Chain metallicity and antiferro-paramagnetism competition in underdoped YBa2_2Cu3_3O6+x_{6+x}: a first principles description

We describe from advanced first principles calculations the energetics of oxygen doping and its relation to insulator-metal transitions in underdoped YBa$_2$Cu$_3$O$_{6+x}$. We find a strong tendency of doping oxygens to order into non-magnetic Cu$^{1+}$O$_x$ chains at any $x$. Ordering produces one-dimensional metallic bands, while configurations with non-aligned oxygens are insulating. The Cu$^{2+}$O$_2$ planes remain insulating and antiferromagnetic up to a threshold between $x$=0.25 and 0.5, above which a paramagnetic normal-metal state prevails. The in-plane antiferro-paramagnetic competition depends on $x$, but only weakly on the ordering state of the chains.Comment: 4 pages, 6 figures, 2 table

Fractional Quantum Mechanics

A path integral approach to quantum physics has been developed. Fractional path integrals over the paths of the L\'evy flights are defined. It is shown that if the fractality of the Brownian trajectories leads to standard quantum and statistical mechanics, then the fractality of the L\'evy paths leads to fractional quantum mechanics and fractional statistical mechanics. The fractional quantum and statistical mechanics have been developed via our fractional path integral approach. A fractional generalization of the Schr\"odinger equation has been found. A relationship between the energy and the momentum of the nonrelativistic quantum-mechanical particle has been established. The equation for the fractional plane wave function has been obtained. We have derived a free particle quantum-mechanical kernel using Fox's H function. A fractional generalization of the Heisenberg uncertainty relation has been established. Fractional statistical mechanics has been developed via the path integral approach. A fractional generalization of the motion equation for the density matrix has been found. The density matrix of a free particle has been expressed in terms of the Fox's H function. We also discuss the relationships between fractional and the well-known Feynman path integral approaches to quantum and statistical mechanics.Comment: 27 page

Density functional theory based screening of ternary alkali-transition metal borohydrides: A computational material design project

The dissociation of molecules, even the most simple hydrogen molecule, cannot be described accurately within density functional theory because none of the currently available functionals accounts for strong on-site correlation. This problem led to a discussion of properties that the local Kohn-Sham potential has to satisfy in order to correctly describe strongly correlated systems. We derive an analytic expression for the nontrivial form of the Kohn-Sham potential in between the two fragments for the dissociation of a single bond. We show that the numerical calculations for a one-dimensional two-electron model system indeed approach and reach this limit. It is shown that the functional form of the potential is universal, i.e., independent of the details of the two fragments.We acknowledge funding by the Spanish MEC (Grant No. FIS2007-65702-C02-01), “Grupos Consolidados UPV/EHU del Gobierno Vasco” (Grant No. IT-319-07), and the European Community through e-I3 ETSF project (Grant Agreement No. 211956).Peer reviewe

First-principles calculation of electronic and structural properties of YBa2Cu3O6+y

The normal state of the prototypical high-T-c superconductor YBa2Cu3O6+y is described via advanced ab initio band-theory techniques suited for strongly correlated materials. We describe the system at generic oxygen doping y between the Mott-insulating limit (y=0) and the optimally doped Fermi liquid (y=1), exploring the metal-insulating transitions related to the paramagnetic-antiferromagnetic competition in the CuO2 planes, and to the order-disorder competition in the CuOy chains. Our study demonstrates the usefulness of ab initio calculations based on density-functional theory, when suitably adapted to strongly correlated systems, to describe doped cuprates

Managing and transforming policy stigmas in international finance: Emerging markets and controlling capital inflows after the crisis

The past three decades have shown the increasing importance of the efforts of the international financial community to socialize emerging markets to accept norms of financial governance. Social sanctions often have been used to mark non-compliant states and their policies as deviant. Yet, we know little about how deviant states strategically manage such policy stigmas in international finance and how this management shapes the international normative order. Recent scholarship in international relations suggests that stigma management strategies tend to either reinforce or fracture the international normative order. This article, by contrast, contends that such strategies also have the potential to transform the international normative order so that it resembles more closely the preferences of the deviant. This argument is illustrated using evidence drawn from Brazil and South Korea's management of the policy stigma associated with controls on capital inflows