385 research outputs found
The absorption spectrum around nu=1: evidence for a small size Skyrmion
We measure the absorption spectrum of a two-dimensional electron system
(2DES) in a GaAs quantum well in the presence of a perpendicular magnetic
field. We focus on the absorption spectrum into the lowest Landau Level around
nu=1. We find that the spectrum consists of bound electron-hole complexes,
trion and exciton like. We show that their oscillator strength is a powerful
probe of the 2DES spatial correlations. We find that near nu=1 the 2DES ground
state consists of Skyrmions of small size (a few magnetic lengths).Comment: To be published in Phys Rev Lett. To be presented in ICSP2004,
Flagstaff, Arizona. 4 figures (1 of them in color). 5 page
Sensing electric and magnetic fields with Bose-Einstein Condensates
We discuss the application of Bose-Einstein condensates (BECs) as sensors for
magnetic and electric fields. In an experimental demonstration we have brought
one-dimensional BECs close to micro-fabricated wires on an atom chip and
thereby reached a sensitivity to potential variations of ~10e-14eV at 3 micron
spatial resolution. We demonstrate the versatility of this sensor by measuring
a two-dimensional magnetic field map 10 micron above a 100-micron-wide wire. We
show how the transverse current-density component inside the wire can be
reconstructed from such maps. The field sensitivity in dependence on the
spatial resolution is discussed and further improvements utilizing Feshbach
resonances are outlined.Comment: 4 pages, 3 figure
Atom Chips: Fabrication and Thermal Properties
Neutral atoms can be trapped and manipulated with surface mounted microscopic
current carrying and charged structures. We present a lithographic fabrication
process for such atom chips based on evaporated metal films. The size limit of
this process is below 1m. At room temperature, thin wires can carry more
than 10A/cm current density and voltages of more than 500V. Extensive
test measurements for different substrates and metal thicknesses (up to 5
m) are compared to models for the heating characteristics of the
microscopic wires. Among the materials tested, we find that Si is the best
suited substrate for atom chips
The Fermi edge singularity of spin polarized electrons
We study the absorption spectrum of a two-dimensional electron gas (2DEG) in
a magnetic field. We find that that at low temperatures, when the 2DEG is spin
polarized, the absorption spectra, which correspond to the creation of spin up
or spin down electron, differ in magnitude, linewidth and filling factor
dependence. We show that these differences can be explained as resulting from
creation of a Mahan exciton in one case, and of a power law Fermi edge
singularity in the other.Comment: 4 pages, 4 figures, published in Phys. Rev. Let
Multi-layer atom chips for versatile atom micro manipulation
We employ a combination of optical UV- and electron-beam-lithography to
create an atom chip combining sub-micron wire structures with larger
conventional wires on a single substrate. The new multi-layer fabrication
enables crossed wire configurations, greatly enhancing the flexibility in
designing potentials for ultra cold quantum gases and Bose-Einstein
condensates. Large current densities of >6 x 10^7 A/cm^2 and high voltages of
up to 65 V across 0.3 micron gaps are supported by even the smallest wire
structures. We experimentally demonstrate the flexibility of the next
generation atom chip by producing Bose-Einstein condensates in magnetic traps
created by a combination of wires involving all different fabrication methods
and structure sizes.Comment: 4 pages, 5 figure
An atom fiber for guiding cold neutral atoms
We present an omnidirectional matter wave guide on an atom chip. The
rotational symmetry of the guide is maintained by a combination of two current
carrying wires and a bias field pointing perpendicular to the chip surface. We
demonstrate guiding of thermal atoms around more than two complete turns along
a spiral shaped 25mm long curved path (curve radii down to 200m) at
various atom--surface distances (35-450m). An extension of the scheme for
the guiding of Bose-Einstein condensates is outlined
Optical absorption to probe the quantum Hall ferromagnet at filling factor
Optical absorption measurements are used to probe the spin polarization in
the integer and fractional quantum Hall effect regimes. The system is fully
spin polarized only at filling factor and at very low
temperatures( mK). A small change in filling factor
() leads to a significant depolarization. This
suggests that the itinerant quantum Hall ferromagnet at is surprisingly
fragile against increasing temperature, or against small changes in filling
factor.Comment: 4 pages, 2 figure
Optical Probing of the Spin Polarization of the nu=5/2 Quantum Hall State
We apply polarization resolved photoluminescence spectroscopy to measure the
spin polarization of a two dimensional electron gas in perpendicular magnetic
field. In the vicinity of filling factor nu=5/2, we observe a sharp
discontinuity in the energy of the zero Landau level emission line. We find
that the splitting between the two circular polarizations exhibits a sharp drop
at nu=5/2 and is equal to the bare Zeeman energy, which resembles the behavior
at even filling factors. We show that this behavior is consistent with filling
factor nu=5/2 being unpolarized
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