1,337 research outputs found
Probing optically silent superfluid stripes in cuprates
Unconventional superconductivity in the cuprates emerges from, or coexists
with, other types of electronic order. However, these orders are sometimes
invisible because of their symmetry. For example, the possible existence of
superfluid charge stripes in the normal state of single layer cuprates cannot
be validated with infrared optics, because interlayer tunneling fluctuations
vanish on average. Similarly, it is not easy to establish if charge orders are
responsible for dynamical decoupling of the superconducting layers over broad
ranges of doping and temperatures. Here, we show that TeraHertz pulses can
excite nonlinear tunneling currents between linearly de-coupled charge-ordered
planes. A giant TeraHertz third harmonic signal is observed in
La1.885Ba0.115CuO4 far above Tc=13 K and up to the charge ordering temperature
TCO = 55 K. We model these results by considering large order-parameter-phase
oscillations in a pair density wave condensate, and show how nonlinear mixing
of optically silent tunneling modes can drive large dipole-carrying
super-current oscillations. Our results provide compelling experimental support
for the presence of hidden superfluid order in the normal state of cuprates.
These experiments also underscore the power of nonlinear TeraHertz optics as a
sensitive probe of frustrated excitations in quantum solids.Comment: 9 pages main text, 5 figures, 12 page supplementar
Magnetic properties of the spin Heisenberg chain with hexamer modulation of exchange
We consider the spin-1/2 Heisenberg chain with alternating spin exchange %on
even and odd sites in the presence of additional modulation of exchange on odd
bonds with period three. We study the ground state magnetic phase diagram of
this hexamer spin chain in the limit of very strong antiferromagnetic (AF)
exchange on odd bonds using the numerical Lanczos method and bosonization
approach. In the limit of strong magnetic field commensurate with the
dominating AF exchange, the model is mapped onto an effective Heisenberg
chain in the presence of uniform and spatially modulated fields, which is
studied using the standard continuum-limit bosonization approach. In absence of
additional hexamer modulation, the model undergoes a quantum phase transition
from a gapped string order into the only one gapless L\"uttinger liquid (LL)
phase by increasing the magnetic field. In the presence of hexamer modulation,
two new gapped phases are identified in the ground state at magnetization equal
to 1/3 and 2/3 of the saturation value. These phases reveal themselves also in
magnetization curve as plateaus at corresponding values of magnetization. As
the result, the magnetic phase diagram of the hexamer chain shows seven
different quantum phases, four gapped and three gapless and the system is
characterized by six critical fields which mark quantum phase transitions
between the ordered gapped and the LL gapless phases.Comment: 21 pages, 5 figures, Journal of Physics: Condensed Matter, 24,
116002, (2012
Magnetic properties of the quantum spin-1/2 XX diamond chain: The Jordan-Wigner approach
The Jordan-Wigner transformation is applied to study magnetic properties of
the quantum spin-1/2 model on the diamond chain. Generally, the
Hamiltonian of this quantum spin system can be represented in terms of spinless
fermions in the presence of a gauge field and different gauge-invariant ways of
assigning the spin-fermion transformation are considered. Additionally, we
analyze general properties of a free-fermion chain, where all gauge terms are
neglected and discuss their relevance for the quantum spin system. A
consideration of interaction terms in the fermionic Hamiltonian rests upon the
Hartree-Fock procedure after fixing the appropriate gauge. Finally, we discuss
the magnetic properties of this quantum spin model at zero as well as non-zero
temperatures and analyze the validity of the approximation used through a
comparison with the results of the exact diagonalization method for finite (up
to 36 spins) chains. Besides the plateau the most prominent feature of
the magnetization curve is a jump at intermediate field present for certain
values of the frustrating vertical bond.Comment: 12 pages, 9 figures, accepted for publication in Eur. Phys. J.
Topics in Meson Spectroscopy
In this mini-review I discuss three topics in meson spectroscopy. The
production of heavy quarkonium states, S-wave scattering below 1 GeV, and
exotic hybrid meson production. This is not intended to be a comprehensive
review, just an overview of several topics of current interest.Comment: Invited talk given at 31st International Conference on High Energy
Physics (ICHEP 2002), Amsterdam, The Netherlands, 24-31 Jul 200
Cooperative Chiral Order in Copolymers of Chiral and Achiral Units
Polyisocyanates can be synthesized with chiral and achiral pendant groups
distributed randomly along the chains. The overall chiral order, measured by
optical activity, is strongly cooperative and depends sensitively on the
concentration of chiral pendant groups. To explain this cooperative chiral
order theoretically, we map the random copolymer onto the one-dimensional
random-field Ising model. We show that the optical activity as a function of
composition is well-described by the predictions of this theory.Comment: 13 pages, including 3 postscript figures, uses REVTeX 3.0 and
epsf.st
Fiber association and network formation in PLA/lignocellulosic fiber composites.
