Origin of Large Dielectric Constant with Large Remnant Polarization and Evidence of Magnetoelectric Coupling in Multiferroic La modified BiFeO3-PbTiO3 Solid Solution

The presence of superlattice reflections and detailed analyses of the powder neutron and x-ray diffraction data reveal that La rich (BF$_{0.50}$-LF$_{0.50}$)$_{0.50}$-(PT)$_{0.50}$ (BF-LF-PT) has ferroelectric rhombohedral crystal structure with space group \textit{$R3c$} at ambient conditions. The temperature dependence of lattice parameters, tilt angle, calculated polarization $(P_{s})$, volume, and integrated intensity of superlattice and magnetic reflections show an anomaly around 170 K. Impedance spectroscopy, dielectric and ac conductivity measurements were performed in temperature range $473K \leq T \leq 573K$ to probe the origin of large remnant polarization and frequency dependent broad transitions with large dielectric constant near $T_c^{FE}$. Results of impedance spectroscopy measurements clearly show contributions of both grain and grain boundaries throughout the frequency range ($10^{3}$ Hz$\leq f\leq 10^{7}$ Hz). It could be concluded that the grain boundaries are more resistive and capacitive as compared to the grains, resulting in inhomogeneities in the sample causing broad frequency dependent dielectric anomalies. Enhancement in dielectric constant and remnant polarization values are possibly due to space charge polarization caused by piling of charges at the interface of grains and grain boundaries. The imaginary parts of dielectric constant ($\epsilon^{\prime\prime}$) Vs frequency data were fitted using Maxwell-Wagner model at $T_c^{FE}(\sim 523$K) and model fits very well with the data up to $10^{5}$ Hz. Magnetodielectric measurements prove that the sample starts exhibiting magnetoelectric coupling at $\sim 170$ K, which is also validated by neutron diffraction data.Comment: 20 pages, 10 figure

Self-bound many-body states of quasi-one-dimensional dipolar Fermi gases: Exploiting Bose-Fermi mappings for generalized contact interactions

Using a combination of results from exact mappings and from mean-field theory we explore the phase diagram of quasi-one-dimensional systems of identical fermions with attractive dipolar interactions. We demonstrate that at low density these systems provide a realization of a single-component one-dimensional Fermi gas with a generalized contact interaction. Using an exact duality between one-dimensional Fermi and Bose gases, we show that when the dipole moment is strong enough, bound many-body states exist, and we calculate the critical coupling strength for the emergence of these states. At higher densities, the Hartree-Fock approximation is accurate, and by combining the two approaches we determine the structure of the phase diagram. The many-body bound states should be accessible in future experiments with ultracold polar molecules

Knowledge based capital and value creation in global supply chains

This paper investigates the role of knowledge-based capital for participation and value appropriation in global value chains (GVC) for a sample of European countries over 1995\u20132011. We distinguish between different forms of participation in GVC entailing a different degree of capability to create value added domestically and examine how different intangible assets contribute to countries' engagement and value appropriation in GVC. We find that knowledge-based capital is positively correlated with participation and value appropriation along the value chain. This finding is robust to introducing separately R&D and non-R&D intangibles. In particular, training and organizational capital have the largest positive effect on value appropriation [JEL Classification: F23, O30]

Induced polarization at a paraelectric/superconducting interface

We examine the modified electronic states at the interface between superconducting and ferro(para)-electric heterostructures. We find that electric polarization $P$ and superconducting $\psi$ order parameters can be significantly modified due to coupling through linear terms brought about by explicit symmetry breaking at the interface. Using an effective action and a Ginzburg-Landau formalism, we show that an interaction term linear in the electric polarization will modify the superconducting order parameter $\psi$ at the interface. This also produces modulation of a ferroelectric polarization. It is shown that a paraelectric-superconductor interaction will produce an interface-induced ferroelectric polarization.Comment: 4 pages, 3 figures, Submitted to Phys. Rev.

Zener tunneling in two-dimensional photonic lattices

We discuss the interband light tunneling in a two-dimensional periodic photonic structure, as was studied recently in experiments for optically-induced photonic lattices [H. Trompeter et al., Phys. Rev. Lett. \textbf{96}, 053903 (2006)]. We identify the Zener tunneling regime at the crossing of two Bloch bands, which occurs in a generic case of the Bragg reflection when the Bloch index crosses the edge of the irreducible Brillouin zone. Similarly, the higher-order Zener tunneling involves four Bloch bands when the Bloch index passes through a high-symmetry point on the edge of the Brillouin zone. We derive simple analytical models that describe the tunneling effect, and calculate the corresponding tunneling probabilities.Comment: 6 pages, 6 figures, submitted to Phys Rev E; changes: band structure added (fig1) and the error estimates for the Landau-Zener model (fig 6

Chaotic properties of quantum many-body systems in the thermodynamic limit

By using numerical simulations, we investigate the dynamics of a quantum system of interacting bosons. We find an increase of properly defined mixing properties when the number of particles increases at constant density or the interaction strength drives the system away from integrability. A correspondence with the dynamical chaoticity of an associated $c$-number system is then used to infer properties of the quantum system in the thermodynamic limit.Comment: 4 pages RevTeX, 4 postscript figures included with psfig; Completely restructured version with new results on mixing properties added

Ideal barriers to polarization reversal and domain-wall motion in strained ferroelectric thin films

The ideal intrinsic barriers to domain switching in c-phase PbTiO_3 (PTO), PbZrO_3 (PZO), and PbZr_{1-x}Ti_xO_3 (PZT) are investigated via first-principles computational methods. The effects of epitaxial strain on the atomic structure, ferroelectric response, barrier to coherent domain reversal, domain-wall energy, and barrier to domain-wall translation are studied. It is found that PTO has a larger polarization, but smaller energy barrier to domain reversal, than PZO. Consequentially the idealized coercive field is over two times smaller in PTO than PZO. The Ti--O bond length is more sensitive to strain than the other bonds in the crystals. This results in the polarization and domain-wall energy in PTO having greater sensitivity to strain than in PZO. Two ordered phases of PZT are considered, the rock-salt structure and a (100) PTO/PZO superlattice. In these simple structures we find that the ferroelectric properties do not obey Vergard's law, but instead can be approximated as an average over individual 5-atom unit cells.Comment: 9 pages, 13 figure

Universal behavior at discontinuous quantum phase transitions

Discontinuous quantum phase transitions besides their general interest are clearly relevant to the study of heavy fermions and magnetic transition metal compounds. Recent results show that in many systems belonging to these classes of materials, the magnetic transition changes from second order to first order as they approach the quantum critical point (QCP). We investigate here some mechanisms that may be responsible for this change. Specifically the coupling of the order parameter to soft modes and the competition between different types of order near the QCP. For weak first order quantum phase transitions general results are obtained. In particular we describe the thermodynamic behavior at this transition when it is approached from finite temperatures. This is the discontinuous equivalent of the non-Fermi liquid trajectory close to a conventional QCP in a heavy fermion material.Comment: 7 pages, 3 figure