3 research outputs found
Electron-momentum dependence of electron-phonon coupling underlies dramatic phonon renormalization in YNiBC
Electron-phonon coupling, i.e., the scattering of lattice vibrations by electrons and vice versa,
is ubiquitous in solids and can lead to emergent ground states such as superconductivity and
charge-density wave order. A broad spectral phonon line shape is often interpreted as a
marker of strong electron-phonon coupling associated with Fermi surface nesting, i.e., parallel
sections of the Fermi surface connected by the phonon momentum. Alternatively broad
phonons are known to arise from strong atomic lattice anharmonicity. Here, we show that
strong phonon broadening can occur in the absence of both Fermi surface nesting and lattice
anharmonicity, if electron-phonon coupling is strongly enhanced for specific values of electron-
momentum, k. We use inelastic neutron scattering, soft x-ray angle-resolved photoemission
spectroscopy measurements and ab-initio lattice dynamical and electronic band
structure calculations to demonstrate this scenario in the highly anisotropic tetragonal
electron-phonon superconductor YNi2B2C. This new scenario likely applies to a wide range of
compounds
Mott versus hybridization gap in the low-temperature phase of -TaS
We compute the correlated electronic structure of stacked -TaS
bilayers using the + EDMFT method. Depending on the surface termination,
the semi-infinite uncorrelated system is either band-insulating or exhibits a
metallic surface state. For realistic values of the onsite and intersite
interactions, a Mott gap opens in the surface state, but this gap is smaller
than the gap originating from the bilayer structure. Our results are consistent
with recent scanning tunneling spectroscopy measurements for different
terminating layers, and with our own photoemission measurements, which indicate
the coexistence of spatial regions with different gaps in the electronic
spectrum
Electron-momentum dependence of electron-phonon coupling underlies dramatic phonon renormalization in YNi2B2C
International audienceElectron-phonon coupling, i.e., the scattering of lattice vibrations by electrons and vice versa, is ubiquitous in solids and can lead to emergent ground states such as superconductivity and charge-density wave order. A broad spectral phonon line shape is often interpreted as a marker of strong electron-phonon coupling associated with Fermi surface nesting, i.e., parallel sections of the Fermi surface connected by the phonon momentum. Alternatively broad phonons are known to arise from strong atomic lattice anharmonicity. Here, we show that strong phonon broadening can occur in the absence of both Fermi surface nesting and lattice anharmonicity, if electron-phonon coupling is strongly enhanced for specific values of electron-momentum, k. We use inelastic neutron scattering, soft x-ray angle-resolved photoemission spectroscopy measurements and ab-initio lattice dynamical and electronic band structure calculations to demonstrate this scenario in the highly anisotropic tetragonal electron-phonon superconductor YNiBC. This new scenario likely applies to a wide range of compounds