

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Diamond is an electrical insulator well known for its exceptional hardness. It also conducts heat even more effectively than copper, and can withstand very high electric fields 1 . With these physical properties, diamond is attractive for electronic applications 2 , particularly when charge carriers are introduced (by chemical doping) into the system. Boron has one less electron than carbon and, because of its small atomic radius, boron is relatively easily incorporated into diamond 3 ; as boron acts as a charge acceptor, the resulting diamond is effectively hole-doped. Here we report the discovery of superconductivity in boron-doped diamond synthesized at high pressure (8-9 GPa) and temperature (2,500-2,800 K).Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond is a bulk, type-II superconductor below the superconducting transition temperature T c ≈4 K; superconductivity survives in a magnetic field up to H c2 (0)≥3.5 T. The discovery of superconductivity in diamond-structured carbon suggests that Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions.With their potential for electronic applications as microchip substrates, high efficiency electron emitters, photodetectors and transistors, diamond and carrier-doped diamond have been studied extensively 3-6 . The extremely short covalent bonds of carbon atoms in diamond give diamond many of its desirable properties, but also constrain geometrically which dopants can be incorporated and their concentration. Because of its small atomic radius compared to other potential dopants, boron is readily incorporated into the dense (1.763×10 23 atoms cm −3 ) diamond lattice. Boron dopes holes into a shallow acceptor level close to the top of the valence band that is separated from the conduction band of diamond by E g ≈5.5 eV. Electrical transport studies of B-doped diamond, including high-pressure synthesized crystals and CVD (chemical vapour deposition) films, find that low boron concentrations n≈10 17 -10 19 cm −3 give a semiconducting conductivity with an activation energy of ~0.35 eV (refs 7-11). Increasing the concentration to 10 20 cm −3 gradually decreases the activation energy 9,10 , and for n≥10 20 cm −3 , the electrical conductivity acquires metallic-like behaviour near room temperature [8][9][10][11] that signals an insulator-metal transition near this concentration. A metallic-like conductivity has not been found, however, at low temperatures for any presently available B concentration, which has reached (2-3)×10 21 cm −3 (refs 8-11).We have studied B-doped diamond synthesized by reacting B 4 C and graphitic carbon at pressure, 8-9 GPa, and temperature, 2,500-2,800 K, for ~5 s. Under these conditions, polycrystalline diamond aggregates 1-2 mm in size formed at the interface between graphite and B 4 C. All the diamond aggregates had a metal-like lustre. Scanning electron microscopy (SEM) showed that the di...

The properties of an organic molecular ferromagnet [C(60)TDAE(0.86); TDAE is tetrakis(dimethylamino)ethylene] with a Curie temperature ;T(c) = 16.1 kelvin are described. The ferromagnetic state shows no remanence, and the temperature dependence of the magnetization below ;T(c) does not follow the behavior expected of a conventional ferromagnet. These results are interpreted as a reflection of a three-dimensional system leading to a soft ferromagnet.

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Plutonium is a metal of both technological relevance and fundamental scientific interest. Nevertheless, the electronic structure of plutonium, which directly influences its metallurgical properties, is poorly understood. For example, plutonium's 5f electrons are poised on the border between localized and itinerant, and their theoretical treatment pushes the limits of current electronic structure calculations. Here we extend the range of complexity exhibited by plutonium with the discovery of superconductivity in PuCoGa5. We argue that the observed superconductivity results directly from plutonium's anomalous electronic properties and as such serves as a bridge between two classes of spin-fluctuation-mediated superconductors: the known heavy-fermion superconductors and the high-T(c) copper oxides. We suggest that the mechanism of superconductivity is unconventional; seen in that context, the fact that the transition temperature, T(c) approximately 18.5 K, is an order of magnitude greater than the maximum seen in the U- and Ce-based heavy-fermion systems may be natural. The large critical current displayed by PuCoGa5, which comes from radiation-induced self damage that creates pinning centres, would be of technological importance for applied superconductivity if the hazardous material plutonium were not a constituent.

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

Low temperature specific heat and thermal conductivity measurements on the ambient pressure heavy fermion superconductors CeIrIn5 and CeCoIn5 reveal power law temperature dependences of these quantities below T(c). The low temperature specific heat in both CeIrIn5 and CeCoIn5 includes T2 terms, consistent with the presence of nodes in the superconducting energy gap. The thermal conductivity data present a T-linear term consistent with the universal limit (CeIrIn5), and a low temperature T3 variation in the clean limit (CeCoIn5), also in accord with prediction for an unconventional superconductor with lines of nodes.