1,081 research outputs found
Explanation of the discrepancy between the measured and atomistically calculated yield stresses in body-centered cubic metals
We propose a mesoscopic model that explains the factor of two to three
discrepancy between experimentally measured yield stresses of BCC metals at low
temperatures and typical Peierls stresses determined by atomistic simulations
of isolated screw dislocations. The model involves a Frank-Read type source
emitting dislocations that become pure screws at a certain distance from the
source and, owing to their high Peierls stress, control its operation. However,
due to the mutual interaction between emitted dislocations the group consisting
of both non-screw and screw dislocations can move at an applied stress that is
about a factor of two to three lower than the stress needed for the glide of
individual screw dislocations.Comment: 4 pages, 2 figures; RevTex4; submitted to PR
Kondo effect and anti-ferromagnetic correlation in transport through tunneling-coupled double quantum dots
We propose to study the transport through tunneling-coupled double quantum
dots (DQDs) connected in series to leads, using the finite- slave-boson mean
field approach developed initially by Kotliar and Ruckenstein [Phys. Rev. Lett.
{\bf 57}, 1362 (1986)]. This approach treats the dot-lead coupling and the
inter-dot tunnelling nonperturbatively at arbitrary Coulomb correlation
, thus allows the anti-ferromagnetic exchange coupling parameter
to appear naturally. We find that, with increasing the inter-dot hopping, the
DQDs manifest three distinct physical scenarios: the Kondo singlet state of
each dot with its adjacent lead, the spin singlet state consisting of local
spins on each dot and the doubly occupied bonding orbital of the coupled dots.
The three states exhibit remarkably distinct behavior in transmission spectrum,
linear and differential conductance and their magnetic-field dependence.
Theoretical predictions agree with numerical renormalization group and Lanczos
calculations, and some of them have been observed in recent experiments.Comment: 5 pages, 5 figures. Physics Review B (Rapid Communication) (in press
Kondo effect in coupled quantum dots under magnetic fields
The Kondo effect in coupled quantum dots is investigated theoretically under
magnetic fields. We show that the magnetoconductance (MC) illustrates peak
structures of the Kondo resonant spectra. When the dot-dot tunneling coupling
is smaller than the dot-lead coupling (level broadening), the
Kondo resonant levels appear at the Fermi level (). The Zeeman splitting
of the levels weakens the Kondo effect, which results in a negative MC. When
is larger than , the Kondo resonances form bonding and
anti-bonding levels, located below and above , respectively. We observe a
positive MC since the Zeeman splitting increases the overlap between the levels
at . In the presence of the antiferromagnetic spin coupling between the
dots, the sign of MC can change as a function of the gate voltage.Comment: 6 pages, 3 figure
Fabrication of nanoscale gaps using a combination of self-assembled molecular and electron beam lithographic techniques
Copyright 2006 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters, 88(22), 223111, 2006 and may be found at http://dx.doi.org/10.1063/1.220920
I-V characteristics of single electron tunneling from symmetric and asymmetric double-barrier tunneling junctions
Copyright 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters, 90(22), 223112, 2007 and may be found at http://dx.doi.org/10.1063/1.274525
Phase diagrams of period-4 spin chains consisting of three kinds of spins
We study a period-4 antiferromagnetic mixed quantum spin chain consisting of
three kinds of spins. When the ground state is singlet, the spin magnitudes in
a unit cell are arrayed as (s-t, s, s+t, s) with integer or half-odd integer s
and t (0 <= t < s). The spin Hamiltonian is mapped onto a nonlinear sigma model
(NLSM) in a previously developed method. The resultant NLSM includes only two
independent parameters originating from four exchange constants for fixed s and
t. The topological angle in the NLSM determines the gapless phase boundaries
between disordered phases in the parameter space. The phase diagrams for
various s and t shows rich structures. We systematically explain the phases in
the singlet-cluster-solid picture.Comment: 8 pages (16 figures included
Electron Transport through T-Shaped Double-Dots System
Correlation effects on electron transport through a system of T-shaped
double-dots are investigated, for which only one of the dots is directly
connected to the leads. We evaluate the local density of states and the
conductance by means of the non-crossing approximation at finite temperatures
as well as the slave-boson mean field approximation at zero temperature. It is
found that the dot which is not directly connected to the leads considerably
influences the conductance, making its behavior quite different from the case
of a single-dot system. In particular, we find a novel phenomenon in the Kondo
regime with a small inter-dot coupling, i.e.
Fano-like suppression of the Kondo-mediated conductance, when two dot levels
coincide with each other energetically.Comment: 6 pages,7 figure
- âŠ