2,588 research outputs found
Odd parity charge density-wave scattering in cuprates
We investigate a model where superconducting electrons are coupled to a
frequency dependent charge-density wave (CDW) order parameter Delta(w). Our
approach can reconcile the simultaneous existence of low energy Bogoljubov
quasiparticles and high energy electronic order as observed in scanning
tunneling microscopy (STM) experiments. The theory accounts for the contrast
reversal in the STM spectra between positive and negative bias observed above
the pairing gap. An intrinsic relation between scattering rate and
inhomogeneities follows naturally.Comment: 5 pages, 3 figure
Theory of isotope effect in photoemission spectra of high-T_c superconducting cuprates
We investigate the effect of isotope substitution on the electronic spectral
functions within a model where the charge carriers are coupled to bosonic
charge-order (CO) fluctuations centered around some mean frequency \omega_0 and
with enhanced scattering at wave-vector q_c. It is shown that a mass dependence
of \omega_0 is not sufficient in order to account, especially at high energies,
for the dispersion shifts experimentally observed in an optimally doped
superconducting cuprate. We argue that isotope substitution induces a change of
the spatial CO correlations which gives good account of the experimental data.Comment: 5 pages and 2 figure
Joint superexchange--Jahn-Teller mechanism for A-type antiferromagnetism in
We propose a mechanism for A-type antiferromagnetism in orthorombic LaMnO_3,
compatible with the large Jahn-Teller splitting inferred from structural data.
Orbital ordering resulting from Jahn-Teller distortions effectively leads to
A-type ordering (antiferromagnetic in the c axis and ferromagnetic in the ab
plane) provided the in-plane distorsion Q_2 is large enough, a condition
generally fulfilled in existing data.Comment: 4 pages Late
Negative electronic compressibility and nanoscale inhomogeneity in ionic-liquid gated two-dimensional superconductors
When the electron density of highly crystalline thin films is tuned by
chemical doping or ionic liq- uid gating, interesting effects appear including
unconventional superconductivity, sizeable spin-orbit coupling, competition
with charge-density waves, and a debated low-temperature metallic state that
seems to avoid the superconducting or insulating fate of standard
two-dimensional electron systems. Some experiments also find a marked tendency
to a negative electronic compressibility. We suggest that this indicates an
inclination for electronic phase separation resulting in a nanoscopic inhomo-
geneity. Although the mild modulation of the inhomogeneous landscape is
compatible with a high electron mobility in the metallic state, this
intrinsically inhomogeneous character is highlighted by the peculiar behaviour
of the metal-to-superconductor transition. Modelling the system with super-
conducting puddles embedded in a metallic matrix, we fit the peculiar
resistance vs. temperature curves of systems like TiSe2, MoS2, and ZrNCl. In
this framework also the low-temperature debated metallic state finds a natural
explanation in terms of the pristine metallic background embedding
non-percolating superconducting clusters. An intrinsically inhomogeneous
character naturally raises the question of the formation mechanism(s). We
propose a mechanism based on the interplay be- tween electrons and the charges
of the gating ionic liquid.Comment: substantially modified presentation: 12 pages 7 figure
Phase separation and long wave-length charge instabilities in spin-orbit coupled systems
We investigate a two-dimensional electron model with Rashba spin-orbit
interaction where the coupling constant depends on the electronic
density. It is shown that this dependence may drive the system unstable towards
a long-wave length charge density wave (CDW) where the associated second order
instability occurs in close vicinity to global phase separation. For very low
electron densities the CDW instability is nesting-induced and the modulation
follows the Fermi momentum . At higher density the instability criterion
becomes independent of and the system may become unstable in a broad
momentum range. Finally, upon filling the upper spin-orbit split band, finite
momentum instabilities disappear in favor of phase separation alone. We discuss
our results with regard to the inhomogeneous phases observed at the
LaAlO/SrTiO or LaTiO/SrTiO interfaces.Comment: 6 pages, 6 figure
Theory of the spin galvanic effect at oxide interfaces
The spin galvanic effect (SGE) describes the conversion of a non-equilibrium
spin polarization into a transverse charge current. Recent experiments have
demonstrated a large conversion efficiency for the two-dimensional electron gas
formed at the interface between two insulating oxides, LaAlO and SrTiO.
