40 research outputs found
Charge redistribution at YBa2Cu3O7-metal interfaces
Charge redistribution at interfaces is crucial for electronic applications of
high-Tc superconductors, since the band structure is modified on a local scale.
We address the normal-state electronic structure of YBa2Cu3O7 (YBCO) at an
YBCO-metal contact by first principles calculations for prototypical interface
configurations. We derive quantitative results for the intrinsic doping of the
superconducting CuO2 planes due to the metal contact. Our findings can be
explained in terms of a band-bending mechanism, complemented by local screening
effects. We determine a net charge transfer of 0.09 to 0.13 electrons in favour
of the intraplane Cu sites, depending on the interface orientation.Comment: 3 pages, 2 figures, submitted to Appl. Phys. Let
Interaction versus dimerization in one-dimensional Fermi systems
In order to study the effect of interaction and lattice distortion on quantum
coherence in one-dimensional Fermi systems, we calculate the ground state
energy and the phase sensitivity of a ring of interacting spinless fermions on
a dimerized lattice. Our numerical DMRG (Density Matrix Renormalization Group)
studies, in which we keep up to 1000 states for systems of about 100 sites, are
supplemented by analytical considerations using bosonization techniques. We
find a delocalized phase for an attractive interaction, which differs from that
obtained for random lattice distortions. The extension of this delocalized
phase depends strongly on the dimerization induced modification of the
interaction. Taking into account the harmonic lattice energy, we find a
dimerized ground state for a repulsive interaction only. The dimerization is
suppressed at half filling, when the correlation gap becomes large.Comment: EPJ-style, 8 pages including 12 figures, to be published in EPJ
On the ferromagnetic character of (LaVO)/SrVO superlattices
The experimental observation that vanadate superlattices
(LaVO)/SrVO show ferromagnetism up to room temperature [U.\
L\"uders {\it et al.}, Phys.\ Rev.\ B {\bf 80}, 241102R (2009)] is investigated
by means of density functional theory. First, the influence of the density
functional on the electronic and magnetic structure of bulk is
discussed. Second, the band structure of a (LaVO)/SrVO slab for
and 6 is calculated. Very different behaviors for odd and even values of
are found: In the odd case lattice relaxation results into a buckling of
the interface VO layers that leads to spin-polarized interfaces. In the
even case a decoupling of the interface VO layers from the LaO layers is
obtained, confining the interface electrons into a two-dimensional electron
gas. The orbital reconstruction at the interface due to the lattice relaxation
is discussed.Comment: 8 pages, 7 figure
Tailoring the intrinsic doping at YBa2Cu3O7-metal-contacts
Charge redistribution at interfaces between high-Tc superconductors and metals is problematic for technological applications due to local variations in the electronic structure. In particular, the interface affects the charge density in the superconducting CuO2-planes. For obtaining quantitative insight into effects of interface doping, we address YBCO-metal-contacts by means of first principle supercell calculations within density functional theory. On the one hand, we find that the CuO2-planes are intrinsically electron-overdoped, i.e. hole-underdoped. On the other hand, very strong effects on the near-contact electronic states are also caused by electronegative impurities incorporated into the metal. Doping of such impurities consequently paves the way for a controlled re-extracting of charge from intrinsically doped interfaces and, therefore, for a tailoring of the interface properties
Electronic Transport Through EuO Spin Filter Tunnel Junctions
Epitaxial spin filter tunnel junctions based on the ferromagnetic
semiconductor europium monoxide, EuO, are investigated by means of density
functional theory. In particular, we focus on the spin transport properties of
Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission
coefficient and the current-voltage curves on the interface spacing and on the
EuO thickness is explained in terms of the EuO density of states and the
complex band structure. Furthermore we also discuss the relation between the
spin transport properties and the Cu-EuO interface geometry. The level
alignment of the junction is sensitively affected by the interface spacing,
since this determines the charge transfer between EuO and the Cu electrodes.
Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect
spin filter, with a spin polarization of the current close to 100%, and with
both the Eu-5d conduction band and the Eu-4f valence band states contributing
to the coherent transport. For epitaxial EuO on Cu a symmetry filtering is
observed, with the \Delta_1 states dominating the transmission. This leads to a
transport gap larger than the fundamental EuO band gap. Importantly the high
spin polarization of the current is preserved up to large bias voltages
Interacting particles at a metal-insulator transition
We study the influence of many-particle interaction in a system which, in the
single particle case, exhibits a metal-insulator transition induced by a finite
amount of onsite pontential fluctuations. Thereby, we consider the problem of
interacting particles in the one-dimensional quasiperiodic Aubry-Andre chain.
We employ the density-matrix renormalization scheme to investigate the finite
particle density situation. In the case of incommensurate densities, the
expected transition from the single-particle analysis is reproduced. Generally
speaking, interaction does not alter the incommensurate transition. For
commensurate densities, we map out the entire phase diagram and find that the
transition into a metallic state occurs for attractive interactions and
infinite small fluctuations -- in contrast to the case of incommensurate
densities. Our results for commensurate densities also show agreement with a
recent analytic renormalization group approach.Comment: 8 pages, 8 figures The original paper was splitted and rewritten.
This is the published version of the DMRG part of the original pape