27,326 research outputs found
Cryogenic thermocouple calibration tables
Thermocouple calibration standards are developed for low-temperature thermocouple materials. Thermovoltage, thermopower, and the thermopower derivative are presented in tabular and graphical form
Level crossing in the three-body problem for strongly interacting fermions in a harmonic trap
We present a solution of the three-fermion problem in a harmonic potential
across a Feshbach resonance. We compare the spectrum with that of the two-body
problem and show that it is energetically unfavorable for the three fermions to
occupy one lattice site rather than two. We also demonstrate the existence of
an energy level crossing in the ground state with a symmetry change of its wave
function, suggesting the possibility of a phase transition for the
corresponding many-body case.Comment: 5 pages, 6 figures, typos corrected, references adde
Crafting knowledge exchange in the social science agenda
To any social science researcher the term “Knowledge Exchange” is a key buzzword in the academic
community and wider society. In an article by Contandriopoulos, Lemire, Denis, and Tremblay (2010,
p. 456) it was pointed out that knowledge exchange “rests on an implicit commonsense notion that
this ‘knowledge’ must be evidence based”. This evidence,
based within a social science context, relies
upon two strands: theoretical data and empirical data. When examining the notion of Knowledge
Exchange it becomes apparent that the concept has deep and meaningful connotations. These connotations
have been driven by the involvements of the public and private sectors. Moreover, work
carried out by Benneworth and Cunha (2015, p. 509) concludes that higher education institutions’
involvement in knowledge exchange “remains dynamic and influenced by universities” own strategic
choices and relationships’. Traditionally, universities have had two key missions: to teach undergraduate/postgraduate
students and to undertake research. Striukova and Rayna (2015, p. 488)
have recently observed that universities now have a third mission, “knowledge exchange”, and that
knowledge exchange plays a vital “integral part of the mix, without which the other two missions
cannot run successfully.” Knowledge exchange is also a fundamental feature of “sustainable communities”
(Powell, 2013) through the partnerships between HEIs and communities by which they
serve. This is a point we will return to
Heisenberg and Dzyaloshinskii-Moriya interactions controlled by molecular packing in tri-nuclear organometallic clusters
Motivated by recent synthetic and theoretical progress we consider magnetism
in crystals of multi-nuclear organometallic complexes. We calculate the
Heisenberg symmetric exchange and the Dzyaloshinskii-Moriya antisymmetric
exchange. We show how, in the absence of spin-orbit coupling, the interplay of
electronic correlations and quantum interference leads to a quasi-one
dimensional effective spin model in a typical tri-nuclear complex,
MoS(dmit), despite its underlying three dimensional band structure.
We show that both intra- and inter-molecular spin-orbit coupling can cause an
effective Dzyaloshinskii-Moriya interaction. Furthermore, we show that, even
for an isolated pair of molecules the relative orientation of the molecules
controls the nature of the Dzyaloshinskii-Moriya coupling. We show that
interference effects also play a crucial role in determining the
Dzyaloshinskii-Moriya interaction. Thus, we argue, that multi-nuclear
organometallic complexes represent an ideal platform to investigate the effects
of Dzyaloshinskii-Moriya interactions on quantum magnets.Comment: This update incorporates the corrections described in a recently
submitted erratum. Changes are confined to sections IV.A and B. The
conclusions of the paper are unchanged. 12 + 4 pages, 9 figure
Effects of anisotropy in spin molecular-orbital coupling on effective spin models of trinuclear organometallic complexes
We consider layered decorated honeycomb lattices at two-thirds filling, as
realized in some trinuclear organometallic complexes. Localized moments
with a single-spin anisotropy emerge from the interplay of Coulomb repulsion
and spin molecular-orbit coupling (SMOC). Magnetic anisotropies with bond
dependent exchange couplings occur in the honeycomb layers when the direct
intracluster exchange and the spin molecular-orbital coupling are both present.
We find that the effective spin exchange model within the layers is an XXZ +
120 honeycomb quantum compass model. The intrinsic non-spherical
symmetry of the multinuclear complexes leads to very different transverse and
longitudinal spin molecular-orbital couplings, which greatly enhances the
single-spin and exchange coupling anisotropies. The interlayer coupling is
described by a XXZ model with anisotropic biquadratic terms. As the correlation
strength increases the systems becomes increasingly one-dimensional. Thus, if
the ratio of SMOC to the interlayer hopping is small this stabilizes the
Haldane phase. However, as the ratio increases there is a quantum phase
transition to the topologically trivial `-phase'. We also predict a quantum
phase transition from a Haldane phase to a magnetically ordered phase at
sufficiently strong external magnetic fields.Comment: 22 pages, 11 figures. Final version of paper to be published in PRB.
Important corrections to appendix
Spin-orbit coupling in {MoS(dmit)}
Spin-orbit coupling in crystals is known to lead to unusual direction
dependent exchange interactions, however understanding of the consequeces of
such effects in molecular crystals is incomplete. Here we perform four
component relativistic density functional theory computations on the
multi-nuclear molecular crystal {MoS(dmit)} and show that both
intra- and inter-molecular spin-orbit coupling are significant. We determine a
long-range relativistic single electron Hamiltonian from first principles by
constructing Wannier spin-orbitals. We analyse the various contributions
through the lens of group theory. Intermolecular spin-orbit couplings like
those found here are known to lead to quantum spin-Hall and topological
insulator phases on the 2D lattice formed by the tight-binding model predicted
for a single layer of {MoS(dmit)}
High precision cryogenic thermal conductivity standards
New apparatus allows accurate simultaneous measurement of thermal conductivity, electrical resistivity, and thermopower for technically important materials, such as new or uncommon alloys. A list of materials investigated is presented. Sources for obtaining data on these materials, as well as the source giving a description of the apparatus, are cited
Universal monopole scaling near transitions from the Coulomb phase
Certain frustrated systems, including spin ice and dimer models, exhibit a
Coulomb phase at low temperatures, with power-law correlations and
fractionalized monopole excitations. Transitions out of this phase, at which
the effective gauge theory becomes confining, provide examples of
unconventional criticality. This work studies the behavior at nonzero monopole
density near such transitions, using scaling theory to arrive at universal
expressions for the crossover phenomena. For a particular transition in spin
ice, quantitative predictions are made through a duality mapping to the XY
model, and confirmed using Monte Carlo simulations.Comment: 4.5 pages, 4 figure
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