645 research outputs found
Orbital structure in oscillating galactic potentials
This paper focuses on symmetric potentials subjected to periodic driving.
Four unperturbed potentials V_0(r) were considered, namely the Plummer
potential and Dehnen potentials with \gamma=0.0, 0.5, and 1.0, each subjected
to a time-dependence of the form V(r,t)=V_0(r)(1+m_0\sin(\omega t)). In each
case, the orbits divide clearly into regular and chaotic, distinctions which
appear absolute. In particular, transitions from regularity to chaos are
seemingly impossible. Over finite time intervals, chaotic orbits subdivide into
what can be termed `sticky' chaotic orbits, which exhibit no large scale
secular changes in energy and remain trapped in the phase space region where
they started; and `wildly chaotic' orbits, which do exhibit systematic drifts
in energy as the orbits diffuse to inhabit different phase space regions. This
latter distinction is not absolute, apparently corresponding instead to orbits
penetrating a `leaky' phase space barrier. The three different orbit types can
be identified simply in terms of the frequencies for which their Fourier
spectra have the most power. An examination of the statistical properties of
orbit ensembles as a function of driving frequency \omega allows one to
identify the specific resonances that determine orbital structure. Attention
focuses also on how, for fixed amplitude m_0, such quantities as the mean
energy shift, the relative measure of chaotic orbits, and the mean value of the
largest Lyapunov exponent vary with driving frequency \omega and how, for fixed
\omega, the same quantities depend on m_0.Comment: 16 pages, 9 figures. Accepted for publication to MNRAS. Minor
editions and deletions. Updated reference
Tuning electronic structures via epitaxial strain in Sr2IrO4 thin films
We have synthesized epitaxial Sr2IrO4 thin-films on various substrates and
studied their electronic structures as a function of lattice-strains. Under
tensile (compressive) strains, increased (decreased) Ir-O-Ir bond-angles are
expected to result in increased (decreased) electronic bandwidths. However, we
have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are
shifted to higher (lower) energies under tensile (compressive) strains,
indicating that the electronic-correlation energy is also affected by in-plane
lattice-strains. The effective tuning of electronic structures under
lattice-modification provides an important insight into the physics driven by
the coexisting strong spin-orbit coupling and electronic correlation.Comment: 9 pages, 5 figures, 1 tabl
Observation of a pressure-induced transition from interlayer ferromagnetism to intralayer antiferromagnetism in Sr4Ru3O10
Sr4Ru3O10 is a Ruddlesden-Popper compound with triple Ru-O perovskite layers
separated by Sr-O alkali layers. This compound presents a rare coexistence of
interlayer (c-axis) ferromagnetism and intralayer (basal-plane) metamagnetism
at ambient pressure. Here we report the observation of pressure-induced,
intralayer itinerant antiferromagnetism arising from the interlayer
ferromagnetism. The application of modest hydrostatic pressure generates an
anisotropy that causes a flattening and a tilting of RuO6 octahedra. All
magnetic and transport results from this study indicate these lattice
distortions diminish the c-axis ferromagnetism and basal-plane metamagnetism,
and induce a basal-plane antiferromagnetic state. The unusually large
magnetoelastic coupling and pressure tunability of Sr4Ru3O10 makes it a unique
model system for studies of itinerant magnetism.Comment: 6 figure
Doping Evolution of Magnetic Order and Magnetic Excitations in (SrLa)IrO
We use resonant elastic and inelastic X-ray scattering at the Ir- edge
to study the doping-dependent magnetic order, magnetic excitations and
spin-orbit excitons in the electron-doped bilayer iridate
(SrLa)IrO (). With increasing
doping , the three-dimensional long range antiferromagnetic order is
gradually suppressed and evolves into a three-dimensional short range order
from to , followed by a transition to two-dimensional short range
order between and . Following the evolution of the
antiferromagnetic order, the magnetic excitations undergo damping, anisotropic
softening and gap collapse, accompanied by weakly doping-dependent spin-orbit
excitons. Therefore, we conclude that electron doping suppresses the magnetic
anisotropy and interlayer couplings and drives
(SrLa)IrO into a correlated metallic state hosting
two-dimensional short range antiferromagnetic order and strong
antiferromagnetic fluctuations of moments, with
the magnon gap strongly suppressed.Comment: 6 Pages, 3 Figures, with supplementary in Sourc
