10 research outputs found
Variational Monte Carlo Study of a Spinless Fermion t-V Model on a Triangular Lattice: Formation of a Pinball Liquid
We analyze a model of spinless fermions on a triangular lattice at
half-filling interacting via strong nearest-neighbor repulsive interactions, V,
using the variational Monte Carlo simulation technique. The existence of
three-sublattice long-range order is confirmed by the finite-size scaling
analysis of the charge structural factor at V_c/t > 12. This ordered phase
shows characteristics expected for a so called "pinball liquid" state, which
has the spontaneous separation of fermionic degrees of freedom into coexisting
Wigner crystal-like charge order (pin) and a metal (ball). The pins are fixed
in order to maximize the kinetic energy gain of balls which move almost freely.
The Fermi surface is reconstructed at V=V_c and remains towards the strong
coupling limit. These features reminiscent of the strong correlation together
with the large value of V_c/t distinguishes the pinball liquid from the
conventional charge-density-wave.Comment: 7 pages, 7 figure
In Vitro Photodynamic Therapy with Chlorin e6 Leads to Apoptosis of Human Vascular Smooth Muscle Cells
Percutaneous coronary intervention has become the most common and widely implemented method of heart revascularization. However, the development of restenosis remains the major limitation of this method. Photodynamic therapy (PDT) recently emerged as a new and promising method for the prevention of arterial restenosis. Here the efficacy of chlorin e6 in PDT was investigated in vitro using human vascular smooth muscle cells (TG/HA-VSMCs) as one of the cell types crucial in the development of restenosis. PDT-induced cell death was studied on many levels, including annexin V staining, measurement of the generation reactive oxygen species (ROS) and caspase-3 activity, and assessment of changes in mitochondrial membrane potential and fragmentation of DNA. Photosensitization of TG/HA-VSMCs with a 170Â ÎŒM of chlorin e6 and subsequent illumination with the light of a 672-nm diode laser (2Â J/cm2) resulted in the generation of ROS, a decrease in cell membrane polarization, caspase-3 activation, as well as DNA fragmentation. Interestingly, the latter two apoptotic events could not be observed in photosensitized and illuminated NIH3T3 fibroblasts, suggesting different outcomes of the model of PDT in various types of cells. The results obtained with human VSMCs show that chlorin e6 may be useful in the PDT of aerial restenosis, but its efficacy still needs to be established in an animal model
Magnetic structures of Ce<SUB>2</SUB>Pd<SUB>1−x</SUB>Co<SUB>x</SUB>Si<SUB>3</SUB> (x=0.0, 0.2, 0.4, 0.6) compounds
Polycrystalline samples of Ce2Pd1−xCoxSi3 for x
equal to 0.0, 0.2, 0.4 and 0.6 have been studied by neutron diffraction. All these compounds exhibit a hexagonal crystal structure of
the AlB2-type. In Ce2PdSi3 below 3.5 K, features attributable to short-range
magnetic order are observed. The neutron diffraction patterns for the other compositions are typical of simple magnetic structures
described by an orthorhombic unit cell (a, √3, c).The magnetic moment at low temperatures equals
0.37(14)μB at 1.6 K for x=0.2, 1.27(5)μB at 1.6 K for x=0.4 and
0.55(8)μB at 1.85 K for x=0.6. The moments are parallel to the b-axis of the orthorhombic magnetic unit
cell
Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2
We report a high-resolution neutron diffraction study on the
orbitally-degenerate spin-1/2 hexagonal antiferromagnet AgNiO2. A structural
transition to a tripled unit cell with expanded and contracted NiO6 octahedra
indicates root(3) x root(3) charge order on the Ni triangular lattice. This
suggests charge order as a possible mechanism of lifting the orbital degeneracy
in the presence of charge fluctuations, as an alternative to Jahn-Teller
distortions. A novel magnetic ground state is observed at base temperatures
with the electron-rich S = 1 Ni sites arranged in alternating ferromagnetic
rows on a triangular lattice, surrounded by a honeycomb network of non-magnetic
and metallic Ni ions. We also report first-principles band-structure
calculations that explain microscopically the origin of these phenomena.Comment: 4 pages including 4 eps figures, improved Fig 4, to appear in
Physical Review Letter
Charge disproportionation and collinear magnetic order in the frustrated triangular antiferromagnet AgNiO2
We report a high-resolution neutron diffraction study of the crystal and
magnetic structure of the orbitally-degenerate frustrated metallic magnet
AgNiO2. At high temperatures the structure is hexagonal with a single
crystallographic Ni site, low-spin Ni3+ with spin-1/2 and two-fold orbital
degeneracy, arranged in an antiferromagnetic triangular lattice with frustrated
spin and orbital order. A structural transition occurs upon cooling below 365 K
to a tripled hexagonal unit cell containing three crystallographically-distinct
Ni sites with expanded and contracted NiO6 octahedra, naturally explained by
spontaneous charge order on the Ni triangular layers. No Jahn-Teller
distortions occur, suggesting that charge order occurs in order to lift the
orbital degeneracy. Symmetry analysis of the inferred Ni charge order pattern
and the observed oxygen displacement pattern suggests that the transition could
be mediated by charge fluctuations at the Ni sites coupled to a soft oxygen
optical phonon breathing mode. At low temperatures the electron-rich Ni
sublattice (assigned to a valence close to Ni2+ with S = 1) orders magnetically
into a collinear stripe structure of ferromagnetic rows ordered
antiferromagnetically in the triangular planes. We discuss the stability of
this uncommon spin order pattern in the context of an easy-axis triangular
antiferromagnet with additional weak second neighbor interactions and
interlayer couplings.Comment: 16 pages, 11 figures include