538 research outputs found
Superconductivity in SrFe_(2-x)Co_xAs_2: Internal Doping of the Iron Arsenide Layers
In the electron doped compounds SrFe_(2-x)Co_xAs_2 superconductivity with T_c
up to 20 K is observed for 0.2 < x < 0.4. Results of structure determination,
magnetic susceptibility, electrical resistivity, and specific heat are
reported. The observation of bulk superconductivity in all thermodynamic
properties -- despite strong disorder in the Fe-As layer -- favors an itinerant
picture in contrast to the cuprates and renders a p- or d-wave scenario
unlikely. DFT calculations find that the substitution of Fe by Co (x > 0.3)
leads to the suppression of the magnetic ordering present in SrFe_2As_2 due to
a rigid down-shift of the Fe-3d_(x^2-y^2) related band edge in the density of
states.Comment: 5 pages, 3 figure
Scaling Study and Thermodynamic Properties of the cubic Helimagnet FeGe
The critical behavior of the cubic helimagnet FeGe was obtained from
isothermal magnetization data in very close vicinity of the ordering
temperature. A thorough and consistent scaling analysis of these data revealed
the critical exponents , , and . The
anomaly in the specific heat associated with the magnetic ordering can be well
described by the critical exponent . The values of these
exponents corroborate that the magnetic phase transition in FeGe belongs to the
isotropic 3D-Heisenberg universality class. The specific heat data are well
described by ab initio phonon calculations and confirm the localized character
of the magnetic moments.Comment: 10 pages, 8 figure
Large Noncollinearity and Spin Reorientation in the Novel Mn2RhSn Heusler Magnet
Noncollinear magnets provide essential ingredients for the next generation
memory technology. It is a new prospect for the Heusler materials, already well
known due to the diverse range of other fundamental characteristics. Here, we
present a combined experimental and theoretical study of novel noncollinear
tetragonal Mn2RhSn Heusler material exhibiting unusually strong canting of its
magnetic sublattices. It undergoes a spin-reorientation transition, induced by
a temperature change and suppressed by an external magnetic field. Because of
the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, Mn2RhSn
is suggested to be a promising candidate for realizing the Skyrmion state in
the Heusler family
Electronic structure and magnetic properties of the spin-1/2 Heisenberg system CuSe2O5
A microscopic magnetic model for the spin-1/2 Heisenberg chain compound
CuSe2O5 is developed based on the results of a joint experimental and
theoretical study. Magnetic susceptibility and specific heat data give evidence
for quasi-1D magnetism with leading antiferromagnetic (AFM) couplings and an
AFM ordering temperature of 17 K. For microscopic insight, full-potential DFT
calculations within the local density approximation (LDA) were performed. Using
the resulting band structure, a consistent set of transfer integrals for an
effective one-band tight-binding model was obtained. Electronic correlations
were treated on a mean-field level starting from LDA (LSDA+U method) and on a
model level (Hubbard model). In excellent agreement of experiment and theory,
we find that only two couplings in CuSe2O5 are relevant: the nearest-neighbour
intra-chain interaction of 165 K and a non-frustrated inter-chain coupling of
20 K. From a comparison with structurally related systems (Sr2Cu(PO4)2,
Bi2CuO4), general implications for a magnetic ordering in presence of
inter-chain frustration are made.Comment: 20 pages, 8 figures, 3 table
Growth dynamics of a Bose-Einstein condensate in a dimple trap without cooling
We study the formation of a Bose-Einstein condensate in a cigar-shaped
three-dimensional harmonic trap, induced by the controlled addition of an
attractive "dimple" potential along the weak axis. In this manner we are able
to induce condensation without cooling due to a localized increase in the phase
space density. We perform a quantitative analysis of the thermodynamic
transformation in both the sudden and adiabatic regimes for a range of dimple
widths and depths. We find good agreement with equilibrium calculations based
on self-consistent semiclassical Hartree-Fock theory describing the condensate
and thermal cloud. We observe there is an optimal dimple depth that results in
a maximum in the condensate fraction. We also study the non-equilibrium
dynamics of condensate formation in the sudden turn-on regime, finding good
agreement for the observed time dependence of the condensate fraction with
calculations based on quantum kinetic theory.Comment: v1: 9 pages, 7 figures, submitted to Phys. Rev. A; v2: 10 pages, 8
figures, fixed typos, added references, additional details on experimental
procedure, values of phase-space density, new figure and discussion on
effects of three-body loss in Appendix B (replaced with published version
Versatile two-dimensional potentials for ultra-cold atoms
We propose and investigate a technique for generating smooth two-dimensional
potentials for ultra-cold atoms based on the rapid scanning of a far-detuned
laser beam using a two-dimensional acousto-optical modulator (AOM). We
demonstrate the implementation of a feed-forward mechanism for fast and
accurate control of the spatial intensity of the laser beam, resulting in
improved homogeneity for the atom trap. This technique could be used to
generate a smooth toroidal trap that would be useful for static and dynamic
experiments on superfluidity and persistent currents with ultra-cold atoms.Comment: 8 pages, 5 figure
- …