7 research outputs found
Defect and anisotropic gap induced quasi-one-dimensional modulation of local density of states in YBaCuO
Motivated by recent angle-resolved photoemission spectroscopy (ARPES)
measurement that superconducting YBaCuO (YBCO) exhibits a
-symmetry gap, we show possible quasi-one-dimensional
modulations of local density of states in YBCO. These aniostropic gap and
defect induced stripe structures are most conspicuous at higher biases and
arise due to the nesting effect associated with a Fermi liquid. Observation of
these spectra by scanning tunneling microscopy (STM) would unify the picture
among STM, ARPES, and inelastic neutron scattering for YBCO.Comment: 4 pages, 4 figure
Quantum Interference between Impurities: Creating Novel Many-Body States in s-wave Superconductors
We demonstrate that quantum interference of electronic waves that are
scattered by multiple magnetic impurities in an s-wave superconductor gives
rise to novel bound states. We predict that by varying the inter-impurity
distance or the relative angle between the impurity spins, the states' quantum
numbers, as well as their distinct frequency and spatial dependencies, can be
altered. Finally, we show that the superconductor can be driven through
multiple local crossovers in which its spin polarization, , changes
between and 1.Comment: 4 pages, 4 figure
Quantum interference between non-magnetic impurities in d_x2-y2-wave superconductors
We study quantum interference of electronic waves that are scattered by
multiple non-magnetic impurities in a d_x2-y2-wave superconductor. We show that
the number of resonance states in the density-of-states (DOS), as well as their
frequency and spatial dependence change significantly as the distance between
the impurities or their orientation relative to the crystal lattice is varied.
Since the latter effect arises from the momentum dependence of the
superconducting gap, we argue that quantum interference is a novel tool to
identify the symmetry of unconventional superconductors.Comment: 4 pages, 4 figure
Friedel oscillations in a two-band Hubbard model for CuO chains
Friedel oscillations induced by open boundary conditions in a two-band
Hubbard model for CuO chains are numerically studied. We find that for
physically realistic parameters and close to quarter filling, these
oscillations have a 2k_F modulation according with experimental results on
YBa_2Cu_3O_{7-delta}. In addition, we predict that, for the same parameters, as
hole doping is reduced from quarter filling to half filling, Friedel
oscillations would acquire a 4k_F modulation, typical of a strongly correlated
electrons regime. The 4k_F modulation dominates also in the electron doped
region. The range of parameters varied is very broad, and hence the results
reported could apply to other cuprates and other strongly correlated compounds
with quasi-one dimensional structures. On a more theoretical side, we stress
the fact that the copper and oxygen subsystems should be described by two
different Luttinger liquid exponents.Comment: 7 pages, 7 eps figure
Two nonmagnetic impurities in the DSC and DDW state of the cuprate superconductors as a probe for the pseudogap
The quantum interference between two nonmagnetic impurities is studied
numerically in both the d-wave superconducting (DSC) and the d-density wave
(DDW) state. In all calculations we include the tunnelling through excited
states from the CuO planes to the BiO layer probed by the STM tip. Compared
to the single impurity case, a systematic study of the modulations in the
two-impurity local density of states can distinguish between the DSC or DDW
states. This is important if the origin of the pseudogap phase is caused by
preformed pairs or DDW order. Furthermore, in the DSC state the study of the
LDOS around two nonmagnetic impurities provide further tests for the potential
scattering model versus more strongly correlated models.Comment: 6 pages, 6 figure
Quantum interference between multiple impurities in anisotropic superconductors
We study the quantum interference between impurities in d-wave
superconductors within a potential scattering formalism that easily applies to
multiple impurities. The evolution of the low-energy local density of states
for both magnetic and nonmagnetic short-ranged scatterers are studied as a
function of the spatial configuration of the impurities. Further we discuss the
influence of subdominant bulk superconducting order parameters on the
interference pattern from multiple impurities.Comment: 4 pages, 6 figure