1,243 research outputs found
High-magnetic field phase diagram and failure of magnetic Gr\"uneisen scaling in LiFePO
We report the magnetic phase diagram of single-crystalline LiFePO in
magnetic fields up to 58~T and present a detailed study of magneto-elastic
coupling by means of high-resolution capacitance dilatometry. Large anomalies
at \tn\ in the thermal expansion coefficient imply pronounced
magneto-elastic coupling. Quantitative analysis yields the magnetic Gr\"uneisen
parameter ~mol/J. The positive
hydrostatic pressure dependence ~K/GPa is dominated
by uniaxial effects along the -axis. Failure of Gr\"uneisen scaling below
~K, i.e., below the peak temperature in the magneto-electric
coupling coefficient [\onlinecite{toft2015anomalous}], implies several
competing degrees of freedom and indicates relevance of recently observed
hybrid excitations~[\onlinecite{yiu2017hybrid}]. A broad and strongly
magnetic-field-dependent anomaly in in this temperature regime
highlight the relevance of structure changes. Upon application of magnetic
fields -axis, a pronounced jump in the magnetisation implies
spin-reorientation at ~T as well as a precursing phase at 29~T
and ~K. In a two-sublattice mean-field model, the saturation field
~T enables the determination of the effective
antiferromagnetic exchange interaction ~meV as well as
the anisotropies ~meV and ~meV
Bulk, surface and corner free energy series for the chromatic polynomial on the square and triangular lattices
We present an efficient algorithm for computing the partition function of the
q-colouring problem (chromatic polynomial) on regular two-dimensional lattice
strips. Our construction involves writing the transfer matrix as a product of
sparse matrices, each of dimension ~ 3^m, where m is the number of lattice
spacings across the strip. As a specific application, we obtain the large-q
series of the bulk, surface and corner free energies of the chromatic
polynomial. This extends the existing series for the square lattice by 32
terms, to order q^{-79}. On the triangular lattice, we verify Baxter's
analytical expression for the bulk free energy (to order q^{-40}), and we are
able to conjecture exact product formulae for the surface and corner free
energies.Comment: 17 pages. Version 2: added 4 further term to the serie
Specific heat and high-temperature series of lattice models: interpolation scheme and examples on quantum spin systems in one and two dimensions
We have developed a new method for evaluating the specific heat of lattice
spin systems. It is based on the knowledge of high-temperature series
expansions, the total entropy of the system and the low-temperature expected
behavior of the specific heat as well as the ground-state energy. By the choice
of an appropriate variable (entropy as a function of energy), a stable
interpolation scheme between low and high temperature is performed. Contrary to
previous methods, the constraint that the total entropy is log(2S+1) for a spin
S on each site is automatically satisfied. We present some applications to
quantum spin models on one- and two- dimensional lattices. Remarkably, in most
cases, a good accuracy is obtained down to zero temperature.Comment: 10 pages (RevTeX 4) including 11 eps figures. To appear in Phys. Rev.
Resolving the molecular architecture of the photoreceptor active zone with 3D-MINFLUX
Cells assemble macromolecular complexes into scaffoldings that serve as substrates for catalytic processes. Years of molecular neurobiology research indicate that neurotransmission depends on such optimization strategies. However, the molecular topography of the presynaptic active zone (AZ), where transmitter is released upon synaptic vesicle (SV) fusion, remains to be visualized. Therefore, we implemented MINFLUX optical nanoscopy to resolve the AZ of rod photoreceptors. This was facilitated by a novel sample immobilization technique that we name heat-assisted rapid dehydration (HARD), wherein a thin layer of rod synaptic terminals (spherules) was transferred onto glass coverslips from fresh retinal slices. Rod ribbon AZs were readily immunolabeled and imaged in 3D with a precision of a few nanometers. Our 3D-MINFLUX results indicate that the SV release site in rods is a molecular complex of bassoonâRIM2âubMunc13-2âCav1.4, which repeats longitudinally on both sides of the ribbon
Foundation and empire : a critique of Hardt and Negri
In this article, Thompson complements recent critiques of Hardt and Negri's Empire (see Finn Bowring in Capital and Class, no. 83) using the tools of labour process theory to critique the political economy of Empire, and to note its unfortunate similarities to conventional theories of the knowledge economy
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