162 research outputs found
Dynamical Mean-Field Theory within the Full-Potential Methods: Electronic structure of Ce-115 materials
We implemented the charge self-consistent combination of Density Functional
Theory and Dynamical Mean Field Theory (DMFT) in two full-potential methods,
the Augmented Plane Wave and the Linear Muffin-Tin Orbital methods. We
categorize the commonly used projection methods in terms of the causality of
the resulting DMFT equations and the amount of partial spectral weight
retained. The detailed flow of the Dynamical Mean Field algorithm is described,
including the computation of response functions such as transport coefficients.
We discuss the implementation of the impurity solvers based on hybridization
expansion and an analytic continuation method for self-energy. We also derive
the formalism for the bold continuous time quantum Monte Carlo method. We test
our method on a classic problem in strongly correlated physics, the
isostructural transition in Ce metal. We apply our method to the class of heavy
fermion materials CeIrIn_5, CeCoIn_5 and CeRhIn_5 and show that the Ce 4f
electrons are more localized in CeRhIn_5 than in the other two, a result
corroborated by experiment. We show that CeIrIn_5 is the most itinerant and has
a very anisotropic hybridization, pointing mostly towards the out-of-plane In
atoms. In CeRhIn_5 we stabilized the antiferromagnetic DMFT solution below 3K,
in close agreement with the experimental N\'eel temperature.Comment: The implementation of Bold-CTQMC added and some test of the method
adde
Temperature-dependent Fermi surface evolution in heavy fermion CeIrIn5
In Cerium-based heavy electron materials, the 4f electron's magnetic moments
bind to the itinerant quasiparticles to form composite heavy quasiparticles at
low temperature. The volume of the Fermi surfacein the Brillouin zone
incorporates the moments to produce a "large FS" due to the Luttinger theorem.
When the 4f electrons are localized free moments, a "small FS" is induced since
it contains only broad bands of conduction spd electrons. We have addressed
theoretically the evolution of the heavy fermion FS as a function of
temperature, using a first principles dynamical mean-field theory (DMFT)
approach combined with density functional theory (DFT+DMFT). We focus on the
archetypical heavy electrons in CeIrIn5, which is believed to be near a quantum
critical point. Upon cooling, both the quantum oscillation frequencies and
cyclotron masses show logarithmic scaling behavior (~ ln(T_0/T)) with different
characteristic temperatures T_0 = 130 and 50 K, respectively. The resistivity
coherence peak observed at T ~ 50 K is the result of the competition between
the binding of incoherent 4f electrons to the spd conduction electrons at Fermi
level and the formation of coherent 4f electrons.Comment: 5 pages main article,3 figures for the main article, 2 page
Supplementary information, 2 figures for the Supplementary information.
Supplementary movie 1 and 2 are provided on the
webpage(http://www-ph.postech.ac.kr/~win/supple.html
X-ray absorption branching ratio in actinides: LDA+DMFT approach
To investigate the x-ray absorption (XAS) branching ratio from the core 4d to
valence 5f states, we set up a theoretical framework by using a combination of
density functional theory in the local density approximation and Dynamical Mean
Field Theory (LDA+DMFT), and apply it to several actinides. The results of the
LDA+DMFT reduces to the band limit for itinerant systems and to the atomic
limit for localized f electrons, meaning a spectrum of 5f itinerancy can be
investigated. Our results provides a consistent and unified view of the XAS
branching ratio for all elemental actinides, and is in good overall agreement
with experiments.Comment: 6 pages, 4 figure
Combining the Hybrid Functional Method with Dynamical Mean-Field Theory
We present a new method to compute the electronic structure of correlated
materials combining the hybrid functional method with the dynamical mean-field
theory. As a test example of the method we study cerium sesquioxide, a strongly
correlated Mott-band insulator. The hybrid functional part improves the
magnitude of the pd-band gap which is underestimated in the standard
approximations to density functional theory while the dynamical mean-field
theory part splits the 4f-electron spectra into a lower and an upper Hubbard
band.Comment: 5 pages, 2 figures, replaced with revised version, published in
Europhys. Let
Landauer Theory, Inelastic Scattering and Electron Transport in Molecular Wires
In this paper we address the topic of inelastic electron scattering in
mesoscopic quantum transport. For systems where only elastic scattering is
present, Landauer theory provides an adequate description of transport that
relates the electronic current to single-particle transmission and reflection
probabilities. A formalism proposed recently by Bonca and Trugman facilitates
the calculation of the one-electron transmission and reflection probabilities
for inelastic processes in mesoscopic conductors connected to one-dimensional
ideal leads. Building on their work, we have developed a self-consistent
procedure for the evaluation of the non-equilibrium electron distributions in
ideal leads connecting such mesoscopic conductors to electron reservoirs at
finite temperatures and voltages. We evaluate the net electronic current
flowing through the mesoscopic device by utilizing these non-equilibrium
distributions. Our approach is a generalization of Landauer theory that takes
account of the Pauli exclusion principle for the various competing elastic and
inelastic processes while satisfying the requirement of particle conservation.