Coexisting charge and magnetic orders in the dimer-chain iridate Ba5AlIr2O11
We have synthesized and studied single-crystal Ba5AlIr2O11 that features
dimer chains of two inequivalent octahedra occupied by tetravalent and
pentavalent ions, respectively. Ba5AlIr2O11 is a Mott insulator that undergoes
a subtle structural phase transition near 210 K and a magnetic transition at
4.5 K; the latter transition is surprisingly resistant to applied magnetic
fields up to 12 T, but sensitive to modest applied pressure. All results
indicate that the phase transition at 210 K signals an enhanced charge order
that induces electrical dipoles and strong dielectric response near 210 K. It
is clear that the strong covalency and spin-orbit interaction (SOI) suppress
double exchange in Ir dimers and stabilize a novel magnetic state. The behavior
of Ba5AlIr2O11 therefore provides unique insights into the physics of SOI along
with strong covalency in competition with double exchange interactions of
comparable strength.Comment: 6 figures, 20 pages. arXiv admin note: text overlap with
arXiv:1505.0087
Electrical Control of Structural and Physical Properties via Strong Spin-Orbit Interactions in Sr\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e
Electrical control of structural and physical properties is a long-sought, but elusive goal of contemporary science and technology. We demonstrate that a combination of strong spin-orbit interactions (SOI) and a canted antiferromagnetic Mott state is sufficient to attain that goal. The antiferromagnetic insulator Sr2IrO4 provides a model system in which strong SOI lock canted Ir magnetic moments to IrO6 octahedra, causing them to rigidly rotate together. A novel coupling between an applied electrical current and the canting angle reduces the Néel temperature and drives a large, nonlinear lattice expansion that closely tracks the magnetization, increases the electron mobility, and precipitates a unique resistive switching effect. Our observations open new avenues for understanding fundamental physics driven by strong SOI in condensed matter, and provide a new paradigm for functional materials and devices
Electrical Control of Structural and Physical Properties via Strong Spin-Orbit Interactions in Sr2IrO4
Electrical control of structural and physical properties is a long-sought,
but elusive goal of contemporary science and technology. We demonstrate that a
combination of strong spin-orbit interactions (SOI) and a canted
antiferromagnetic (AFM) Mott state is sufficient to attain that goal. The AFM
insulator Sr2IrO4 provides a model system in which strong SOI lock canted Ir
magnetic moments to IrO6-octahedra, causing them to rigidly rotate together. A
novel coupling between an applied electrical current and the canting angle
reduces the N\'eel temperature and drives a large, non-linear lattice expansion
that closely tracks the magnetization, increases the electron mobility, and
precipitates a unique resistive switching effect. Our observations open new
avenues for understanding fundamental physics driven by strong SOI in condensed
matter, and provide a new paradigm for functional materials and devices.Comment: 5 figures; to be published in Physical Review Letter
Cardiopoietic programming of embryonic stem cells for tumor-free heart repair
Embryonic stem cells have the distinct potential for tissue regeneration, including cardiac repair. Their propensity for multilineage differentiation carries, however, the liability of neoplastic growth, impeding therapeutic application. Here, the tumorigenic threat associated with embryonic stem cell transplantation was suppressed by cardiac-restricted transgenic expression of the reprogramming cytokine TNF-α, enhancing the cardiogenic competence of recipient heart. The in vivo aptitude of TNF-α to promote cardiac differentiation was recapitulated in embryoid bodies in vitro. The procardiogenic action required an intact endoderm and was mediated by secreted cardio-inductive signals. Resolved TNF-α–induced endoderm-derived factors, combined in a cocktail, secured guided differentiation of embryonic stem cells in monolayers produce cardiac progenitors termed cardiopoietic cells. Characterized by a down-regulation of oncogenic markers, up-regulation, and nuclear translocation of cardiac transcription factors, this predetermined population yielded functional cardiomyocyte progeny. Recruited cardiopoietic cells delivered in infarcted hearts generated cardiomyocytes that proliferated into scar tissue, integrating with host myocardium for tumor-free repair. Thus, cardiopoietic programming establishes a strategy to hone stem cell pluripotency, offering a tumor-resistant approach for regeneration
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