2,713 research outputs found
Intrinsic instability of electronic interfaces with strong Rashba coupling
We consider a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures, which includes a Rashba spin-orbit
coupling proportional to the electric field perpendicular to the interface.
Based on the standard mechanism of polarity catastrophe, we assume that the
electric field is proportional to the electron density. Under these simple and
general assumptions, we show that a phase separation instability occurs for
realistic values of the spin-orbit coupling and of the band parameters. This
could provide an intrinsic mechanism for the recently observed inhomogeneous
phases at the LaAlO_3/SrTiO_3 or LaTiO_3/SrTiO_3 interfaces.Comment: 5 pages, 4 figure
Jahn-Teller, Charge and Magnetic Ordering in half-doped Manganese Oxides
The phase diagram of half-doped manganite systems of formula
A_{0.5}A'_{0.5}MnO_3 is investigated within a single-orbital model
incorporating magnetic double-exchange and superexchange, together with
intersite Coulomb and electron-lattice interactions. Strong Jahn-Teller and
breathing mode deformations compete together and result in shear lattice
deformations. The latters stabilize the charge-ordered CE-type phase, which
undergo first-order transitions with temperature or magnetic field to either
Ferromagnetic metallic or Paramagnetic insulating phases. An essential feature
is the self-consistent screening of Coulomb and electron-phonon interactions in
the ferromagnetic phase.Comment: 10 pages, six figures (eps files) +two class file
Collective transport and optical absorption near the stripe criticality
Within the stripe quantum critical point scenario for high
superconductors, we point out the possible direct contribution of charge
collective fluctuations to the optical absorption and to the d.c. resistivity.Comment: 2 pages 2 figures 1 style fil
Single-particle spectra near a stripe instability
We analyze the single-particle spectra of a bi-layered electron system near a
stripe instability and compare the results with ARPES experiments on the Bi2212
cuprate superconductor near optimum doping, addressing also the issue of the
puzzling absence of bonding-antibonding splitting.Comment: Proceedings of the XXII International Conference on Low Temperature
Physics August 4-11, 1999, Espoo and Helsinki, Finland (minor changes to the
figure) Similar results in the Proceedings of the International Workshop on
``Electronic crystals, ECRYS-99'', May 31-June 5 1999, La Colle sur Loup
(France), J. Phys. IV France 9, Pr10-337 (1999
A large-N analysis of the local quantum critical point and the spin-liquid phase
We study analytically the Kondo lattice model with an additional
nearest-neighbor antiferromagnetic interaction in the framework of large-N
theory. We find that there is a local quantum critical point between two
phases, a normal Fermi-liquid and a spin-liquid in which the spins are
decoupled from the conduction electrons. The local spin susceptibility displays
a power-law divergence throughout the spin liquid phase. We check the
reliability of the large-N results by solving by quantum Monte Carlo simulation
the N=2 spin-liquid problem with no conduction electrons and find qualitative
agreement. We show that the spin-liquid phase is unstable at low temperatures,
suggestive of a first-order transition to an ordered phase.Comment: 4 pages and 1 figur
Anomalous isotopic effect near the charge-ordering quantum criticality
Within the Hubbard-Holstein model, we evaluate the various crossover lines
marking the opening of pseudogaps in the cuprates, which, in our scenario, are
ruled by the proximity to a charge-ordering quantum criticality (stripe
formation). We provide also an analysis of their isotopic dependencies, as
produced by critical fluctuations. We find no isotopic shift of the temperature
marked as a reduction of the quasiparticle density of states in various
experiments, and a substantial positive shift of the pseudogap-formation
temperature . We infer that the superconducting critical temperature
has almost no shift in the optimally- and overdoped regimes while it has a
small negative isotopic shift in the underdoped, which increses upon
underdoping. We account also for the possible dynamical nature of the
charge-ordering transition, and explain in this way the spread of the values of
and its of isotopic shift, obtained with experimental probes having
different characteristic timescales.Comment: 4 pages, 3 figure
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
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