4,116 research outputs found
Ultrafast nematic-orbital excitation in FeSe
The electronic nematic phase is an unconventional state of matter that
spontaneously breaks the rotational symmetry of electrons. In
iron-pnictides/chalcogenides and cuprates, the nematic ordering and
fluctuations have been suggested to have as-yet-unconfirmed roles in
superconductivity. However, most studies have been conducted in thermal
equilibrium, where the dynamical property and excitation can be masked by the
coupling with the lattice. Here we use femtosecond optical pulse to perturb the
electronic nematic order in FeSe. Through time-, energy-, momentum- and
orbital-resolved photo-emission spectroscopy, we detect the ultrafast dynamics
of electronic nematicity. In the strong-excitation regime, through the
observation of Fermi surface anisotropy, we find a quick disappearance of the
nematicity followed by a heavily-damped oscillation. This short-life nematicity
oscillation is seemingly related to the imbalance of Fe 3dxz and dyz orbitals.
These phenomena show critical behavior as a function of pump fluence. Our
real-time observations reveal the nature of the electronic nematic excitation
instantly decoupled from the underlying lattice
Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting
In layered polar semiconductor BiTeI, giant Rashba-type spin-split band
dispersions show up due to the crystal structure asymmetry and the strong
spin-orbit interaction. Here we investigate the 3-dimensional (3D) bulk band
structures of BiTeI using the bulk-sensitive -dependent soft x-ray angle
resolved photoemission spectroscopy (SX-ARPES). The obtained band structure is
shown to be well reproducible by the first-principles calculations, with huge
spin splittings of meV at the conduction-band-minimum and
valence-band-maximum located in the plane. It provides the first
direct experimental evidence of the 3D Rashba-type spin splitting in a bulk
compound.Comment: 9 pages, 4 figure
Strongly spin-orbit coupled two-dimensional electron gas emerging near the surface of polar semiconductors
We investigate the two-dimensional (2D) highly spin-polarized electron
accumulation layers commonly appearing near the surface of n-type polar
semiconductors BiTeX (X = I, Br, and Cl) by angular-resolved photoemission
spectroscopy. Due to the polarity and the strong spin-orbit interaction built
in the bulk atomic configurations, the quantized conduction-band subbands show
giant Rashba-type spin-splitting. The characteristic 2D confinement effect is
clearly observed also in the valence-bands down to the binding energy of 4 eV.
The X-dependent Rashba spin-orbit coupling is directly estimated from the
observed spin-split subbands, which roughly scales with the inverse of the
band-gap size in BiTeX.Comment: 15 pages 4 figure
Orbital-dependent modifications of electronic structure across magneto-structural transition in BaFe2As2
Laser angle-resolved photoemission spectroscopy (ARPES) is employed to
investigate the temperature (T) dependence of the electronic structure in
BaFe2As2 across the magneto-structural transition at TN ~ 140 K. A drastic
transformation in Fermi surface (FS) shape across TN is observed, as expected
by first-principles band calculations. Polarization-dependent ARPES and band
calculations consistently indicate that the observed FSs at kz ~ pi in the
low-T antiferromagnetic (AF) state are dominated by the Fe3dzx orbital, leading
to the two-fold electronic structure. These results indicate that
magneto-structural transition in BaFe2As2 accompanies orbital-dependent
modifications in the electronic structure.Comment: 13 pages, 4 figures. accepted by Physical Review Letter
Doping-dependence of nodal quasiparticle properties in high- cuprates studied by laser-excited angle-resolved photoemission spectroscopy
We investigate the doping dependent low energy, low temperature ( = 5 K)
properties of nodal quasiparticles in the d-wave superconductor
BiSrCaCuO (Bi2212). By utilizing ultrahigh
resolution laser-excited angle-resolved photoemission spectroscopy, we obtain
precise band dispersions near , mean free paths and scattering rates
() of quasiparticles. For optimally and overdoped, we obtain very sharp
quasiparticle peaks of 8 meV and 6 meV full-width at half-maximum,
respectively, in accord with terahertz conductivity. For all doping levels, we
find the energy-dependence of , while () shows a monotonic increase from overdoping to underdoping. The doping
dependence suggests the role of electronic inhomogeneity on the nodal
quasiparticle scattering at low temperature (5 K \lsim 0.07T_{\rm c}),
pronounced in the underdoped region
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