1,378 research outputs found
External Electric Field Mediated Quantum Phase Transitions in One-Dimensional Charge Ordered Insulators: A DMRG Study
We perform density matrix renormalization group (DMRG) calculations
extensively on one-dimensional chains with on site (U) as well as nearest
neighbour (V) Coulomb repulsions. The calculations are carried out in full
parameter space with explicit inclusion of the static bias and we compare the
nature of spin density wave (SDW) and charge density wave (CDW) insulators
under the influence of external electric field. We find that, although the SDW
(U>2V) and CDW (U<2V) insulators enter into a conducting state after a certain
threshold bias, CDW insulators require much higher bias than the SDW insulators
for insulator-metal transition at zero temperature. We also find the CDW-SDW
phase transition on application of external electric field. The bias required
for the transitions in both cases decreases with increase in system size.Comment: 7 pages, 7 figures, accepted in J. Phys.: Condens. Matte
Charge-transfer induced large nonlinear optical properties of small Al Clusters: Al4M4
We investigate the linear and nonlinear electric polarizabilities of small
Al4M4 (M=Li, Na and K) clusters. Quantum chemical calculations reveal that
these compounds exhibit an exceptionally high magnitude of linear and nonlinear
optical (NLO) coefficients which are orders of magnitude higher than the
conventional pi-conjugated systems of similar sizes. We attribute such
phenomenal increase to non-centrosymmetricity incorporated in the systems by
the alkali atoms surrounding the ring leading to charge transfer with small
optical gap and low bond length alternation (BLA). Such a low magnitude of the
BLA from a different origin, suggests the possibility that these clusters are
aromatic in character and along with the large NLO coefficients they appear to
be better candidates for next generation NLO fabrication devices
- …