8 research outputs found
Imaging the formation of a p-n junction in a suspended carbon nanotube with scanning photocurrent microscopy
We use scanning photocurrent microscopy (SPCM) to investigate individual
suspended semiconducting carbon nanotube devices where the potential profile is
engineered by means of local gates. In situ tunable p-n junctions can be
generated at any position along the nanotube axis. Combining SPCM with
transport measurements allows a detailed microscopic study of the evolution of
the band profiles as a function of the gates voltage. Here we study the
emergence of a p-n and a n-p junctions out of a n-type transistor channel using
two local gates. In both cases the I-V curves recorded for gate configurations
corresponding to the formation of the p-n or n-p junction in the SPCM
measurements reveal a clear transition from resistive to rectification regimes.
The rectification curves can be fitted well to the Shockley diode model with a
series resistor and reveal a clear ideal diode behavior.Comment: Accepted for publication in Journal or Applied Physics. 4 pages, 3
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A Simple Empirically Motivated Template for the Unresolved Thermal Sunyaev-Zeldovich Effect
We develop a model for the power spectrum of unresolved clusters of galaxies
arising from the thermal Sunyaev-Zeldovich (tSZ) effect. The model is based on
a'universal' gas pressure profile constrained by X-ray observations and
includes a parameter to describe departures from self-similar evolution. The
model is consistent with recent Planck observations of the tSZ effect for X-ray
clusters with redshifts z<1 and reproduces the low amplitude for the tSZ
inferred from recent ground based observations. By adjusting two free
parameters, we are able to reproduce the tSZ power spectra from recent
numerical simulations to an accuracy that is well within theoretical
uncertainties. Our model provides a simple, empirically motivated tSZ template
that may be useful for the analysis of new experiments such as Planck.Comment: 6 pages 4 figure
Efimov physics beyond three particles
Efimov physics originally refers to a system of three particles. Here we
review recent theoretical progress seeking for manifestations of Efimov physics
in systems composed of more than three particles. Clusters of more than three
bosons are tied to each Efimov trimer, but no independent Efimov physics exists
there beyond three bosons. The case of a few heavy fermions interacting with a
lighter atom is also considered, where the mass ratio of the constituent
particles plays a significant role. Following Efimov's study of the (2+1)
system, the (3+1) system was shown to have its own critical mass ratio to
become Efimovian. We show that the (4+1) system becomes Efimovian at a mass
ratio which is smaller than its sub-systems thresholds, giving a pure five-body
Efimov effect. The (5+1) and (6+1) systems are also discussed, and we show the
absence of 6- and 7-body Efimov physics there
Evidence for Efimov quantum states in an ultracold gas of cesium atoms
Systems of three interacting particles are notorious for their complex
physical behavior. A landmark theoretical result in few-body quantum physics is
Efimov's prediction of a universal set of bound trimer states appearing for
three identical bosons with a resonant two-body interaction.
Counterintuitively, these states even exist in the absence of a corresponding
two-body bound state. Since the formulation of Efimov's problem in the context
of nuclear physics 35 years ago, it has attracted great interest in many areas
of physics. However, the observation of Efimov quantum states has remained an
elusive goal. Here we report the observation of an Efimov resonance in an
ultracold gas of cesium atoms. The resonance occurs in the range of large
negative two-body scattering lengths, arising from the coupling of three free
atoms to an Efimov trimer. Experimentally, we observe its signature as a giant
three-body recombination loss when the strength of the two-body interaction is
varied. We also detect a minimum in the recombination loss for positive
scattering lengths, indicating destructive interference of decay pathways. Our
results confirm central theoretical predictions of Efimov physics and represent
a starting point with which to explore the universal properties of resonantly
interacting few-body systems. While Feshbach resonances have provided the key
to control quantum-mechanical interactions on the two-body level, Efimov
resonances connect ultracold matter to the world of few-body quantum phenomena.Comment: 18 pages, 3 figure
A Class of Hamiltonians for a Three-Particle Fermionic System at Unitarity,
We consider a quantum mechanical three-particle system made of two identical fermions of mass one and a different particle of mass m, where each fermion interacts via a zero-range force with the different particle. In particular we study the unitary regime, i.e., the case of infinite two-body scattering length. The Hamiltonians describing the system are, by definition, self-adjoint extensions of the free Hamiltonian restricted on smooth functions vanishing at the two-body coincidence planes, i.e., where the positions of two interacting particles coincide. It is known that for m larger than a critical value m* similar or equal to (13.607)(-1) a self-adjoint and lower bounded Hamiltonian H-0 can be constructed, whose domain is characterized in terms of the standard point-interaction boundary condition at each coincidence plane. Here we prove that for m. (m*, m**), where m** similar or equal to (8.62)(-1), there is a further family of self-adjoint and lower bounded Hamiltonians H-0,H-beta, beta epsilon R, describing the system. Using a quadratic form method, we give a rigorous construction of such Hamiltonians and we show that the elements of their domains satisfy a further boundary condition, characterizing the singular behavior when the positions of all the three particles coincide