Finite-Temperature Mott Transition in the Two-Dimensional Hubbard Model

Mott transitions are studied in the two-dimensional Hubbard model by a non-perturbative theory of correlator projection that systematically includes spatial correlations into the dynamical mean-field approximation. Introducing a nonzero second-neighbor transfer, a first-order Mott transition appears at finite temperatures and ends at a critical point or curve.Comment: 2 pages, to appear in J. Mag. Mag. Mat. as proceedings of the International Conference on Magnetism 200

On Second-best Policing Effort against the Illegal Disposal of Recyclable Waste

In this paper, we construct a partial equilibrium model of a product that can be manufactured by using a recycled material as well as a virgin natural resource. In particular, we consider the possibility that a household may resort to the illicit disposal of its waste, such as midnight dumping, instead of discarding it properly. Our focus is on conducting a comparative static analysis on the second-best level of the governmentfs policing effort to counter illegal disposal. More specifically, we examine how the government should adjust the effort level in response to changes in the environmental damage cost of illegal disposal and exported waste.illegal waste disposal, recycling, second-best policy

Intrinsic vs. extrinsic anomalous Hall effect in ferromagnets

A unified theory of the anomalous Hall effect (AHE) is presented for multi-band ferromagnetic metallic systems with dilute impurities. In the clean limit, the AHE is mostly due to the extrinsic skew-scattering. When the Fermi level is located around anti-crossing of band dispersions split by spin-orbit interaction, the intrinsic AHE to be calculated ab initio is resonantly enhanced by its non-perturbative nature, revealing the extrinsic-to-intrinsic crossover which occurs when the relaxation rate is comparable to the spin-orbit interaction energy.Comment: 5 pages including 4 figures, RevTex; minor changes, to appaer in Phys. Rev. Let

Quantum spin ice under a [111] magnetic field: from pyrochlore to kagom\'e

Quantum spin ice, modeled for magnetic rare-earth pyrochlores, has attracted great interest for hosting a U(1) quantum spin liquid, which involves spin-ice monopoles as gapped deconfined spinons, as well as gapless excitations analogous to photons. However, the global phase diagram under a [111] magnetic field remains open. Here we uncover by means of unbiased quantum Monte-Carlo simulations that a supersolid of monopoles, showing both a superfluidity and a partial ionization, intervenes the kagom\'e spin ice and a fully ionized monopole insulator, in contrast to classical spin ice where a direct discontinuous phase transition takes place. We also show that on cooling, kagom\'e spin ice evolves towards a valence bond solid similar to what appears in the associated kagom\'e lattice model [S. V. Isakov et al., Phys. Rev. Lett. 97, 147202 (2006)]. Possible relevance to experiments is discussed.Comment: 5 pages, 4 figures; accepted for publication in PR