27 research outputs found
Two-Fermi-surface superconducting state and a nodal d-wave gap in the electron-doped Sm(1.85)Ce(0.15)CuO(4-d) cuprate superconductor
We report on laser-excited angle-resolved photoemission spectroscopy (ARPES)
in the electron-doped cuprate Sm(1.85)Ce(0.15)CuO(4-d). The data show the
existence of a nodal hole-pocket Fermi-surface both in the normal and
superconducting states. We prove that its origin is long-range
antiferromagnetism by an analysis of the coherence factors in the main and
folded bands. This coexistence of long-range antiferromagnetism and
superconductivity implies that electron-doped cuprates are two-Fermi-surface
superconductors. The measured superconducting gap in the nodal hole-pocket is
compatible with a d-wave symmetry.Comment: 4 pages, 3 figures, accepted to Phys. Rev. Let
Unveiling the orbital-selective electronic band reconstruction through the structural phase transition in TaTe
Tantalum ditelluride TaTe belongs to the family of layered transition
metal dichalcogenides but exhibits a unique structural phase transition at
around 170 K that accompanies the rearrangement of the Ta atomic network from a
"ribbon chain" to a "butterfly-like" pattern. While multiple mechanisms
including Fermi surface nesting and chemical bonding instabilities have been
intensively discussed, the origin of this transition remains elusive. Here we
investigate the electronic structure of single-crystalline TaTe with a
particular focus on its modifications through the phase transition, by
employing core-level and angle-resolved photoemission spectroscopy combined
with first-principles calculations. Temperature-dependent core-level
spectroscopy demonstrates a splitting of the Ta core-level spectra through
the phase transition indicative of the Ta-dominated electronic state
reconstruction. Low-energy electronic state measurements further reveal an
unusual kink-like band reconstruction occurring at the Brillouin zone boundary,
which cannot be explained by Fermi surface nesting or band folding effects. On
the basis of the orbital-projected band calculations, this band reconstruction
is mainly attributed to the modifications of specific Ta states, namely
the orbitals (the ones elongating along the ribbon chains) at the
center Ta sites of the ribbon chains. The present results highlight the strong
orbital-dependent electronic state reconstruction through the phase transition
in this system and provide fundamental insights towards understanding complex
electron-lattice-bond coupled phenomena.Comment: 21 pages, 5 figure
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Ultrafast dissolution and creation of bonds in IrTe2 induced by photodoping
The observation and control of interweaving spin, charge, orbital, and structural degrees of freedom in materials on ultrafast time scales reveal exotic quantum phenomena and enable new active forms of nanotechnology. Bond-
ing is the prime example of the relation between electronic and nuclear degrees of freedom. We report direct evidence illustrating that photoexcitation can be used for ultrafast control of the breaking and recovery of bonds in solids on unprecedented time scales, near the limit for nuclear motions. We describe experimental and theoretical studies of IrTe2 using femtosecond electron diffraction and density functional theory to investigate bonding instability. Ir-Ir dimerization shows an unexpected fast dissociation and recovery due to the filling of the antibonding dxy orbital. Bond length changes of 20% in IrTe2 are achieved by effectively addressing the bonds directly through this relaxation process. These results could pave the way to ultrafast switching between metastable structures by
photoinduced manipulation of the relative degree of bonding in this manner
Ultrafast Control of Crystal Structure in a Topological Charge-Density-Wave Material
Optical control of crystal structures is a promising route to change physical
properties including topological nature of a targeting material. Time-resolved
X-ray diffraction measurements using the X-ray free-electron laser are
performed to study the ultrafast lattice dynamics of VTe, which shows a
unique charge-density-wave (CDW) ordering coupled to the topological surface
states as a first-order phase transition. A significant oscillation of the CDW
amplitude mode is observed at a superlattice reflection as well as Bragg
reflections. The frequency of the oscillation is independent of the fluence of
the pumping laser, which is prominent to the CDW ordering of the first-order
phase transition. Furthermore, the timescale of the photoinduced
1 to 1 phase transition is independent of the period of
the CDW amplitude mode
Analysis on photoemission spectrum of superconducting FeSe
In this paper, we present the result of soft X-ray photoemission spectroscopy and its comparison with the density functional calculation. Although local density approximation seems to be a good starting point for describing the electronic structure of FeSe, the simulated spectrum poorly reproduced the structure around E(B) = 2 eV. This result suggests the necessity of theoretical treatment beyond local density approximation