Metal–insulator transition in 2D as a quantum phase transition

We discuss the metal–insulator transition phenomenon in two dimensions in terms of a quantum critical point that controls a range of the low temperature insulator region as well as the usual quantum critical sector. We show that this extended range of criticality permits a determination of both the dynamical critical exponent z and the correlation length critical exponent ν from published data from a single experiment in the insulator critical region. The resulting value of the product zν is consistent with the temperature dependence of the resistance in the quantum critical sector. This provides strong quantitative evidence for the presence of a quantum critical point

Angular distribution of positrons emitted from metal surfaces

The effect of inelastic scattering processes on the angular distribution of positrons spontaneously emitted from metal surfaces is investigated. Angular and energy spectra are calculated for positrons suffering energy loss due to electron-hole excitation in emission from materials with low (aluminum) and high (tungsten) positron work functions.Peer reviewe

Iron Displacements and Magnetoelastic Coupling in the Spin-Ladder Compound BaFe2Se3

We report long-range ordered antiferromagnetism concomitant with local iron displacements in the spin-ladder compound BaFe$_2$Se$_3$. Short-range magnetic correlations, present at room temperature, develop into long-range antiferromagnetic order below T$_N$ = 256 K, with no superconductivity down to 1.8 K. Built of ferromagnetic Fe$_4$ plaquettes, the magnetic ground state correlates with local displacements of the Fe atoms. These iron displacements imply significant magnetoelastic coupling in FeX$_4$-based materials, an ingredient hypothesized to be important in the emergence of superconductivity. This result also suggests that knowledge of these local displacements is essential for properly understanding the electronic structure of these systems. As with the copper oxide superconductors two decades ago, our results highlight the importance of reduced dimensionality spin ladder compounds in the study of the coupling of spin, charge, and atom positions in superconducting materials

Responding to Regulatory Uncertainty: Evidence from Basel III

This paper examines how firms respond to proposed regulation. Specifically, we utilize the time period over which banking authorities discussed, adopted, and implemented Basel III to examine how banks responded to the proposed regulatory framework. We find that banks were not only quick to lobby rule makers against the proposal, but that they also simultaneously altered their business models and made strategic financial reporting changes in response to it. We also provide evidence that banks were more likely to make these anticipatory changes when they: 1) benefitted more from signaling an early commitment, or 2) had less uncertainty about whether they would be subjected to the regulation. Taken together, our findings indicate that firms’ incentives lead them to simultaneously respond through multiple channels when faced with regulatory uncertainty.http://deepblue.lib.umich.edu/bitstream/2027.42/110908/1/1213_Hendricks_Apr2015.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/110908/4/1213_Shakespeare_March2016.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/110908/6/1213_Shakespeare_March2016.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/110908/7/1213_Hendricks_Nov2016.pdfDescription of 1213_Shakespeare_March2016.pdf : Fixed March 2016 revisionDescription of 1213_Shakespeare_March2016.pdf : March 2016 revisionDescription of 1213_Hendricks_Nov2016.pdf : November 2016 revisio

Do correlations create an energy gap in electronic bilayers? Critical analysis of different approaches

This paper investigates the effect of correlations in electronic bilayers on the longitudinal collective mode structure. We employ the dielectric permeability constructed by means of the classical theory of moments. It is shown that the neglection of damping processes overestimates the role of correlations. We conclude that the correct account of damping processes leads to an absence of an energy gap.Comment: 4 page

Universal Features of Terahertz Absorption in Disordered Materials

Using an analytical theory, experimental terahertz time-domain spectroscopy data and numerical evidence, we demonstrate that the frequency dependence of the absorption coupling coefficient between far-infrared photons and atomic vibrations in disordered materials has the universal functional form, C(omega) = A + B*omega^2, where the material-specific constants A and B are related to the distributions of fluctuating charges obeying global and local charge neutrality, respectively.Comment: 5 pages, 3 fig