41 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
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
Antiferromagnetic topological metal near the metal-insulator transition in MnS
Antiferromagnetic (AFM) semiconductor MnS possesses both high-spin and
low-spin magnetic phases that can be reversibly switched by applying pressure.
With increasing pressure, the high-spin state undergoes pressure-induced
metalization before transforming into a low-spin configuration, which is then
closely followed by a volume collapse and structural transition. We show that
the pressure driven band inversion is in fact topological, resulting in an
antiferromagnetic topological metal (Z2AFTM) phase with a small
gap and a Weyl metal phase at higher pressures, both of which precede the
spin-state crossover and volume collapse. In the Z2AFTM phase, the magnetic
order results in a doubling of the periodic unit cell, and the resulting
folding of the Brillouin zone leads to a topological invariant
protected by the persisting combined time-reversal and half-translation
symmetries. Such a topological phase was proposed theoretically by Mong, Essin,
and Moore in 2010 for a system with AFM order on a face-centered cubic (FCC)
lattice, which until now has not been found in the pool of real materials.
MnS represents a realization of this original proposal through AFM order on
the Mn FCC sublattice. A rich phase diagram of topological and magnetic phases
tunable by pressure, establishes MnS as a candidate material for exploring
magnetic topological phase transitions and for potential applications in AFM
spintronics.Comment: 7 pages, 5 figure