We present measurements of the low temperature Hall effect and magnetoresistance in the heavy fermion superconductor CeCo(In 0.925Cd0.075)5 as a function of applied magnetic field. The Hall resistivity ρxy is observed to be negative indicating electron dominated transport. Features corresponding to the possible destabilization of the antiferromagnetic ground state are observed. Magnetic field sweeps show that the resistivity ρxx(H) is hysteretic in this regime, indicating that these transitions could be first order in nature. © 2009 IOP Publishing Ltd.

Hall effect measurements have been conducted on high-quality single crystals of the heavy-fermion superconductor CeCoIn5. The anomalous Hall contribution is negligible in the investigated temperature range from 0.05 to 5 K. The measured Hall resistivities ρxy show a noticeable change in slope between the low-field (initial Hall coefficient) and the high-field region. In the superconducting regime, T < 2.3 K, Hall measurements are restricted to high magnetic fields H > Hc 2, the upper critical field of superconductivity. The high-field Hall coefficient is almost constant for temperatures down to 250 mK. At T {less-than or slanted equal to} 250 mK, an additional change in curvature of ρxy vs. H is observed. © 2006 Elsevier B.V. All rights reserved.

We present Hall effect and magnetoresistance measurements in the heavy fermion superconductor CeIrIn(5). At low temperature, a Kondo coherent state is established. Deviations from Kohler's rule and a quadratic temperature dependence of the cotangent of the Hall angle are reminiscent of properties observed in the high-temperature superconducting cuprates. A striking observation pertains to the presence of a precursor state--characterized by a change in the Hall mobility--that precedes the superconductivity in this material, in similarity to the pseudogap in the cuprate superconductors.

We report Hall Effect measurements under pressure in the normal state of CeCoIn5, from 60 to 355 mK and for fields exceeding the superconducting upper critical field Hc 2, with the field oriented parallel to [0 0 1]. At low pressures, the field dependence of the Hall coefficient exhibits a scaling consistent with the one reported in the normal state at higher temperatures, but at odds with the Δ H / T scaling expected near a field tuned quantum critical point. The breakdown of this scaling at higher pressures, concomitant with the suppression of spin fluctuations, suggests that it is a hallmark of the spin fluctuations.

We present low-temperature thermal expansion measurements on the nominally 10% Cd doped CeCoIn5. While the superconducting transition temperature is monotonically suppressed, an antiferromagnetic phase evolves in CeCoIn5 by Cd-doping. For the uniaxial pressure dependence of the Néel temperature along c, we find (∂ TN / ∂ p)∥ c = 0.206 K / GPa. The magnetic field dependence (for B ∥ c) of TN is stronger compared to CeRhIn5. As no traces of a superconducting transition are resolved in thermal expansion along the c-axis, we estimate a lower limit of the in-plane pressure dependence to (∂ Tc / ∂ p)⊥ c = 0.38 K / GPa. © 2007 Elsevier B.V. All rights reserved.

The heavy-fermion superconductor CeCo In5 is believed to be close to a magnetic instability, but no static magnetic order has been found. Cadmium doping on the In site shifts the balance between superconductivity and antiferromagnetism to the latter with an extended concentration range where both types of order coexist at low temperatures. We investigated the magnetic structure of nominally 10% Cd-doped CeCo In5, being antiferromagnetically ordered below TN ≈3 K and superconducting below Tc ≈1.3 K, by elastic neutron scattering. Magnetic intensity was observed only at the ordering wave vector QAF = (1 2, 1 2, 1 2) commensurate with the crystal lattice. Upon entering the superconducting state, the magnetic intensity seems to change only little. The commensurate magnetic ordering in CeCo (In1-x Cdx) 5 is in contrast to the incommensurate antiferromagnetic ordering observed in the closely related compound CeRh In5. Our results give insights into the interplay between superconductivity and magnetism in the family of CeT In5 (T=Co, Rh, and Ir) based compounds. © 2007 The American Physical Society.

We present highly sensitive Hall effect measurements of the heavy fermion compound CeCoIn5 down to temperatures of 55 mK. A pronounced dip in the differential Hall coefficient | partial differential rho(xy)/ partial differential H| at low temperature and above the upper critical field of superconductivity, H(c2), is attributed to critical spin fluctuations associated with the departure from Landau Fermi liquid behavior. This identification is strongly supported by a systematic suppression of this feature at elevated pressures. The resulting crossover line in the field-temperature phase diagram favors a field induced quantum critical point at mu(0)H(qc) approximately 4.1 T below H(c2)(T=0) suggesting related, yet separate, critical fields.

We conducted Hall effect measurements on the heavy-fermion superconductor CeCoIn5 for temperatures 0.05-5 K and for pressures up to 1.2 GPa. A scaling of the magnetic field H is introduced for the differential Hall coefficient, RHd = ∂ ρxy (T, H) / ∂ H resulting in a single generic curve for RHd (H) curves obtained at different T. We argue that the peak feature apparent in this generic curve corresponds to the crossover from non-Fermi liquid to Landau Fermi liquid behavior. © 2007 Elsevier B.V. All rights reserved.

The possible existence of a sign-changing gap symmetry in BaFe2As2-derived superconductors (SC) has been an exciting topic of research in the last few years. To further investigate this subject we combine Electron Spin Resonance (ESR) and pressure-dependent transport measurements to investigate magnetic pair-breaking effects on BaFe1.9M0.1As2 (M = Mn, Co, Cu, and Ni) single crystals. An ESR signal, indicative of the presence of localized magnetic moments, is observed only for M = Cu and Mn compounds, which display very low SC transition temperature (Tc) and no SC, respectively. From the ESR analysis assuming the absence of bottleneck effects, the microscopic parameters are extracted to show that this reduction of Tc cannot be accounted by the Abrikosov-Gorkov pair-breaking expression for a sign-preserving gap function. Our results reveal an unconventional spin- and pressure-dependent pair-breaking effect and impose strong constraints on the pairing symmetry of these materials.

The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity.