CuxBi2Se3 hosts both topological surface states and bulk superconductivity. It has been identified recently as a topological superconductor (TSC) with an extraordinary nematic, i. e. C2-symmetric, superconducting state and odd-parity pairing. Here, using scanning tunneling microscopy (STM), we directly examine the response of the superconductivity of CuxBi2Se3 to magnetic field. Under outof-plane fields (B⊥), we discover elongated magnetic vortices hosting zero-bias conductance peaks consistent with the Majorana bound states expected in a TSC. Under in-plane fields (B//), the average superconducting gap exhibits two-fold symmetry with field orientation; the long C2 symmetry axes are pinned to the dihedral mirror planes under B//=0.5 T but rotate slightly under B//=1.0 T. Moreover, a nodeless Δ4x gap structure is semi-quantitatively determined for the first time. Our data paint a microscopic picture of the nematic superconductivity in CuxBi2Se3 and pose strong constraints on theory.

Li0.8Fe0.2)OHFeSe is a newly-discovered intercalated iron-selenide superconductor with a Tc above 40 K, which is much higher than the Tc of bulk FeSe (8 K). Here we report a systematic study of (Li0.8Fe0.2)OHFeSe by low temperature scanning tunneling microscopy (STM). We observed two kinds of surface terminations, namely FeSe and (Li0.8Fe0.2)OH surfaces. On the FeSe surface, the superconducting state is fully gapped with double coherence peaks, and a vortex core state with split peaks near EF is observed. Through quasiparticle interference (QPI) measurements, we clearly observed intra-and interpocket scatterings in between the electron pockets at the M point, as well as some evidence of scattering that connects Г and M points. Upon applying magnetic field, the QPI intensity of all the scattering channels are found to behave similarly. Furthermore, we studied impurity effects on the superconductivity by investigating intentionally introduced impurities and intrinsic defects. We observed that magnetic impurities such as Cr adatoms can induce in-gap states and suppress superconductivity. However, nonmagnetic impurities such as Zn adatoms do not induce visible in-gap states. Meanwhile, we show that Zn adatoms can induce in-gap states in thick FeSe films, which is believed to have an s±-wave pairing symmetry. Our experimental results suggest it is likely that (Li0.8Fe0.2)OHFeSe is a plain s-wave superconductor, whose order parameter has the same sign on all Fermi surface sections.

Synthesis of 1-(cyclohexylmethyl)-3-methyl imidazolium bis[(trifluoromethane)sulfonyl]amide ([CyhmC 1 im][NTf 2 ])A one-neck round bottom flask, under nitrogen, equipped with a magnetic stirrer and a condenser, was charged with 1-methylimidazole (6.65 g, 81.02 mmol). To this mixture, an excess (1.05 eq.) of (bromomethyl)cyclohexane (15.06 g, 85.07 mmol) was added. The reaction was left under constant stirring at 50 °C, until complete consumption of the 1-methylimidazole.The 1-(cyclohexylmethyl)-3-methylimidazolium bromide formed was then washed three times with 50 mL mixture of hexanes: dichloromethane (4:1 v/v) to remove the unreacted excess of halide. The product was concentrated in vacuo on a rotary evaporator. 3 g of activated charcoal and 60 mL of dichloromethane were added to the viscous, colored bromide, and left under stirring for 96 h. The black slurry was then filtered through a gravitational column packed with 10 cm of aluminum oxide (activated, basic, 50-200 micron) and 3 cm of celite 545. The removal of the solvent under reduced pressure afforded [CyhmC 1 im][Br] as a colorless, viscous liquid at room temperature. The second stage of synthesis was accomplished via a metathesis reaction. 1 An aqueous solution of lithium bis[(trifluoromethane)sulfonyl]amide (0.98 eq., 20.65 g, 71.91 mmol) was added to the [CyhmC 1 im][Br] and left to stir overnight. The two-phase system was then repeatedly washed with triple-deionized water until no bromide ions could be detected by the silver nitrate test. The final product, [CyhmC 1 im][NTf 2 ], a colorless liquid at room temperature, was dried with benzene azeotrope. The residual benzene was removed under vacuum. Yield: 91%.

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Bulk and shear rheological studies were performed on a 10 wt % silica nanoparticle-filled polystyrene nanocomposite. The limiting moduli in glassy and rubbery states are higher for the nanocomposite than for the neat polymer; the increase is consistent with hydrodynamic reinforcement and is slightly higher than the lower bound of the rule of mixtures prediction. All evidence indicates that the presence of nanoparticles does not significantly change the polymer dynamics associated with glass transition, except to increase the T g by 3 K. Comparison of the bulk and shear retardation spectra sug-gests that the underlying mechanisms for both responses are similar at short times and that the long-time chain modes available to the shear are not available to the bulk, consistent with Plazek's earlier findings. In addition, T 2 T g and TV c scaling, along with the findings of thermorheological complexity, are discussed.