Skyrme and Wigner crystals in graphene

At low-energy, the band structure of graphene can be approximated by two degenerate valleys $(K,K^{\prime})$ about which the electronic spectra of the valence and conduction bands have linear dispersion relations. An electronic state in this band spectrum is a linear superposition of states from the $A$ and $B$ sublattices of the honeycomb lattice of graphene. In a quantizing magnetic field, the band spectrum is split into Landau levels with level N=0 having zero weight on the $B(A)$ sublattice for the $$ valley. Treating the valley index as a pseudospin and assuming the real spins to be fully polarized, we compute the energy of Wigner and Skyrme crystals in the Hartree-Fock approximation. We show that Skyrme crystals have lower energy than Wigner crystals \textit{i.e.} crystals with no pseudospin texture in some range of filling factor $\nu$ around integer fillings. The collective mode spectrum of the valley-skyrmion crystal has three linearly-dispersing Goldstone modes in addition to the usual phonon mode while a Wigner crystal has only one extra Goldstone mode with a quadratic dispersion. We comment on how these modes should be affected by disorder and how, in principle, a microwave absorption experiment could distinguish between Wigner and Skyrme crystals.Comment: 14 pages with 11 figure

Mobility within Europe – The Attitudes of European Youngsters

Intensified European integration, enlargement of the EU, and increasing migration activity worldwide have pushed migration and migration policy to the forefront of the European agenda. While many observers hesitate to embrace immigration emanating from outside Europe, sectoral skill shortages and social security systems under demographic pressure have fostered an almost unanimous call for larger mobility within Europe. Yet, neither does intra-European migration respond to this request, nor are the possible consequences of increased migration activity well understood. This paper embeds this discussion into a systematic classification of economic migration research according to its major conceptual and applied questions. The state of theoretical and empirical research in this literature is reviewed briefly, with a focus on intra-European migration. We conclude that the relatively positive assessment of this type of migration mainly derives from its high skill content. To prepare the prediction of future developments, we offer empirical evidence on the determinants of intra-EU-migration by an analysis of the Eurobarometer survey. Unless information deficits, traces of xenophobic tendencies, and the perception of prohibitively high levels of bureaucratic red tape are overcome, intra-European migration will not play the role it is hoped for.Labor mobility, migration intention, intra-EU-migration

Mobility within Europe - What Do We (Still Not) Know?

Intensified European integration, enlargement of the EU, and increasing migration activity worldwide have pushed migration and migration policy to the forfront of the European agenda. This paper identifies the salient questions to be addressed by any educated migration policy. It embeds this discussion into a systematic classification of economic migration research according to its major conceptual and applied questions. The state of theoretical and empirical research in the different strands of the taxonomy is reviewed briefly, with a focus on European aspects. Furthermore, we offer some empirical evidence on the determinants of intra-EU-migration by an analysis of the Eurobarometer. The paper concludes with an outline of the major open research questions in the European context. Specifically, at this junctur e the generation of individual-based detailed and comprehensive data material covering the phenomenon is imperative.

Gerontocracy in Motion? – European Cross-Country Evidence on the Labor Market Consequences of Population Ageing

Taking a European cross-country perspective, this paper addresses the most important issues in the nexus of population ageing and labor markets.We start from a descriptive overview of the demographic change currently shaping European societies.The subsequent section intensively discusses the potential consequences of these demographic processes for and interdependencies with the labor market situation in Europe.We place particular emphasis on the issue of non-competitive wage setting. In our empirical application we demonstrate that moderately large birth cohorts seem to experience lower employment rates, but also that education investments might be able to mitigate these consequences, and that the relative economic success of large cohorts might even be disproportionately positive. Finally, in the concluding section we review possible policy options for coping with the consequences of population ageing.Demographic change, cohort size, unemployment

The impact of EU enlargement on migration flows

This document is a report commissioned by the Home Office in order to assess the magnitude of potential migration flows to the UK after the enlargement of the European Union (EU). The countries which are expected to join the EU on 1 May 2004 are Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia. The aim of the report is to provide extensive information that will be helpful in evaluating the migration potential from these countries to the UK. This is done by (i) describing the socio-economic situation of the accession countries nowadays and since the early 1990s and comparing it to that of the UK and Germany, (ii) critically reviewing the existing literature that attempts to predict the effects of the current EU enlargement on migration flows, (iii) analysing the so-called Southern enlargement (the accessions of Greece, Portugal and Spain) and comparing it to the current one, and (iv) presenting a quantitative analysis of the effect of the current enlargement on migration to the UK

The Impact of Demographic Change on Human Capital Accumulation

This paper investigates whether and to what extent demographic change has an impact on human capital accumulation. The effect of the relative cohort size on educational attainment of young adults in Germany is analyzed utilizing data from the German Socio-Economic Panel for West-German individuals of the birth cohorts 1966 to 1986. These are the cohorts which entered the labor market since the 1980's. Particular attention is paid to the effect of changes in labor market conditions, which constitute an important channel through which demographic change may affect human capital accumulation. Our findings suggest that the variables measuring demographic change exert a considerable though heterogeneous impact on the human capital accumulation of young Germans. Changing labor market conditions during the 1980's and 1990's exhibit a sizeable impact on both the highest schooling and the highest professional degree obtained by younger cohorts.schooling, vocational training, demographic change

The Impact of Demographic Change on Human Capital Accumulation

This paper investigates whether and to what extent demographic change has an impact on human capital accumulation. The effect of the relative cohort size on educational attainment of young adults in Germany is analyzed utilizing data from the German Socio-Economic Panel for West-German individuals of the birth cohorts 1966 to 1986. These are the cohorts which entered the labor market since the 1980's. Particular attention is paid to the effect of changes in labor market conditions, which constitute an important channel through which demographic change may affect human capital accumulation. Our findings suggest that the variables measuring demographic change exert a considerable though heterogeneous impact on the human capital accumulation of young Germans. Changing labor market conditions during the 1980's and 1990's exhibit a sizeable impact on both the highest schooling and the highest professional degree obtained by younger cohorts.Demographic Change, Schooling, Vocational Training

The Impact of Demographic Change on Human Capital Accumulation

This paper investigates whether and to what extent demographic change has an impact on human capital accumulation. The effect of the relative cohort size on educational attainment of young adults in Germany is analyzed utilizing data from the German Socio-Economic Panel forWest-German individuals of the birth cohorts 1966 to 1986. These are the cohorts which entered the labor market since the 1980’s. Particular attention is paid to the effect of changes in labor market conditions, which constitute an important channel through which demographic change may affect human capital accumulation. Our findings suggest that the variables measuring demographic change exert a considerable though heterogeneous impact on the human capital accumulation of young Germans. Changing labor market conditions during the 1980’s and 1990’s exhibit a sizeable impact on both the highest schooling and the highest professional degree obtained by younger cohorts.Demographic change, schooling, vocational training

Luttinger Liquid at the Edge of a Graphene Vacuum

We demonstrate that an undoped two-dimensional carbon plane (graphene) whose bulk is in the integer quantum Hall regime supports a non-chiral Luttinger liquid at an armchair edge. This behavior arises due to the unusual dispersion of the non-interacting edges states, causing a crossing of bands with different valley and spin indices at the edge. We demonstrate that this stabilizes a domain wall structure with a spontaneously ordered phase degree of freedom. This coherent domain wall supports gapless charged excitations, and has a power law tunneling $I-V$ with a non-integral exponent. In proximity to a bulk lead, the edge may undergo a quantum phase transition between the Luttinger liquid phase and a metallic state when the edge confinement is sufficiently strong relative to the interaction energy scale.Comment: 4 pages, 3 figure