• P Gegenwart

      Articles written in Pramana – Journal of Physics

    • Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

      P Gegenwart H Aoki T Cichorek J Custers M Jaime A Ochiai F Steglich

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      The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb4As3 have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT2 with huge and nearly field-independent coefficient A ≈ 3 µΩ cm/K2 is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m0 and a charge-carrier mean-free path of 215 Å are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.

    • Influence of disorder on superconductivity in non-magnetic rare-earth nickel borocarbides

      G Fuchs K-H Müller J Freudenberger K Nenkov S-L Drechsler SV Shulga D Lipp A Gladun T Cichorek P Gegenwart

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      The effect of substitutional disorder on the superconducting properties of YNi2B2C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. For the two series of (Y, Lu)Ni2B2C and Y(Ni, Pt)2B2C compounds, the upper critical field Hc2(T) and the specific heat cp(T, H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as Tc, the upper critical field Hc2(0) at T=0 and a characteristic positive curvature of Hc2(T) observed for these compounds near Tc. The Hc2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni, Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(Ni1−x, Ptx)2B2C samples for x=0.1.

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