2,123 research outputs found
Localization of massless Dirac particles via spatial modulations of the Fermi velocity
The electrons found in Dirac materials are notorious for being difficult to
manipulate due to the Klein phenomenon and absence of backscattering. Here we
investigate how spatial modulations of the Fermi velocity in two-dimensional
Dirac materials can give rise to localization effects, with either full
(zero-dimensional) confinement or partial (one-dimensional) confinement
possible depending on the geometry of the velocity modulation. We present
several exactly solvable models illustrating the nature of the bound states
which arise, revealing how the gradient of the Fermi velocity is crucial for
determining fundamental properties of the bound states such as the zero-point
energy. We discuss the implications for guiding electronic waves in few-mode
waveguides formed by Fermi velocity modulation.Comment: 9 pages, 6 figure
Time domain phase measuring apparatus
The phase and/or period stability of a device is determined by connecting the device in one orthogonal arm of a phase detector having a mixer. In the other arm is an adjustable, variable phase shift device. The output of the mixer is fed through an active low pass filter to derive a DC voltage indicative of the phase shift. The variable phase device is adjusted so that the DC voltage will nullify the phase shift of the tested device under normal conditions. The DC voltage level is converted into a time interval indicative of the phase change of the tested device by determining when the level equals the amplitude of a low frequency ramp voltage. The interval between adjacent equality points can be measured or the period between a reference point on the ramp voltage and the quality be measured
Field-theoretical approach to the Casimir-like interaction in a one-dimensional Bose gas
We study the fluctuation-induced interaction between two impurities in a
weakly-interacting one-dimensional Bose gas using the field theoretical
approach. At separations between impurities shorter and of the order of the
healing length of the system, the induced interaction has a classical origin
and behaves exponentially. At separations longer than the healing length, the
interaction is of a quantum origin and scales as the third power of the inverse
distance. Finite temperature destroys the quasi-long-range order of the Bose
gas and, accordingly, the induced interaction becomes exponentially suppressed
beyond the thermal length. We obtain analytical expressions for the induced
interaction at zero and finite temperature that are valid at arbitrary
distances. We discuss experimental realizations as well as possible formation
of bound states of two impurities, known as bipolarons.Comment: 14 pages, 1 figure; accepted to Physical Review
Fragmentation with a Steady Source
We investigate fragmentation processes with a steady input of fragments. We
find that the size distribution approaches a stationary form which exhibits a
power law divergence in the small size limit, P(x) ~ x^{-3}. This algebraic
behavior is robust as it is independent of the details of the input as well as
the spatial dimension. The full time dependent behavior is obtained
analytically for arbitrary inputs, and is found to exhibit a universal scaling
behavior.Comment: 4 page
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