44 research outputs found
Coupling of a high-energy excitation to superconducting quasiparticles in a cuprate from Coherent Charge Fluctuation Spectroscopy
Dynamical information on spin degrees of freedom of proteins or solids can be
obtained by Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR).
A technique with similar versatility for charge degrees of freedom and their
ultrafast correlations could move forward the understanding of systems like
unconventional superconductors. By perturbing the superconducting state in a
high-Tc cuprate using a femtosecond laser pulse, we generate coherent
oscillations of the Cooper pair condensate which can be described by an NMR/ESR
formalism. The oscillations are detected by transient broad-band reflectivity
and found to resonate at the typical scale of Mott physics (2.6 eV), suggesting
the existence of a non-retarded contribution to the pairing interaction, as in
unconventional (non Migdal-Eliashberg) theories.Comment: Accepted for publication in the Proceedings of the National Academy
of Sciences of the U.S.A. (PNAS
Evidence for a Peierls phase-transition in a three-dimensional multiple charge-density waves solid
The effect of dimensionality on materials properties has become strikingly
evident with the recent discovery of graphene. Charge ordering phenomena can be
induced in one dimension by periodic distortions of a material's crystal
structure, termed Peierls ordering transition. Charge-density waves can also be
induced in solids by strong Coulomb repulsion between carriers, and at the
extreme limit, Wigner predicted that crystallization itself can be induced in
an electrons gas in free space close to the absolute zero of temperature.
Similar phenomena are observed also in higher dimensions, but the microscopic
description of the corresponding phase transition is often controversial, and
remains an open field of research for fundamental physics. Here, we photoinduce
the melting of the charge ordering in a complex three-dimensional solid and
monitor the consequent charge redistribution by probing the optical response
over a broad spectral range with ultrashort laser pulses. Although the
photoinduced electronic temperature far exceeds the critical value, the
charge-density wave is preserved until the lattice is sufficiently distorted to
induce the phase transition. Combining this result with it ab initio}
electronic structure calculations, we identified the Peierls origin of multiple
charge-density waves in a three-dimensional system for the first time.Comment: Accepted for publication in Proc. Natl. Acad. Sci. US
Transfer of spectral weight across the gap of Sr2IrO4 induced by La doping
We study with Angle Resolved PhotoElectron Spectroscopy (ARPES) the evolution
of the electronic structure of Sr2IrO4, when holes or electrons are introduced,
through Rh or La substitutions. At low dopings, the added carriers occupy the
first available states, at bottom or top of the gap, revealing an anisotropic
gap of 0.7eV in good agreement with STM measurements. At further doping, we
observe a reduction of the gap and a transfer of spectral weight across the
gap, although the quasiparticle weight remains very small. We discuss the
origin of the in-gap spectral weight as a local distribution of gap values
Significant reduction of electronic correlations upon isovalent Ru substitution of BaFe2As2
We present a detailed investigation of Ba(Fe0.65Ru0.35)2As2 by transport
measurements and Angle Resolved photoemission spectroscopy. We observe that Fe
and Ru orbitals hybridize to form a coherent electronic structure and that Ru
does not induce doping. The number of holes and electrons, deduced from the
area of the Fermi Surface pockets, are both about twice larger than in
BaFe2As2. The contribution of both carriers to the transport is evidenced by a
change of sign of the Hall coefficient with decreasing temperature. Fermi
velocities increase significantly with respect to BaFe2As2, suggesting a
significant reduction of correlation effects. This may be a key to understand
the appearance of superconductivity at the expense of magnetism in undoped iron
pnictides
Doping-Dependent and Orbital-Dependent Band Renormalization in Ba(Fe_1-xCo_x)_2As_2 Superconductors
Angle resolved photoemission spectroscopy of Ba(Fe1-xCox)2As2 (x = 0.06,
0.14, and 0.24) shows that the width of the Fe 3d yz/zx hole band depends on
the doping level. In contrast, the Fe 3d x^2-y^2 and 3z^2-r^2 bands are rigid
and shifted by the Co doping. The Fe 3d yz/zx hole band is flattened at the
optimal doping level x = 0.06, indicating that the band renormalization of the
Fe 3d yz/zx band correlates with the enhancement of the superconducting
transition temperature. The orbital-dependent and doping-dependent band
renormalization indicates that the fluctuations responsible for the
superconductivity is deeply related to the Fe 3d orbital degeneracy.Comment: 5 pages, 4 figure
Satellites and large doping- and temperature-dependence of electronic properties in hole-doped BaFe2As2
Over the last years, superconductivity has been discovered in several
families of iron-based compounds. Despite intense research, even basic
electronic properties of these materials, such as Fermi surfaces, effective
electron masses, or orbital characters are still subject to debate. Here, we
address an issue that has not been considered before, namely the consequences
of dynamical screening of the Coulomb interactions among Fe-d electrons. We
demonstrate its importance not only for correlation satellites seen in
photoemission spectroscopy, but also for the low-energy electronic structure.
