438 research outputs found
Direct probing of band-structure Berry phase in diluted magnetic semiconductors
We report on experimental evidence of the Berry phase accumulated by the
charge carrier wave function in single-domain nanowires made from a
(Ga,Mn)(As,P) diluted ferromagnetic semiconductor layer. Its signature on the
mesoscopic transport measurements is revealed as unusual patterns in the
magnetoconductance, that are clearly distinguished from the universal
conductance fluctuations. We show that these patterns appear in a magnetic
field region where the magnetization rotates coherently and are related to a
change in the band-structure Berry phase as the magnetization direction
changes. They should be thus considered as a band structure Berry phase
fingerprint of the effective magnetic monopoles in the momentum space. We argue
that this is an efficient method to vary the band structure in a controlled way
and to probe it directly. Hence, (Ga,Mn)As appears to be a very interesting
test bench for new concepts based on this geometrical phase.Comment: 7 pages, 6 figure
IMPORTING JOBS AND EXPORTING FIRMS? ON THE WAGE AND EMPLOYMENT IMPLICATIONS OF ITALY’S TRADE AND FOREIGN DIRECT INVESTMENT FLOWS
International economic integration is often blamed for the deteriorating fortunes of unskilled workers in industrial countries. We look at the labor market impact of trade and foreign direct investment in the case of Italy. Our empirical framework allows for trade, technology and factor supply effects. We find that international trade did not contribute to Italy’s labor market problems. Indeed, given that Italy holds quite a distinct pattern of trade specialization, compared to other industrialized countries, international integration as reflected in falling import prices may have boosted the demand for labor there. We also argue that the inability of the Mezzogiorno’s economy to adjust to the changing international environment is one of the main stumbling blocks in Italy’s economy. Finally, we find that greater firm’s mobility may have weakened the power of trade unions and contributed to wage moderation.international trade, foreign direct investment,wages, employment
High-Quality Planar high-Tc Josephson Junctions
Reproducible high-Tc Josephson junctions have been made in a rather simple
two-step process using ion irradiation. A microbridge (1 to 5 ?m wide) is
firstly designed by ion irradiating a c-axis-oriented YBa2Cu3O7-? film through
a gold mask such as the non-protected part becomes insulating. A lower Tc part
is then defined within the bridge by irradiating with a much lower fluence
through a narrow slit (20 nm) opened in a standard electronic photoresist.
These planar junctions, whose settings can be finely tuned, exhibit
reproducible and nearly ideal Josephson characteristics. This process can be
used to produce complex Josephson circuits.Comment: 4 pages, 5 figures, to be published in Applied Physics Letter
Tuning decoherence with a voltage probe
We present an experiment where we tune the decoherence in a quantum
interferometer using one of the simplest object available in the physic of
quantum conductors : an ohmic contact. For that purpose, we designed an
electronic Mach-Zehnder interferometer which has one of its two arms connected
to an ohmic contact through a quantum point contact. At low temperature, we
observe quantum interference patterns with a visibility up to 57%. Increasing
the connection between one arm of the interferometer to the floating ohmic
contact, the voltage probe, reduces quantum interferences as it probes the
electron trajectory. This unique experimental realization of a voltage probe
works as a trivial which-path detector whose efficiency can be simply tuned by
a gate voltage
Improving HTc Josephson Junctions (HTc JJ) by annealing: the role of vacancy-interstitial annihilation
We have studied the annealing effect in transport properties of High
temperature Josephson Junctions (HTc JJ) made by ion irradiation. Low
temperature annealing (80 degrees Celsius) increases the JJ transition
temperature (TJ) and the Ic.Rn product, where Ic is the critical current and Rn
the normal resistance. We found that the spread in JJ characteristics can be
lowered by sufficient long annealing times. Using random walk numerical
simulations, we showed that the characteristic annealing time and the evolution
of the spread in JJ characteristics can be explained by a vacancy-interstitial
annihilation process rather than by an oxygen diffusion one.Comment: 7 pages and 3 figures submitted to Applied Physics Letter
Study and optimization of ion-irradiated High-Tc Josephson nanoJunctions by Monte Carlo simulations
High Tc Josephson nanoJunctions (HTc JnJ) made by ion irradiation have
remarkable properties for technological applications. However, the spread in
their electrical characteristics increases with the ion dose. We present a
simple model to explain the JnJ inhomogeneities, which accounts quantitatively
for experimental data. The spread in the slit's width of the irradiation mask
is the limiting factor.Monte Carlo simulations have been performed using
different irradiation conditions to study their influence on the spread of the
JnJ charcateristics. A "universal" behavior has been evidenced, which allows to
propose new strategies to optimize JnJ reproducibility.Comment: 14 pages, 6 Figures. accepted in Journal of Applied Physic
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