3,020 research outputs found
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 BaFeSe. Short-range magnetic
correlations, present at room temperature, develop into long-range
antiferromagnetic order below T = 256 K, with no superconductivity down to
1.8 K. Built of ferromagnetic Fe plaquettes, the magnetic ground state
correlates with local displacements of the Fe atoms. These iron displacements
imply significant magnetoelastic coupling in FeX-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
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