Nonequilibrium electron spin polarization in a double quantum dot. Lande mechanism

In moderately strong magnetic fields, the difference in Lande g-factors in each of the dots of a coupled double quantum dot device may induce oscillations between singlet and triplet states of the entangled electron pair and lead to a nonequilibrium electron spin polarization. We will show that this polarization may partially survive the rapid inhomogeneous decoherence due to random nuclear magnetic fields.Comment: New version contains figures. New title better reflects the content of the pape

Novel Nonreciprocal Acoustic Effects in Antiferromagnets

The possible occurrence of nonreciprocal acoustic effects in antiferromagnets in the absence of an external magnetic field is investigated using both (i) a microscopic formulation of the magnetoelastic interaction between spins and phonons and (ii) symmetry arguments. We predict for certain antiferromagnets the existence of two new nonreciprocal (non-time invariant) effects: A boundary-condition induced nonreciprocal effect and the occurrence of transversal phonon modes propagating in opposite directions having different velocities. Estimates are given and possible materials for these effects to be observed are suggested.Comment: Euro. Phys. Lett. (in press

A Logic of Blockchain Updates

Blockchains are distributed data structures that are used to achieve consensus in systems for cryptocurrencies (like Bitcoin) or smart contracts (like Ethereum). Although blockchains gained a lot of popularity recently, there is no logic-based model for blockchains available. We introduce BCL, a dynamic logic to reason about blockchain updates, and show that BCL is sound and complete with respect to a simple blockchain model

Yield Curve Shapes and the Asymptotic Short Rate Distribution in Affine One-Factor Models

We consider a model for interest rates, where the short rate is given by a time-homogenous, one-dimensional affine process in the sense of Duffie, Filipovic and Schachermayer. We show that in such a model yield curves can only be normal, inverse or humped (i.e. endowed with a single local maximum). Each case can be characterized by simple conditions on the present short rate. We give conditions under which the short rate process will converge to a limit distribution and describe the limit distribution in terms of its cumulant generating function. We apply our results to the Vasicek model, the CIR model, a CIR model with added jumps and a model of Ornstein-Uhlenbeck type

Enhanced external radiative efficiency for 20.8 efficient single-junction GaInP solar cells

We demonstrate 1.81 eV GaInP solar cells approaching the Shockley-Queisser limit with 20.8% solar conversion efficiency, 8% external radiative efficiency, and 80–90% internal radiative efficiency at one-sun AM1.5 global conditions. Optically enhanced voltage through photon recycling that improves light extraction was achieved using a back metal reflector. This optical enhancement was realized at one-sun currents when the non-radiative Sah-Noyce-Shockley junction recombination current was reduced by placing the junction at the back of the cell in a higher band gap AlGaInP layer. Electroluminescence and dark current-voltage measurements show the separate effects of optical management and non-radiative dark current reduction

Zn(O, S) layers for chalcoyprite solar cells sputtered from a single target

A simplified Cu(In, Ga)(S, Se)2/Zn(O, S)/ZnO:Al stack for chalcopyrite thin- film solar cells is proposed. In this stack the Zn(O, S) layer combines the roles of the traditional CdS buffer and undoped ZnO layers. It will be shown that Zn(O, S) films can be sputtered in argon atmosphere from a single mixed target without substrate heating. The photovoltaic performance of the simplified stack matches that of the conventional approach. Replacing the ZnO target with a ZnO/ZnS target may therefore be sufficient to omit the CdS buffer layer and avoid the associated complexity, safety and recycling issues, and to lower production cost

Anisotropic spin freezing in the S=1/2 zigzag ladder compound SrCuO2

Using magnetic neutron scattering we characterize an unusual low temperature phase in orthorhombic SrCuO2. The material contains zigzag spin ladders formed by pairs of S=1/2 chains (J=180 meV) coupled through a weak frustrated interaction |J'|<0.1J. At T<Tc1=5.0(4)K an elastic peak develops in a gapless magnetic excitation spectrum indicating spin freezing on a time scale larger than 200 picoseconds. While the frozen state has long range commensurate antiferromagnetic order along the chains with the correlation length exceeding 200 lattice periods along the c-axis and a substantial correlation length of 60(25) spacings along the a-axis perpendicular to the zigzag plane, only 2 lattice units are correlated along the b-axis which is the direction of the frustrated interactions. The frozen magnetic moment of each Cu ion is very small, 0.033(7) Bohr magneton even at T=0.35K, and has unusual temperature dependence with a cusp at Tc2=1.5K reminiscent of a phase transition. We argue that slow dynamics of stripe-like cooperative magnetic defects in tetragonal a-c planes yield this anisotropic frozen state.Comment: 4 pages, LaTeX, submitted to PR

The Cosmic Battery and the Inner Edge of the Accretion Disk

The Poynting-Robertson Cosmic Battery proposes that the innermost part of the accretion disk around a black hole is threaded by a large scale dipolar magnetic field generated in situ, and that the return part of the field diffuses outward through the accretion disk. This is different from the scenario that the field originates at large distances and is carried inward by the accretion flow. In view of the importance of large scale magnetic fields in regulating the processes of accretion and outflows, we study the stability of the inner edge of a magnetized disk in general relativity when the distribution of the magnetic field is the one predicted by the Poynting-Robertson Cosmic Battery. We found that as the field grows, the inner edge of the disk gradually moves outward. In a fast spinning black hole with a>0.8M the inner edge moves back in towards the black hole horizon as the field grows beyond some threshold value. In all cases, the inner part of the disk undergoes a dramatic structural change as the field approaches equipartition.Comment: 7 pages, 3 figures, accepted for publication in Monthly Notices of the RA

Single parameter scaling in one-dimensional localization revisited

The variance of the Lyapunov exponent is calculated exactly in the one-dimensional Anderson model with random site energies distributed according to the Cauchy distribution. We find a new significant scaling parameter in the system, and derive an exact analytical criterion for single parameter scaling which differs from the commonly used condition of phase randomization. The results obtained are applied to the Kronig-Penney model with the potential in the form of periodically positioned $\delta$-functions with random strength.Comment: Phys. Rev. Lett. 84, 2678 (2000

Thermodynamic properties of a tetramer ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain as a model system for Cu(3-Clpy)2_2(N3_3)2_2

Thermodynamic properties of a tetramer ferro-ferro-antiferro-antiferromagnetic Ising-Heisenberg bond alternating chain are investigated by the use of an exact mapping transformation technique. Exact results for the magnetization, susceptibility and specific heat in the zero as well as nonzero magnetic field are presented and discussed in detail. The results obtained from the mapping are compared with the relevant experimental data of Cu(3-Clpy)$_2$(N$_3$)$_2$ (3-Clpy=3-Chloropyridine).Comment: 10 pages, 1 table, 14 figures, to be presented at CSMAG04 conferenc