139 research outputs found
Nodal Landau Fermi-Liquid Quasiparticles in Overdoped LaSrCuO
Nodal angle resolved photoemission spectra taken on overdoped
LaSrCuO are presented and analyzed. It is proven that the
low-energy excitations are true Landau Fermi-liquid quasiparticles. We show
that momentum and energy distribution curves can be analyzed self-consistently
without quantitative knowledge of the bare band dispersion. Finally, by
imposing Kramers-Kronig consistency on the self-energy , insight into
the quasiparticle residue is gained. We conclude by comparing our results to
quasiparticle properties extracted from thermodynamic, magneto-resistance, and
high-field quantum oscillation experiments on overdoped
TlBaCuO.Comment: Accepted for publication in Phys. Rev.
Temperature dependence of the resonance and low energy spin excitations in superconducting FeTeSe
We use inelastic neutron scattering to study the temperature dependence of
the low-energy spin excitations in single crystals of superconducting
FeTeSe ( K). In the low-temperature superconducting
state, the imaginary part of the dynamic susceptibility at the electron and
hole Fermi surfaces nesting wave vector ,
, has a small spin gap, a two-dimensional
neutron spin resonance above the spin gap, and increases linearly with
increasing for energies above the resonance. While the intensity
of the resonance decreases like an order parameter with increasing temperature
and disappears at temperature slightly above , the energy of the mode is
weakly temperature dependent and vanishes concurrently above . This
suggests that in spite of its similarities with the resonance in electron-doped
superconducting BaFe(Co,Ni)As, the mode in
FeTeSe is not directly associated with the superconducting
electronic gap.Comment: 7 pages, 6 figure
Anisotropic Neutron Spin Resonance in Superconducting BaFeNiAs
We use polarized inelastic neutron scattering to show that the neutron spin
resonance below in superconducting BaFeNiAs (
K) is purely magnetic in origin. Our analysis further reveals that the
resonance peak near 7~meV only occurs for the planar response. This challenges
the common perception that the spin resonance in the pnictides is an isotropic
triplet excited state of the singlet Cooper pairs, as our results imply that
only the components of the triplet are involved
Spin fluctuations associated with the collapse of the pseudogap in a cuprate superconductor
Theories of the origin of superconductivity in cuprates are dependent on an
understanding of their normal state which exhibits various competing orders.
Transport and thermodynamic measurements on LaSrCuO show
signatures of a quantum critical point, including a peak in the electronic
specific heat versus doping p, near the doping p*, where the pseudogap
collapses. The fundamental nature of the fluctuations associated with this peak
is unclear. Here we use inelastic neutron scattering to show that close to
and near p*, there are low-energy collective spin excitations with
characteristic energies 5 meV. The correlation length of the spin
fluctuations does not diverge in spite of the low energy scale and we conclude
that the underlying quantum criticality is not due to antiferromagnetism but
most likely to a collapse of the pseudogap. We show that the large specific
heat near p* can be understood in terms of collective spin fluctuations. The
spin fluctuations we measure exist across the superconducting phase diagram and
may be related to the strange metal behaviour observed in overdoped cuprates
Three-Dimensional Fermi Surface of Overdoped La-Based Cuprates
We present a soft x-ray angle-resolved photoemission spectroscopy study of
the overdoped high-temperature superconductors LaSrCuO and
LaEuSrCuO. In-plane and out-of-plane components of
the Fermi surface are mapped by varying the photoemission angle and the
incident photon energy. No dispersion is observed along the nodal
direction, whereas a significant antinodal dispersion is identified.
Based on a tight-binding parametrization, we discuss the implications for the
density of states near the van-Hove singularity. Our results suggest that the
large electronic specific heat found in overdoped LaSrCuO can
not be assigned to the van-Hove singularity alone. We therefore propose quantum
criticality induced by a collapsing pseudogap phase as a plausible explanation
for observed enhancement of electronic specific heat
Spin density wave induced disordering of the vortex lattice in superconducting LaSrCuO
We use small angle neutron scattering to study the superconducting vortex
lattice in LaSrCuO as a function of doping and magnetic field.
We show that near optimally doping the vortex lattice coordination and the
superconducting coherence length are controlled by a van-Hove singularity
crossing the Fermi level near the Brillouin zone boundary. The vortex lattice
properties change dramatically as a spin-density-wave instability is approached
upon underdoping. The Bragg glass paradigm provides a good description of this
regime and suggests that SDW order acts as a novel source of disorder on the
vortex lattice.Comment: Accepted in Phys. Rev.
Field-Induced Magnetostructural Transitions in Antiferromagnetic Fe1+yTe1-xSx
The transport and structural properties of Fe1+yTe1-xSx (x=0, 0.05, and 0.10)
crystals were studied in pulsed magnetic fields up to 65 T. The application of
high magnetic fields results in positive magnetoresistance effect with
prominent hystereses in the antiferromagnetic state. Polarizing microscope
images obtained at high magnetic fields showed simultaneous occurrence of
structural transitions. These results indicate that magnetoelastic coupling is
the origin of the bicollinear magnetic order in iron chalcogenides.Comment: 5 pages, 5 figures, accepted for publication in Journal of the
Physical Society of Japa
Electronic and Magnetic Structures of Chain Structured Iron Selenide Compounds
Electronic and magnetic structures of iron selenide compounds Ce2O2FeSe2
(2212\ast) and BaFe2Se3(123\ast) are studied by the first-principles
calculations. We find that while all these compounds are composed of
one-dimensional (1D) Fe chain (or ladder) structures, their electronic
structures are not close to be quasi-1D. The magnetic exchange couplings
between two nearest-neighbor (NN) chains in 2212\ast and between two NN
two-leg-ladders in 123\ast are both antiferromagnetic (AFM), which is
consistent with the presence of significant third NN AFM coupling, a common
feature shared in other iron-chalcogenides, FeTe (11\ast) and KyFe2-xSe2
(122\ast). In magnetic ground states, each Fe chain of 2212\ast is
ferromagnetic and each two-leg ladder of 123\ast form a block-AFM structure. We
suggest that all magnetic structures in iron-selenide compounds can be unified
into an extended J1-J2-J3 model. Spin-wave excitations of the model are
calculated and can be tested by future experiments on these two systems.Comment: 6 pages, 6 figures, 2 table
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