31 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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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
Observation of an Efimov spectrum in an atomic system
In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is
still of great interest today. He found that three particles subjected to a
resonant pairwise interaction can join into an infinite number of loosely bound
states even though each particle pair cannot bind. Interestingly, the
properties of these aggregates, such as the peculiar geometric scaling of their
energy spectrum, are universal, i.e. independent of the microscopic details of
their components. Despite an extensive search in many different physical
systems, including atoms, molecules and nuclei, the characteristic spectrum of
Efimov trimer states still eludes observation. Here we report on the discovery
of two bound trimer states of potassium atoms very close to the Efimov
scenario, which we reveal by studying three-particle collisions in an ultracold
gas. Our observation provides the first evidence of an Efimov spectrum and
allows a direct test of its scaling behaviour, shedding new light onto the
physics of few-body systems.Comment: 10 pages, 3 figures, 1 tabl
Molecular physics: Ultracold ménage à trois
One of the fundamental problems in few-body physics is the formation of diatomic molecules in three-atom collisions. An experimental technique now explores the resulting distribution of molecular quantum states in an ultracold gas