Rotational Symmetry Breaking in a Trigonal Superconductor Nb-Doped Bi₂Se₃

The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi2Se3) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi2Se3. As a result, the in-plane magnetic torque signal vanishes every 60°. More importantly, the superconducting hysteresis loop amplitude is enhanced along one preferred direction, spontaneously breaking the rotational symmetry. This observation indicates the presence of nematic order in the superconducting ground state of Nb-doped Bi2Se3

The Krusell–Smith Algorithm: Are Self-Fulfilling Equilibria Likely?

I investigate whether the popular Krusell and Smith algorithm used to solve heterogeneousagent economies with aggregate uncertainty and incomplete markets is likely to be subject to multiple self-fulfilling equilibria. In a benchmark economy, the parameters representing the equilibrium aggregate law of motion are randomly perturbed 500 times, and are used as the new initial guess to compute the equilibrium with this algorithm. In a sequence of cases, differing only in the magnitude of the perturbations, I do not find evidence of multiple self-fulfilling equilibria. The economic reason behind the result lies in a self-correcting mechanism present in the algorithm: compared to the equilibrium law of motion, a candidate one implying a higher (lower) expected future capital reduces (increases) the equilibrium interest rates, increasing (reducing) the savings of the wealth-rich agents only. These, on the other hand, account for a small fraction of the population and cannot compensate for the opposite change triggered by the wealth-poor agents, who enjoy higher (lower) future wages and increase (reduce) their current consumption. Quantitatively, the change in behavior of the wealth-rich agents has a negligible impact on the determination of the change in the aggregate savings, inducing stability in the algorithm as a by-product

Demographic transition and the real exchange rate in Australia: An empirical investigation

This article utilizes the empirical findings that age structure of the population affects saving, investment and capital flow and hypothesizes that age structure influences the real exchange rate. Based on this link, an empirical model is specified for Australia and estimated with annual data for the period 1970–2011. An autoregressive distributed lag model of cointegration indicates that Australia's real exchange rate is cointegrated with its productivity differential and the relative share of young dependents (0–14 years) in the population. Long-run estimates show that young cohort has an appreciating influence on the real exchange rate. Also, the short-run adjustment is substantial, with more than 65% of the disequilibrium corrected in a year

The People's Republic of China's Potential Growth Rate: The Long-Run Constraints

We estimate the People's Republic of China's (PRC's potential growth rate in 2012 at 8.7% and at 9.2% for the average of 2008-2012, about the same as the average actual growth rate for this period. This rate is the natural growth rate, that is, the rate consistent with a constant unemployment rate and stable inflation. The PRC's natural growth rate displays a downward trend since 2006, when it peaked at 11.1%. Probably the Great Recession has been an important factor, although we argue that there are other factors. We show that the PRC's potential growth rate is not demand constrained, in particular by the balance of payments. The PRC's potential growth rate is determined by the supply side of the economy, in particular by: (i) changes in the structure of the economy, in particular in the share of industrial employment; (ii) the working-age population; (iii) the share of net exports in gross domestic product (GDP); (iv) export growth; (v) the share of foreign direct investment (FDI) in GDP; and (vi) human capital accumulation

The Farm, the city, and the emergence of social security

We study the social, demographic and economic origins of social security. The data for the U.S. and for a cross section of countries suggest that urbanization and industrialization are associated with the rise of social insurance. We describe an OLG model in which demographics, technology, and social security are linked together in a political economy equilibrium. In the model economy, there are two locations (sectors), the farm (agricultural) and the city (industrial) and the decision to migrate from rural to urban locations is endogenous and linked to productivity differences between the two locations and survival probabilities. Farmers rely on land inheritance for their old age and do not support a pay-as-you-go social security system. With structural change, people migrate to the city, the land loses its importance and support for social security arises. We show that a calibrated version of this economy, where social security taxes are determined by majority voting, is consistent with the historical transformation in the United States

Payment Networks in a Search Model of Money

In a simple search model of money, we study a special kind of memory that gives rise to an arrangement resembling a payment network. Specifically, we assume that agents can pay a cost to access a central database that tracks payments made and received. Incentives must be provided to agents to access the central database and to produce when they participate in this arrangement. We also study policies that can loosen these incentive constraints. In particular, we show that a “no-surcharge” rule has good incentive properties. Finally, we compare our model with that of Cavalcanti and Wallace