From our analysis of the normal phase of BaFe2As2 emerges the picture of a
strongly correlated compound with strongly doping- and temperature-dependent
properties. In the hole overdoped regime, an incoherent metal is found, while
Fermi-liquid behavior is recovered in the undoped compound. At optimal doping,
the self-energy exhibits an unusual square-root energy dependence which leads
to strong band renormalizations near the Fermi level
Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott-Hubbard material
The study of photoexcited strongly correlated materials is attracting growing interest since their rich phase diagram often translates into an equally rich out-of-equilibrium behaviour. With femtosecond optical pulses, electronic and lattice degrees of freedom can be transiently decoupled, giving the opportunity of stabilizing new states inaccessible by quasi-adiabatic pathways. Here we show that the prototype Mott-Hubbard material V2O3 presents a transient non-thermal phase developing immediately after ultrafast photoexcitation and lasting few picoseconds. For both the insulating and the metallic phase, the formation of the transient configuration is triggered by the excitation of electrons into the bonding a1g orbital, and is then stabilized by a lattice distortion characterized by a hardening of the A1g coherent phonon, in stark contrast with the softening observed upon heating. Our results show the importance of selective electron-lattice interplay for the ultrafast control of material parameters, and are relevant for the optical manipulation of strongly correlated systems. \ua9 The Author(s) 2017
Temperature-dependent electron-phonon coupling in LaSrCuO probed by femtosecond X-ray diffraction
The strength of the electron-phonon coupling parameter and its evolution
throughout a solid's phase diagram often determines phenomena such as
superconductivity, charge- and spin-density waves. Its experimental
determination relies on the ability to distinguish thermally activated phonons
from those emitted by conduction band electrons, which can be achieved in an
elegant way by ultrafast techniques. Separating the electronic from the
out-of-equilibrium lattice subsystems, we probed their re-equilibration by
monitoring the transient lattice temperature through femtosecond X-ray
diffraction in LaSrCuO single crystals with =0.1 and 0.21.
The temperature dependence of the electron-phonon coupling is obtained
experimentally and shows similar trends to what is expected from the
\textit{ab-initio} calculated shape of the electronic density-of-states near
the Fermi energy. This study evidences the important role of band effects in
the electron-lattice interaction in solids, in particular in superconductors
Reply to: Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott-Hubbard material
International audienceReplying to D. Moreno-Mencía et al. Nature Communicationshttps://doi.org/10.1038/s41467-019-11743-3 (2019)
Erratum: A microscopic view on the Mott transition in chromium-doped V 2 O 3
Nature Communications 1, Article number: 105 (2010); published: 02 November 2010; updated: 17 January 2012. In Figure 2 of this Article, panel labels c and d were inadvertently switched. A typographical error was also introduced in the last sentence of the legend, which should have read 'The scale bar in panel c represents 10 μm'