10,920 research outputs found
Super-poissonian noise, negative differential conductance, and relaxation effects in transport through molecules, quantum dots and nanotubes
We consider charge transport through a nanoscopic object, e.g. single
molecules, short nanotubes, or quantum dots, that is weakly coupled to metallic
electrodes. We account for several levels of the molecule/quantum dot with
level-dependent coupling strengths, and allow for relaxation of the excited
states. The current-voltage characteristics as well as the current noise are
calculated within first-order perturbation expansion in the coupling strengths.
For the case of asymmetric coupling to the leads we predict
negative-differential-conductance accompanied with super-poissonian noise. Both
effects are destroyed by fast relaxation processes. The non-monotonic behavior
of the shot noise as a function of bias and relaxation rate reflects the
details of the electronic structure and level-dependent coupling strengths.Comment: 8 pages, 7 figures, submitted to Phys. Rev. B, added reference
Constraints on a possible dineutron state from pionless EFT
We investigate the sensitivity of the three-nucleon system to changes in the
neutron-neutron scattering length to next-to-leading order in the pionless
effective field theory, focusing on the the triton-3He binding energy
difference and neutron-deuteron elastic scattering. Due to the appearance of an
electromagnetic three-body counterterm at this order, the triton-3He binding
energy difference remains consistent with the experimental value even for large
positive neutron-neutron scattering lengths while the elastic neutron-deuteron
scattering phase shifts are insensitive. We conclude that a bound dineutron
cannot be excluded to next-to-leading order in pionless EFT.Comment: 11 pages, 5 figure
The complex Busemann-Petty problem on sections of convex bodies
The complex Busemann-Petty problem asks whether origin symmetric convex
bodies in \C^n with smaller central hyperplane sections necessarily have
smaller volume. We prove that the answer is affirmative if and
negative if Comment: 18 page
Magnetic domains in III-V magnetic semiconductors
Recent progress in theoretical understanding of magnetic anisotropy and
stiffness in III-V magnetic semiconductors is exploited for predictions of
magnetic domain characteristics and methods of their tuning. We evaluate the
width and the energy of domain walls as well as the period of stripe domains in
perpendicular films. The computed stripe width d = 1.1 um for
Ga_0.957Mn_0.043As/In_0.16Ga_0.84As compares favorably to the experimental
value 1.5 um, as determined by Shono et al. [Appl. Phys. Lett. 77, 1363
(2000)].Comment: 4 RevTex pages, 2 figures spelling of author's names corrected in
abstract pag
Low-energy p-d scattering and He-3 in pionless EFT
We calculate low-energy proton--deuteron scattering in the framework of
pionless effective field theory. In the quartet channel, we calculate the
elastic scattering phase shift up to next-to-next-to-leading order in the power
counting. In the doublet channel, we perform a next-to-leading order
calculation. We obtain good agreement with the available phase shift analyses
down to the scattering threshold. The phase shifts in the region of
non-perturbative Coulomb interactions are calculated by using an optimised
integration mesh. Moreover, the Coulomb contribution to the 3He-3H binding
energy difference is evaluated in first order perturbation theory. We comment
on the implications of our results for the power counting of subleading
three-body forces.Comment: 27 pages, 13 figures, typos corrected in Sec. V.A (trinucleon wave
functions
Strong Tunneling in Double-Island Structures
We study the electron transport through a system of two low-capacitance metal
islands connected in series between two electrodes. The work is motivated in
part by experiments on semiconducting double-dots, which show intriguing
effects arising from coherent tunneling of electrons and mixing of the
single-electron states across tunneling barriers. In this article, we show how
coherent tunneling affects metallic systems and leads to a mixing of the
macroscopic charge states across the barriers. We apply a recently formulated
RG approach to examine the linear response of the system with high tunnel
conductances (up to 8e^2/h). In addition we calculate the (second order)
cotunneling contributions to the non-linear conductance. Our main results are
that the peaks in the linear and nonlinear conductance as a function of the
gate voltage are reduced and broadened in an asymmetric way, as well as shifted
in their positions. In the limit where the two islands are coupled weakly to
the electrodes, we compare to theoretical results obtained by Golden and
Halperin and Matveev et al. In the opposite case when the two islands are
coupled more strongly to the leads than to each other, the peaks are found to
shift, in qualitative agreement with the recent prediction of Andrei et al. for
a similar double-dot system which exhibits a phase transition.Comment: 12 page
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