243 research outputs found
Boundary effect on CDW: Friedel oscillations, STM image
We study the effect of open boundary condition on charge density waves (CDW).
The electron density oscillates rapidly close to the boundary, and additional
non-oscillating terms (~ln(r)) appear. The Friedel oscillations survive beyond
the CDW coherence length (v_F/Delta), but their amplitude gets heavily
suppressed. The scanning tunneling microscopy image (STM) of CDW shows clear
features of the boundary. The local tunneling conductance becomes asymmetric
with respect to the Fermi energy, and considerable amount of spectral weight is
transferred to the lower gap edge. Also it exhibits additional zeros reflecting
the influence of the boundary.Comment: 7 pages, 6 figure
Impurity effects in unconventional density waves in the unitary limit
We investigate the effect of strong, nonmagnetic impurities on
quasi-one-dimensional conventional and unconventional density waves (DW and
UDW). The conventional case remains unaffected similarly to s-wave
superconductors in the presence of weak, nonmagnetic impurities. The
thermodynamic properties of UDW were found to be identical to those of a d-wave
superconductor in the unitary limit. The real and imaginary part of the optical
conductivity is determined for electric fields applied in the perpendicular
directions. A new structure can be present corresponding to excitations from
the bound state at the Fermi energy to the gap maximum in addition to the usual
peak at 2\Delta. In the dc limit, universal electric conductivity is found.Comment: 9 pages, 5 figure
IRIS SIBIRICA HAS UNUSUAL, PRACTICALLY NON-DIFFERENT HEAT TOLERANCE OF PS II AT DIFFERENT GEOGRAPHICAL EXPOSURES ON THE BÜKK-PLATEAU (NORTH-HUNGARY)
Heat tolerance of photosystem II (PSII) was examined in Siberian flag
(Iris sibirica L.) living in different microhabitats of a non-forested enclosed
depression surface (doline) on the Bükk-plateau. Although the microclimatic
parameters of the habitats with different facing sites show sharp contrasts, there
was no significant difference between the heat tolerance of PSII in leaves of I.
sibirica growing in these expositions neither in dark- nor in light-adapted state
Optical conductivity of superconducting Sr_2RuO_4
We compute the optical conductivity of 2D f-wave superconductors and also of
the multigap model proposed recently by Zhitomirsky and Rice at T=0K in the
Born limit. The presence of interband impurity scattering was found to play an
important role: the contributions from the two bands mix up, and new structures
are seen in the tunneling density of states and in the optical spectrum as
well, corresponding to interband transitions.
This will provide a sensitive test in selecting the competing models for the
triplet superconductivity in Sr_2RuO_4.Comment: 7 pages, 9 figure
Iris sibirica has unusual, practically non-different heat tolerance of PSII at different geographical exposures on the Bükk-plateau (North-Hungary)
Heat tolerance of photosystem II (PSII) was examined in Siberian flag
(Iris sibirica L.) living in different microhabitats of a non-forested enclosed
depression surface (doline) on the Bükk-plateau. Although the microclimatic
parameters of the habitats with different facing sites show sharp contrasts, there
was no significant difference between the heat tolerance of PSII in leaves of I.
sibirica growing in these expositions neither in dark- nor in light-adapted state
Vasopressin deficiency diminishes acute and long-term consequences of maternal deprivation in male rat pups.
Early life events have special importance in the development as postnatal environmental alterations may permanently affect the lifetime vulnerability to diseases. For the interpretation of the long-term consequences it is important to understand the immediate effects. As the role of vasopressin in hypothalamic-pituitary-adrenal axis regulation as well as in affective disorders seem to be important we addressed the question whether the congenital lack of vasopressin will modify the stress reactivity of the pups and will influence the later consequences of single 24h maternal deprivation (MD) on both stress-reactivity and stress-related behavioral changes. Vasopressin-producing (di/+) and deficient (di/di) Brattleboro rat were used. In 10-day-old pups MD induced a remarkable corticosterone rise in both genotypes without adrenocorticotropin (ACTH) increase in di/di rats. Studying the later consequences at around weaning (25-35-day-old rats) we found somatic and hormonal alterations (body weight reduction, dysregulation of the stress axis) which were not that obvious in di/di rats. The more anxious state of MD rats was not detectable in di/di rats both at weaning and in adulthood (7-12-week-old). The lack of vasopressin abolished all chronic stress and anxiety-like tendencies both at weaning and in adulthood probably as a consequence of reduced ACTH rise immediately after MD in pups. This finding suggests that postnatal stress-induced ACTH rise may have long-term developmental consequences
The Same Magnocellular Neurons Send Axon Collaterals to the Posterior Pituitary and Retina or to the Posterior Pituitary and Autonomic Preganglionic Centers of the Eye in Rats
Persistent currents in Dirac fermion rings
The persistent current in strictly one-dimensional Dirac systems is investigated within two different models, defined in the continuum and on a lattice, respectively. The object of the study is the effect of a single magnetic or nonmagnetic impurity in the two systems. In the continuum Dirac model, an analytical expression for the persistent current flowing along a ring with a single delta-like magnetic impurity is obtained after regularization of the unbounded negative energy states. The predicted decay of the persistent current agrees with the lattice simulations. The results are generalized to finite temperatures. To realize a single Dirac massless fermion, the lattice model breaks the time-reversal symmetry, and in contrast with the continuum model, a pointlike nonmagnetic impurity can lead to a decay in the persistent current
Gaps and tails in graphene and graphane
We study the density of states in monolayer and bilayer graphene in the
presence of a random potential that breaks sublattice symmetries. While a
uniform symmetry-breaking potential opens a uniform gap, a random
symmetry-breaking potential also creates tails in the density of states. The
latter can close the gap again, preventing the system to become an insulator.
However, for a sufficiently large gap the tails contain localized states with
nonzero density of states. These localized states allow the system to conduct
at nonzero temperature via variable-range hopping. This result is in agreement
with recent experimental observations in graphane by Elias {\it et al.}.Comment: 16 pages, 7 figure
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