948 research outputs found
Electrical 2-omega-cm 0.046-cm-thick silicon solar cells as a function of intensity and temperature
Electrical characteristics of Mariner '71 type silicon solar cells are presented in graphical and tabular format as a function of intensity and temperature
Magnon Dispersion and Anisotropies in SrCu(BO)
We study the dispersion of the magnons (triplet states) in
SrCu(BO) including all symmetry-allowed Dzyaloshinskii-Moriya
interactions. We can reduce the complexity of the general Hamiltonian to a new
simpler form by appropriate rotations of the spin operators. The resulting
Hamiltonian is studied by both perturbation theory and exact numerical
diagonalization on a 32-site cluster. We argue that the dispersion is dominated
by Dzyaloshinskii-Moriya interactions. We point out which combinations of these
anisotropies affect the dispersion to linear-order, and extract their
magnitudes.Comment: 11 pages, 7 figures, 1 table, v2 conclusion shortened, figs clarifie
Triplon mean-field analysis of an antiferromagnet with degenerate Shastry-Sutherland ground states
We look into the quantum phase diagram of a spin-
antiferromagnet on the square lattice with degenerate Shastry-Sutherland ground
states, for which only a schematic phase diagram is known so far. Many exotic
phases were proposed in the schematic phase diagram by the use of exact
diagonalization on very small system sizes. In our present work, an important
extension of this antiferromagnet is introduced and investigated in the
thermodynamic limit using triplon mean-field theory. Remarkably, this
antiferromagnet shows a stable plaquette spin-gapped phase like the original
Shastry-Sutherland antiferromagnet, although both of these antiferromagnets
differ in the Hamiltonian construction and ground state degeneracy. We propose
a sublattice columnar dimer phase which is stabilized by the second and third
neighbor antiferromagnetic Heisenberg exchange interactions. There are also
some commensurate and incommensurate magnetically ordered phases, and other
spin-gapped phases which find their places in the quantum phase diagram.
Mean-field results suggest that there is always a level-crossing phase
transition between two spin gapped phases, whereas in other situations, either
a level-crossing or a continuous phase transition happens
Field-Induced Effects of Anisotropic Magnetic Interactions in SrCu2(BO3)2
We observed a field-induced staggered magnetization in the 2D frustrated
dimer-singlet spin system SrCu2(BO3)2 by 11B NMR, from which the magnitudes of
the intradimer Dzyaloshinsky-Moriya interaction and the staggered g-tensor were
determined. These anisotropic interactions cause singlet-triplet mixing and
eliminate a quantum phase transition at the expected critical field Hc for gap
closing. They also provide a quantitative account for some puzzling phenomena
such as the onset of a uniform magnetization below the and the persistence of
the excitation gap above Hc. The gap was accurately determined from the
activation energy of the nuclear relaxation rate.Comment: 8 pages, 5 figures, published versio
Magnetic Superstructure in the Two-Dimensional Quantum Antiferromagnet SrCu2(BO3)2
We report the observation of magnetic superstructure in a magnetization
plateau state of SrCu2(BO3)2, a frustrated quasi-two-dimensional quantum spin
system. The Cu and B nuclear magnetic resonance (NMR) spectra at 35 mllikelvin
indicate an apparently discontinuous phase transition from uniform
magnetization to a modulated superstructure near 27 tesla, above which a
magnetization plateau at 1/8 of the full saturation has been observed.
Comparison of the Cu NMR spectrum and the theoretical analysis of a Heisenberg
spin model demonstrates the crystallization of itinerant triplets in the
plateau phase within a large rhomboid unit cell (16 spins per layer) showing
oscillations of the spin polarization. Thus we are now in possession of an
interesting model system to study a localization transition of strongly
interacting quantum particles.Comment: PDF file, 16 pages, 5 figure
Unconventional magnetization plateaus in a Shastry-Sutherland spin tube
Using density matrix renormalization group (DMRG) and perturbative continuous
unitary transformations (PCUTs), we study the magnetization process in a
magnetic field for all coupling strengths of a quasi-1D version of the 2D
Shastry-Sutherland lattice, a frustrated spin tube made of two orthogonal dimer
chains. At small inter-dimer coupling, plateaus in the magnetization appear at
1/6, 1/4, 1/3, 3/8, and 1/2. As in 2D, they correspond to a Wigner crystal of
triplons. However, close to the boundary of the product singlet phase, plateaus
of a new type appear at 1/5 and 3/4. They are stabilized by the localization of
{\it bound states} of triplons. Their magnetization profile differs
significantly from that of single triplon plateaus and leads to specific NMR
signatures. We address the possibility to stabilize such plateaus in further
geometries by analyzing small finite clusters using exact diagonalizations and
the PCUTs.Comment: Final version as published in EP
Magnetization plateaus of SrCu_2(BO_3)_2 from a Chern-Simons theory
The antiferromagnetic Heisenberg model on the frustrated Shastry-Sutherland
lattice is studied by a mapping onto spinless fermions carrying one quantum of
statistical flux. Using a mean-field approximation these fermions populate the
bands of a generalized Hofstadter problem. Their filling leads to the
magnetization curve. For SrCu_2(BO_3)_2 we reproduce plateaus at 1/3 and 1/4 of
the saturation moment and predict a new one at 1/2. Gaussian fluctuations are
shown to be massive at these plateau values.Comment: 4 pages, 5 figure
Field Induced Staggered Magnetization and Magnetic Ordering in
We present a D NMR investigation of the gapped spin-1/2 compound . Our measurements reveal the presence of a magnetic
field induced transverse staggered magnetization (TSM) which persists well
below and above the field-induced 3D long-range magnetically ordered (FIMO)
phase. The symmetry of this TSM is different from that of the TSM induced by
the order parameter of the FIMO phase. Its origin, field dependence and
symmetry can be explained by an intra-dimer Dzyaloshinskii-Moriya interaction,
as shown by DMRG calculations on a spin-1/2 ladder. This leads us to predict
that the transition into the FIMO phase is not in the BEC universality class.Comment: 4 page
Magnetization plateaux in the classical Shastry-Sutherland lattice
We investigated the classical Shastry-Sutherland lattice under an external
magnetic field in order to understand the recently discovered magnetization
plateaux in the rare-earth tetraborides compounds RB. A detailed study of
the role of thermal fluctuations was carried out by mean of classical spin
waves theory and Monte-Carlo simulations. Magnetization quasi-plateaux were
observed at 1/3 of the saturation magnetization at non zero temperature. We
showed that the existence of these quasi-plateaux is due to an entropic
selection of a particular collinear state. We also obtained a phase diagram
that shows the domains of existence of different spin configurations in the
magnetic field versus temperature plane.Comment: 4 pages, proceedings of HFM200
Magnetization plateaux in an extended Shastry-Sutherland model
We study an extended two-dimensional Shastry-Sutherland model in a magnetic
field where besides the usual Heisenberg exchanges of the Shastry-Sutherland
model two additional SU(2) invariant couplings are included. Perturbative
continous unitary transformations are used to determine the leading order
effects of the additional couplings on the pure hopping and on the long-range
interactions between the triplons which are the most relevant terms for small
magnetization. We then compare the energy of various magnetization plateaux in
the classical limit and we discuss the implications for the two-dimensional
quantum magnet SrCu(BO).Comment: 8 pages, Proceedings of the HFM2008 Conferenc
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