18 research outputs found
Solitons explore the quantum classical boundary
It is an open fundamental question how the classical appearance of our
environment arises from the underlying quantum many-body theory. We propose
that the quantum-classical boundary can be probed in collisions of bright
solitons in Bose-Einstein condensates, where thousands of atoms form a large
compound object at ultra cold temperatures. We show that these collisions
exhibit intricate many-body quantum behavior, invalidating mean field theory.
Prior to collision, solitons can loose their well defined quantum phase
relation through phase diffusion, essentially caused by atom number
fluctuations. This dephasing should typically render the subsequent dynamics
more classical. Instead, we find that it opens the door for a tremendous
proliferation of mesoscopic entanglement: After collision the two solitons find
themselves in a superposition state of various constituent atom numbers,
positions and velocities, in which all these quantities are entangled with
those of the collision partner.
As the solitons appear to traverse the quantum-classical boundary back and
forth during their scattering process, they emerge as natural probe of
mesoscopic quantum coherence and decoherence phenomena.Comment: 6 pages, 4 figure
Ab initio guided minimal model for the "Kitaev" material BaCo(AsO): Importance of direct hopping, third-neighbor exchange and quantum fluctuations
We present a simple three-parameter exchange model to describe the
interactions of the lowest doublet of the honeycomb cobaltate
BaCo(AsO), which has been proposed as a possible candidate for
Kitaev physics. Remarkably, it is the third-neighbor interactions, both
isotropic and anisotropic, that are responsible for the unique ground state of
BaCo(AsO), stabilized by quantum fluctuations. By considering two
{\it ab initio}-based complementary approaches, we analyze the electronic
structure of BaCo(AsO) and extract effective spin models that
justify the minimal model. Both methods show that the dominant direct hopping
makes the bond-dependent Kitaev term negligible moving the material away from
the sought-after spin-liquid regime. Moreover, a significantly large
third-nearest neighbor hopping supports the observed importance of the
third-neighbor interactions in the stabilization of the standout double-zigzag
ground state of BaCo(AsO).Comment: 8 pages, 4 figure
Unexpected 3+valence of iron in FeO2, a geologically important material lying "in between" oxides and peroxides
Recent discovery of pyrite FeO, which can be an important ingredient of
the Earth's lower mantle and which in particular may serve as an extra source
of water in the Earth's interior, opens new perspectives for geophysics and
geochemistry, but this is also an extremely interesting material from physical
point of view. We found that in contrast to naive expectations Fe is nearly 3+
in this material, which strongly affects its magnetic properties and makes it
qualitatively different from well known sulfide analogue - FeS. Doping,
which is most likely to occur in the Earth's mantle, makes FeO much more
magnetic. In addition we show that unique electronic structure places FeO
"in between" the usual dioxides and peroxides making this system interesting
both for physics and solid state chemistry
Importance of the many-body effects for structural properties of the novel iron oxide: FeO
The importance of many-body effects on electronic and magnetic properties and
stability of different structural phases was studied in novel iron oxide -
FeO. It was found that while Hubbard repulsion hardly affects the
electronic spectrum of this material (), but it strongly
changes its phase diagram shifting critical pressures of structural transitions
to much lower values. Moreover, one of the previously obtained in the density
functional theory (DFT) structures (Pm1) becomes energetically unstable
if many-body effects are taken into consideration. It is shown that this is an
account of magnetic moment fluctuations in the DFT+DMFT approach, which
strongly contributes to modification of the phase diagram of FeO.Comment: Main article: 6 pages, 7 figures, Supplementary information: 5
figure
Orbital-selective behavior in cubanite CuFe2S3
Using ab initio band structure calculations we show that mineral cubanite, CuFe2S3, demonstrates an orbital-selective behavior with some of the electrons occupying molecular orbitals of x(2) - y(2) symmetry and others localized at atomic orbitals. This is a rare situation for 3d transition metal compounds that explains the experimentally observed absence of charge disproportionation, anomalous Mossbauer data, and ferromagnetic ordering in between nearest-neighbor Fe ions
Old puzzle of incommensurate crystal structure of calaverite AuTe2 and predicted stability of novel AuTe compound
Gold is a very inert element, which forms relatively few compounds. Among them is a unique material-mineral calaverite, AuTe2. Besides being the only compound in nature from which one can extract gold on an industrial scale, it is a rare example of a natural mineral with incommensurate crystal structure. Moreover, it is one of few systems based on Au, which become superconducting (at elevated pressure or doped by Pd and Pt). Using ab initio calculations we theoretically explain these unusual phenomena in the picture of negative charge-transfer energy and self-doping, with holes being largely in the Te 5p bands. This scenario naturally explains incommensurate crystal structure of AuTe2, and it also suggests a possible mechanism of superconductivity. An ab initio evolutionary search for stable compounds in the Au-Te system confirms stability of AuTe2 and AuTe3 and leads to a prediction of an as yet unknown stable compound AuTe, which until now has not been synthesized