[en] We present resistivity measurements at ambient pressure on high purity crystals of YNi₃ and Ni₃Al in the temperature range from 50 mK to 7 K. Although both systems are well in their low moment ferromagnetic state, there is no evidence for a T²-temperature dependence of the resistivity as would be expected from Fermi liquid theory. Instead, we observe an anomalous temperature exponent of 1.5-1.6 down to low temperatures

[en] We have measured the temperature dependence of the resistivity of Sr₂RuO₄ under pressure under hydrostatic conditions. Many-body enhancements and the superconducting transition temperature all fall gradually with increasing pressure, contrary to previous suggestions of a ferromagnetic quantum critical point around 3 GPa

[en] We survey recent experimental results including quantum oscillations and complementary measurements probing the electronic structure of underdoped cuprates, and theoretical proposals to explain them. We discuss quantum oscillations measured at high magnetic fields in the underdoped cuprates that reveal a small Fermi surface section, comprising quasiparticles that obey Fermi–Dirac statistics, unaccompanied by other states of comparable thermodynamic mass at the Fermi level. The location of the observed Fermi surface section at the nodes is indicated by a body of evidence including the collapse in Fermi velocity measured by quantum oscillations, which is found to be associated with the nodal density of states observed in angular resolved photoemission, the persistence of quantum oscillations down to low fields in the vortex state, the small value of density of states from heat capacity and the multiple frequency quantum oscillation pattern consistent with nodal magnetic breakdown of bilayer-split pockets. A nodal Fermi surface pocket is further consistent with the observation of a density of states at the Fermi level concentrated at the nodes in photoemission experiments, and the antinodal pseudogap observed by photoemission, optical conductivity, nuclear magnetic resonance (NMR) Knight shift, as well as other complementary diffraction, transport and thermodynamic measurements. One of the possibilities considered is that the small Fermi surface pockets observed at high magnetic fields can be understood in terms of Fermi surface reconstruction by a form of small wavevector charge order, observed over long lengthscales in experiments such as NMR and x-ray scattering, potentially accompanied by an additional mechanism to gap the antinodal density of states. (key issues reviews)

[en] We report the discovery of superconductivity at high pressure in SrFe₂As₂ and BaFe₂As₂. The superconducting transition temperatures are up to 27 K in SrFe₂As₂ and 29 K in BaFe₂As₂, the highest obtained for materials with pressure-induced superconductivity thus far. (fast track communication)

[en] Understanding the emergence and subsequent behavior of heavy electrons in Kondo lattice materials is one of the grand challenges in condensed matter physics. From this perspective we review the progress that has been made during the past decade and suggest some directions for future research. Our focus will be on developing a new microscopic framework that incorporates the basic concepts that emerge from a phenomenological description of the key experimental findings. (report on progress)

[en] The layered perovskite Ca₂RuO₄ is a spin-one Mott insulator at ambient pressure and exhibits metallic ferromagnetism at least up to ∼80 kbar with a maximum Curie temperature of 28 K. Above ∼90 and up to 140 kbar, the highest pressure reached, the resistivity and ac susceptibility show pronounced downturns below ∼0.4 K in applied magnetic fields of up to ∼10 mT. This indicates that our specimens of Ca₂RuO₄ are weakly superconducting on the border of a quasi-2D ferromagnetic state. (fast track communication)

[en] The cubic pyrite compound CoS₂ is an itinerant-electron ferromagnet with a Curie temperature of T_c=122K. Measurements of its electrical resistivity in quasi-hydrostatic Bridgman cells were performed up to pressures of p=15GPa. T_c is monotonically decreased by the application of external pressure and a first-order quantum phase transition was inferred at a pressure of p_c∼6GPa. The temperature dependence of the resistivity at low temperatures (T=0.3-20K) changes from a power-law with temperature exponent n=2 in the ferromagnetic phase to n<1.7 in the paramagnetic phase at pressures beyond p_c