Ferroelectricity driven by the non-centrosymmetric magnetic ordering in multiferroic TbMn_2O_5: a first-principles study

The ground state structural, electronic and magnetic properties of multiferroic TbMn$_2$O$_5$ are investigated via first-principles calculations. We show that the ferroelectricity in TbMn$_2$O$_5$ is driven by the non-centrosymmetric magnetic ordering, without invoking the spin-orbit coupling and non-collinear spins. The {\it intrinsic} electric polarization in this compound is calculated to be 1187 $nC\cdot$ cm$^{-2}$, an order of magnitude larger than previously thought

Public pension and household saving: Evidence from China

We relate household saving to pension reform, to explain the high household saving rates in urban China from a new perspective. We use the exogenous – policy induced - variation in pension wealth to explicitly estimate the impact of pension wealth on household saving, and obtain a significant offset effect of pension wealth on household saving. Our estima-tions show that pension reform boosted the household saving rate in 1999 by about 6 per-centage points for cohort aged 25-29 and by about 3 percentage points for cohort aged 50-59. Our results also indicate that declining pension wealth reduces expenditure on educa-tion and health more than on other consumption items.pensions; pension reform; household savings rate; China

Asymmetry in self-assembled quantum dot-molecules made of identical InAs/GaAs quantum dots

We show that a diatomic dot molecule made of two identical, vertically stacked, strained InAs/GaAs self-assembled dots exhibits an asymmetry in its single-particle and may-particle wavefunctions. The single-particle wave function is asymmetric due to the inhomogeneous strain, while the asymmetry of the many-particle wavefunctions is caused by the correlation induced localization: the lowest singlet $^1\Sigma_g$ and triplet $^3\Sigma$ states show that the two electrons are each localized on different dots within the molecule, for the next singlet states $^1\Sigma_u$ both electrons are localized on the same (bottom) dot for interdot separation $d>$ 8 nm. The singlet-triplet splitting is found to be $\sim 0.1$ meV at inter-dot separation $d$=9 nm and as large as 100 meV for $d$=4 nm, orders of magnitude larger than the few meV found in the large (50 - 100 nm) electrostatically confined dots