The recently discovered family of vanadium-based kagome metals with topological band structures offer new opportunities to study frustrated, correlated topological quantum states. These layered compounds are nonmagnetic and undergo charge density wave (CDW) transitions before developing superconductivity at low temperatures. Here we report the observation of unconventional superconductivity and pair density wave (PDW) in the vanadium-based kagome metal CsV3Sb5 using scanning tunneling microscope/spectroscopy (STM/STS) and Josephson STS. The differential conductance exhibits a V-shaped pairing gap Δ~0.5 meV below a transition temperature Tc~2.3 K. Superconducting phase coherence is observed by Josephson effect and Cooper-pair tunneling using a superconducting tip. We find that CsV3Sb5 is a strong-coupling superconductor (2∆/kBTc~5) and coexists with long-range 4a0 unidirectional and 2×2 charge order. Remarkably, we discover a bidirectional PDW accompanied by 4a0/3 spatial modulations of the coherence peak and gap-depth in the tunneling conductance. We term this novel quantum state a roton-PDW that can produce a commensurate vortex-antivortex lattice and account for the observed conductance modulations. Above Tc, we observe a large V-shaped pseudogap in the 4a0 unidirectional and 2a0 bidirectional CDW state. Electron-phonon calculations attribute the 2×2 CDW to phonon softening induced structural reconstruction, but the phonon mediated pairing cannot describe the observed strong-coupling superconductor. Our findings show that electron correlations drive the 4a0 unidirectional CDW, unconventional superconductivity, and roton-PDW with striking analogies and distinctions to the phenomenology of high-Tc cuprate superconductors, and provide groundwork for understanding their microscopic origins in vanadium-based kagome superconductors.

The Relativistic Heavy Ion Collider (RHIC), as the world's first and only polarized proton collider, offers a unique environment in which to study the spin structure of the proton. In order to study the proton's transverse spin structure, the PHENIX experiment at RHIC took data with transversely polarized beams in 2001-02 and 2005, and it has plans for further running with transverse polarization in 2006 and beyond. Results from early running as well as prospective measurements for the future will be discussed.

Despite recent advances in understanding high-transition-temperature (high-T(c)) superconductors, there is no consensus on the origin of the superconducting 'glue': that is, the mediator that binds electrons into superconducting pairs. The main contenders are lattice vibrations (phonons) and spin-excitations, with the additional possibility of pairing without mediators. In conventional superconductors, phonon-mediated pairing was unequivocally established by data from tunnelling experiments. Proponents of phonons as the high-T(c) glue were therefore encouraged by the recent scanning tunnelling microscopy experiments on hole-doped Bi2Sr2CaCu2O8-delta (BSCCO) that reveal an oxygen lattice vibrational mode whose energy is anticorrelated with the superconducting gap energy scale. Here we report high-resolution scanning tunnelling microscopy measurements of the electron-doped high-T(c) superconductor Pr0.88LaCe0.12CuO4 (PLCCO) (T(c) = 24 K) that reveal a bosonic excitation (mode) at energies of 10.5 +/- 2.5 meV. This energy is consistent with both spin-excitations in PLCCO measured by inelastic neutron scattering (resonance mode) and a low-energy acoustic phonon mode, but differs substantially from the oxygen vibrational mode identified in BSCCO. Our analysis of the variation of the local mode energy and intensity with the local gap energy scale indicates an electronic origin of the mode consistent with spin-excitations rather than phonons.