8,253 research outputs found
Quantum phase transition induced by Dzyaloshinskii-Moriya in the kagome antiferromagnet
We argue that the S=1/2 kagome antiferromagnet undergoes a quantum phase
transition when the Dzyaloshinskii-Moriya coupling is increased. For
the system is in a moment-free phase and for the system develops
antiferromagnetic long-range order. The quantum critical point is found to be
using exact diagonalizations and finite-size scaling. This
suggests that the kagome compound ZnCu_6_3$ may be in a quantum
critical region controlled by this fixed point.Comment: 5 pages, 4 figures; v2: add. data included, show that D=0.1J is at a
quantum critical poin
Supercritical multicomponent solvent coal extraction
The yield of organic extract from the supercritical extraction of coal with larger diameter organic solvents such as toluene is increased by use of a minor amount of from 0.1 to 10% by weight of a second solvent such as methanol having a molecular diameter significantly smaller than the average pore diameter of the coal
On Measuring Condensate Fraction in Superconductors
An analysis of off-diagonal long-range order in superconductors shows that
the spin-spin correlation function is significantly influenced by the order if
the order parameter is anisotropic on a microscopic scale. Thus, magnetic
neutron scattering can provide a direct measurement of the condensate fraction
of a superconductor. It is also argued that recent measurements in high
temperature superconductors come very close to achieving this goal.Comment: 4 pages, 1 eps figure, RevTex. A new possibility in the underdoped
regime is added. Other corrections are mino
Recommended from our members
The Mercury-Tolerant Microbiota of the Zooplankton Daphnia Aids in Host Survival and Maintains Fecundity under Mercury Stress.
Many aquatic organisms can thrive in polluted environments by having the genetic capability to withstand suboptimal conditions. However, the contributions of microbiomes under these stressful environments are poorly understood. We investigated whether a mercury-tolerant microbiota can extend its phenotype to its host by ameliorating host survival and fecundity under mercury-stress. We isolated microbiota members from various clones of Daphnia magna, screened for the mercury-biotransforming merA gene, and determined their mercury tolerance levels. We then introduced the mercury-tolerant microbiota, Pseudomonas-10, to axenic D. magna and quantified its merA gene expression, mercury reduction capability, and measured its impact on host survival and fecundity. The expression of the merA gene was up-regulated in Pseudomonas-10, both in isolation and in host-association with mercury exposure. Pseudomonas-10 is also capable of significantly reducing mercury concentration in the medium. Notably, mercury-exposed daphnids containing only Pseudomonas-10 exhibited higher survival and fecundity than mercury-exposed daphnids supplemented with parental microbiome. Our study showed that zooplankton, such as Daphnia, naturally harbor microbiome members that are eco-responsive and tolerant to mercury exposure and can aid in host survival and maintain host fecundity in a mercury-contaminated environment. This study further demonstrates that under stressful environmental conditions, the fitness of the host can depend on the genotype and the phenotype of its microbiome
The scaling properties of exchange and correlation holes of the valence shell of second row atoms
We study the exchange and correlation hole of the valence shell of second row
atoms using variational Monte Carlo techniques, especially correlated
estimates, and norm-conserving pseudopotentials. The well-known scaling of the
valence shell provides a tool to probe the behavior of exchange and correlation
as a functional of the density and thus test models of density functional
theory. The exchange hole shows an interesting competition between two scaling
forms -- one caused by self-interaction and another that is approximately
invariant under particle number, related to the known invariance of exchange
under uniform scaling to high density and constant particle number. The
correlation hole shows a scaling trend that is marked by the finite size of the
atom relative to the radius of the hole. Both trends are well captured in the
main by the Perdew-Burke-Ernzerhof generalized-gradient approximation model for
the exchange-correlation hole and energy.Comment: 18 pages, 8 figure
Is the pi-particle responsible for the 41 meV peak in YBa_2Cu_3O_7?
It is argued that there is no low-energy resonance associated with the
pi-operators introduced by Demler and Zhang. This implies that the Hubbard
model does not possess an approximate SO(5) symmetry generated by these
operators. Recent finite-size studies are re-interpreted accordingly.Comment: 3 pages, latex (revtex
Observation of Pure Spin Transport in a Diamond Spin Wire
Spin transport electronics - spintronics - focuses on utilizing electron spin
as a state variable for quantum and classical information processing and
storage. Some insulating materials, such as diamond, offer defect centers whose
associated spins are well-isolated from their environment giving them long
coherence times; however, spin interactions are important for transport,
entanglement, and read-out. Here, we report direct measurement of pure spin
transport - free of any charge motion - within a nanoscale quasi 1D 'spin
wire', and find a spin diffusion length ~ 700 nm. We exploit the statistical
fluctuations of a small number of spins ( < 100 net spins) which are
in thermal equilibrium and have no imposed polarization gradient. The spin
transport proceeds by means of magnetic dipole interactions that induce
flip-flop transitions, a mechanism that can enable highly efficient, even
reversible, pure spin currents. To further study the dynamics within the spin
wire, we implement a magnetic resonance protocol that improves spatial
resolution and provides nanoscale spectroscopic information which confirms the
observed spin transport. This spectroscopic tool opens a potential route for
spatially encoding spin information in long-lived nuclear spin states. Our
measurements probe intrinsic spin dynamics at the nanometre scale, providing
detailed insight needed for practical devices which seek to control spin.Comment: 7 pages, 2 figures, under consideration at Nature Nanotechnolog
Magnetic resonance peak and nonmagnetic impurities
Nonmagnetic Zn impurities are known to strongly suppress superconductivity.
We review their effects on the spin excitation spectrum in , as investigated by inelastic neutron scattering measurements.Comment: Proceedings of Mato Advanced Research Workshop BLED 2000. To appear
in Nato Science Series: B Physic
High energy spin excitations in YBa_2 Cu_3 O_{6.5}
Inelastic neutron scattering has been used to obtain a comprehensive
description of the absolute dynamical spin susceptibility
of the underdoped superconducting cuprate YBa_2 Cu_3 O_{6.5} ()
over a wide range of energies and temperatures ( and ). Spin excitations of two different
symmetries (even and odd under exchange of two adjacent CuO_2 layers) are
observed which, surprisingly, are characterized by different temperature
dependences. The excitations show dispersive behavior at high energies.Comment: 15 pages, 5 figure
- …