22 research outputs found
First-principles treatment of Mott insulators: linearized QSGW+DMFT approach
The theoretical understanding of emergent phenomena in quantum materials is
one of the greatest challenges in condensed matter physics. In contrast to
simple materials such as noble metals and semiconductors, macroscopic
properties of quantum materials cannot be predicted by the properties of
individual electrons. One of the examples of scientific importance is strongly
correlated electron system. Neither localized nor itinerant behaviors of
electrons in partially filled 3d, 4f, and 5f orbitals give rise to rich physics
such as Mott insulators, high-temperature superconductors, and superior
thermoelectricity, but hinder quantitative understanding of low-lying
excitation spectrum. Here we present a new first-principles approach to
strongly correlated solids. It is Q4 based on a combination of the
quasiparticle self-consistent GW approximation and the dynamical mean-field
theory. The sole input in this method is the projector to the set of correlated
orbitals for which all local Feynman graphs are being evaluated. For that
purpose, we choose very localized quasiatomic orbitals spanning large energy
window, which contains most strongly hybridized bands, as well as upper and
lower Hubbard bands. The self-consistency is carried out on the Matsubara axis.
This method enables the first-principles study of Mott insulators in both their
paramagnetic and antiferromagnetic phases. We illustrate the method on the
archetypical charge transfer correlated insulators La2CuO4 and NiO, and obtain
spectral properties and magnetic moments in good agreement with experiments
Spin-wave interference
Spin-wave interference is demonstrated in the micromagnetic modeling of a specially designed geometry made of variously shaped magnetic thin-film waveguides. When spin waves are diffracted through two separate openings, corresponding to the two pinholes in the second screen of Young's apparatus, they interfere constructively or destructively in a magnetic medium, thereby showing distinct interference patterns. Furthermore, the radiation, propagation, transmission, and dispersion behaviors of spin waves as well as the filtering of their lower frequencies are investigated in the present modeling study. These results directly confirm not only the wave characteristics of spin waves traveling at ultrafast speeds in variously shaped magnetic waveguides but also their interference effect, that is similar to that observed in well-known Young's double slit experiment with light.open312
Frozen spin ratio and the detection of Hund correlations
We propose a way to detect strongly Hund-correlated materials by unveiling
key signatures of Hund correlations at the two-particle level. The defining
feature is the {\it sign} of the response of the {\it frozen spin ratio} (the
long-time local spin-spin correlation function divided by the instantaneous
value) under variation of electron density. The underlying physical reason is
that the sign is closely related to the strength of charge fluctuations between
the dominant atomic multiplets and higher-spin ones in a neighboring charge
subspace. It is the predominance of these fluctuations that promotes Hund
metallicity. Furthermore, the temperature dependence of the frozen spin ratio
can reveal a non-Fermi-liquid behavior. We analyze both degenerate and
non-degenerate multiorbital Hubbard models and corroborate our argument by
taking doped cuprates and Fe-pnictides as representative material examples,
respectively, of Mott and Hund metals
Localization of Metal-Induced Gap States at the Metal-Insulator Interface:Origin of Flux Noise in SQUIDs and Superconducting Qubits
The origin of magnetic flux noise in Superconducting Quantum Interference
Devices with a power spectrum scaling as ( is frequency) has been a
puzzle for over 20 years. This noise limits the decoherence time of
superconducting qubits. A consensus has emerged that the noise arises from
fluctuating spins of localized electrons with an areal density of
m. We show that, in the presence of potential disorder
at the metal-insulator interface, some of the metal-induced gap states become
localized and produce local moments. A modest level of disorder yields the
observed areal density
Orbital Selective Mott Transition Effects and Non-Trivial Topology of Iron Chalcogenide
The iron-based superconductor FeSeTe (FST) has recently gained
significant attention as a host of two distinct physical phenomena:
(\textit{i}) Majorana zero modes which can serve as potential topologically
protected qubits, and (\textit{ii}) a realization of the orbital selective Mott
transition (OSMT). In this Letter, we connect these two phenomena and provide
new insights into the interplay between strong electronic correlations and
non-trivial topology in FST. Using linearized quasiparticle self-consistent GW
plus dynamical mean-field theory, we show that the topologically protected
Dirac surface state has substantial Fe() character. The proximity to
the OSMT plays a dual role, it facilitates the appearance of the topological
surface state by bringing the Dirac cone close to the chemical potential, but
destroys the Z topological superconductivity when the system is too close
to the orbital selective Mott phase (OSMP). We derive a reduced effective
Hamiltonian that describes the topological band. Its parameters capture all the
chemical trends found in the first principles calculation. Our findings provide
a framework for further study of the interplay between strong electronic
correlations and non-trivial topology in other iron-based superconductors.Comment: 5 pages, 4 figures, and supplemental materia
Total Reflection and Negative Refraction of Dipole-Exchange Spin Waves at Magnetic Interfaces: Micromagnetic Modeling Study
We demonstrated that dipole-exchange spin waves traveling in geometrically
restricted magnetic thin films satisfy the same laws of reflection and
refraction as light waves. Moreover, we found for the first time novel wave
behaviors of dipole-exchange spin waves such as total reflection and negative
refraction. The total reflection in laterally inhomogeneous thin films composed
of two different magnetic materials is associated with the forbidden modes of
refracted dipole-exchange spin waves. The negative refraction occurs at a 90
degree domain-wall magnetic interface that is introduced by a cubic magnetic
anisotropy in the media, through the anisotropic dispersion of dipole-exchange
spin waves.Comment: 13 pages, 5 figure