31 research outputs found
Magnetic field effects and magnetic anisotropy in lightly doped La_{2-x}Sr_xCuO_4
The effects of the application of a magnetic field on the diagonal stripe
spin-glass phase is studied in lightly doped La_{2-x}Sr_xCuO_4 (x=0.014 and
0.024). With increasing magnetic field, the magnetic elastic intensity at the
diagonal incommensurate (DIC) positions (1,\pm\epsilon,0) decreases as opposed
to the increase seen in superconducting samples. This diminution in intensity
with increasing magnetic field originates from a spin reorientation transition,
which is driven by the antisymmetric exchange term in the spin Hamiltonian. On
the other hand, the transition temperature, the incommensurability, and the
peak width of the diagonal incommensurate correlations are not changed with
magnetic field. This result suggests that the magnetic correlations are
determined primarily by the charge disproportionation and that the geometry of
the diagonal incommensurate magnetism is also determined by effects, that is,
stripe formation which are not purely magnetic in origin. The
Dzyaloshinskii-Moriya antisymmetric exchange is nevertheless important in
determining the local spin structure in the DIC stripe phase.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
QED3 theory of underdoped high temperature superconductors
Low-energy theory of d-wave quasiparticles coupled to fluctuating vortex
loops that describes the loss of phase coherence in a two dimensional d-wave
superconductor at T=0 is derived. The theory has the form of 2+1 dimensional
quantum electrodynamics (QED3), and is proposed as an effective description of
the T=0 superconductor-insulator transition in underdoped cuprates. The
coupling constant ("charge") in this theory is proportional to the dual order
parameter of the XY model, which is assumed to be describing the quantum
fluctuations of the phase of the superconducting order parameter. The principal
result is that the destruction of phase coherence in d-wave superconductors
typically, and immediately, leads to antiferromagnetism. The transition can be
understood in terms of the spontaneous breaking of an approximate "chiral"
SU(2) symmetry, which may be discerned at low enough energies in the standard
d-wave superconductor. The mechanism of the symmetry breaking is analogous to
the dynamical mass generation in the QED3, with the "mass" here being
proportional to staggered magnetization. Other insulating phases that break
chiral symmetry include the translationally invariant "d+ip" and "d+is"
insulators, and various one dimensional charge-density and spin-density waves.
The theory offers an explanation for the rounded d-wave-like dispersion seen in
ARPES experiments on Ca2CuO2Cl2 (F. Ronning et. al., Science 282, 2067 (1998)).Comment: Revtex, 20 pages, 5 figures; this is a much extended follow-up to the
Phys. Rev. Lett. vol.88, 047006 (2002) (cond-mat/0110188); improved
presentation, many additional explanations, comments, and references added,
sec. IV rewritten. Final version, to appear in Phys. Rev.
Strategies for Controlled Placement of Nanoscale Building Blocks
The capability of placing individual nanoscale building blocks on exact substrate locations in a controlled manner is one of the key requirements to realize future electronic, optical, and magnetic devices and sensors that are composed of such blocks. This article reviews some important advances in the strategies for controlled placement of nanoscale building blocks. In particular, we will overview template assisted placement that utilizes physical, molecular, or electrostatic templates, DNA-programmed assembly, placement using dielectrophoresis, approaches for non-close-packed assembly of spherical particles, and recent development of focused placement schemes including electrostatic funneling, focused placement via molecular gradient patterns, electrodynamic focusing of charged aerosols, and others
Growth of Candida guilliermondii FTI 20037 on mixed substrate
Candida guilliermondii FTI 20037 was grown on a mixed substrate comprising glucose and xylose. Inocula were grown using xylose or glucose as carbon source. Results showed that xylose utilization was delayed until glucose was utilized. Inoculum prepared on glucose showed a lag phase in xylose consumption. Cell mass production was higher when glucose was utilized during fermentation
CO Line emission surfaces and vertical structure in midinclination protoplanetary disks
Stars and planetary system
Combining TMS and EEG to study cognitive function and cortico-cortico interactions
There has long been an interest in exploring the functional dynamics of the brain's connectivity during cognitive processing, and some recent methodological developments now allow us to test important long-standing hypotheses. This review focuses on the recent development of combined online transcranial magnetic stimulation and electroencephalography (TMS–EEG) and on new studies that have employed this combination to study causal interactions between neural areas involved in perception and cognition