1,004 research outputs found
Co-operative density wave and giant spin gap in the quarter-filled zigzag ladder
Strong co-operative interactions occur between four different broken
symmetries involving charge-ordering and bond distortions in the quarter-filled
correlated zigzag electron ladder. The ground state is singlet, with spin gap
several times larger than in the spin-Peierls state of the one-dimensional
quarter-filled chain with the same parameters. We propose the quarter-filled
zigzag electron ladder model for several different organic charge-transfer
solids with coupled pairs of quasi-one-dimensional stacks, the spin-gap
transition temperatures in which are unusually high.Comment: 4 pages, 4 EPS figures. accepted in Physical Review Letter
Dimerization-induced enhancement of the spin gap in the quarter-filled two-leg rectangular ladder
We report density-matrix renormalization group calculations of spin gaps in
the quarter-filled correlated two-leg rectangular ladder with bond-dimerization
along the legs of the ladder. In the small rung-coupling region, dimerization
along the leg bonds can lead to large enhancement of the spin gap.
Electron-electron interactions further enhance the spin gap, which is nonzero
for all values of the rung electron hopping and for arbitrarily small
bond-dimerization. Very large spin gaps, as are found experimentally in
quarter-filled band organic charge-transfer solids with coupled pairs of
quasi-one-dimensional stacks, however, occur within the model only for large
dimerization and rung electron hopping that are nearly equal to the hopping
along the legs. Coexistence of charge order and spin gap is also possible
within the model for not too large intersite Coulomb interaction
Finite-Field Ground State of the S=1 Antiferromagnetic-Ferromagnetic Bond-Alternating Chain
We investigate the finite-field ground state of the S=1
antiferromagnetic-ferromagnetic bond-alternating chain described by the
Hamiltonian
{\calH}=\sum\nolimits_{\ell}\bigl\{\vecS_{2\ell-1}\cdot\vecS_{2\ell}
+J\vecS_{2\ell}\cdot\vecS_{2\ell+1}\bigr\} +D\sum\nolimits_{\ell}
\bigl(S_{\ell}^z)^2 -H\textstyle\sum\nolimits_\ell S_\ell^z, where
\hbox{} and \hbox{}. We find that two kinds of
magnetization plateaux at a half of the saturation magnetization, the
1/2-plateaux, appear in the ground-state magnetization curve; one of them is of
the Haldane type and the other is of the large--type. We determine the
1/2-plateau phase diagram on the versus plane, applying the
twisted-boundary-condition level spectroscopy methods developed by Kitazawa and
Nomura. We also calculate the ground-state magnetization curves and the
magnetization phase diagrams by means of the density-matrix
renormalization-group method
Spin and chiral orderings of frustrated quantum spin chains
Ordering of frustrated S=1/2 and 1 XY and Heisenberg spin chains with the
competing nearest- and next-nearest-neighbor antiferromagnetic couplings is
studied by exact diagonalization and density-matrix renormalization-group
methods. It is found that the S=1 XY chain exhibits both gapless and gapped
`chiral' phases characterized by the spontaneous breaking of parity, in which
the long-range order parameter is a chirality, , whereas the spin correlation decays either
algebraically or exponentially. Such chiral phases are not realized in the
S=1/2 XY chain nor in the Heisenberg chains.Comment: 4 pages, 5 EPS-figures, LaTeX(RevTeX),to appear in J.Phys.Soc.Japa
Antigen recognition by human γδ T cells: one step closer to knowing
Sensing of self and non‐self phosphoantigens by human Vγ9/Vδ2 T cells in the context of the butyrophilin family members BTN2A1 and BTN3A1
Ground State Property of an Alternating Spin Ladder Involving Two Kinds of Inter-Chain Interactions
The ground state property of the alternating spin ladder is studied in the
case that the system involves an antiferromagnetic intra-chain interaction as
well as two kinds of inter-chain interactions; one is between spins of the same
magnitude and the other is between spins with different magnitudes. The
calculation has been carried out by the exact diagonalization method. As a
consequence of the competition among interactions, the system is revealed to
show an interesting variety of phases in the ground state property. Its phase
diagram is exhibited in the parameter space of the system. We find that,
however small the total amount of the inter-chain interactions is, the
ferrimagnetic ground state becomes unstable in a certain region. In this case,
which of the ferrimagnetic and the singlet ground state to appear is determined
only by the ratio between the inter-chain interactions regardless of their
total amount. The nature of two phases appearing in the singlet region of the
phase diagram and the type of the phase transition between them are also
discussed. The results are ensured by comparing with those of obtained in other
models which are contained in our model as special limiting cases.Comment: 12 pages, 9 PostScript figure
Rehebbilitating Memory
Amnesia is a deficit of memory function that can result from trauma, stress, disease, drug use, or ageing. Though efforts are made to prevent and treat the various causes of amnesia, there remains no treatment for the symptom of memory loss itself. Because the defining feature of amnesia is an inability recall memory, any given case may be due to the possibility that the
memory is damaged, or the alternative that it is present but irretrievable (Squire, 1982). Discriminating between these two scenarios would be of scientific value, because the neurobiology of memory formation is anchored in experimental amnesia. Pathological cases of amnesia that are due to retrieval deficits may in principal be treatable rather than merely preventable. Amnesia could be attributed to a retrieval deficit if the ostensible ‘lost’ memory could be evoked through brain stimulation. The challenge here is to identify exactly where in the brain a particular memory is stored.JPB FoundationRIKEN Brain Science Institut
Magnetic phase diagram of the S=1/2 antiferromagnetic zigzag spin chain in the strongly frustrated region: cusp and plateau
We determine the magnetic phase diagram of the antiferromagnetic(AF) zigzag
spin chain in the strongly frustrated region, using the density matrix
renormalization group method. We find the magnetization plateau at 1/3 of the
full moment accompanying the spontaneous symmetry breaking of the translation,
the cusp singularities above and/or below the plateau, and the even-odd effect
in the magnetization curve. We also discuss the formation mechanisms of the
plateau and cusps briefly.Comment: 4 pages, 8 figures, revised version, to appear in J.Phys.Soc.Jp
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