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We have measured the electrical resistivity, polarized x-ray absorption, and magnetic neutron scattering for Y~"Ca,BaNi 1,zn, 05 to determine how doping affects the charge and spin dynamics of a Haldane chain compound. While Zn doping, which severs the NiO chains, increases the resistivity beyond that of the pure material, Ca doping introduces holes, residing mainly in the 2p, orbital of the oxygens in the NiO chains. Both dopants lead to simple finite size effects above the Haldane gap. In addition, we have discovered that Ca doping yields substantial magnetic states below the Haldane gap.PACS numbers: 75.25.+z, 71.30.+h, 72.80.6a Doping of two-and three-dimensional (3D) transition metal oxides yields phenomena ranging from strongly renormalized Fermi liquid behavior in the vanadates to high temperature superconductivity in the cuprates [1,2]. In view of the enhanced quantum fluctuations in 1D systems, doping of transition metal chain oxides could well lead to equally surprising discoveries. Furthermore, because the theory of 1D systems is less speculative than that of 2D and 3D materials, tests of theory should be simpler than for the cuprates and vanadates. Thus motivated, we have performed transport, x-ray absorption, and neutron scattering experiments to determine how doping affects Y2BaNi05, a charge transfer insulator [3] containing Ni2+ (S = 1) chains with a quantum disordered, Haldane ground state [4 -7]. To the best of our knowledge these experiments are the first on any carrier-doped 1D transition metal oxide, and Y2BaNi05 provides the first gapped spin liquid, of any dimension, to which carriers can be added. The key result is that while substitution of nonmagnetic Zn + for magnetic Ni + on the chains simply produces effects one can associate with chain cutting, replacing the off-chain Y3+ by Ca2+ has far more dramatic consequences. In particular, holes appear in oxygen orbitals along the NiO chains radically changing the temperature dependence of the resistivity from the simple insulating behavior of the parent. In both the parent and doped compounds, electrical conduction is 1D. Carrier doping also yields new magnetics states below the Haldane gap.The specimens were large (-5 cm3) polycrystalline pellets as well as small (0.5 X 1.0 X 3.0 mm3) single crystals. %e prepared the pellets using a standard solid state reaction, while we grew the crystals from Baand Ni-rich melts [8 -10]. The stoichiometry of Y, Ca, Ba, Zn, and Ni in each of these samples was determined by analysis of the y rays produced upon cold neutron capture at the National Institute of Standards and Technology (NIST) research reactor. All four pellets had compositions in agreement with the nominal values. The magnetic susceptibilities of the pellets were consistent with those obtained previously for the same compositions [8,11]. Figure 1 displays the four-terminal dc resistivity (p) [12] for single crystals with silver paste contacts. The conduction in pure Y2BaNi05 is remarkably 1D with p along the chain (a axis) 3 orders of magni...

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We report the measurements of de Haas-van Alphen (dHvA) oscillations in the noncentrosymmetric superconductor BiPd. Several pieces of a complex multi-sheet Fermi surface are identified, including a small pocket (frequency 40 T) which is three dimensional and anisotropic. From the temperature dependence of the amplitude of the oscillations, the cyclotron effective mass is (0.18 ± 0.1) me. Further analysis showed a non-trivial π-Berry phase is associated with the 40 T pocket, which strongly supports the presence of topological states in bulk BiPd and may result in topological superconductivity due to the proximity coupling to other bands.

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