82 research outputs found
Size-dependent properties of dithallium selenide
We report on size-dependent properties of dithallium selenide, Tl2Se. We have
carried out a comparative nuclear magnetic resonance (NMR) study of Tl2Se
nanorods and bulk samples, measuring NMR spectra and spin-lattice relaxation
rate of 203Tl and 205Tl isotopes. Though bulk Tl2Se was reported to be a metal,
the Korringa-like spin-lattice relaxation behavior is observed only at low
temperatures and is transformed to an activation regime above ~200 K. This
finding is interpreted assuming a two-band model in the semimetallic compound.
Our measurements show significant difference in the Knight shift and indirect
nuclear exchange coupling for the bulk and nanorod Tl2Se samples, reflecting
noticeable distinction in their electronic structure. At that, Tl2Se nanorods
are semiconductors and exhibit a characteristic activation behavior in the
spin-lattice relaxation rate due to the thermal excitation of carriers to the
conduction band. The obtained size dependence of the Tl2Se properties is
interpreted in terms of the semimetal-semiconductor transformation due to the
quantum confinement.Comment: 15 pages, 4 figure
Electronic Transport in a Three-dimensional Network of 1-D Bismuth Quantum Wires
The resistance R of a high density network of 6 nm diameter Bi wires in
porous Vycor glass is studied in order to observe its expected semiconductor
behavior. R increases from 300 K down to 0.3 K. Below 4 K, where R varies
approximately as ln(1/T), the order-of-magnitude of the resistance rise, as
well as the behavior of the magnetoresistance are consistent with localization
and electron-electron interaction theories of a one-dimensional disordered
conductor in the presence of strong spin-orbit scattering. We show that this
behaviour and the surface-enhanced carrier density may mask the proposed
semimetal-to-semiconductor transition for quantum Bi wires.Comment: 19 pages total, 4 figures; accepted for publication in Phys. Rev.
Quantum Conductance in Semimetallic Bismuth Nanocontacts
Electronic transport properties of bismuth nanocontacts are analyzed by means
of a low temperature scanning tunneling microscope. The subquantum steps
observed in the conductance versus elongation curves give evidence of atomic
rearrangements in the contact. The underlying quantum nature of the conductance
reveals itself through peaks in the conductance histograms. The shape of the
conductance curves at 77 K is well described by a simple gliding mechanism for
the contact evolution during elongation. The strikingly different behaviour at
4 K suggests a charge carrier transition from light to heavy ones as the
contact cross section becomes sufficiently small.Comment: 5 pages including 4 figures. Accepted for publication in Phys. Rev.
Let
Magnetic-field-dependent zero-bias diffusive anomaly in Pb oxide-n-InAs structures: Coexistence of two- and three-dimensional states
The results of experimental and theoretical studies of zero-bias anomaly
(ZBA) in the Pb-oxide-n-InAs tunnel structures in magnetic field up to 6T are
presented. A specific feature of the structures is a coexistence of the 2D and
3D states at the Fermi energy near the semiconductor surface. The dependence of
the measured ZBA amplitude on the strength and orientation of the applied
magnetic field is in agreement with the proposed theoretical model. According
to this model, electrons tunnel into 2D states, and move diffusively in the 2D
layer, whereas the main contribution to the screening comes from 3D electrons.Comment: 8 double-column pages, REVTeX, 9 eps figures embedded with epsf,
published versio
Virus-Induced Gene Silencing as a Tool for Comparative Functional Studies in Thalictrum
Perennial woodland herbs in the genus Thalictrum exhibit high diversity of floral morphology, including four breeding and two pollination systems. Their phylogenetic position, in the early-diverging eudicots, makes them especially suitable for exploring the evolution of floral traits and the fate of gene paralogs that may have shaped the radiation of the eudicots. A current limitation in evolution of plant development studies is the lack of genetic tools for conducting functional assays in key taxa spanning the angiosperm phylogeny. We first show that virus-induced gene silencing (VIGS) of a PHYTOENE DESATURASE ortholog (TdPDS) can be achieved in Thalictrum dioicum with an efficiency of 42% and a survival rate of 97%, using tobacco rattle virus (TRV) vectors. The photobleached leaf phenotype of silenced plants significantly correlates with the down-regulation of endogenous TdPDS (P<0.05), as compared to controls. Floral silencing of PDS was achieved in the faster flowering spring ephemeral T. thalictroides. In its close relative, T. clavatum, silencing of the floral MADS box gene AGAMOUS (AG) resulted in strong homeotic conversions of floral organs. In conclusion, we set forth our optimized protocol for VIGS by vacuum-infiltration of Thalictrum seedlings or dormant tubers as a reference for the research community. The three species reported here span the range of floral morphologies and pollination syndromes present in Thalictrum. The evidence presented on floral silencing of orthologs of the marker gene PDS and the floral homeotic gene AG will enable a comparative approach to the study of the evolution of flower development in this group
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