1,079 research outputs found
Electrochemical synthesis and properties of CoO2, the x = 0 phase of the AxCoO2 systems (A = Li, Na)
Single-phase bulk samples of the "exotic" CoO2, the x = 0 phase of the AxCoO2
systems (A = Li, Na), were successfully synthesized through electrochemical
de-intercalation of Li from pristine LiCoO2 samples. The samples of pure CoO2
were found to be essentially oxygen stoichiometric and possess a hexagonal
structure consisting of stacked triangular-lattice CoO2 layers only. The
magnetism of CoO2 is featured with a temperature-independent susceptibility of
the magnitude of 10-3 emu/mol Oe, being essentially identical to that of a
Li-doped phase, Li0.12CoO2. It is most likely that the CoO2 phase is a
Pauli-paramagnetic metal with itinerant electrons.Comment: 12 pages, 3 figure
Algebras for parameterised monads
Parameterised monads have the same relationship to adjunctions with parameters as monads do to adjunctions. In this paper, we investigate algebras for parameterised monads. We identify the Eilenberg-Moore category of algebras for parameterised monads and prove a generalisation of Beck’s theorem characterising this category. We demonstrate an application of this theory to the semantics of type and effect systems
Field induced long-range-ordering in an S=1 quasi-one-dimensional Heisenberg antiferromagnet
We have measured the heat capacity and magnetization of the spin one
one-dimensional Heisenberg antiferromagnet NDMAP and constructed a magnetic
field versus temperature phase diagram. We found a field induced long-range
magnetic ordering. We have been successful in explaining the phase diagram
theoretically.Comment: 6 pages, 18 figure
High-field phase diagram of the Haldane-gap antiferromagnet
We have determined the magnetic phase diagram of the quasi-one-dimensional
1 Heisenberg antiferromagnet by
specific heat measurements to 150 mK in temperature and 32 T in magnetic field.
When field is applied along the spin-chain direction, a new phase appears at
T. For the previously known phases of field-induced order,
accurate determination is made of the power-law exponents of the ordering
temperature near the zero-temperature critical field , owing to the
four-fold improvement of the minimum temperature over the previous work. The
results are compared with the predictions based on the Bose-Einstein
condensation of triplet excitations. Substituting deuterium for hydrogen is
found to slightly reduce the interchain exchange.Comment: 6 pages, 6 figure
Anomalous superfluid density in quantum critical superconductors
When a second-order magnetic phase transition is tuned to zero temperature by
a non-thermal parameter, quantum fluctuations are critically enhanced, often
leading to the emergence of unconventional superconductivity. In these `quantum
critical' superconductors it has been widely reported that the normal-state
properties above the superconducting transition temperature often exhibit
anomalous non-Fermi liquid behaviors and enhanced electron correlations.
However, the effect of these strong critical fluctuations on the
superconducting condensate below is less well established. Here we report
measurements of the magnetic penetration depth in heavy-fermion, iron-pnictide,
and organic superconductors located close to antiferromagnetic quantum critical
points showing that the superfluid density in these nodal superconductors
universally exhibit, unlike the expected -linear dependence, an anomalous
3/2 power-law temperature dependence over a wide temperature range. We propose
that this non-integer power-law can be explained if a strong renormalization of
effective Fermi velocity due to quantum fluctuations occurs only for momenta
close to the nodes in the superconducting energy gap .
We suggest that such `nodal criticality' may have an impact on low-energy
properties of quantum critical superconductors.Comment: Main text (5 pages, 3 figures) + Supporting Information (3 pages, 4
figures). Published in PNAS Early Edition on February 12, 201
Electrochemical synthesis and properties of CoO[sub 2], the x=0 phase of the A[sub x]CoO[sub 2] systems (A=Li,Na)
Single-phase bulk samples of the “exotic” CoO2, the x=0 phase of the AxCoO2 systems (A=Li,Na), were successfully synthesized through electrochemical deintercalation of Li from pristine LiCoO2 samples. The samples of pure CoO2 were found to be essentially oxygen stoichiometric and possess a hexagonal structure consisting of stacked triangular-lattice CoO2 layers only. The magnetism of CoO2 is featured with a temperature-independent susceptibility of the magnitude of 10−3emu/molOe, being essentially identical to that of a Li-doped phase, Li0.12CoO2. It is most likely that the CoO2 phase is a Pauli-paramagnetic metal with itinerant electrons.Peer reviewe
A Sharp Peak of the Zero-Temperature Penetration Depth at Optimal Composition in BaFe2(As1-xPx)2
In a superconductor, the ratio of the carrier density, , to their
effective mass, , is a fundamental property directly reflecting the length
scale of the superfluid flow, the London penetration depth, . In two
dimensional systems, this ratio () determines the
effective Fermi temperature, . We report a sharp peak in the
-dependence of at zero temperature in clean samples of
BaFe(AsP) at the optimum composition , where the
superconducting transition temperature reaches a maximum of 30\,K. This
structure may arise from quantum fluctuations associated with a quantum
critical point (QCP). The ratio of at is enhanced,
implying a possible crossover towards the Bose-Einstein condensate limit driven
by quantum criticality.Comment: Main text (5 pages, 4 figures) + Supplementary Materials (5 pages, 5
figures). Published on June 22, 201
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