950 research outputs found
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
Evidence for a Square-Square Vortex Lattice Transition in a High-Tc Cuprate Superconductor
Using sound velocity and attenuation measurements in high magnetic fields, we identify a new transition in the vortex lattice state of La2−xSrxCuO4. The transition, observed in magnetic fields exceeding 35 T and temperatures far below zero field Tc, is detected in the compression modulus of the vortex lattice, at a doping level of x=p=0.17. Our theoretical analysis based on Eilenberger’s theory of the vortex lattice shows that the transition corresponds to the long-sought 45° rotation of the square vortex lattice, predicted to occur in d-wave superconductors near a van Hove singularity
Competition between spin ordering and superconductivity near the pseudogap boundary in La2−xSrxCuO4: Insights from NMR
When superconductivity is suppressed by high magnetic fields in La2−xSrxCuO4, striped antiferromagnetic (AFM) order becomes the magnetic ground state of the entire pseudogap regime, up to its end at the doping p∗ [Frachet, Vinograd et al., Nat. Phys. 16, 1064 (2020)]. Glass-like freezing of this state is detected in 139La NMR measurements of the spin-lattice relaxation rate T−11. Here, we present a quantitative analysis of T−11 data in the hole-doping range p=x=0.12−0.171, based on the Bloembergen-Purcell-Pound (BPP) theory, modified to include statistical distribution of parameters arising from strong spatial inhomogeneity. We observe spin fluctuations to slow down at temperatures T near the onset of static charge order and, overall, the effect of the field B may be seen as equivalent to strengthening stripe order by approaching p=0.12 doping. In details, however, our analysis reveals significant departure from usual field-induced magnetic transitions. The continuous growth of the amplitude of the fluctuating moment with increasing B suggests a nearly-critical state in the B→0 limit, with very weak quasistatic moments possibly confined in small areas like vortex cores. Further, the nucleation of spin order in the vortex cores is shown to account quantitatively for both the value and the p dependence of a field scale characterizing bulk spin freezing. The correlation time of the fluctuating moment appears to depend exponentially on B/T (over the investigated range). This explains the timescale dependence of various experimental manifestations, including why, for transport measurements, the AFM moments may be considered static over a considerable range of B and T. These results make the high-field magnetic ground state up to p∗ an integral part of the discussion on putative quantum criticality
Competition between spin ordering and superconductivity near the pseudogap boundary in La Sr CuO: Insights from NMR
Influence of oxygen-coordination number on the electronic structure of single-layer La-based cuprates
We present an angle-resolved photoemission spectroscopy study of the
single-layer T*-type structured cuprate SmLaSrCuO with unique
five-fold pyramidal oxygen coordination. Upon varying oxygen content,
T*-SmLaSrCuO evolved from a Mott-insulating to a metallic state
where the Luttinger sum rule breaks down under the assumption of a large
hole-like Fermi surface. This is in contrast with the known doping evolution of
the structural isomer LaSrCuO with six-fold octahedral
coordination. In addition, quantitatively characterized Fermi surface suggests
that the empirical rule for octahedral oxygen-coordination
systems does not apply to T*-SmLaSrCuO. The present results
highlight unique properties of the T*-type cuprates possibly rooted in its
oxygen coordination, and necessitate thorough investigation with careful
evaluation of disorder effects.Comment: Accepted for publication in Phys. Rev.
Decoupling of Lattice and Orbital Degrees of Freedom in an Iron-Pnictide Superconductor
The interplay of structural and electronic phases in iron-based
superconductors is a central theme in the search for the superconducting
pairing mechanism. While electronic nematicity, defined as the breaking of
four-fold symmetry triggered by electronic degrees of freedom, is competing
with superconductivity, the effect of purely structural orthorhombic order is
unexplored. Here, using x-ray diffraction (XRD), we reveal a new structural
orthorhombic phase with an exceptionally high onset temperature
( K), which coexists with superconductivity
( K), in an electron-doped iron-pnictide superconductor far
from the underdoped region. Furthermore, our angle-resolved photoemission
spectroscopy (ARPES) measurements demonstrate the absence of electronic nematic
order as the driving mechanism, in contrast to other underdoped iron pnictides
where nematicity is commonly found. Our results establish a new, high
temperature phase in the phase diagram of iron-pnictide superconductors and
impose strong constraints for the modeling of their superconducting pairing
mechanism.Comment: SI available upon reques
A numerical simulation analysis of the effect of the interface drag function on cluster evolution in a CFB riser gas-solid flow
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