1,897 research outputs found
3:1 magnetization plateau and suppression of ferroelectric polarization in an Ising chain multiferroic
Ferroelectric Ising chain magnet CaCoMnO (0.96)
was studied in magnetic fields up to 33 T. Magnetization and neutron scattering
measurements reveal successive metamagnetic transitions from the zero-field
spin configuration to the state with a broad magnetization plateau, and
then to the state. The absence of
hysteresis in these plateaus reveals an intriguing coupling between the
intra-chain state and the three-dimensional geometrically frustrated magnetic
system. Inversion symmetry, broken in the state, is restored in the
state, leading to the complete suppression of the electric polarization driven
by symmetric superexchange.Comment: accepted for publication as a Brief Report in Physical Review
Melting of Quasi-Two-Dimensional Charge Stripes in La5/3Sr1/3NiO4
Commensurability effects for nickelates have been studied by the first
neutron experiments on La5/3Sr1/3NiO4. Upon cooling, this system undergoes
three successive phase transitions associated with quasi-two-dimensional (2D)
commensurate charge and spin stripe ordering in the NiO planes. The two
lower temperature phases (denoted as phase II and III) are stripe lattice
states with quasi-long-range in-plane charge correlation. When the lattice of
2D charge stripes melts, it goes through an intermediate glass state (phase I)
before becoming a disordered liquid state. This glass state shows short-range
charge order without spin order, and may be called a "stripe glass" which
resembles the hexatic/nematic state in 2D melting.Comment: 10 pages, RevTex, 4 figures available on request to
[email protected]
Charge Ordering Fluctuation and Optical Pseudogap in LaCaMnO
Optical spectroscopy was used to investigate the optical gap (2) due
to charge ordering (CO) and related pseudogap developments with x and
temperature (T) in LaCaMnO (0.48 <= x <= 0.67).
Surprisingly, we found 2/k_{B}T_{CO} is as large as 30 for x ~0.5, and
decreases rapidly with increasing x. Simultaneously, the optical pseudogap,
possibly starting from T^* far above T_{CO} becomes drastically enhanced near
x=0.5, producing non-BCS T-dependence of 2 with the large magnitude
far above T_{CO}, and systematic increase of T^* for x~0.5. These results
unequivocally indicate systematically-enhanced CO correlation when x approaches
0.5 even though T_{CO} decreases.Comment: 5 pages, 4 figures embedded, submitted to Phys. Rev. Let
Fabrication and Characterization of Topological Insulator BiSe Nanocrystals
In the recently discovered class of materials known as topological
insulators, the presence of strong spin-orbit coupling causes certain
topological invariants in the bulk to differ from their values in vacuum. The
sudden change of invariants at the interface results in metallic, time reversal
invariant surface states whose properties are useful for applications in
spintronics and quantum computation. However, a key challenge is to fabricate
these materials on the nanoscale appropriate for devices and probing the
surface. To this end we have produced 2 nm thick nanocrystals of the
topological insulator BiSe via mechanical exfoliation. For crystals
thinner than 10 nm we observe the emergence of an additional mode in the Raman
spectrum. The emergent mode intensity together with the other results presented
here provide a recipe for production and thickness characterization of
BiSe nanocrystals.Comment: 4 pages, 3 figures (accepted for publication in Applied Physics
Letters
Quantum secure direct communication network with superdense coding and decoy photons
A quantum secure direct communication network scheme is proposed with quantum
superdense coding and decoy photons. The servers on a passive optical network
prepare and measure the quantum signal, i.e., a sequence of the -dimensional
Bell states. After confirming the security of the photons received from the
receiver, the sender codes his secret message on them directly. For preventing
a dishonest server from eavesdropping, some decoy photons prepared by measuring
one photon in the Bell states are used to replace some original photons. One of
the users on the network can communicate any other one. This scheme has the
advantage of high capacity, and it is more convenient than others as only a
sequence of photons is transmitted in quantum line.Comment: 6 pages, 2 figur
Freezing of a Stripe Liquid
The existence of a stripe-liquid phase in a layered nickelate,
La(1.725)Sr(0.275)NiO(4), is demonstrated through neutron scattering
measurements. We show that incommensurate magnetic fluctuations evolve
continuously through the charge-ordering temperature, although an abrupt
decrease in the effective damping energy is observed on cooling through the
transition. The energy and momentum dependence of the magnetic scattering are
parametrized with a damped-harmonic-oscillator model describing overdamped
spin-waves in the antiferromagnetic domains defined instantaneously by charge
stripes.Comment: 4 2-col pages, including 5 figures; Final version, to be published in
PR
Spin-phonon interactions and magnetoelectric coupling in CoO ( = Nb, Ta)
In order to explore the consequences of spin-orbit coupling on spin-phonon
interactions in a set of chemically-similar mixed metal oxides, we measured the
infrared vibrational properties of CoO ( = Nb, Ta) as a function
of temperature and compared our findings with lattice dynamics calculations and
several different models of spin-phonon coupling. Frequency vs. temperature
trends for the Co shearing mode near 150 cm reveal significant
shifts across the magnetic ordering temperature that are especially large in
relative terms. Bringing these results together and accounting for
noncollinearity, we obtain spin-phonon coupling constants of -3.4 and -4.3
cm for CoNbO and the Ta analog, respectively. Analysis
reveals that these coupling constants derive from interlayer (rather than
intralayer) exchange interactions and that the interlayer interactions contain
competing antiferromagnetic and ferromagnetic contributions. At the same time,
beyond-Heisenberg terms are minimized due to fortuitous symmetry
considerations, different than most other 4- and 5-containing oxides.
Comparison with other contemporary oxides shows that spin-phonon coupling in
this family of materials is among the strongest ever reported, suggesting an
origin for magnetoelectric coupling
Local spin resonance and spin-Peierls-like phase transition in a geometrically frustrated antiferromagnet
Using inelastic magnetic neutron scattering we have discovered a localized
spin resonance at 4.5 meV in the ordered phase of the geometrically frustrated
cubic antiferromagnet . The resonance develops abruptly from
quantum critical fluctuations upon cooling through a first order transition to
a co-planar antiferromagnet at K. We argue that this transition
is a three dimensional analogue of the spin-Peierls transition.Comment: 4 figures, revised and accepted in Phys. Rev. Let
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