44 research outputs found
Turning a Band Insulator Into an Exotic Superconductor
Understanding exotic, non s--wave--like states of Cooper pairs is important
and may lead to new superconductors with higher critical temperatures and novel
properties. Their existence is known to be possible but has always been thought
to be associated with non--traditional mechanisms of superconductivity where
electronic correlations play an important role. Here we use a first principles
linear response calculation to show that in doped BiSe an
unconventional p--wave--like state can be favored via a conventional
phonon--mediated mechanism, as driven by an unusual, almost singular behavior
of the electron--phonon interaction at long wavelengths. This may provide a new
platform for our understanding superconductivity phenomena in doped band
insulators.Comment: Published versio
Computational Design of Axion Insulators Based on 5d Spinels Compounds
Based on density functional calculation with LDA+U method, we propose that
hypothetical Osmium compounds such as CaOs2O4 and SrOs2O4 can be stabilized in
the geometrically frustrated spinel crystal structure. They also show some
exotic electronic and magnetic properties in a reasonable range of on-site
Coulomb correlation U such as ferromagnetism and orbital magnetoelectric effect
characteristic to Axion electrodynamics. Other electronic phases including 3D
Dirac metal and Mott insulator exist and would make perspective 5d spinels
ideal for applications.Comment: 5 pages, 3 figure
Calculated Spin Fluctuational Pairing Interaction in HgBa2CuO4 using LDA+FLEX Method
A combination of density functional theory in its local density approximation
(LDA) with k- and dependent self-energy found from
fluctuational-exchange-type random phase approximation (FLEX-RPA) is utilized
here to study superconducting pairing interaction in a prototype cuprate
superconductor HgBaCuO. Although, FLEX-RPA methodology have been
widely applied in the past to unconventional superconductors, previous studies
were mostly based on tight-binding derived minimal Hamiltonians, while the
approach presented here deals directly with the first principle electronic
structure calculation of the studied material where spin and charge
susceptibilities are evaluated for a correlated subset of the electronic
Hilbert space as it is done in popular LDA+U and LDA+DMFT methods. Based on our
numerically extracted pairing interaction among the Fermi surface electrons we
exactly diagonalize a linearized BCS gap equation, whose highest eigenstate is
expectantly found corresponding to symmetry for a wide
range of on-site Coulomb repulsions U and dopings that we treat using virtual
crystal approximation. Calculated normal state self-energies show a weak k- and
strong frequency dependence with particularly large electronic mass enhancement
in the vicinity of spin density wave instability. Although the results
presented here do not bring any surprisingly new physics to this very old
problem, our approach is an attempt to establish the numerical procedure to
evaluate material specific coupling constant for high T
superconductors without reliance on tight-binding approximations of their
electronic structures.Comment: 10 pages, 7 figure
Origin of Low Thermal Conductivity in Nuclear Fuels
Using a novel many-body approach, we report lattice dynamical properties of
UO2 and PuO2 and uncover various contributions to their thermal conductivities.
Via calculated Grueneisen constants, we show that only longitudinal acoustic
modes having large phonon group velocities are efficient heat carriers. Despite
the fact that some optical modes also show their velocities which are extremely
large, they do not participate in the heat transfer due to their unusual
anharmonicity. Ways to improve thermal conductivity in these materials are
discussed.Comment: 4 pages, 3 figures, 1 tabl
Density-functional calculations of the electronic structure and lattice dynamics of superconducting LaOFBiS: Evidence for an electron-phonon interaction near the charge-density-wave instability
We discuss the electronic structure, lattice dynamics and electron-phonon
interaction of newly discovered superconductor LaOFBiS
using density functional based calculations. A strong Fermi surface nesting at
=(,,0) suggests a proximity to charge density wave
instability and leads to imaginary harmonic phonons at this point
associated with in-plane displacements of S atoms. Total energy analysis
resolves only a shallow double-well potential well preventing the appearance of
static long-range order. Both harmonic and anharmonic contributions to
electron-phonon coupling are evaluated and give a total coupling constant
prompting this material to be a conventional
superconductor contrary to structurally similar FeAs materials.Comment: Supplementary Materials is adde