As an application we examine the influence of elastic and inelastic scattering
on conduction through a two site molecular wire with longitudinal phonons using
the Su-Schrieffer-Heeger model of electron-phonon coupling.Comment: 25 pages, 8 figure
Finite temperature properties of the 2D Kondo lattice model
Using recently developed Lanczos technique we study finite-temperature
properties of the 2D Kondo lattice model at various fillings of the conduction
band. At half filling the quasiparticle gap governs physical properties of the
chemical potential and the charge susceptibility at small temperatures. In the
intermediate coupling regime quasiparticle gap scales approximately linearly
with Kondo coupling. Temperature dependence of the spin susceptibility reveals
the existence of two different temperature scales. A spin gap in the
intermediate regime leads to exponential drop of the spin susceptibility at low
temperatures. Unusual scaling of spin susceptibility is found for temperatures
above 0.6 J. Charge susceptibility at finite doping reveals existence of heavy
quasiparticles. A new low energy scale is found at finite doping.Comment: REVTeX, 7 pages, 7 figure
Magnetic Exciton Mediated Superconductivity in the Hidden-Order Phase of URu2Si2
We propose the magnetic exciton mediated superconductivity occurring in the
enigmatic hidden-order phase of URu2Si2. The characteristic of the massive
collective excitation observed only in the hidden-order phase is well
reproduced by the antiferro hexadecapole ordering model as the trace of the
dispersive crystalline-electric-field excitation. The disappearance of the
superconductivity in the high-pressure antiferro magnetic phase can naturally
be understood by the sudden suppression of the magnetic-exciton intensity. The
analysis of the momentum dependence of the magnetic-exciton mode leads to the
exotic chiral d-wave singlet pairing in the Eg symmetry. The Ising-like
magnetic-field response of the mode yields the strong anisotropy observed in
the upper critical field even for the rather isotropic 3-dimensional Fermi
surfaces of this compound.Comment: 5 pages, 4 figure
High energy pseudogap and its evolution with doping in Fe-based superconductors as revealed by optical spectroscopy
We report optical spectroscopic measurements on electron- and hole-doped
BaFe2As2. We show that the compounds in the normal state are not simple metals.
The optical conductivity spectra contain, in addition to the free carrier
response at low frequency, a temperature-dependent gap-like suppression at
rather high energy scale near 0.6 eV. This suppression evolves with the
As-Fe-As bond angle induced by electron- or hole-doping. Furthermore, the
feature becomes much weaker in the Fe-chalcogenide compounds. We elaborate that
the feature is caused by the strong Hund's rule coupling effect between the
itinerant electrons and localized electron moment arising from the multiple Fe
3d orbitals. Our experiments demonstrate the coexistence of itinerant and
localized electrons in iron-based compounds, which would then lead to a more
comprehensive picture about the metallic magnetism in the materials.Comment: 6 pages, 7 figure
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