947 research outputs found
Valence bond spin liquid state in two-dimensional frustrated spin-1/2 Heisenberg antiferromagnets
Fermionic valence bond approach in terms of SU(4) representation is proposed
to describe the frustrated Heisenberg antiferromagnetic (AF)
model on a {\it bipartite} square lattice. A uniform mean field solution
without breaking the translational and rotational symmetries describes a
valence bond spin liquid state, interpolating the two different AF ordered
states in the large and large limits, respectively. This novel
spin liquid state is gapless with the vanishing density of states at the Fermi
nodal points. Moreover, a sharp resonance peak in the dynamic structure factor
is predicted for momenta and in the strongly
frustrated limit , which can be checked by neutron
scattering experiment.Comment: Revtex file, 4 pages, 4 figure
Transverse force generated by an electric field and transverse charge imbalance in spin-orbit coupled systems
We use linear response theory to study the transverse force generated by an
external electric field and hence possible charge Hall effect in spin-orbit
coupled systems. In addition to the Lorentz force that is parallel to the
electric field, we find that the transverse force perpendicular to the applied
electric field may not vanish in a system with an anisotropic energy
dispersion. Surprisingly, in contrast to the previous results, the transverse
force generated by the electric field does not depend on the spin current, but
in general, it is related to the second derivative of energy dispersion only.
Furthermore, we find that the transverse force does not vanish in the
Rashba-Dresselhaus system. Therefore, the non-vanishing transverse force acts
as a driving force and results in charge imbalance at the edges of the sample.
The estimated ratio of the Hall voltage to the longitudinal voltage is . The disorder effect is also considered in the study of the
Rashba-Dresselhaus system. We find that the transverse force vanishes in the
presence of impurities in this system because the vertex correction and the
anomalous velocity of the electron accidently cancel each other
Concatenating dynamical decoupling with decoherence-free subspaces for quantum computation
A scheme to implement a quantum computer subjected to decoherence and
governed by an untunable qubit-qubit interaction is presented. By concatenating
dynamical decoupling through bang-bang (BB) pulse with decoherence-free
subspaces (DFSs) encoding, we protect the quantum computer from
environment-induced decoherence that results in quantum information dissipating
into the environment. For the inherent qubit-qubit interaction that is
untunable in the quantum system, BB control plus DFSs encoding will eliminate
its undesired effect which spoils quantum information in qubits. We show how
this quantum system can be used to implement universal quantum computation.Comment: 6 pages,2 figures, 1 tabl
Dynamical signature of fractionalization at a deconfined quantum critical point
Deconfined quantum critical points govern continuous quantum phase transitions at which fractionalized (deconfined) degrees of freedom emerge. Here we study dynamical signatures of the fractionalized excitations in a quantum magnet (the easy-plane J-Q model) that realize a deconfined quantum critical point with emergent O(4) symmetry. By means of large-scale quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation functions, we obtain the dynamic spin-structure factors in the
S
x
and
S
z
channels. In both channels, we observe broad continua that originate from the deconfined excitations. We further identify several distinct spectral features of the deconfined quantum critical point, including the lower edge of the continuum and its form factor on moving through the Brillouin zone. We provide field-theoretical and lattice model calculations that explain the overall shapes of the computed spectra, which highlight the importance of interactions and gauge fluctuations to explain the spectral-weight distribution. We make further comparisons with the conventional Landau O(2) transition in a different quantum magnet, at which no signatures of fractionalization are observed. The distinctive spectral signatures of the deconfined quantum critical point suggest the feasibility of its experimental detection in neutron scattering and nuclear magnetic resonance experiments.First author draf
Calpain 1 Knockdown Improves Tissue Sparing and Functional Outcomes after Spinal Cord Injury in Rats
To evaluate the hypothesis that calpain 1 knockdown would reduce pathological damage and functional deficits after spinal cord injury (SCI), we developed lentiviral vectors encoding calpain 1 shRNA and eGFP as a reporter (LV-CAPN1 shRNA). The ability of LV-CAPN1 shRNA to knockdown calpain 1 was confirmed in rat NRK cells using Northern and Western blot analysis. To investigate the effects on spinal cord injury, LV-CAPN1shRNA or LV-mismatch control shRNA (LV-control shRNA) were administered by convection enhanced diffusion at spinal cord level T10 in Long-Evans female rats (200β250βg) 1 week before contusion SCI, 180 kdyn force, or sham surgery at the same thoracic level. Intraspinal administration of the lentiviral particles resulted in transgene expression, visualized by eGFP, in spinal tissue at 2 weeks after infection. Calpain 1 protein levels were reduced by 54% at T10 2 weeks after shRNA-mediated knockdown (p\u3c0.05, compared with the LV-control group, n=3 per group) while calpain 2 levels were unchanged. Intraspinal administration of LV-CAPN1shRNA 1 week before contusion SCI resulted in a significant improvement in locomotor function over 6 weeks postinjury, compared with LV-control administration (p\u3c0.05, n=10 per group). Histological analysis of spinal cord sections indicated that pre-injury intraspinal administration of LV-CAPN1shRNA significantly reduced spinal lesion volume and improved total tissue sparing, white matter sparing, and gray matter sparing (p\u3c0.05, n=10 per group). Together, results support the hypothesis that calpain 1 activation contributes to the tissue damage and impaired locomotor function after SCI, and that calpain1 represents a potential therapeutic target
Dependence of the decoherence of polarization states in phase-damping channels on the frequency spectrum envelope of photons
We consider the decoherence of photons suffering in phase-damping channels.
By exploring the evolutions of single-photon polarization states and two-photon
polarization-entangled states, we find that different frequency spectrum
envelopes of photons induce different decoherence processes. A white frequency
spectrum can lead the decoherence to an ideal Markovian process. Some color
frequency spectrums can induce asymptotical decoherence, while, some other
color frequency spectrums can make coherence vanish periodically with variable
revival amplitudes. These behaviors result from the non-Markovian effects on
the decoherence process, which may give rise to a revival of coherence after
complete decoherence.Comment: 7 pages, 4 figures, new results added, replaced by accepted versio
Tunneling conductance of graphene ferromagnet-insulator-superconductor junctions
We study the transport properties of a graphene ferromagnet-insulator
superconductor (FIS) junction within the Blonder-Tinkham-Klapwijk formalism by
solving spin-polarized Dirac-Bogoliubov-de-Gennes equation. We find that the
retro and specular Andreev reflections in the graphene FIS junction are
drastically modified in the presence of exchange interaction and that the
spin-polarization () of tunneling current can be tuned from the positive
to negative value by bias voltage (). In the thin-barrier limit, the
conductance of a graphene FIS junction oscillates as a function of barrier
strength . Both the amplitude and phase of the conductance oscillation
varies with the exchange energy . For (Fermi energy), the
amplitude of oscillation decreases with . For ,
the amplitude of oscillation increases with , where
( is the applied electrostatic potential on
the superconducting segment of the junction). For , the
amplitude of oscillation decreases with again. Interestingly, a
universal phase difference of in exists between the
curves for and . Finally, we find that the transitions
between retro and specular Andreev reflections occur at and
, and hence the singular behavior of the conductance near
these bias voltages results from the difference in transport properties between
specular and retro Andreev reflections.Comment: Accepted for publication in Physical Review
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