368 research outputs found
Orbital Subband Structures and Chiral Orbital Angular Momentum in the (001) Surface States of SrTiO
We have performed angle resolved photoemission spectroscopy (ARPES)
experiments on the surface states of SrTiO(001) using linearly and
circularly polarized light to investigate the subband structures of
out-of-plane orbitals and chiral orbital angular momentum (OAM).
The data taken in the first Brillouin zone reveal new subbands for
orbitals with Fermi wave vectors of 0.25 and 0.45 in
addition to the previously reported ones. As a result, there are at least two
subbands for all the Ti 3d t orbitals. Our circular dichroism ARPES data
is suggestive of a chiral OAM structure in the surface states and may provide
clues to the origin of the linear Rashba-like surface band splitting.Comment: 7 pages, 3 figures, Journal pape
Buried double CuO chains in YBaCuO uncovered by nano-ARPES
The electron dynamics in the CuO chains has been elusive in Y-Ba-Cu-O cuprate
systems by means of standard angle-resolved photoemission spectroscopy (ARPES);
cleaved sample exhibits areas terminated by both CuO-chain or BaO layers, and
the size of a typical beam results in ARPES signals that are superposed from
both terminations. Here, we employ spatially-resolved ARPES with submicrometric
beam (nano-ARPES) to reveal the surface-termination-dependent electronic
structures of the double CuO chains in YBaCuO. We present the first
observation of sharp metallic dispersions and Fermi surfaces of the double CuO
chains buried underneath the CuO-plane block on the BaO terminated surface.
While the observed Fermi surfaces of the CuO chains are highly one-dimensional,
the electrons in the CuO-chains do not undergo significant electron
correlations and no signature of a Tomonaga-Luttinger liquid nor a marginal
Fermi liquid is found. Our works represent an important experimental step
toward understanding of the charge dynamics and provides a starting basis for
modelling the high- superconductivity in YBCO cuprate systems.Comment: 10 pages, 5 figures including supplementary material (4 pages, 2
figures
The role of inter-plane interaction in the electronic structure of high Tc cuprates
This thesis represents a systematic study of electronic structure of the modulation-free Pb-doped Bi2212 superconducting cuprates with respect to interlayer coupling done by using the angle-resolved photoemission spectroscopy (ARPES), which is a leading technique in the experimental investigation of the single particle excitations in solids. The results presented in this work indicate a very different origin for the observed complex spectra lineshape. Specifically, the peak-dip-hump lineshape can be easily understood in terms of the superposition of spectral features due to bilayer band splitting, namely the splitting of the CuO2 plane derived electronic structure in bonding and antibonding bands due to the interlayer coupling of CuO2 bilayer blocks within the unit cell of Bi2212. By performing experiments at synchrotron beamlines where the energy of the incoming photons can be tuned over a very broad range, the detailed matrix elements energy dependence for both bonding and antibonding bands was determined. This gave the opportunity to study the electronic properties these two bands separately. For the first time, it was proved that the superconducting gap has the same value and symmetry for both bands. Furthermore, having recognized and sorted out the bilayer splitting effects, it became possible to identify more subtle effects hidden in the details of the ARPES lineshapes. On underdoped samples an "intrinsic" peak-dip-hump structure due to the interaction between electrons and a bosonic mode was observed. Studying the doping, temperature, and momentum dependence of the photoemission spectra it was established that: the mode has a characteristic energy of 38-40 meV and causes strong renormalization of the electronic structure only in the superconducting state; the electron-mode coupling is maximal around the (?à,0) point in momentum space and is strongly doping dependent (being greatly enhanced in the underdoped regime). From the above, it was concluded that the bosonic mode must correspond to the sharp magnetic resonance mode observed in inelastic neutron scattering experiments, and that this coupling is relevant to superconductivity and the pairing mechanism in the cuprates
Observation of band crossings protected by nonsymmorphic symmetry in the layered ternary telluride Ta3SiTe6
We have performed angle-resolved photoemission spectroscopy of layered
ternary telluride Ta3SiTe6 which is predicted to host nodal lines associated
with nonsymmorphic crystal symmetry. We found that the energy bands in the
valence-band region show Dirac-like dispersions which present a band degeneracy
at the R point of the bulk orthorhombic Brillouin zone. This band degeneracy
extends one-dimensionally along the whole SR high-symmetry line, forming the
nodal lines protected by the glide mirror symmetry of the crystal. We also
observed a small band splitting near EF which supports the existence of
hourglass-type dispersions predicted by the calculation. The present results
provide an excellent opportunity to investigate the interplay between exotic
nodal fermions and nonsymmorphic crystal symmetry.Comment: 6 pages, 4 figure
Kz selective scattering within quasiparticle interference measurements of FeSe
Quasiparticle interference (QPI) provides a wealth of information relating to the electronic structure of a material. However, it is often assumed that this information is constrained to two-dimensional electronic states. We show that this is not necessarily the case. For FeSe, a system dominated by surface defects, we show that it is actually all electronic states with negligible group velocity in the z axis that are contained within the experimental data. By using a three-dimensional tight-binding model of FeSe, fit to photoemission measurements, we directly reproduce the experimental QPI scattering dispersion, within a T-matrix formalism, by including both kz=0 and kz=π electronic states. This result unifies both tunnelling based and photoemission based experiments on FeSe and highlights the importance of kz within surface sensitive measurements of QPI.Publisher PDFPeer reviewe
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