Monte Carlo Simulation of the Semimetal-Insulator Phase Transition in Monolayer Graphene

A 2+1 dimensional fermion field theory is proposed as a model for the low-energy electronic excitations in monolayer graphene. The model consists of N=2 four-component Dirac fermions moving in the plane and interacting via a contact interaction between charge densities. For strong couplings there is a continuous transition to a Mott insulting phase. We present results of an extensive numerical study of the model's critical region, including the order parameter, its associated susceptibility, and for the first time the quasiparticle propagator. The data enables an extraction of the critical exponents at the transition, including the dynamical critical exponent, which are hypothesised to be universal features of a quantum critical point. The relation of our model with others in the literature is discussed, along with the implications for physical graphene following from our value of the critical coupling.Comment: 19 page

Shareholder Primacy and the Trajectory of UK Corporate Governance

Core institutions of UK corporate governance, in particular those relating to takeovers, board structure and directors’ duties, are strongly orientated towards a norm of shareholder primacy. Beyond the core, in particular at the intersection of insolvency and employment law, stakeholder interests are better represented, thanks to European Community influence. Moreover, institutional shareholders are redirecting their investment strategies away from a focus on short-term returns, in such a way as to favour stakeholder-inclusive practices. We therefore suggest that the UK system is currently in a state of flux and that the debate over shareholder primacy has not been concluded.corporate governance, stakeholding, hostile takeovers, company law, insolvency, employee representation, shareholder activism

Shareholder Protection and Stock Market Development: An Empirical Test of the Legal Origins Hypothesis

We test the 'law matters' and 'legal origin' claims using a newly created panel dataset meas-uring legal change over time in a sample of developed and developing countries. Our dataset improves on previous ones by avoiding country-specific variables in favour of functional and generic descriptors, by taking into account a wider range of legal data, and by considering the effects of weighting variables in different ways, thereby ensuring greater consistency of cod-ing. Our analysis shows that legal origin explains part of the pattern of change in the adop-tion of shareholder protection measures over the period from the mid-1990s to the present day: in both developed and developing countries, common law systems were more protective of shareholder interests than civil law ones. We explain this the result on the basis of the head start common law systems had in adjusting to an emerging 'global' standard based mainly on Anglo-American practice. Our analysis also shows, however, that civil law origin was not much of an obstacle to convergence around this model, since civilian systems were catching up with their counterparts in the common law. We then investigate whether there was a link in this period between increased shareholder protection and stock market devel-opment, using a number of measures such as stock market capitalisation, the value of stock-trading and the number of listed firms, after controlling for legal origin, the state of economic development of particular countries, and their position on the World Bank rule of law index. We find no evidence of a long-run impact of legal change on stock market development. This finding is incompatible with the claim that legal origin affects the efficiency of legal rules and ultimately economic development. Possible explanations for our result are that laws have been overly protective of shareholders; transplanted laws have not worked as ex-pected; and, more generally, the exogenous legal origin effect is not as strong as widely sup-posed.Law and finance, shareholder rights, corporate governance, corporate finance, legal origins, comparative law.

Strong interaction effects at a Fermi surface in a model for voltage-biased bilayer graphene

Monte Carlo simulation of a 2+1 dimensional model of voltage-biased bilayer graphene, consisting of relativistic fermions with chemical potential mu coupled to charged excitations with opposite sign on each layer, has exposed non-canonical scaling of bulk observables near a quantum critical point found at strong coupling. We present a calculation of the quasiparticle dispersion relation E(k) as a function of exciton source j in the same system, employing partially twisted boundary conditions to boost the number of available momentum modes. The Fermi momentum k_F and superfluid gap Delta are extracted in the limit j tends to zero for three different values of mu, and support a strongly interacting scenario at the Fermi surface with Delta of order O(mu). We propose an explanation for the observation mu < k_F in terms of a dynamical critical exponent z < 1.Comment: 12 pages, 5 figure