5,243 research outputs found
Four-wave mixing enhanced white-light cavity
We discuss in-medium propagation dynamics in a white light cavity that leads
to an enhancement of the cavity's bandwidth without reducing its maximum
intensity buildup. We analyze the spatiotemporal dynamics of our system with a
full simulation of the field propagation in a regime that leads to strong
absorption of the control fields. We find that an additional coherent field is
generated within the medium via four-wave mixing. This self-generated field
leads to a backaction of the medium onto the probe field. Counter intuitively,
this pronounced in-medium dynamics throughout the propagation leads to an
additional enhancement of the cavity bandwidth.Comment: 5 pages, 4 figure
Zero-bias molecular electronics: Exchange-correlation corrections to Landauer's formula
Standard first principles calculations of transport through single molecules
miss exchange-correlation corrections to the Landauer formula. From Kubo
response theory, both the Landauer formula and these corrections in the limit
of zero bias are derived and calculations are presented.Comment: 4 pages, 3 figures, final version to appear in Phys. Rev. B, Rapid
Communication
Wave function statistics at the symplectic 2D Anderson transition: bulk properties
The wavefunction statistics at the Anderson transition in a 2d disordered
electron gas with spin-orbit coupling is studied numerically. In addition to
highly accurate exponents (), we report three qualitative results: (i) the anomalous dimensions are
invariant under which is in agreement with a recent analytical
prediction and supports the universality hypothesis. (ii) The multifractal
spectrum is not parabolic and therefore differs from behavior suspected, e.g.,
for (integer) quantum Hall transitions in a fundamental way. (iii) The critical
fixed point satisfies conformal invariance.Comment: 4 pages, 3 figure
Negative refraction with tunable absorption in an active dense gas of atoms
Applications of negative index materials (NIM) presently are severely limited
by absorption. Next to improvements of metamaterial designs, it has been
suggested that dense gases of atoms could form a NIM with negligible losses. In
such gases, the low absorption is facilitated by quantum interference. Here, we
show that additional gain mechanisms can be used to tune and effectively remove
absorption in a dense gas NIM. In our setup, the atoms are coherently prepared
by control laser fields, and further driven by a weak incoherent pump field to
induce gain. We employ nonlinear optical Bloch equations to analyze the optical
response. Metastable Neon is identified as a suitable experimental candidate at
infrared frequencies to implement a lossless active negative index material.Comment: 10 pages, 9 figure
Tax Competition under Minimum Rates: The Case of European Diesel Excises
This paper estimates Nash-type fiscal reaction functions for European governments competing for revenue from diesel excises. It appears that European governments strategically set their excise levels by responding to their neighbors’ tax rates. This provides evidence for the presence of tax competition in diesel excises. In fact, a 10 percent higher rate in neighboring countries (in terms of the user price) induces a country to raise its own rate by between 2 and 3 percent. This impact is robust for alternative specifications. By imposing restrictions on excise levels, EU harmonization of excises in 1987 and the introduction of a minimum in 1992 exerted a positive impact on the excise level in a number of EU countries. It has not, however, significantly reduced the intensity of tax competition. Indeed, strategic tax responses have not significantly been reduced by these harmonization policies. We also find that high-tax countries appear to compete more aggressively than low-tax countries in the sense that they feature larger strategic tax responses. There is no significant difference between large and small countries.Diesel excise, strategic tax setting, minimum rates, European Union
Elastic properties of graphene flakes: boundary effects and lattice vibrations
We present a calculation of the free energy, the surface free energy and the
elastic constants ("Lam'e parameters" i.e, Poisson ratio, Young's modulus) of
graphene flakes on the level of the density functional theory employing
different standard functionals. We observe that the Lam'e parameters in small
flakes can differ from the bulk values by 30% for hydrogenated zig-zag edges.
The change results from the edge of the flake that compresses the interior.
When including the vibrational zero point motion, we detect a decrease in the
bending rigidity by ~26%. This correction is depending on the flake size, N,
because the vibrational frequencies flow with growing N due to the release of
the edge induced compression. We calculate Grueneisen parameters and find good
agreement with previous authors.Comment: 11 pages, 12 figure
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
Griffiths phase in the thermal quantum Hall effect
Two dimensional disordered superconductors with broken spin-rotation and
time-reversal invariance, e.g. with p_x+ip_y pairing, can exhibit plateaus in
the thermal Hall coefficient (the thermal quantum Hall effect). Our numerical
simulations show that the Hall insulating regions of the phase diagram can
support a sub-phase where the quasiparticle density of states is divergent at
zero energy, \rho(E)\sim |E|^{1/z-1}, with a non-universal exponent , due
to the effects of rare configurations of disorder (``Griffiths phase'').Comment: 4+ pages, 5 figure
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