37,501 research outputs found
Electronic structure of multilayer graphene
We study the electronic structure of multilayer graphene using a
-orbital continuum model with nearest-neighbor intralayer and interlayer
tunneling. Using degenerate state perturbation theory, we show that the
low-energy electronic structure of arbitrarily stacked graphene multilayers
consists of chiral pseudospin doublets with a conserved chirality sum.Comment: 25 pages, 15 figures; Expanded version of PRB 77,155416 (2008),
arXiv:0711.4333; Published in the proceedings of YKIS2007; Typos correcte
Squeezed states of light from an optical parametric oscillator
Squeezed states of the electromagnetic field are generated by degenerate parametric downconversion in a subthreshold optical parametric oscillator. Reductions in photocurrent noise greater than 60% (-4 dB) below the limit set by the vacuum fluctuations of the field are observed in a balanced homodyne detector. A quantitative comparison with theory suggests that the observed noise reductions result from a field that in the absence of avoidable linear attenuation would be squeezed more than tenfold. A degree of squeezing of approximately fivefold is inferred for the actual field emitted through one mirror of the optical parametric oscillator. An explicit demonstration of the Heisenberg uncertainty principle for the electromagnetic field is made from the measurements, which show that the field state produced by the downconversion process is a state of minimum uncertainty
Relativistic Heavy Quark Effective Action
We study the fermion action needed to accurately describe the low energy
physics of systems including heavy quarks in lattice QCD even when the heavy
fermion mass is on the order of, or larger than, the inverse lattice
spacing: . We carry out an expansion through first order in (where is the heavy quark momentum) and all orders in ,
refining the analysis of the Fermilab and Tsukuba groups. We demonstrate that
the spectrum of heavy quark bound states can be determined accurately through
and for arbitrary exponent by using a lattice action
containing only three unknown coefficients: , and (a
generalization of ), which are functions of . In a companion paper,
we show how these three coefficients can be precisely determined using
non-perturbative techniques.Comment: 40 pages, 1 figur
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