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Highlights • Experimental and theoretical investigation of electron–phonon coupling strength in spin–split valence bands of single-layer MoS 2 near K point. • Excellent agreement of calculation and experiment at the K point. • Explained using spin and phase space restricted scattering channels. • Weak electron–phonon coupling for upper valence band for wider k range due to hybridization with substrate. Graphical abstract Abstract The electron–phonon coupling strength in the spin–split valence band maximum of single-layer MoS 2 is studied using angle-resolved photoemission spectroscopy and density functional theory-based calculations. Values of the electron–phonon coupling parameter λ are obtained by measuring the linewidth of the spin–split bands as a function of temperature and fitting the data points using a Debye model. The experimental values of λ for the upper and lower spin–split bands at K are found to be 0.05 and 0.32, respectively, in excellent agreement with the calculated values for a free-standing single-layer MoS 2. The results are discussed in the context of spin and phase-space restricted scattering channels, as reported earlier for single-layer WS 2 on Au(111). The fact that the absolute valence band maximum in single-layer MoS 2 at K is almost degenerate with the local valence band maximum at Γ can potentially be used to tune the strength of the electron–phonon interaction in this material. [ABSTRACT FROM AUTHOR]

The detection of inelastically scattered soft x-rays with high energy resolution usually requires large grating spectrometers. Recently, photoelectron spectrometry for analysis of x-rays (PAX) has been rediscovered for modern spectroscopy experiments at synchrotron light sources. By converting scattered photons to electrons and using an electron energy analyser, the energy resolution for resonant inelastic x-ray scattering (RIXS) becomes decoupled from the x-ray spot size and instrument length. In this work, we develop PAX towards high energy resolution using a modern photoemission spectroscopy setup studying Ba2Cu3O4Cl2 at the Cu L 3-edge. We measure a momentum transfer range of 24% of the first Brillouin zone simultaneously. Our results hint at the observation of a magnon excitation below 100 meV energy transfer and show intensity variations related to the dispersion of dd -excitations. With dedicated setups, PAX can complement the best and largest RIXS instruments, while at the same time opening new opportunities to acquire RIXS at a range of momentum transfers simultaneously and combine it with angle-resolved photoemission spectroscopy in a single instrument. [ABSTRACT FROM AUTHOR]

Identifying the microscopic nature of non-equilibrium energy transfer mechanisms among electronic, spin, and lattice degrees of freedom is central to understanding ultrafast phenomena such as manipulating magnetism on the femtosecond timescale. Here, we use time-and angle-resolved photoemission spectroscopy to go beyond the often-used ensemble-averaged view of non-equilibrium dynamics in terms of quasiparticle temperature evolutions. We show for ferromagnetic Ni that the non-equilibrium electron and spin dynamics display pronounced variations with electron momentum, whereas the magnetic exchange interaction remains isotropic. This highlights the influence of lattice-mediated scattering processes and opens a pathway toward unraveling the still elusive microscopic mechanism of spin-lattice angular momentum transfer. [ABSTRACT FROM AUTHOR]

The commensurate charge-density wave (CDW) in the layered compound 1T-TaS2 has hitherto mostly been treated as a quasi-two-dimensional phenomenon. Recent band structure calculations have, however, predicted that the CDW coexists with a nearly one-dimensional metallic dispersion perpendicular to the crystal planes. Using synchrotron radiation-based angle-resolved photoemission spectroscopy, we show that this metallic band does in fact exist. Its occupied band width is in excellent agreement with predictions for a simple τc stacking order of the CDW between adjacent layers, and its periodicity in the c direction is 2π/c. [ABSTRACT FROM AUTHOR]

Materials with insulator-metal transitions promise advanced functionalities for future information technology. Patterning on the microscale is key for miniaturized functional devices, but material properties may vary spatially across microstructures. Characterization of these miniaturized devices requires electronic structure probes with sufficient spatial resolution to understand the influence of structure size and shape on functional properties. The present study demonstrates the use of imaging soft X-ray absorption spectroscopy with a spatial resolution better than 2 μ m to study the insulator-metal transition in vanadium dioxide thin-film microstructures. This novel technique reveals that the transition temperature for the conversion from insulating to metallic vanadium dioxide is lowered by 1.2 K ± 0.4 K close to the structure edges compared to the center. Facilitated strain release during the phase transition is discussed as origin of the observed behavior. The experimental approach enables a detailed understanding of how the electronic properties of quantum materials depend on their patterning at the micrometer scale. [ABSTRACT FROM AUTHOR]

Band splittings, chiral spin polarization, and topological surface states generated by spin-orbit interactions at crystal surfaces are receiving a lot of attention for their potential device applications as well as fascinating physical properties. Most studies have focused on sp states near the Fermi energy, which are relevant for transport and have long lifetimes. Far less explored, though in principle stronger, are spin-orbit interaction effects within d states, including those deep below the Fermi energy. Here, we report a joint photoemission and ab initio study of spin-orbit effects in the deep 4-orbital surface states of a 24-layer Au film grown on Ag(111) and a 24-layer Ag film grown on Au(111), singling out a conical intersection (Dirac cone) between two surface states in a large surface-projectedgap at the time-reversal symmetric M points. Unlike the often isotropic dispersion at F point Dirac cones, the M point cones are strongly anisotropic. An effective k.p Hamiltonian is derived to describe the anisotropic band splitting and spin polarization near the Dirac cone. [ABSTRACT FROM AUTHOR]

The quasiparticle spectra of atomically thin semiconducting transition metal dichalcogenides (TMDCs) and their response to an ultrafast optical excitation critically depend on interactions with the underlying substrate. Here, we present a comparative time- and angle-resolved photoemission spectroscopy (TR-ARPES) study of the transient electronic structure and ultrafast carrier dynamics in the single- and bilayer TMDCs MoS 2 and WS 2 on three different substrates: Au(111), Ag(111) and graphene/SiC. The photoexcited quasiparticle bandgaps are observed to vary over the range of 1.9–2.5 eV between our systems. The transient conduction band signals decay on a sub-50 fs timescale on the metals, signifying an efficient removal of photoinduced carriers into the bulk metallic states. On graphene, we instead observe a fast timescale on the order of 170 fs, followed by a slow dynamics for the conduction band decay in MoS 2. These timescales are explained by Auger recombination involving MoS 2 and in-gap defect states. In bilayer TMDCs on metals we observe a complex redistribution of excited holes along the valence band that is substantially affected by interactions with the continuum of bulk metallic states. • Time-resolved photoemission study of semiconducting transition metal dichalcogenides. • The quasiparticle bandgaps are observed to vary between 1.9 to 2.5 eV. • Conduction band population decays on a sub-50 fs timescale on metallic substrates. • On graphene/SiC, carriers relax on a timescale of 170 fs followed by a slow decay. • Strong momentum-dependence of hole dynamics observed on metallic substrates. [ABSTRACT FROM AUTHOR]

The absence of inversion symmetry leads to a strong spin-orbit splitting of the upper valence band of semiconducting single-layer transition-metal dichalchogenides such as MoS2 or WS2. This permits a direct comparison of the electron-phonon coupling strength in states that only differ by their spin. Here, the electron-phonon coupling in the valence band maximum of single-layer WS2 is studied by first-principles calculations and angle-resolved photoemission. The coupling strength is found to be drastically different for the two spin-split branches, with calculated values of λK=0.0021 and 0.40 for the upper and lower spin-split valence band of the freestanding layer, respectively. This difference is somewhat reduced when including scattering processes involving the Au(111) substrate present in the experiment but it remains significant, in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]