50 research outputs found
Phonon-assisted excitation transfer in quantum dot molecules
We derive a quantum-kinetic description of phonon-assisted F{\"o}rster
transfer between two coupled quantum dots (a quantum dot molecule). We show
that the exciton state decays to the ground state of the QDM via a combination
of the Rabi rotation and exponential decay. For moderately spaced dots this
process takes place on a picosecond time scale.Comment: To be presented at the school Jaszowiec 200
Anomalous Hall conductivity of clean Sr2RuO4 at finite temperatures
Building on previous work, we calculate the temperature- and
frequency-dependent {\it anomalous} Hall conductivity for the putative
multiband chiral superconductor \Sr using a simple microscopic two-orbital
model without impurities. A Hall effect arises in this system without the
application of an external magnetic field due to the time-reversal-symmetry
breaking chiral superconducting state. The anomalous Hall conductivity is
nonzero only when there is more than one superconducting order parameter,
involving inter- as well as intra-band Cooper pairing. We find that such a
multiband superconducting state gives rise to a distinctive resonance in the
frequency-dependence of the Hall conductivity at a frequency close to the
inter-orbital hopping energy scale that describes hopping between Ru
and orbitals. The detection of this feature, robust to temperature and
impurity effects in the superconducting phase, would thus constitute compelling
evidence in favour of a multiband origin of superconductivity in \Sr, with
strong superconductivity on the and bands. The temperature
dependence of the Hall conductivity and Kerr rotation angle are studied within
this model at the one-loop approximation.Comment: 14 pages, 8 figures. Invited submission, proceedings of M2S 2012.
Published versio
Identifying spin-triplet pairing in spin-orbit coupled multi-band superconductors
We investigate the combined effect of Hund's and spin-orbit (SO) coupling on
superconductivity in multi-orbital systems. Hund's interaction leads to
orbital-singlet spin-triplet superconductivity, where the Cooper pair wave
function is antisymmetric under the exchange of two orbitals. We identify three
d-vectors describing even-parity orbital-singlet spin-triplet pairings among
t2g-orbitals, and find that the three d-vectors are mutually orthogonal to each
other. SO coupling further assists pair formation, pins the orientation of the
d-vector triad, and induces spin-singlet pairings with a relative phase
difference of \pi/2. In the band basis the pseudospin d-vectors are aligned
along the z-axis and correspond to momentum-dependent inter- and intra-band
pairings. We discuss quasiparticle dispersion, magnetic response, collective
modes, and experimental consequences in light of the superconductor Sr2RuO4.Comment: 6 pages, 5 figure
Strong electron correlations in the normal state of FeSe0.42Te0.58
We investigate the normal state of the '11' iron-based superconductor
FeSe0.42Te0.58 by angle resolved photoemission. Our data reveal a highly
renormalized quasiparticle dispersion characteristic of a strongly correlated
metal. We find sheet dependent effective carrier masses between ~ 3 - 16 m_e
corresponding to a mass enhancement over band structure values of m*/m_band ~ 6
- 20. This is nearly an order of magnitude higher than the renormalization
reported previously for iron-arsenide superconductors of the '1111' and '122'
families but fully consistent with the bulk specific heat.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
Formation of heavy d-electron quasiparticles in SrâRuâOâ
The phase diagram of Sr3Ru2O7 shows hallmarks of strong electron correlations despite the modest Coulomb interaction in the Ru 4d shell. We use angle-resolved photoelectron spectroscopy measurements to provide microscopic insight into the formation of the strongly renormalized heavy d-electron liquid that controls the physics of Sr3Ru2O7. Our data reveal itinerant Ru 4d-states confined over large parts of the Brillouin zone to an energy range of <6 meV, nearly three orders of magnitude lower than the bare band width. We show that this energy scale agrees quantitatively with a characteristic thermodynamic energy scale associated with quantum criticality and illustrate how it arises from a combination of back-folding due to a structural distortion and the hybridization of light and strongly renormalized, heavy quasiparticle bands. The resulting heavy Fermi liquid has a marked k-dependence of the renormalization which we relate to orbital mixing along individual Fermi surface sheets
Structural origin of apparent Fermi surface pockets in angle-resolved photoemission of BiSrLaCuO
We observe apparent hole pockets in the Fermi surfaces of single-layer
Bi-based cuprate superconductors from angle-resolved photoemission (ARPES).
From detailed low-energy electron diffraction measurements and an analysis of
the ARPES polarization-dependence, we show that these pockets are not
intrinsic, but arise from multiple overlapping superstructure replicas of the
main and shadow bands. We further demonstrate that the hole pockets reported
recently from ARPES [Meng et al, Nature 462, 335 (2009)] have a similar
structural origin, and are inconsistent with an intrinsic hole pocket
associated with the electronic structure of a doped CuO plane. The nature
of the Fermi surface topology in the enigmatic pseudogap phase therefore
remains an open question.Comment: 5 pages, 4 figure
Dense active matter model of motion patterns in confluent cell monolayers
Epithelial cell monolayers show remarkable displacement and velocity
correlations over distances of ten or more cell sizes that are reminiscent of
supercooled liquids and active nematics. We show that many observed features
can be described within the framework of dense active matter, and argue that
persistent uncoordinated cell motility coupled to the collective elastic modes
of the cell sheet is sufficient to produce swirl-like correlations. We obtain
this result using both continuum active linear elasticity and a normal modes
formalism, and validate analytical predictions with numerical simulations of
two agent-based cell models, soft elastic particles and the self-propelled
Voronoi model together with in-vitro experiments of confluent corneal
epithelial cell sheets. Simulations and normal mode analysis perfectly match
when tissue-level reorganisation occurs on times longer than the persistence
time of cell motility. Our analytical model quantitatively matches measured
velocity correlation functions over more than a decade with a single fitting
parameter.Comment: updated version accepted for publication in Nat. Com
Publishing and sharing multi-dimensional image data with OMERO
Imaging data are used in the life and biomedical sciences to measure the molecular and structural composition and dynamics of cells, tissues, and organisms. Datasets range in size from megabytes to terabytes and usually contain a combination of binary pixel data and metadata that describe the acquisition process and any derived results. The OMERO image data management platform allows users to securely share image datasets according to specific permissions levels: data can be held privately, shared with a set of colleagues, or made available via a public URL. Users control access by assigning data to specific Groups with defined membership and access rights. OMEROâs Permission system supports simple data sharing in a lab, collaborative data analysis, and even teaching environments. OMERO software is open source and released by the OME Consortium at www.openmicroscopy.org
High-resolution photoemission on Sr2RuO4 reveals correlation-enhanced effective spin-orbit coupling and dominantly local self-energies
We explore the interplay of electron-electron correlations and spin-orbit
coupling in the model Fermi liquid Sr2RuO4 using laser-based angle-resolved
photoemission spectroscopy. Our precise measurement of the Fermi surface
confirms the importance of spin-orbit coupling in this material and reveals
that its effective value is enhanced by a factor of about two, due to
electronic correlations. The self-energies for the and sheets
are found to display significant angular dependence. By taking into account the
multi-orbital composition of quasiparticle states, we determine self-energies
associated with each orbital component directly from the experimental data.
This analysis demonstrates that the perceived angular dependence does not imply
momentum-dependent many-body effects, but arises from a substantial orbital
mixing induced by spin-orbit coupling. A comparison to single-site dynamical
mean-field theory further supports the notion of dominantly local orbital
self-energies, and provides strong evidence for an electronic origin of the
observed non-linear frequency dependence of the self-energies, leading to
`kinks' in the quasiparticle dispersion of Sr2RuO4.Comment: PRX accepte