79 research outputs found
Fermi Surface Nesting and Nanoscale Fluctuating Charge/Orbital Ordering in Colossal Magnetoresistive Oxides
We used high resolution angle-resolved photoemission spectroscopy to reveal
the Fermi surface and key transport parameters of the metallic state of the
layered Colossal Magnetoresistive (CMR) oxide La1.2Sr1.8Mn2O7. With these
parameters the calculated in-plane conductivity is nearly one order of
magnitude larger than the measured DC conductivity. This discrepancy can be
accounted for by including the pseudogap which removes at least 90% of the
spectral weight at the Fermi energy. Key to the pseudogap and many other
properties are the parallel straight Fermi surface sections which are highly
susceptible to nesting instabilities. These nesting instabilities produce
nanoscale fluctuating charge/orbital modulations which cooperate with
Jahn-Teller distortions and compete with the electron itinerancy favored by
double exchange
ARPES in the normal state of the cuprates: comparing the marginal Fermi liquid and spin fluctuation scenarios
We address the issue whether ARPES measurements of the spectral function near the Fermi surface in the normal state of near optimally doped
cuprates can distinguish between the marginal Fermi liquid scenario and the
spin-fluctuation scenario. We argue that the data for momenta near the Fermi
surface are equally well described by both theories, but this agreement is
nearly meaningless as in both cases one has to add to a large constant of yet unknown origin. We show that the data can be
well fitted by keeping only this constant term in the self-energy. To
distinguish between the two scenarios, one has to analyze the data away from
the Fermi surface, when the intrinsic piece in becomes
dominant.Comment: Accepted for publication in Europhysics Letters, Incorrect
interpretation of reference 10 correcte
Sperm death and dumping in Drosophila
Mating with more than one male is the norm for females of many species. In addition to generating competition between the ejaculates of different males, multiple mating may allow females to bias sperm use. In Drosophila melanogaster, the last male to inseminate a female sires approximately 80% of subsequent progeny. Both sperm displacement, where resident sperm are removed from storage by the incoming ejaculate of the copulating male, and sperm incapacitation, where incoming seminal fluids supposedly interfere with resident sperm, have been implicated in this pattern of sperm use. But the idea of incapacitation is problematic because there are no known mechanisms by which an individual could damage rival sperm and not their own. Females also influence the process of sperm use, but exactly how is unclear. Here we show that seminal fluids do not kill rival sperm and that any 'incapacitation' is probably due to sperm ageing during sperm storage. We also show that females release stored sperm from the reproductive tract (sperm dumping) after copulation with a second male and that this requires neither incoming sperm nor seminal fluids. Instead, males may cause stored sperm to be dumped or females may differentially eject sperm from the previous mating
Doubling of the bands in overdoped Bi2Sr2CaCu2O8-probable evidence for c-axis bilayer coupling
We present high resolution ARPES data of the bilayer superconductor
Bi2Sr2CaCu2O8 (Bi2212) showing a clear doubling of the near EF bands. This
splitting approaches zero along the (0,0)-(pi,pi) nodal line and is not
observed in single layer Bi2Sr2CuO6 (Bi2201), suggesting that the splitting is
due to the long sought after bilayer splitting effect. The splitting has a
magnitude of approximately 75 meV near the middle of the zone, extrapolating to
about 100 meV near the (pi,0) poin
Doping dependence of the many-body effects along the nodal direction in the high-Tc cuprate (Bi,Pb)_2Sr_2CaCu_2O_8
Angle-resolved photoemission spectroscopy (ARPES) is used to study the doping
dependence of the lifetime and the mass renormalization of the low energy
excitations in the high-Tc cuprate (Bi,Pb)_2Sr_2CaCu_2O_8 along the zone
diagonal. We find a linear energy de-pendence of the scattering rate for the
underdoped samples and a quadratic energy depend-ence in the overdoped case.
The mass enhancement of the quasiparticles due to the many body effects at the
Fermi energy is found to be in the order of 2 and the renormalization extends
over a large energy range for both the normal and the superconducting state.
The much discussed kink in the dispersion around 70 meV is interpreted as a
small additional effect at low temperatures.Comment: 12 pages, 3 figure
- …