22,126 research outputs found
Non-adiabatic molecular association in thermal gases driven by radio-frequency pulses
The molecular association process in a thermal gas of Rb is
investigated where the effects of the envelope of the radio-frequency field are
taken into account. For experimentally relevant parameters our analysis shows
that with increasing pulse length the corresponding molecular conversion
efficiency exhibits low-frequency interference fringes which are robust under
thermal averaging over a wide range of temperatures. This dynamical
interference phenomenon is attributed to St\"uckelberg phase accumulation
between the low-energy continuum states and the dressed molecular state which
exhibits a shift proportional to the envelope of the radio-frequency pulse
intensity.Comment: 5 pages, 3 figure
"So what will you do if string theory is wrong?"
I briefly discuss the accomplishments of string theory that would survive a
complete falsification of the theory as a model of nature and argue the
possibility that such a survival may necessarily mean that string theory would
become its own discipline, independently of both physics and mathematics
Recommended from our members
Sipping Fuel and Saving Lives: Increasing Fuel Economy without Sacrificing Safety
Demonstrates how new fuel-efficiency technologies make it possible, and advisable, to significantly increase the fuel economy of motor vehicles without compromising their safety
Suppressed Andreev Reflection at the Normal-Metal / Heavy-Fermion Superconductor CeCoIn Interface
Dynamic conductance spectra are taken from Au/CeCoIn point contacts in
the Sharvin limit along the (001) and (110) directions. Our conductance
spectra, reproducibly obtained over wide ranges of temperature, constitute the
cleanest data sets ever reported for HFSs. A signature for the emerging
heavy-fermion liquid is evidenced by the development of the asymmetry in the
background in the normal state. Below , an enhancement of the sub-gap
conductance arising from Andreev reflection is observed, with the magnitude of
13.3 % and 11.8 % for the (001) and the (110) point contacts,
respectively, an order of magnitude smaller than those observed in conventional
superconductors but consistent with those in other HFSs. Our zero-bias
conductance data for the (001) point contacts are best fit with the extended
BTK model using the d-wave order parameter. The fit to the full conductance
curve of the (001) point contact indicates the strong coupling nature
(). However, our observed suppression of both the
Andreev reflection signal and the energy gap indicates the failure of existing
models. We provide possible directions for theoretical formulations of the
electronic transport across an N/HFS interface. Several qualitative features
observed in the (110) point contacts provide the first clear spectroscopic
evidence for the symmetry.Comment: 13 pages, 7 figures, LaTeX, paper invited and submitted to SPIE
Conference on Strongly Correlated Electron Materials: Physics and
Nanoengineering, in San Diego, California, July 31 - August 4, 200
Point-contact spectroscopy in heavy-fermion superconductors
We develop a minimal model to calculate point-contact spectra between a
metallic tip and a superconducting heavy-fermion system. We apply our tunneling
model to the heavy fermion CeCoIn5, both in the normal and superconducting
state. In point-contact and scanning tunneling spectroscopy many heavy-fermion
materials, like CeCoIn5, exhibit an asymmetric differential conductance, dI/dV,
combined with a strongly suppressed Andreev reflection signal in the
superconducting state. We argue that both features may be explained in terms of
a multichannel tunneling model in the presence of localized states near the
interface. We find that it is not sufficient to tunnel into two itinerant bands
of light and heavy electrons to explain the Fano line shape of the differential
conductance. Localized states in the bulk or near the interface are an
essential component for quantum interference to occur when an electron tunnels
from the metallic tip of the point contact into the heavy-fermion system.Comment: 13 pages, 9 figures. Accepted for publication in Physical Review
ALMA Observations of a Candidate Molecular Outflow in an Obscured Quasar
We present Atacama Large Millimeter/Submillimeter Array (ALMA) CO (1-0) and
CO (3-2) observations of SDSS J135646.10+102609.0, an obscured quasar and
ultra-luminous infrared galaxy (ULIRG) with two merging nuclei and a known
20-kpc-scale ionized outflow. The total molecular gas mass is M_{mol} ~
9^{+19}_{-6} x 10^8 Msun, mostly distributed in a compact rotating disk at the
primary nucleus (M_{mol} ~ 3 x 10^8 Msun) and an extended tidal arm (M_{mol} ~
5 x 10^8 Msun). The tidal arm is one of the most massive molecular tidal
features known; we suggest that it is due to the lower chance of shock
dissociation in this elliptical/disk galaxy merger. In the spatially resolved
CO (3-2) data, we find a compact (r ~ 0.3 kpc) high velocity (v ~ 500 km/s)
red-shifted feature in addition to the rotation at the N nucleus. We propose a
molecular outflow as the most likely explanation for the high velocity gas. The
outflowing mass of M_{mol} ~ 7 x 10^7 Msun and the short dynamical time of
t_{dyn} ~ 0.6 Myr yield a very high outflow rate of \dot{M}_{mol} ~ 350 Msun/yr
and can deplete the gas in a million years. We find a low star formation rate
(< 16 Msun/yr from the molecular content and < 21 Msun/yr from the far-infrared
spectral energy distribution decomposition) that is inadequate to supply the
kinetic luminosity of the outflow (\dot{E} ~ 3 x 10^43 erg/s). Therefore, the
active galactic nucleus, with a bolometric luminosity of 10^46 erg/s, likely
powers the outflow. The momentum boost rate of the outflow (\dot{p}/(Lbol/c) ~
3) is lower than typical molecular outflows associated with AGN, which may be
related to its compactness. The molecular and ionized outflows are likely two
distinct bursts induced by episodic AGN activity that varies on a time scale of
10^7 yr.Comment: 16 pages, 7 figures, ApJ accepte
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