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Register a new userNodeless superconductivity arising from strong (pi,pi) antiferromagnetism in the infinite-layer electron-doped cuprate Sr1-xLaxCuO2
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The asymmetry between electron and hole doping remains one of the central issues in high-temperature cuprate superconductivity, but our understanding of the electron-doped cuprates has been hampered by apparent discrepancies between the only two known families: Re2-xCexCuO4 and A1-xLaxCuO2. Here we report in situ angle-resolved photoemission spectroscopy measurements of epitaxially-stabilized films of Sr1-xLaxCuO2 synthesized by oxide molecular-beam epitaxy. Our results reveal a strong coupling between electrons and (pi,pi) antiferromagnetism that induces a Fermi surface reconstruction which pushes the nodal states below the Fermi level. This removes the hole pocket near (pi/2,pi/2), realizing nodeless superconductivity without requiring a change in the symmetry of the order parameter and providing a universal understanding of all electron-doped cuprates.
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We report on measurements of the in-plane magnetic penetration depth lambda_{ab} in the infinite-layer electron-doped high-temperature cuprate superconductor Sr_0.9La_0.1CuO_2 by means of muon-spin rotation. The observed temperature and magnetic field dependences of lambda_{ab} are consistent with the presence of a substantial s-wave component in the superconducting order parameter in good agreement with the results of tunneling, specific heat, and small-angle neutron scattering experiments.
Quantum spin liquids (QSLs), in which spins are highly entangled, have been considered a groundwork for generating exotic superconductivity.Despite numerous efforts, superconductivity emerging from QSLs has been unrealized in actual materials due to the difficulties in stabilizing QSL states with metallic conductivity.Recently, an organic compound, $kappa$-(BEDT-TTF)$_4$Hg$_{2.89}$Br$_8$, with a nearly regular triangular lattice of molecular dimers was recognized as a candidate for doped QSLs. In this study, we report an unusual superconducting phase of $kappa$-(BEDT-TTF)$_4$Hg$_{2.89}$Br$_8$: unexpectedly large ratios of the upper critical field to the critical temperature $H_{rm c2}$/$T_{rm c}$ in fields not only parallel but also perpendicular to the two-dimensional conducting layers and a very wide region of fluctuating superconductivity above $T_{rm c}$.Our results reveal that these peculiarities arise from strong electron correlations and possible quantum criticality unique to the doped QSL state, leading to a heavy mass of itinerant carriers and a large superconducting energy gap.
We report a comprehensive study of the centrosymmetric Re$_3$B and noncentrosymmetric Re$_7$B$_3$ superconductors. At a macroscopic level, their bulk superconductivity (SC), with $T_c$ = 5.1 K (Re$_3$B) and 3.3 K (Re$_7$B$_3$), was characterized via electrical-resistivity, magnetization, and heat-capacity measurements, while their microscopic superconducting properties were investigated by means of muon-spin rotation/relaxation ($mu$SR). In both Re$_3$B and Re$_7$B$_3$ the low-$T$ zero-field electronic specific heat and the superfluid density (determined via tranverse-field $mu$SR) suggest a nodeless SC. Both compounds exhibit some features of multigap SC, as evidenced by temperature-dependent upper critical fields $H_mathrm{c2}(T)$, as well as by electronic band-structure calculations. The absence of spontaneous magnetic fields below the onset of SC, as determined from zero-field $mu$SR measurements, indicates a preserved time-reversal symmetry in the superconducting state of both Re$_3$B and Re$_7$B$_3$. Our results suggest that a lack of inversion symmetry and the accompanying antisymmetric spin-orbit coupling effects are not essential for the occurrence of multigap SC in these rhenium-boron compounds.
Recently, a new family of iron-based superconductors called 12442 was discovered and the muon spin relaxation ($mu$SR) measurements on KCa$_2$Fe$_4$As$_4$F$_2$ and CsCa$_2$Fe$_4$As$_4$F$_2$ polycrystals, two members of the family, indicated that both have a nodal superconducting gap structure with $s+d$ pairing symmetry. Here we report the ultralow-temperature thermal conductivity measurements on CsCa$_2$Fe$_4$As$_4$F$_2$ single crystals ($T_c$ = 29.3 K). A negligible residual linear term $kappa_0/T$ in zero field and the field dependence of $kappa_0/T$ suggest multiple nodeless superconducting gaps in CsCa$_2$Fe$_4$As$_4$F$_2$. This gap structure is similar to CaKFe$_4$As$_4$ and moderately doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$, but contrasts to the nodal gap structure indicated by the $mu$SR measurements on CsCa$_2$Fe$_4$As$_4$F$_2$ polycrystals.
One of the central questions in the cuprate research is the nature of the normal state which develops into high temperature superconductivity (HTSC). In the normal state of hole-doped cuprates, the existence of charge density wave (CDW) is expected to shed light on the mechanism of HTSC. With evidence emerging for CDW order in the electron-doped cuprates, the CDW would be thought to be a universal phenomenon in high-$T_c$ cuprates. However, the CDW phenomena in electron-doped cuprate are quite different than those in hole-doped cuprates. Here we study the nature of the putative CDW in an electron-doped cuprate through direct comparisons between as-grown and post-annealed Nd$_{1.86}$Ce$_{0.14}$CuO$_4$ (NCCO) single crystals using Cu $L_3$-edge resonant soft x-ray scattering (RSXS) and angle resolved photoemission spectroscopy (ARPES). The RSXS result reveals that the non-superconducting NCCO shows the same reflections at the wavevector (~1/4, 0, $l$) as like the reported superconducting NCCO. This superconductivity-insensitive signal is quite different with the characteristics of the CDW reflection in hole-doped cuprates. Moreover, the ARPES result suggests that the fermiology cannot account for such wavevector. These results call into question the universality of CDW phenomenon in the cuprates.
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