Resistivity, magnetization and microscopic 75 As nuclear magnetic resonance (NMR) measurements in the antiferromagnetically ordered state of the iron-based superconductor parent material CaFe2As2 exhibit anomalous features that are consistent with the collective freezing of domain walls. Below T * ≈ 10 K, the resistivity exhibits a peak and downturn, the bulk magnetization exhibits a sharp increase, and 75 As NMR measurements reveal the presence of slow fluctuations of the hyperfine field. These features in both the charge and spin response are strongly field dependent, are fully suppressed by H * ≈ 15 T, and suggest the presence of filamentary superconductivity nucleated at the antiphase domain walls in this material.

No abstract

Local-mode and localized surface plasmons generated on the silver thin film can selectively enhance the Raman signal from the surface. Further improvement of surface signal can be obtained by using the polarized Raman technique that results in a dramatic enhancement of the surface sensitivity by up to 25.4 times as compared to that without a silver coating. This technique will be very useful for Raman study on samples that suffer overlapping background signal. In this article, we show that it can be used to significantly improve the signal of thin strained-Si layer on top of SiGe buffer layer.

We measured the magnetic penetration depth λ(T ) in single crystals of LaOs4Sb12 (Tc=0.74 K) down to 85 mK using a tunnel diode oscillator technique. The observed low-temperature exponential dependence indicates a s-wave gap. Fitting the low temperature data to BCS s-wave expression gives the zero temperature gap value ∆(0) = (1.34 ± 0.07)kB Tc which is significantly smaller than the BCS value of 1.76kB Tc. In addition, the normalized superfluid density ρ(T ) shows an unusually long suppresion near Tc, and are best fit by a two-band s-wave model.The skutterudite PrOs 4 Sb 12 has been receiving much attention due to the discovery of its unconventional heavy fermion superconductivity, and the possible role played by quadrupolar fluctuations in its pairing mechanism. 1-4An important step in clarifying its superconductivity is to determine the symmetry of the superconducting gap. Conflicting results had been reported. On one hand, scanning tunneling microscopy (STM), muon spin rotation (µSR), and nuclear quadrupolar relaxation (NQR) experiments point to an isotropic superconducting energy gap.5-7 On the other hand, magnetic penetration depth, angle-dependent thermal conductivity, and neutron scattering measurements revealed point nodes on the superconducting gap.8-10 Angle-dependent thermal conductivity data revealed two distinct superconducting phases of twofold and fourfold symmetries, both with point nodes on the superconducting gap.9 Recently, multiband superconductivity was proposed as a reconciliation for these conflicting results. According to field-dependent thermal conductivity data, PrOs 4 Sb 12 is a two-band superconductor, with nodes on one band and an isotropic gap on the other.11-13 A similar two-gap structure was observed in Li 2 Pt 3 B, the nodes there arising from the interference of singlet and triplet pairing.14 LaOs 4 Sb 12 (superconducting transition temperature T c =0.74 K) and PrOs 4 Sb 12 (T c =1.85 K) are isostructural superconductors. The substitution of La by Pr introduces the 4f electrons, while largely preserving the crystal structure 15-17 and Fermi surface topology.16 The 4f energy levels of the Pr 3+ ion are split by the crystal electric field (CEF), resulting in a nonmagnetic Γ 1 singlet ground state, a 0.7-meV Γ 5 first excited state, and 11-meV Γ 4 second excited state (in O h cubic symmetry).18 The higher T c of PrOs 4 Sb 12 compared to LaOs 4 Sb 12 is attributed to the type of scattering between the conduction electrons and these lowlying CEF-split 4f levels 18-20 -the inelastic scattering of the conduction electron by the Γ 1 →Γ 5 transition has a strong quadrupole matrix element that enhances pair formation and consequently T c . This interaction, known as aspherical Coulomb scattering, overcomes the magnetic pair breaking effect due to the s-f exchange scattering of the conduction electron by the Γ 1 →Γ 4 transition, which has a strong dipole matrix element that suppresses T c . The f electrons thus play an important role in skutterudite/heavy-fermion superconductivity via the...

No abstract