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...

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We have performed 75As nuclear magnetic resonance measurements on aligned powders of the new LaFeAsO0.9F0.1 superconductor. In the normal state, we find a strong temperature dependence of the spin shift and Korringa behavior of the spin lattice relaxation rate. In the superconducting state, we find evidence for line nodes in the superconducting gap and spin-singlet pairing. Our measurements reveal a strong anisotropy of the spin lattice relaxation rate, which suggests that superconducting vortices contribute to the relaxation rate when the field is parallel to the c axis but not for the perpendicular direction.

We show that the NMR Knight shift anomaly exhibited by a large number of heavy electron materials can be understood in terms of the different hyperfine couplings of probe nuclei to localized spins and to conduction electrons. The onset of the anomaly is at a temperature T * , below which an itinerant component of the magnetic susceptibility develops. This second component characterizes the polarization of the conduction electrons by the local moments and is a signature of the emerging heavy electron state. The heavy electron component grows as log T below T * , and scales universally for all measured Ce, Yb and U based materials. Our results suggest that T * is not related to the single ion Kondo temperature, TK, but rather represents a correlated Kondo temperature that provides a measure of the strength of the intersite coupling between the local moments. Our analysis strongly supports the two-fluid description of heavy electron materials developed by Nakatsuji, Pines and Fisk.

We report Cu and La nuclear magnetic resonance (NMR) measurements in the title compound that reveal an inhomogeneous glassy behavior of the spin dynamics. A low temperature peak in the La spin lattice relaxation rate and the "wipeout" of Cu intensity both arise from these slow electronic spin fluctuations that reveal a distribution of activation energies. Inhomogeneous slowing of spin fluctuations appears to be a general feature of doped lanthanum cuprate. PACS 74.72.Bk, 75.30.Ds, 75.40.Gb Lanthanum cuprate, the prototypical single layer high temperature superconductor, has been extensively studied for several years to understand the origin of its unusual normal state behavior as well as the mechanism for superconductivity. Rare earth co-doped lanthanum cuprate has received attention recently because elastic neutron scattering experiments have revealed ordering of doped holes into charged stripes that constitute antiphase domain walls producing incommensurate antiferromagnetic (AF) order in the intervening undoped domains [1]. Charge stripe order is likely intimately related to the high temperature superconductivity [2][3][4][5]. Isostructural lanthanum nickelate demonstrates clear stripe order [6], and it has been shown there that both the charge order and the magnetic order are glassy [6,7]. It is also known that the magnetic order associated with charge ordering in lanthanum cuprate is glassy [8,9], but this situation is more difficult because the charge superlattice peaks are very hard to observe, presumably because the stripes tend to be dynamic. As a consequence little detail is known about the glassy behavior. Hunt et al. have observed suppression of the Cu NQR signal intensity ("wipeout") with decreasing temperature that they attribute to charge stripe order [10].NMR provides information complementary to neutron scattering because the nuclei are sensitive to the local magnetic field and the dynamic behavior of the electronic system without requiring spatial correlations. Chou et al., first proposed that the very strong peak in the 139 La nuclear spin relaxation rate displays an activated temperature dependence [13]. Furthermore, these data demonstrate a distribution P (E a ) of activation energies E a centered at E a /k B T ∼ 50 K and with a width comparable this center value indicating strongly inhomogeneous magnetic properties [13]. To understand if this inhomogeneity arises from disorder due to, e.g., substitutional dopants, we have applied this analysis to several lanthanum cuprate systems exhibiting AF order at low temperatures to allow us to explore the effect of varying the density and character of the disorder: in-plane doping by Li substitution for Cu, variation of doping density in LTT phase La 1.8−x Eu 0.2 Sr x CuO 4 : 0.01 ≤ x ≤ 0.15. Remarkably, we find that the character of the inhomogeneity, that is, the distribution of activation energies is essentially unchanged in all these cases and very similar to lightly doped La 2−x Sr x CuO 4 [11], suggesting that this inhomogeneity is intrinsi...

The Ni1+/Ni2+ states of nickelates have the identical (3d(9)/3d(8)) electronic configuration as Cu2+/Cu3+ in the high temperature superconducting cuprates, and are expected to show interesting properties. An intriguing question is whether mimicking the electronic and structural features of cuprates would also result in superconductivity in nickelates. Here we report experimental evidence for a bulklike magnetic transition in La4Ni3O8 at 105 K. Density functional theory calculations relate the transition to a spin density wave nesting instability of the Fermi surface.

We present NMR data in the normal and superconducting states of CeCoIn5 for fields close to Hc2(0)= 11.8 T in the ab plane. Recent experiments identified a first-order transition from the normal to superconducting state for H > 10.5 T, and a new thermodynamic phase below 290 mK within the superconducting state. We find that the Knight shifts of the In(1), In(2) and the Co are discontinuous across the first-order transition and the magnetic linewidths increase dramatically. The broadening differs for the three sites, unlike the expectation for an Abrikosov vortex lattice, and suggests the presence of static spin moments in the vortex cores. In the low-temperature and highfield phase the broad NMR lineshapes suggest ordered local moments, rather than a long wavelength quasiparticle spin density modulation expected for an FFLO phase.PACS numbers: 71.27.+a, 74.70.Tx, 75.20.Hr One of the most intriguing properties observed in Kondo lattice systems is the emergence of unconventional superconductivity near a quantum critical point (QCP). By varying some external parameter such as field or pressure, an antiferromagnetic ground state can be tuned such that the transition temperature goes to zero at the QCP. As the tuning parameter increases past the QCP, conventional Fermi-liquid behavior is recovered below a characteristic temperature T FL [1]. Superconductivity often emerges as the ground state of the system for sufficiently low temperatures in the vicinity of the QCP [2]. The heavy-fermion superconductor CeCoIn 5 exhibits many properties typical of a Kondo lattice system at a QCP. In particular, T FL appears to vanish at the superconducting critical field H c2 (T = 0) for fields along the c axis, suggesting the presence of a field-tuned QCP [3,4]. This interpretation has remained contentious because the ordered state associated with the QCP is superconductivity rather than antiferromagnetism. One explanation is that an antiferromagnetic (AFM) phase is hidden within the superconducting phase diagram, which is the genitor of both the QCP and non-Fermi liquid behavior in the vicinity of H c2 (0). However, when the superconductivity is suppressed with Sn doping, the QCP tracks H c2 (0), and no magnetic state emerges in the phase diagram, whereas pressure separates the QCP [5].In fact, there is a field-induced state, which we will refer to as the B phase, in the H − T phase diagram of CeCoIn 5 that exists just below H c2 (0). The order parameter of the B phase could be either (1) a different symmetry of the superconducting order parameter, (2) a fieldinduced magnetic phase, or (3) a Fulde-Ferrell-LarkinOvchinnikov (FFLO) superconducting phase [6,7,8,9]. The normal to superconducting transition in this system has a critical point at (H, T ) ∼ (10.5T, 0.75K), separating a second to first order transition, and the B phase exists below a temperature T 0 (H) ∼ 290 mK and is bounded by T c (H). NMR experiments suggest the presence of excess quasiparticles associated with nodes in the superconducting FFLO wavefunction [10,11,1...

The heavy fermion superconductor CeCoIn 5 can be tuned between superconducting and antiferromagnetic ground states by hole doping with Cd. Nuclear magnetic resonance data indicate that these two orders coexist microscopically with an ordered moment 0:7 B . As the ground state evolves, there is no change in the low-frequency spin dynamics in the disordered state. These results suggest that the magnetism emerges locally in the vicinity of the Cd dopants.