46,135 research outputs found
Singlet and Triplet Superfluid Competition in a Mixture of Two-Component Fermi and One-Component Dipolar Bose Gases
We consider a mixture of two-component Fermi and (one-component) dipolar Bose
gases in which both dipolar interaction and s-wave scattering between fermions
of opposite spins are tunable. We show that in the long wavelength limit, the
anisotropy in the Fermi-Fermi interaction induced by phonons of the dipolar
condensate can strongly enhance the scattering in the triplet channel. We
investigate in detail the conditions for achieving optimal critical temperature
at which the triplet superfluid begins to compete with the singlet superfluid.Comment: 5 pages, 2 figure
Modeling Mobility Degradation in Scanning Capacitance Microscopy for Semiconductor Dopant Profile Measurement
Scanning capacitance microscopy (SCM) based on the MOS capacitor C-V characteristics is a comparative new technique for dopant profile extraction. It utilises the high spatial resolution of scanning probe microscopy. However extraction of dopant profile near a p-n junction has not been successful due to the complex physics involved: typically unrealistically high dopant concentration near the junction is deduced (corresponding to low SCM dC/dV data). Better understanding of SCM measurement and modelling is required to enhance the accuracy of the extracted dopant concentration. This paper addresses the influence of mobility degradation on the SCM measurement via modelling and comparison with experimental SCM data. The rational for looking into mobility effect is that SCM capacitance measurement is carried out at 915 MHz. At this frequency, resistance of semiconductor surface can be comparable to the reactance of the SCM capacitance. In our simulation carrier mobilities at the semiconductor surface are set low compared to their bulk values to reflect surface mobility degradation. Our results show that the simulated SCM dC/dV is significantly reduced in the vicinity of p-n junction reflecting what is observed experimentally. We attribute this to the fact that the capacitance between the inverted surface and the SCM probe is not detected due to the high resistance (compared to the reactance of the SCM capacitance) of the inversion layer below the semiconductor and oxide interface. Only the capacitance on the accumulation side is extracted thus leading to the lowering of the detected SCM capacitance and dC/dV. The major conclusion is that the effect of high resistance due to mobility degradation has to be treated carefully for accurate extraction of dopant profile from experimental SCM data
Modeling the Effects of Interface Traps on Scanning Capacitance Microscopy dC/dV Measurement
Scanning capacitance microscopy (SCM) measurement is a proposed tool for dopant profile extraction for semiconductor material. The influence of interface traps on SCM dC/dV data is still unclear. In this paper we report on the simulation work used to study the nature of SCM dC/dV data in the presence of interface traps. A technique to correctly simulate dC/dV of SCM measurement is then presented based on our justification. We also analyze how charge of interface traps surrounding SCM probe would affect SCM dC/dV due the small SCM probe dimension
Spontaneous phase oscillation induced by inertia and time delay
We consider a system of coupled oscillators with finite inertia and
time-delayed interaction, and investigate the interplay between inertia and
delay both analytically and numerically. The phase velocity of the system is
examined; revealed in numerical simulations is emergence of spontaneous phase
oscillation without external driving, which turns out to be in good agreement
with analytical results derived in the strong-coupling limit. Such
self-oscillation is found to suppress synchronization and its frequency is
observed to decrease with inertia and delay. We obtain the phase diagram, which
displays oscillatory and stationary phases in the appropriate regions of the
parameters.Comment: 5 pages, 6 figures, to pe published in PR
Exact solution of gyration radius of individual's trajectory for a simplified human mobility model
Gyration radius of individual's trajectory plays a key role in quantifying
human mobility patterns. Of particular interests, empirical analyses suggest
that the growth of gyration radius is slow versus time except the very early
stage and may eventually arrive to a steady value. However, up to now, the
underlying mechanism leading to such a possibly steady value has not been well
understood. In this Letter, we propose a simplified human mobility model to
simulate individual's daily travel with three sequential activities: commuting
to workplace, going to do leisure activities and returning home. With the
assumption that individual has constant travel speed and inferior limit of time
at home and work, we prove that the daily moving area of an individual is an
ellipse, and finally get an exact solution of the gyration radius. The
analytical solution well captures the empirical observation reported in [M. C.
Gonz`alez et al., Nature, 453 (2008) 779]. We also find that, in spite of the
heterogeneous displacement distribution in the population level, individuals in
our model have characteristic displacements, indicating a completely different
mechanism to the one proposed by Song et al. [Nat. Phys. 6 (2010) 818].Comment: 4 pages, 4 figure
Superfluid pairing in a mixture of a spin-polarized Fermi gas and a dipolar condensate
We consider a mixture of a spin-polarized Fermi gas and a dipolar
Bose-Einstein condensate in which s-wave scattering between fermions and the
quasiparticles of the dipolar condensate can result in an effective attractive
Fermi-Fermi interaction anisotropic in nature and tunable by the dipolar
interaction. We show that such an interaction can significantly increase the
prospect of realizing a superfluid with a gap parameter characterized with a
coherent superposition of all odd partial waves. We formulate, in the spirit of
the Hartree-Fock-Bogoliubov mean-field approach, a theory which allows us to
estimate the critical temperature when the anisotropic Fock potential is taken
into consideration and to determine the system parameters that optimize the
critical temperature at which such a superfluid emerges before the system
begins to phase separate.Comment: 10 pages, 3 figure
Effects of Domain Wall on Electronic Transport Properties in Mesoscopic Wire of Metallic Ferromagnets
We study the effect of the domain wall on electronic transport properties in
wire of ferromagnetic 3 transition metals based on the linear response
theory. We considered the exchange interaction between the conduction electron
and the magnetization, taking into account the scattering by impurities as
well. The effective electron-wall interaction is derived by use of a local
gauge transformation in the spin space. This interaction is treated
perturbatively to the second order. The conductivity contribution within the
classical (Boltzmann) transport theory turns out to be negligiblly small in
bulk magnets, due to a large thickness of the wall compared with the fermi
wavelength. It can be, however, significant in ballistic nanocontacts, as
indicated in recent experiments. We also discuss the quantum correction in
disordered case where the quantum coherence among electrons becomes important.
In such case of weak localization the wall can contribute to a decrease of
resistivity by causing dephasing. At lower temperature this effect grows and
can win over the classical contribution, in particular in wire of diameter
, being the inelastic diffusion
length. Conductance change of the quantum origin caused by the motion of the
wall is also discussed.Comment: 30 pages, 4 figures. Detailed paper of Phys. Rev. Lett. 78, 3773
(1997). Submitted to J. Phys. Soc. Jp
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