Here we analyze the SGE for oxide interfaces within a three-band model for the
Ti t orbitals which displays an interesting variety of effective
spin-orbit couplings in the individual bands that contribute differently to the
spin-charge conversion. Our analytical approach is supplemented by a numerical
treatment where we also investigate the influence of disorder and temperature,
which turns out to be crucial to provide an appropriate description of the
experimental data.Comment: 5 pages, 3 figure
Electron-phonon Interaction close to a Mott transition
The effect of Holstein electron-phonon interaction on a Hubbard model close
to a Mott-Hubbard transition at half-filling is investigated by means of
Dynamical Mean-Field Theory. We observe a reduction of the effective mass that
we interpret in terms of a reduced effective repulsion. When the repulsion is
rescaled to take into account this effect, the quasiparticle low-energy
features are unaffected by the electron-phonon interaction. Phonon features are
only observed within the high-energy Hubbard bands. The lack of electron-phonon
fingerprints in the quasiparticle physics can be explained interpreting the
quasiparticle motion in terms of rare fast processes.Comment: 4 pages, 3 color figures. Slightly revised text and references. Kondo
effect result added in Fig. 2 for comparison with DMFT dat
Checkerboard and stripe inhomogeneities in cuprates
We systematically investigate charge-ordering phases by means of a restricted
and unrestricted Gutzwiller approximation to the single-band Hubbard model with
nearest () and next-nearest neighbor hopping (). When is small,
as appropriate for , stripes are found, whereas in
compounds with larger (such as and
) checkerboard structures are favored. In
contrast to the linear doping dependence found for stripes the charge
periodicity of checkerboard textures is locked to 4 unit cells over a wide
doping range. In addition we find that checkerboard structures are favored at
surfaces.Comment: 5 pages, 3 figure
Fermi surface dichotomy on systems with fluctuating order
We investigate the effect of a dynamical collective mode coupled with
quasiparticles at specific wavevectors only. This coupling describes the
incipient tendency to order and produces shadow spectral features at high
energies, while leaving essentially untouched the low energy quasiparticles.
This allows to interpret seemingly contradictory experiments on underdoped
cuprates, where many converging evidences indicate the presence of charge
(stripe or checkerboard) order, which remains instead elusive in the Fermi
surface obtained from angle-resolved photoemission experiments.Comment: 11 pages, 10 figure
Dynamical charge density waves rule the phase diagram of cuprates
In the last few years charge density waves (CDWs) have been ubiquitously
observed in high-temperature superconducting cuprates and are now the most
investigated among the competing orders in the still hot debate on these
systems. A wealth of new experimental data raise several fundamental issues
that challenge the various theoretical proposals. Here, we account for the
complex experimental temperature vs. doping phase diagram and we provide a
coherent scenario explaining why different CDW onset curves are observed by
different experimental probes and seem to extrapolate at zero temperature into
seemingly different quantum critical points (QCPs) in the intermediate and
overdoped region. We also account for the pseudogap and its onset temperature
T*(p) on the basis of dynamically fluctuating CDWs. The nearly singular
anisotropic scattering mediated by these fluctuations also account for the
rapid changes of the Hall number seen in experiments and provides the first
necessary step for a possible Fermi surface reconstruction fully establishing
at lower doping. Finally we show that phase fluctuations of the CDWs, which are
enhanced in the presence of strong correlations near the Mott insulating phase,
naturally account for the disappearance of the CDWs at low doping with yet
another QCP.Comment: 13 pages, 7 figure
- …