The recent discovery of superconductivity at the interfaces between KTaO 3 and EuO (or LaAlO 3 ) gives birth to the second generation of oxide interface superconductors. This superconductivity exhibits a strong dependence on the surface plane of KTaO 3 , in contrast to the seminal LaAlO 3 /SrTiO 3 interface, and the superconducting transition temperature T c is enhanced by one order of magnitude. For understanding its nature, a crucial issue arises: Is the formation of oxide interfaces indispensable for the occurrence of superconductivity? Exploiting ionic liquid (IL) gating, we are successful in achieving superconductivity at KTaO 3 (111) and KTaO 3 (110) surfaces with T c up to 2.0 and 1.0 K, respectively. This oxide-IL interface superconductivity provides a clear evidence that the essential physics of KTaO 3 interface superconductivity lies in the KTaO 3 surfaces doped with electrons. Moreover, the controllability with IL technique paves the way for studying the intrinsic superconductivity in KTaO 3 .

No abstract

We report the discovery of superconductivity with a maximum T c ≈1.28 K in Br-doped (PbSe) 1.12 (TaSe 2 ), which is a new misfit compound consisting of alternating layers of distorted rocksalt PbSe and dichalcogenide TaSe 2 . It is found that the Br-doping is required for the formation of this misfit compound and superconductivity can be tuned by the Br content. The large anisotropic parameter of resistivity c ab g r r = r ≈100 and that of the upper critical field H c2 g = H H c ab c c 2 2 ≈10 are obtained. The estimated c-axis coherence length cx ≈6.3 nm, larger than the c-axis lattice constant, which implies that this compound is an anisotropic threedimensional superconductor. The Hall coefficient measurements suggest that the charge transport is dominated by the hole-type charge carrier and there is a charge transfer from the PbSe layer to the conducting TaSe 2 layer. The small normalized specific heat jump ΔC/γ T c =1.16 and electron-phonon coupling constant λ ep ≈0.61 indicate that Br-doped (PbSe) 1.12 (TaSe 2 ) is a weak coupling Bardeen-Cooper-Schrieffer superconductor.

The Hall and Seebeck effects of the stripe-ordered superconductor La(1.6-x)Nd(0.4)Sr(x)CuO(4) single crystals (x = 0.10, 0.12 and 0.15) were investigated systematically. The sign change of Hall and Seebeck coefficients (R(H) and S) from positive to negative with decreasing temperature suggests the presence of electron pockets in the Fermi surface due to the stripe ordering. We successfully tune this behavior through an epitaxial strain induced by the mismatch between the thin film and the substrate. The negative R(H) disappears in the thinner film in which the static charge stripe is greatly suppressed by the strong epitaxial strain, and for a strain released thicker film the negative R(H) recovers. These results indicate the possibility of Fermi surface reconstruction caused by the static charge stripe order in the system.