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In high-temperature cuprate superconductors, the anti-ferromagnetic spin fluctuations are thought to have a very important role in naturally producing an attractive interaction between the electrons in the d-wave channel. The connection between superconductivity and spin fluctuations is expected to be especially consequential at the overdoped end point of the superconducting dome. In some materials, that point seems to coincide with a Lifshitz transition, where the Fermi surface changes from the hole-like centered at to the electron-like, centered at the Γ point causing a loss of large momentum anti-ferromagnetic fluctuations. Here, we study the doping dependence of the electronic structure of Bi1.8Pb0.4Sr2CuO in angle-resolved photoemission and find that the superconductivity vanishes at lower doping than that at which the Lifshitz transition occurs. This requires a more detailed re-examination of a spin fluctuation scenario. [ABSTRACT FROM AUTHOR]

In the present work, we investigate the electronic structure of the two-dimensional ferromagnet Cr2Ge2Te6 by photoemission spectroscopy and ab initio calculations. Our results demonstrate the presence of multi-hole–type bands in the vicinity of the Fermi level indicating that the material can support high electrical conductivity by manipulating the chemical potential. Also, our photon energy-dependent angle-resolved photoemission experiment shows that several of the hole bands exhibit weak dispersion with varied incident photon energy providing experimental signature for the two-dimensional nature of Cr2Ge2Te6. Thereby, these findings can pave the way for further studies towards the application of Cr2Ge2Te6 in electronic devices. [ABSTRACT FROM AUTHOR]

We report a new, cleavable, strong topological metal, Zr2Te2P, which has the same tetradymite-type crystal structure as the topological insulator Bi2Te2Se. Instead of being a semiconductor, however, Zr2Te2P is metallic with a pseudogap between 0.2 and 0.7 eV above the Fermi energy (EF). Inside this pseudogap, two Dirac dispersions are predicted: one is a surface-originated Dirac cone protected by time-reversal symmetry (TRS), while the other is a bulk-originated and slightly gapped Dirac cone with a largely linear dispersion over a 2 eV energy range. A third surface TRS-protected Dirac cone is predicted, and observed using angle-resolved photoemission spectroscopy, making Zr2Te2P the first system, to our knowledge, to realize TRS-protected Dirac cones at M points. The high anisotropy of this Dirac cone is similar to the one in the hypothetical Dirac semimetal BiO2. We propose that if EF can be tuned into the pseudogap where the Dirac dispersions exist, it may be possible to observe ultrahigh carrier mobility and large magnetoresistance in this material. [ABSTRACT FROM AUTHOR]

We analyze renormalization of the π* band of n-doped epitaxial graphene on Ir(lll) induced by electronphonon coupling. Our procedure of extracting the bare band relies on recursive self-consistent refining of the functional form of the bare band until the convergence. We demonstrate that the components of the selfenergy, as well as the spectral intensity obtained from angle-resolved photoelectron spectroscopy, show that the renormalization is due to the coupling to two distinct phonon excitations. From the velocity renormalization and an increase of the imaginary part of the self-energy we find the electron-phonon coupling constant to be ∼0.2, which is in fair agreement with a previous study of the same system, despite the notable difference in the width of spectroscopic curves. Our experimental results also suggest that potassium intercalated between graphene and Ir( 111) does not introduce any additional increase of the quasiparticle scattering rate. [ABSTRACT FROM AUTHOR]

In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted versus the doping level p. In most materials, p cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature, Tc, using the assumption that the Tc dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi2Sr2CaCu2O8+δ, cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to Tc = 91 K. We show that p can be determined from the underlying Fermi surfaces and that in-situ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of 2Δ0 = (4 ± 1)kBTc The doping level of cuprate superconductors is usually difficult to determine. Here, Drozdov et al. report spectroscopic studies of in-situ modified Bi2Sr2CaCu2O8+δ, exploring not only the superconducting dome but also the previously inaccessible, non-superconducting regime of the phase diagram, with absolute determination of the doping level. [ABSTRACT FROM AUTHOR]

It is common knowledge that even a trace amount of a chemisorbed species can strongly perturb the surface electronic structure, in particular the surface states, to the point of their complete eradication. We have confirmed this behavior by adsorbing Li on the Ir(111), but surprisingly, we have discovered that in the presence of graphene Li does not suppress the Ir surface state. By combining the results of the low-energy electron diffraction and angle-resolved photoemission spectroscopy with the density functional theory for modeling of the studied systems we can provide a detailed explanation for the observed phenomena. The quenching of the surface state by the electronic states of disordered Li layer on a bare Ir surface is efficiently deactivated by the presence of graphene which shifts the Li states to lower energies thereby leading to the unexpected reappearance of the surface state. Such protection of the surface state coherence from disorder upon intercalation could be used as a benchmark in the toolbox of surface science. [ABSTRACT FROM AUTHOR]

Three-dimensional topological insulators and topological crystalline insulators represent new quantum states of matter, which are predicted to have insulating bulk states and spin-momentum-locked gapless surface states. Experimentally, it has proven difficult to achieve the high bulk resistivity that would allow surface states to dominate the transport properties over a substantial temperature range. Here we report a series of indium-doped Pb1-xSnx vTe compounds that manifest huge bulk resistivities together with evidence consistent with the topological character of the surface states for x ≳ 0.35, based on thickness-dependent transport studies and magnetoresistance measurements. For these bulk-insulating materials, the surface states determine the resistivity for temperatures beyond 20 K. [ABSTRACT FROM AUTHOR]