G. M. Luke

Time-reversal symmetry-breaking superconductivity in Sr2RuO4

We report muon spin relaxation measurements on the superconductor Sr2RuO4 that reveal the spontaneous appearance of an internal magnetic field below the transition temperature: the appearance of such a field indicates that the superconducting state in this material is characterized by the breaking of time-reversal symmetry. These results, combined with other symmetry considerations, suggest that superconductivity in Sr2RuO4 is of p-wave (odd-parity) type, analogous to superfluid 3He.Although the properties of most superconducting materials are well described by the theory of Bardeen, Cooper and Schrieffer (BCS), considerable effort has been devoted to the search for exotic superconducting systems in which BCS theory does not apply. The transition to the superconducting state in conventional BCS superconductors involves the breaking of gauge symmetry only, whereby the wavefunction describing the Cooper pairs—the paired electron states responsible for superconductivity—adopt a definite phase. In contrast, a signature of an unconventional superconducting state is the breaking of additional symmetries, which can lead to anisotropic pairing (such as the ‘d-wave’ symmetry observed in the copper oxide superconductors) and the presence of multiple superconducting phases (as seen in UPt3 and analogous behaviour in superfluid 3He; refs 3–5). Here we report muon spin-relaxation measurements on the superconductor Sr2RuO4 that reveal the spontaneous appearance of an internal magnetic field below the transition temperature: the appearance of such a field indicates that the superconducting state in this material is characterized by the breaking of time-reversal symmetry. These results, combined with other symmetry considerations, suggest that superconductivity in Sr2RuO4 is of ‘p-wave’ (odd-parity) type, analogous to superfluid 3He.

Gapped itinerant spin excitations account for missing entropy in the hidden-order state of URu 2 Si 2

Gapped itinerant spin excitations account for missing entropy in the hidden-order state of URu 2 Si 2

Comment on the origin(s) of the giant permittivity effect in CaCu3Ti4O12 single crystals and ceramics

Impedance spectroscopy has been performed on CaCu3Ti4O12 (CCTO) single crystals and ceramics using Au and InGa alloy electrodes. The extrinsic effect responsible for the giant permittivity observed at radio-frequencies near room temperature is shown to be different for single crystals and ceramics. For single crystals it is attributed to a non-ohmic electrode contact to semiconducting CCTO. For ceramics it is attributed to an internal barrier layer capacitor mechanism associated with semiconducting CCTO grains and insulating grain boundaries.

Li(Zn,Mn)As as a new generation ferromagnet based on a I–II–V semiconductor

In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li(1+y)(Zn(1-x)Mn(x))As in bulk materials. Ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess (y=0.05-0.2) compounds with Mn concentrations of x=0.02-0.15, which have p-type metallic carriers. This is presumably due to excess Li in substitutional Zn sites. Semiconducting LiZnAs, ferromagnetic Li(Zn,Mn)As, antiferromagnetic LiMnAs, and superconducting LiFeAs systems share square lattice As layers, which may enable development of novel junction devices in the future.

Absence of superconductivity in single-phase CaFe2As2 under hydrostatic pressure

Recent high-pressure studies found that structural/magnetic phase transitions are very pressure sensitive in

Superconducting state coexisting with a phase-separated static magnetic order in (Ba,K)Fe2As2, (Sr,Na)Fe2As2, and CaFe2As2

{\text{CaFe}}_{2}{\text{As}}_{2}

Reduction of Ordered Moment and Néel Temperature of Quasi-One-Dimensional Antiferromagnets Sr2CuO3 and Ca2CuO3

and that superconductivity can be achieved under modest pressure, although details of the sharpness and temperature of transitions vary between liquid medium and gas medium measurements. To better understand this issue, we performed high-pressure susceptibility and transport studies on

Static magnetic order in La1.875Ba0.125CuO4

{\text{CaFe}}_{2}{\text{As}}_{2}

Searching for spontaneous magnetic order in an organic ferromagnet. μSR studies of β-phase p-NPNN

, using helium as the pressure medium. The signatures of the transitions to the low-temperature orthorhombic and collapsed tetragonal phases remained exceptionally sharp, and no signature of bulk superconductivity was found under our hydrostatic conditions. Our results suggest that superconductivity in

Muon level-crossing spectroscopy of organic free radicals

{\text{CaFe}}_{2}{\text{As}}_{2}