Ultracold gas of polar molecules
1 November 2008
D. Jin and his colleagues at the NIST/JILA Laboratory in the USA obtained ultracold gas of
molecules possessing considerable electric dipole moments. Earlier attempts to create such
a gas failed because of difficulties with cooling. The new experiment began with forming a
mixture of potassium and rubidium atoms in an optical trap. Magnetic field triggered
attraction between atoms of different type through the Feshbach resonance mechanism (see
e.g. Phys. Usp. 49 333 (2006) ), and polar diatomic molecules 40K87Rb were formed in
excited state. The difficulty in cooling stemmed from the fact that the energy of
rotational and vibrational modes of molecules converted to kinetic energy of molecules and
the gas heated up. The researchers from NIST/JILA developed a new technique of radiative
cooling: the gas was irradiated by laser light of specially selected frequency in the
near-IR range. As molecules dropped to lower energy levels, released energy did not go
into heating the gas but was carried away by the emitted photons. The success of the
method of cooling is based on the progress in theoretical calculations of the structure of
energy levels of molecules, which made it possible to choose the radiation frequency
correctly. In this way it was possible to cool the gas to a temperature of 350 nK and
achieve a transition to a nearly degenerate state at a density 1012 molecules per
cm3. Ultracold gas consisting of polar molecules may find applications in quantum
Source: Science 322 231 (2008)
5 November 2008
A team of researchers led by I. Bozovic (Brookhaven National Laboratory) created and
studied two-layer films in which each of the layers is non-superconducting in itself but
the thin zone close to the common interface (1 to 2 nm in thickness) is superconducting.
Layers of lanthanum cuprate doped with strontium were deposited using molecular epitaxy
which created an almost ideal interface between the layers. Depending on the amount of
admixture, the cuprates are insulators, superconductors or ordinary conductors. The layer
of La2CuO4 in the specimen obtained was insulating while the layer of
La1,55Sr0,45CuO4 was a conductor. However, the boundary layer only several atoms thick was superconducting with a critical temperature of about 50 K, which is 10 K higher than the critical temperature of one thick layer in which the admixture
concentration corresponds to the superconducting state. It was shown using
transmission electron microscopy that the interface between the layers is sharp, that is,
there is no transition region in the specimen with an intermediate concentration of
admixture. Therefore, the two-dimensional superconductivity of the specimen is essentially
an effect induced by the boundary between two physically and chemically different layers.
The researchers hope that thin superconducting films like this may constitute a basis for creating
superconducting field transistors and other nanometer-scale devices. For superconductivity
of cuprate thin films, see Phys. Usp. 51 170 (2008) .
Sources: Nature 455 782 (2008)
Anomalous spin-state segregation
1 November 2008
J. Thomas and his colleagues at Duke University discovered an effect which still resists attempts to give a theoretical explanation. Cold gas of lithium-6 atoms with identical spit orientation was put
into an optical trap. Then the researchers tried to apply radiofrequency radiation to transfer the
atoms to the state of superposition at a probability of 50%
for each of the two directions of spin. However, several tenths of a second later the atoms
unexpectedly separated spatially, with atoms with one spin direction rushing towards the center of
the trap while atoms with the opposite spin shifting to the periphery; the gas remained in this
state for several seconds. Forces between individual atoms are too small for explaining this effect.
The researchers believe that segregation in spin states occurred through formation of spin waves;
however, according to the reigning theoretical models the spin waves mechanism is also
insufficiently efficient for such a strong segregation.
Source: Phys. Rev. Lett. 101 150401 (2008)
Magnetic field in a remote galaxy
1 November 2008
Observations with Green Bank radio telescope were used to measure the magnetic field in the
DLA-3C286 galaxy that we see at the epoch when the Universe was 6.5 billion years younger. The field
was found to be approximately 10 times higher than the average magnetic field in our Galaxy. This
result came as very unexpected since it was assumed that the magnetic field in galaxies increases
gradually over billions of years through the dynamo mechanism. Another interesting fact is that the
rate of new star formation in DLA-3C286 is relatively low, which may be related to unusually high
magnetic field. It is possible that the dynamo theory needs modification to suit the DLA-ăĐ286
galaxy. Another hypothesis suggests that the high magnetic field is a result of shock waves in the
gas produced by a collision of two galaxies.
Massive dwarf galaxy
1 November 2008
╠. Geha and coworkers using KEK discovered a dwarf galaxy Ś a satellite of our Galaxy populated by
only several tens or perhaps hundreds of stars; however, the mass of this galaxy is almost a 1000
times larger than is deduced from its luminosity. This Galaxy, now known as Segue 1, is not a
globular cluster. This was derived from large virial velocities of stars and the corresponding large
mass of the galaxy. Furthermore, the metals content in the stars of Segue 1 is considerably lower
than in stars of globular clusters of our Galaxy. The large invisible mass of Segue 1 rests in the
dark matter whose nature is so far unknown. The mass-to-luminosity ratio for Segue 1 is record high
among all known galaxies.
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.
Permanent editor is Yu.N. Eroshenko.
It is compiled from a multitude of Internet sources.