1,294 research outputs found
Raman Scattering in Cuprate Superconductors
A theory for electronic Raman scattering in the cuprate superconductors is
presented with a specific emphasis on the polarization dependence of the
spectra which can infer the symmetry of the energy gap. Signatures of the
effects of disorder on the low frequency and low temperature behavior of the
Raman spectra for different symmetry channels provide detailed information
about the magnitude and the phase of the energy gap. Properties of the theory
for finite T are discussed and compared to recent data concerning the doping
dependence of the Raman spectra in cuprate superconductors, and remaining
questions are addressed.Comment: 27 pages, 11 figures, style file include
Mirages, anti-mirages, and further surprises in quantum corrals with non-magnetic impurities
We investigate the local density of states (LDOS) for non-interacting
electrons in a hard wall ellipse in the presence of a single non-magnetic
scattering center. Using a T-matrix analysis we calculate the local Green's
function and observe a variety of quantum mirage effects for different impurity
positions. Locating the impurity near positions with LDOS maxima for the
impurity free corral can either lead to a reduction or an enhancement of the
LDOS at the mirror image point, i.e. a mirage or anti-mirage effect, or even
suppress LDOS maxima in the entire area of the corral.Comment: 6 pages, 7 figure
Interfacial Magnetism in Manganite Superlattices
We use a two-orbital double-exchange model including Jahn-Teller lattice
distortions, superexchange interactions, and long-range Coulomb (LRC)
interactions to investigate the origin of magnetically disordered interfaces
between ferromagnetic metallic (FM) and antiferromagnetic insulating (AFI)
manganites in FM/AFI superlattices. The induced magnetic moment in the AFI
layer varies non-monotonically with increasing AFI layer width as seen in the
experiment. We provide a framework for understanding this non-monotonic
behavior which has a one-to-one correspondence with the magnetization of the FM
interface. The obtained insights provide a basis for improving the tunneling
magnetoresistance in FM/AFI manganite superlattices by avoiding a magnetic dead
layer (MDL) in the FM manganite.Comment: 5 pages, 5 figures. To appear in PR
Anisotropy of the Energy Gap in the Insulating Phase of the U-t-t' Hubbard Model
We apply a diagrammatic expansion method around the atomic limit (U >> t) for
the U-t-t' Hubbard model at half filling and finite temperature by means of a
continued fraction representation of the one-particle Green's function. From
the analysis of the spectral function A(\vec{k},\omega) we find an energy
dispersion relation with a (cos k_x-cos k_y)^2 modulation of the energy gap in
the insulating phase. This anisotropy is compared with experimental ARPES
results on insulating cuprates.Comment: 4 pages Revtex, 6 embedded eps figures; Figures 5 and 6 were in error
and have been replaced including the discussion of the figure
Combined Effect of Bond- and Potential-Disorder in Half-Doped Manganites
We analyze the effects of both bond- and potential-disorder in the vicinity
of a first-order metal insulator transition in a two-band model for manganites
using a real-space Monte Carlo method. Our results reveal a novel
charge-ordered state coexisting with spin-glass behavior. We provide the basis
for understanding the phase diagrams of half-doped manganites, and contrast the
effects of bond- and potential-disorder and the combination of both.Comment: 4 pages, 3 figures, published versio
Electronic and Magnetic Reconstructions in Manganite Superlattices
We investigate the electronic reconstruction at the interface between
ferromagnetic metallic (FM) and antiferromagnetic insulating (AFI) manganites
in superlattices using a two-orbital double-exchange model including
superexchange interactions, Jahn-Teller lattice distortions, and long range
Coulomb interactions. The magnetic and the transport properties critically
depend on the thickness of the AFI layers. We focus on superlattices where the
constituent parent manganites have the same electron density n = 0.6. The
induced ferromagnetic moment in the AFI layers decreases monotonically with
increasing layer width, and the electron-density profile and the magnetic
structure in the center of the AFI layer gradually return to the bulk limit.
The width of the AFI layers and the charge-transfer profile at the interfaces
control the magnitude of the magnetoresistance and the metal-insulator
transition of the FM/AFI superlattices.Comment: 11 pages, 10 figure
Competing phases in the extended U-V-J Hubbard model near the van Hove fillings
The phase diagram of the two-dimensional extended one-band U-V-J Hubbard
model is considered within a mean-field approximation and two- and many-patch
renormalization group (RG) approaches near the van Hove band fillings. At small
t' and J>0 mean-field and many-patch RG approaches give similar results for the
leading spin-density-wave (SDW) instability, while the two-patch RG approach,
which predicts a wide region of charge-flux (CF) phase becomes unreliable due
to nesting effect. At the same time, there is a complex competition between
SDW, CF phases, and d-wave superconductivity in two- and many-patch RG
approaches. While the spin-flux (SF) phase is not stable at the mean-field
level, it is identified as a possible ground state at J<0 in both RG
approaches. With increasing t' the results of all three approaches merge:
d-wave superconductivity at J>0 and ferromagnetism at J<0 become the leading
instabilities. For large enough V the charge-density-wave (CDW) state occurs.Comment: This is the extended version of the paper, which includes both two-
and many-patch RG analyse
Renormalization group analysis of magnetic and superconducting instabilities near van Hove band fillings
Phase diagrams of the two-dimensional one-band t-t' Hubbard model are
obtained within the two-patch and the temperature-cutoff many-patch
renormalization group approach. At small t' and at van Hove band fillings
antiferromagnetism dominates, while with increasing t' or changing filling
antiferromagnetism is replaced by d-wave superconductivity. Near t'=t/2 and
close to van Hove band fillings the system is unstable towards ferromagnetism.
Away from van Hove band fillings this ferromagnetic instability is replaced by
a region with dominating triplet p-wave superconducting correlations. The
results of the renormalization-group approach are compared with the mean-field
results and the results of the T-matrix approximation.Comment: 29 pages, 17 figure
- …