PLA composites were prepared in an internal mixer with a lignocellulosic fiber having relatively large aspect ratio. Fiber content changed between 0 and 60 vol% and the homogenized material was compression molded to 1 mm thick plates. The composites showed anomalous behavior above certain fiber content. Their modulus and especially their strength decreased drastically and modeling also proved the loss of reinforcement at large fiber contents. Micromechanical testing showed that the mechanism of deformation and failure changes at a critical fiber content. Microscopic analysis indi-cated the formation of a network purely from geometrical reasons. The inherent strength of the network is very small because of the weak forces acting among the fibers. This weak inherent strength makes the structure of the composites very sensitive to pro-cessing conditions, and decreases strength, reproducibility as well as reliability
Doping Dependence of Collective Spin and Orbital Excitations in Spin 1 Quantum Antiferromagnet LaSrNiO Observed by X-rays
We report the first empirical demonstration that resonant inelastic x-ray
scattering (RIXS) is sensitive to \emph{collective} magnetic excitations in
systems by probing the Ni -edge of LaSrNiO (). The magnetic excitation peak is asymmetric, indicating the
presence of single and multi spin-flip excitations. As the hole doping level is
increased, the zone boundary magnon energy is suppressed at a much larger rate
than that in hole doped cuprates. Based on the analysis of the orbital and
charge excitations observed by RIXS, we argue that this difference is related
to the orbital character of the doped holes in these two families. This work
establishes RIXS as a probe of fundamental magnetic interactions in nickelates
opening the way towards studies of heterostructures and ultra-fast pump-probe
experiments.Comment: 8 pages, 4 figures, see ancillary files for the supplemental materia
Hot Jupiter Magnetospheres
(Abridged) The upper atmospheres of close-in gas giant exoplanets are
subjected to intense heating/tidal forces from their parent stars.
Atomic/ionized hydrogen (H) layers are sufficiently rarefied that magnetic
pressure may dominate gas pressure for expected planetary magnetic field
strength. We examine the magnetospheric structure using a 3D isothermal
magnetohydrodynamic model that includes: a static "dead zone" near the magnetic
equator containing magnetically confined gas; a "wind zone" outside the
magnetic equator in which thermal pressure gradients and the
magneto-centrifugal-tidal effect give rise to transonic outflow; and a region
near the poles where sufficiently strong tidal forces may suppress transonic
outflow. Using dipole field geometry, we estimate the size of the dead zone to
be ~1-10 planetary radii for a range of parameters. To understand appropriate
base conditions for the 3D isothermal model, we compute a 1D thermal model in
which photoelectric heating from the stellar Lyman continuum is balanced by
collisionally-excited Lyman {\alpha} cooling. This 1D model exhibits a H layer
with temperatures T=5000-10000K down to pressures of 10-100 nbar. Using the 3D
isothermal model, we compute H column densities and Lyman {\alpha} transmission
spectra for parameters appropriate to HD 209458b. Line-integrated transit
depths of 5-10% can be achieved for the above base conditions. Strong magnetic
fields increase the transit signal while decreasing the mass loss, due to
higher covering fraction and density of the dead zone. In our model, most of
the transit signal arises from magnetically confined gas, some of which may be
outside the L1 equipotential. Hence the presence of gas outside the L1
equipotential does not directly imply mass loss. Lastly, we discuss the domain
of applicability for the magnetic wind model described in this paper and in the
Roche-lobe overflow model.Comment: 26 pages, 17 figures (5 color), 2 appendices; submitted to ApJ;
higher resolution version available at
http://www.astro.virginia.edu/~gbt8f/HotJupMag_fullres_astroph.pd
Magnetic and quantum entanglement properties of the distorted diamond chain model for azurite
We present the results of magnetic properties and entanglement of the
distorted diamond chain model for azurite using pure quantum exchange
interactions. The magnetic properties and concurrence as a measure of pairwise
thermal entanglement have been studied by means of variational mean-field like
treatment based on Gibbs-Bogoliubov inequality. Such a system can be considered
as an approximation of the natural material azurite, Cu3(CO3)2(OH)2. For values
of exchange parameters, which are taken from experimental results, we study the
thermodynamic properties, such as azurite specific heat and magnetic
susceptibility. We also have studied the thermal entanglement properties and
magnetization plateau of the distorted diamond chain model for azurite
Revisiting Frank–Starling: regulatory light chain phosphorylation alters the rate of force redevelopment (ktr) in a length-dependent fashion
Force and power in cardiac muscle have a known dependence on phosphorylation of the myosin-associated regulatory light chain (RLC). We explore the effect of RLC phosphorylation on the ability of cardiac preparations to redevelop force (ktr ) in maximally activating [Ca2+ ]. Activation was achieved by rapidly increasing the temperature (temperature-jump of 0.5-20ºC) of permeabilized trabeculae over a physiological range of sarcomere lengths (1.85-1.94 μm). The trabeculae were subjected to shortening ramps over a range of velocities and the extent of RLC phosphorylation was varied. The latter was achieved using an RLC-exchange technique, which avoids changes in the phosphorylation level of other proteins. The results show that increasing RLC phosphorylation by 50% accelerates ktr by ∼50%, irrespective of the sarcomere length, whereas decreasing phosphorylation by 30% slows ktr by ∼50%, relative to the ktr obtained for in vivo phosphorylation. Clearly, phosphorylation affects the magnitude of ktr following step shortening or ramp shortening. Using a two-state model, we explore the effect of RLC phosphorylation on the kinetics of force development, which proposes that phosphorylation affects the kinetics of both attachment and detachment of cross-bridges. In summary, RLC phosphorylation affects the rate and extent of force redevelopment. These findings were obtained in maximally activated muscle at saturating [Ca2+ ] and are not explained by changes in the Ca2+ -sensitivity of acto-myosin interactions. The length-dependence of the rate of force redevelopment, together with the modulation by the state of RLC phosphorylation, suggests that these effects play a role in the Frank-Starling law of the heart.Published versio
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