We present angle-resolved photoemission data from Cu(111). Using a focused 6 eV continuous wave laser for photo-excitation, we achieve a high effective momentum resolution enabling the first detection of the Rashba spin splitting in the Shockley surf
ace state on Cu(111). The magnitude of the spin-splitting of Delta k ~ 0.006 A^-1 is surprisingly large and exceeds values predicted for the analogous surface state on Ag(111) but is reproduced by first principles calculations. We further resolve a kink in the dispersion which we attribute to electron-phonon coupling.
Reply to comment by Zhou et al. (arXiv:1012.3602) on arXiv:1012.1484 / Phys. Rev. Lett. 106, 127005 (2011).
We observe apparent hole pockets in the Fermi surfaces of single-layer Bi-based cuprate superconductors from angle-resolved photoemission (ARPES). From detailed low-energy electron diffraction measurements and an analysis of the ARPES polarization-de
pendence, we show that these pockets are not intrinsic, but arise from multiple overlapping superstructure replicas of the main and shadow bands. We further demonstrate that the hole pockets reported recently from ARPES [Meng et al, Nature 462, 335 (2009)] have a similar structural origin, and are inconsistent with an intrinsic hole pocket associated with the electronic structure of a doped CuO$_2$ plane. The nature of the Fermi surface topology in the enigmatic pseudogap phase therefore remains an open question.
Much progress has been made recently in the study of the effects of electron-phonon (el-ph) coupling in doped insulators using angle resolved photoemission (ARPES), yielding evidence for the dominant role of el-ph interactions in underdoped cuprates.
As these studies have been limited to doped Mott insulators, the important question arises how this compares with doped band insulators where similar el-ph couplings should be at work. The archetypical case is the perovskite SrTiO$_3$ (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La$_2$CuO$_4$ by a factor of 500. Based on this fact, it has been suggested that doped STO should be the archetypical bipolaron superconductor. Here we report an ARPES study from high-quality surfaces of lightly doped SrTiO$_3$. Comparing to lightly doped Mott insulators, we find the signatures of only moderate electron-phonon coupling: a dispersion anomaly associated with the low frequency optical phonon with a $lambdasim0.3$ and an overall bandwidth renormalization suggesting an overall $lambdasim0.7$ coming from the higher frequency phonons. Further, we find no clear signatures of the large pseudogap or small polaron phenomena. These findings demonstrate that a large dielectric constant itself is not a good indicator of el-ph coupling and highlight the unusually strong effects of the el-ph coupling in doped Mott insulators.
Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy waterfall or high energy anomaly (HEA). This paper d
emonstrates, using a combination of new ARPES measurements and quantum Monte Carlo simulations, that the HEA is not simply the by-product of matrix element effects, but rather represents a cross-over from a quasiparticle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character, in both hole- and electron-doped cuprates. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. the waterfall-like behavior, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying both hole and electron doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram.
The temperature dependent evolution of the renormalization effect in optimally-doped Bi2212 along the nodal direction has been studied via angle-resolved photoemission spectroscopy. Fine structure is observed in the real part of the self-energy (Re$S
igma$), including a subkink and maximum, suggesting that electrons couple to a spectrum of bosonic modes, instead of just one mode. Upon cooling through the superconducting phase transition, the fine structures of the extracted Re$Sigma$ exhibit a two-processes evolution demonstrating an interplay between kink renormalization and superconductivity. We show that this two-process evolution can be qualitatively explained by a simple Holstein model in which a spectrum of bosonic modes is considered.
Recently, angle-resolved photoemission spectroscopy (ARPES) has revealed a dispersion anomaly at high binding energy near 0.3-0.5eV in various families of the high-temperature superconductors. For further studies of this anomaly we present a new two-
dimensional fitting-scheme and apply it to high-statistics ARPES data of the strongly-overdoped Bi2Sr2CuO6 cuprate superconductor. The procedure allows us to extract theself-energy in an extended energy and momentum range. It is found that the spectral function of Bi2Sr2CuO6 can be parameterized using a small set of tight-binding parameters and a weakly-momentum-dependent self-energy up to 0.7 eV in binding energy and over the entire first Brillouin zone. Moreover the analysis gives an estimate of the momentum dependence of the matrix element, a quantity, which is often neglected in ARPES analyses.
