1,116 research outputs found
The stochastic pump current and the non-adiabatic geometrical phase
We calculate a pump current in a classical two-state stochastic chemical
kinetics by means of the non-adiabatic geometrical phase interpretation. The
two-state system is attached to two particle reservoirs, and under a periodic
perturbation of the kinetic rates, it gives rise to a pump current between the
two-state system and the absorbing states. In order to calculate the pump
current, the Floquet theory for the non-adiabatic geometrical phase is extended
from a Hermitian case to a non-Hermitian case. The dependence of the pump
current on the frequency of the perturbative kinetic rates is explicitly
derived, and a stochastic resonance-like behavior is obtained.Comment: 11 page
Noncyclic and nonadiabatic geometric phase for counting statistics
We propose a general framework of the geometric-phase interpretation for
counting statistics. Counting statistics is a scheme to count the number of
specific transitions in a stochastic process. The cumulant generating function
for the counting statistics can be interpreted as a `phase', and it is
generally divided into two parts: the dynamical phase and a remaining one. It
has already been shown that for cyclic evolution the remaining phase
corresponds to a geometric phase, such as the Berry phase or Aharonov-Anandan
phase. We here show that the remaining phase also has an interpretation as a
geometric phase even in noncyclic and nonadiabatic evolution.Comment: 12 pages, 1 figur
Spin-filter tunnel junction with matched Fermi surfaces
Efficient injection of spin-polarized current into a semiconductor is a basic
prerequisite for building semiconductor-based spintronic devices. Here, we use
inelastic electron tunneling spectroscopy to show that the efficiency of
spin-filter-type spin injectors is limited by spin scattering of the tunneling
electrons. By matching the Fermi-surface shapes of the current injection source
and target electrode material, spin injection efficiency can be significantly
increased in epitaxial ferromagnetic insulator tunnel junctions. Our results
demonstrate that not only structural but also Fermi-surface matching is
important to suppress scattering processes in spintronic devices.Comment: 5 pages, 4 figure
In-situ photoemission study of Pr_{1-x}Ca_xMnO_3 epitaxial thin films with suppressed charge fluctuations
We have performed an {\it in-situ} photoemission study of Pr_{1-x}Ca_xMnO_3
(PCMO) thin films grown on LaAlO_3 (001) substrates and observed the effect of
epitaxial strain on the electronic structure. We found that the chemical
potential shifted monotonically with doping, unlike bulk PCMO, implying the
disappearance of incommensurate charge fluctuations of bulk PCMO. In the
valence-band spectra, we found a doping-induced energy shift toward the Fermi
level (E_F) but there was no spectral weight transfer, which was observed in
bulk PCMO. The gap at E_F was clearly seen in the experimental band dispersions
determined by angle-resolved photoemission spectroscopy and could not be
explained by the metallic band structure of the C-type antiferromagnetic state,
probably due to localization of electrons along the ferromagnetic chain
direction or due to another type of spin-orbital ordering.Comment: 5 pages, 4 figure
Infrared anomalous Hall effect in SrRuO: Evidence for crossover to intrinsic behavior
The origin of the Hall effect in many itinerant ferromagnets is still not
resolved, with an anomalous contribution from the sample magnetization that can
exhibit extrinsic or intrinsic behavior. We report the first mid-infared (MIR)
measurements of the complex Hall (), Faraday (), and Kerr
() angles, as well as the Hall conductivity () in a
SrRuO film in the 115-1400 meV energy range. The magnetic field,
temperature, and frequency dependence of the Hall effect is explored. The MIR
magneto-optical response shows very strong frequency dependence, including sign
changes. Below 200 meV, the MIR changes sign between 120 and 150
K, as is observed in dc Hall measurements. Above 200 meV, the temperature
dependence of is similar to that of the dc magnetization and the
measurements are in good agreement with predictions from a band calculation for
the intrinsic anomalous Hall effect (AHE). The temperature and frequency
dependence of the measured Hall effect suggests that whereas the behavior above
200 meV is consistent with an intrinsic AHE, the extrinsic AHE plays an
important role in the lower energy response.Comment: The resolution of figures is improve
An improved continuous compositional-spread technique based on pulsed-laser deposition and applicable to large substrate areas
A new method for continuous compositional-spread (CCS) thin-film fabrication
based on pulsed-laser deposition (PLD) is introduced. This approach is based on
a translation of the substrate heater and the synchronized firing of the
excimer laser, with the deposition occurring through a slit-shaped aperture.
Alloying is achieved during film growth (possible at elevated temperature) by
the repeated sequential deposition of sub-monolayer amounts. Our approach
overcomes serious shortcomings in previous in-situ implementations of CCS based
on sputtering or PLD, in particular the variations of thickness across the
compositional spread and the differing deposition energetics as function of
position. While moving-shutter techniques are appropriate for PLD-approaches
yielding complete spreads on small substrates (i.e. small as compared to
distances over which the deposition parameters in PLD vary, typically about 1
cm), our method can be used to fabricate samples that are large enough for
individual compositions to be analyzed by conventional techniques, including
temperature-dependent measurements of resistivity and dielectric and magnetic
and properties (i.e. SQUID magnetometry). Initial results are shown for spreads
of (Sr,Ca)RuO.Comment: 6 pages, 8 figures, accepted for publication in Rev. Sci. Instru
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