138 research outputs found
Effect of flux-dependent Friedel oscillations upon the effective transmission of an interacting nano-system
We consider a nano-system connected to measurement probes via non interacting
leads. When the electrons interact inside the nano-system, the coefficient
|ts(E_F)|^2 describing its effective transmission at the Fermi energy E_F
ceases to be local. This effect of electron-electron interactions upon
|ts(E_F)|^2 is studied using a one dimensional model of spinless fermions and
the Hartree-Fock approximation. The non locality of |ts(E_F)|^2 is due to the
coupling between the Hartree and Fock corrections inside the nano-system and
the scatterers outside the nano-system via long range Friedel oscillations.
Using this phenomenon, one can vary |ts(E_F)|^2 by an Aharonov-Bohm flux
threading a ring which is attached to one lead at a distance Lc from the
nano-system. For small distances Lc, the variation of the quantum conductance
induced by this non local effect can exceed 0.1 (e^2/h)
Production of non-local quartets and phase-sensitive entanglement in a superconducting beam splitter
Three BCS superconductors S_a, S_b, and S and two short normal regions N_a
and N_b in a three-terminal S_aN_aSN_bS_b set-up provide a source of non-local
quartets spatially separated as two correlated pairs in S_a and S_b, if the
distance between the interfaces N_aS and SN_b is comparable to the coherence
length in S. Low-temperature dc-transport of non-local quartets from S to S_a
and S_b can occur in equilibrium, and also if S_a and S_b are biased at
opposite voltages. At higher temperatures, thermal excitations result in
correlated current fluctuations which depend on the superconducting phases
phi_a and phi_b in S_a and S_b. Phase-sensitive entanglement is obtained at
zero temperature if N_a and N_b are replaced by discrete levels.Comment: 4 pages, 2 figures; technical details attached in ancillary file
http://arxiv.org/src/1102.2355v4/anc/EPAPS_Freyn_2011.pdf; higher versions:
minor corrections, cleanup and corrected reference
Conductance of nano-systems with interactions coupled via conduction electrons: Effect of indirect exchange interactions
A nano-system in which electrons interact and in contact with Fermi leads
gives rise to an effective one-body scattering which depends on the presence of
other scatterers in the attached leads. This non local effect is a pure
many-body effect that one neglects when one takes non interacting models for
describing quantum transport. This enhances the non-local character of the
quantum conductance by exchange interactions of a type similar to the
RKKY-interaction between local magnetic moments. A theoretical study of this
effect is given assuming the Hartree-Fock approximation for spinless fermions
in an infinite chain embedding two scatterers separated by a segment of length
L\_c. The fermions interact only inside the two scatterers. The dependence of
one scatterer onto the other exhibits oscillations which decay as 1/L\_c and
which are suppressed when L\_c exceeds the thermal length L\_T. The
Hartree-Fock results are compared with exact numerical results obtained with
the embedding method and the DMRG algorithm
A Lightcone Embedding of the Twin Building of a Hyperbolic Kac-Moody Group
The twin building of a Kac–Moody group G encodes the parabolic subgroup structure of G and admits a natural G–action. When G is a complex Kac–Moody group of hyperbolic type, we construct an embedding of the twin building of G into the lightcone of the compact real form of the corresponding Kac–Moody algebra. When G has rank 2, we construct an embedding of the spherical building at infinity into the set of rays on the boundary of the lightcone
The embedding method beyond the single-channel case: Two-mode and Hubbard chains
We investigate the relationship between persistent currents in multi-channel
rings containing an embedded scatterer and the conductance through the same
scatterer attached to leads. The case of two uncoupled channels corresponds to
a Hubbard chain, for which the one-dimensional embedding method is readily
generalized. Various tests are carried out to validate this new procedure, and
the conductance of short one-dimensional Hubbard chains attached to perfect
leads is computed for different system sizes and interaction strengths. In the
case of two coupled channels the conductance can be obtained from a statistical
analysis of the persistent current or by reducing the multi-channel scattering
problem to several single-channel setups.Comment: 14 pages, 13 figures, submitted for publicatio
Orchid diversity of the cape of Kamenjak (Istria, Croatia)
Twenty two taxa have been recorded in the south of Istrian peninsula (north Adriatic coast, Croatia). The research was performed in the period 2003–2004. A great majority of taxa belong to Euri- Mediterranean (seven taxa, 41.18%) and Steno-Mediterranean (six taxa, 35.29%) floral elements. Eurasiatic (two taxa, 11.76%), Atlantic (one taxa, 5.88%) and endemic (one taxon, 5.88%) plants were also present. Almost a half of recorded orchids are abundant or frequent. The most of taxa are endangered s.l.; nine vulnerable (VU) plants (52.94%), and one species endangered s.s. (EN) (5.88%). There are also near threatened (NT) (two taxa, 11.76%), and data deficient (DD) (one taxon, 5.88%) plants, while others have no category assigned (four taxa, 23.53%)
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