Browsing by Author "Kim, H."

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    Evolution of London penetration depth with scattering in single crystals of K1−xNaxFe2As2
    (American Physical Society, 2014) Kim, H.; Tanatar, M.A.; Liu, Yong; Sims, Zachary Cole; Zhang, Chenglin; Dai, Pengcheng; Lograsso, T.A.; Prozorov, R.
    London penetration depth, λ(T), was measured in single crystals of K1−xNaxFe2As2, x=0 and 0.07, down to temperatures of 50 mK, ∼Tc/50. Isovalent substitution of Na for K significantly increases impurity scattering, with ρ(Tc) rising from 0.2 to 2.2 μΩ cm, and leads to a suppression of Tc from 3.5 to 2.8 K. At the same time, a close to T-linear Δλ(T) in pure samples changes to almost T2 in the substituted samples. The behavior never becomes exponential as expected for the accidental nodes, as opposed to T2 dependence in superconductors with symmetry imposed line nodes. The superfluid density in the full temperature range follows a simple clean and dirty d-wave dependence, for pure and substituted samples, respectively. This result contradicts suggestions of multiband scenarios with strongly different gap structure on four sheets of the Fermi surface.
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    Type-I superconductivity in YbSb2 single crystals
    (American Physical Society, 2012) Zhao, Liang L.; Lausberg, Stefan; Kim, H.; Tanatar, M.A.; Brando, Manuel; Prozorov, R.; Morosan, E.
    We present evidence of type-I superconductivity in YbSb2 single crystals from dc and ac magnetization, heat capacity, and resistivity measurements. The critical temperature and critical field are determined to be Tc ≈ 1.3 K and Hc ≈ 55 Oe. A small Ginzburg-Landau parameter κ = 0.05, together with typical magnetization isotherms of type-I superconductors, small critical field values, a strong differential paramagnetic effect signal, and a fieldinduced change from second- to first-order phase transition, confirms the type-I nature of the superconductivity in YbSb2. A possible second superconducting state is observed in the radio-frequency susceptibility measurements, with T (2) c ≈ 0.41 K and H(2) c ≈ 430 Oe.