Photoemission evidence for crossover from Peierls-like to Mott-like transition in highly strained VO2_2

We present a spectroscopic study that reveals that the metal-insulator transition of strained VO$_2$ thin films may be driven towards a purely electronic transition, which does not rely on the Peierls dimerization, by the application of mechanical strain. Comparison with a moderately strained system, which does involve the lattice, demonstrates the crossover from Peierls- to Mott-like transitions

Origin of the π -band replicas in the electronic structure of graphene grown on 4H -SiC(0001)

The calculated electronic band structure of graphene is relatively simple, with a Fermi surface consisting only of six Dirac cones in the first Brillouin zone-one at each (K) over bar. In contrast, angle-resolved photoemission measurements of graphene grown on SiC(0001) often show six satellite Dirac cones surrounding each primary Dirac cone. Recent studies have reported two further Dirac cones along the (Gamma) over bar-(K) over bar line, and argue that these are not photoelectron diffraction artifacts but real bands deriving from a modulation of the ionic potential in the graphene layer. Here we present measurements using linearly polarized synchrotron light which show all of these replicas as well as several additional ones. Using information obtained from dark corridor orientations and angular warping, we demonstrate that all but one of these additional features-including those previously assigned as real initial-state bands-are possible to explain by simple final-state photoelectron diffraction

Direct observation of spin-polarised bulk bands in an inversion-symmetric semiconductor

Methods to generate spin-polarised electronic states in non-magnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices. This is generally accepted to require breaking global structural inversion symmetry. In contrast, here we present direct evidence from spin- and angle-resolved photoemission spectroscopy for a strong spin polarisation of bulk states in the centrosymmetric transition-metal dichalcogenide WSe$_2$. We show how this arises due to a lack of inversion symmetry in constituent structural units of the bulk crystal where the electronic states are localised, leading to enormous spin splittings up to $\sim\!0.5$ eV, with a spin texture that is strongly modulated in both real and momentum space. As well as providing the first experimental evidence for a recently-predicted `hidden' spin polarisation in inversion-symmetric materials, our study sheds new light on a putative spin-valley coupling in transition-metal dichalcogenides, of key importance for using these compounds in proposed valleytronic devices.Comment: 6 pages, 4 figure