Tunable superconducting critical temperature in ballistic hybrid structures with strong spin-orbit coupling

We present a theoretical description and numerical simulations of the superconducting transition in hybrid structures including strong spin-orbit interactions. The spin-orbit coupling is taken to be of Rashba type for concreteness, and we allow for an arbitrary magnitude of the spin-orbit strength as well as an arbitrary thickness of the spin-orbit coupled layer. This allows us to make contact with the experimentally relevant case of enhanced interfacial spin-orbit coupling via atomically thin heavy metal layers. We consider both interfacial spin-orbit coupling induced by inversion asymmetry in an S/F-junction, as well as in-plane spin-orbit coupling in the ferromagnetic region of an S/F/S- and an S/F-structure. Both the pair amplitudes, local density of states and critical temperature show dependency on the Rashba strength and, importantly, the orientation of the exchange field. In general, spin-orbit coupling increases the critical temperature of a proximity system where a magnetic field is present, and enhances the superconducting gap in the density of states. We perform a theoretical derivation which explains these results by the appearance of long-ranged singlet correlations. Our results suggest that $T_c$ in ballistic spin-orbit coupled superconducting structures may be tuned by using only a single ferromagnetic layer.Comment: 14 pages, 14 figures. Published in PR

Boundary version of a twin region convergence theorem for continued fractions

AbstractThe starting point of the present paper is a result by Thron (1959) on twin convergence regions, dealing with continued fractions K(cn2/1), where |c2m-1| ⩽ ρ <1 and |c2m±i| ⩾ρ. In the present paper these regions are replaced by their boundaries, and the sets of continued fraction values are determined

Evaluating Macroeconometric Modelling with Regard to Usefulness: a Survey

Macroeconometric models have during the last 40 years played an important role as a tool to guide decision making in public as well as private macroeconomic institutions. However, such models have not been much used in academic circles. We argue that macroeconometric models have problems both with regard to internal and external validity. Although the science of econometrics has partly answered the problem of internal validity, macroeconometric modelling is still dismissed by theorists as inappropriate for theoretical development. We find that the argument over how to evaluate macroeconometric modelling can be viewed as a result of the relationship between observed economic variables and economic theory.econometric models, theory of science

Statistical arbitrage pairs : can cointegration capture market neutral profits?

We back-test a statistical arbitrage strategy, pairs trading, over the ten year period 01.01.2003 – 31.12.2012 at the Oslo Stock Exchange. We construct an unbiased dataset, where stocks are matched into pairs using a cointegration approach and traded according to a set of pre specified rules. The strategy yields consistent negative returns independent of parameterisation of entryand exit thresholds. Our findings are in line with previous literature, where we support the view that absence of profits is not necessarily due to increased activity among hedge funds, but rather changes in fundamental factors governing the relationships between stocks

Volume and Volatility in the FX Market: Does it matter who you are?

The relationship between volume and volatility has received much attention in the literature on financial markets. However, due to the lack of data, few results have been presented for the foreign exchange (FX) market. Furthermore, most studies contain only aggregate series, and cannot distinguish between the impact of different participants or instruments. We study the impact of volume on volatility in the FX market using a unique data set of daily trading in the Swedish krona (SEK) market. The data set covers 95 percent of worldwide SEK trading, and is disaggregated on a number of reporting banks' buying and selling in five different instruments on a daily basis from 1995 until 2002. We find that volume in general show a positive correlation with volatility. However, the strength of the relationship depends on the instrument traded and the identity of the reporting bank. In particular, we find that trading tends to concentrate around the largest banks during periods of high volatility. These banks are probably also best informed. This is especially the case when volatility is high. We interpret this as evidence that heterogeneous expectations are important to an understanding of the volume- volatility relationship.Volume-volatility relation; microstructure; exchange rates

Volume and Volatility in the FX-Market: Does it matter who you are?

The relationship between volume and volatility has received much attention in the the literature of financial markets. However, due to the lack of data, few results have been presented for the foreign exchange market. Further, most studies contain only aggregate series, and can not distinguish between the impact of different instruments or participants.We study the impact of volume on volatility in the the FX-market using a unique data set of daily trading in the Swedish krona (SEK) market. The data set covers 95 per cent of worldwide SEK-trading, and is disaggregated on a number of reporting banks’ buying and selling in five different instruments on a daily basis over a period of nine years. We find that volume in general depict a positive correlation with volatility. However, the strength of the relationship depends on the instrument used and the identity of the reporting bank. In particular we find that it is the large Swedish banks that dominate the relationship. These banks are probably also the best informed banks. We interpret this is as evidence that heterogeneous expectations are important to understand the volume-volatility relationship.volume volatility relation, microstructure, exchange rates.

Higher order multipoles in metamaterial homogenization

The higher order multipoles above the electric quadrupole are commonly neglected in metamaterial homogenization. We show that they nevertheless can be significant when second order spatial dispersive effects, such as the magnetic response, are considered. In this respect, they can be equally important as the magnetization and quadrupole terms, and should not automatically be neglected.Comment: 8 pages, 5 figure