45,379 research outputs found
Carrier transport in 2D graphene layers
Carrier transport in gated 2D graphene monolayers is theoretically considered
in the presence of scattering by random charged impurity centers with density
. Excellent quantitative agreement is obtained (for carrier density ) with existing experimental data (Ref.
\onlinecite{kn:novoselov2004, kn:novoselov2005, kn:zhang2005, kn:kim2006,
kn:fuhrer2006}). The conductivity scales linearly with in the theory,
and shows extremely weak temperature dependence. The experimentally observed
asymmetry between electron and hole conductivities is explained by the
asymmetry in the charged impurity configuration in the presence of the gate
voltage, while the high-density saturation of conductivity for the highest
mobility samples is explained as a crossover between the long-range and the
point scattering dominated regimes. We argue that the experimentally observed
saturation of conductivity at low density arises from the charged impurity
induced inhomogeneity in the graphene carrier density which becomes severe for
.Comment: 5 pages, 4 figures, published in Phys. Rev. Let
Efficient Schemes for Reducing Imperfect Collective Decoherences
We propose schemes that are efficient when each pair of qubits undergoes some
imperfect collective decoherence with different baths. In the proposed scheme,
each pair of qubits is first encoded in a decoherence-free subspace composed of
two qubits. Leakage out of the encoding space generated by the imperfection is
reduced by the quantum Zeno effect. Phase errors in the encoded bits generated
by the imperfection are reduced by concatenation of the decoherence-free
subspace with either a three-qubit quantum error correcting code that corrects
only phase errors or a two-qubit quantum error detecting code that detects only
phase errors, connected with the quantum Zeno effect again.Comment: no correction, 3 pages, RevTe
Improved testing for the efficiency of asset pricing theories in linear factor models
This paper suggests a refinement of the standard T2 test statistic used in testing asset pricing theories in linear factor models. The test is designed to have improved power characteristics and to deal with the empirically important case where there are many more assets than time periods. This is necessary because the case of too few time periods invalidates the conventional T2. Furthermore, the test is shown to have reasonable power in cases where common factors are present in the residual covariance matrix
- …