250 research outputs found
Modelling the Localized to Itinerant Electronic Transition in the Heavy Fermion System CeIrIn5
We address the fundamental question of crossover from localized to itinerant
state of a paradigmatic heavy fermionmaterial CeIrIn5. The temperature
evolution of the one electron spectra and the optical conductivity is predicted
from first principles calculation. The buildup of coherence in the form of a
dispersive many body feature is followed in detail and its effects on the
conduction electrons and optical conductivity of the material is revealed. We
find multiple hybridization gaps and link them to the crystal structure of the
material. Our theoretical approach explains the multiple peak structures
observed in optical experiments and the sensitivity of CeIrIn5 to substitutions
of the transition metal element and may provide a microscopic basis for the
more phenomenological descriptions currently used to interpret experiments in
heavy fermion systems.Comment: 12 pages, 3 figure
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
Shot noise of inelastic tunneling through quantum dot systems
We present a theoretical analysis of the effect of inelastic electron
scattering on current and its fluctuations in a mesoscopic quantum dot (QD)
connected to two leads, based on a recently developed nonperturbative technique
involving the approximate mapping of the many-body electron-phonon coupling
problem onto a multichannel single-electron scattering problem. In this, we
apply the B\"uttiker scattering theory of shot noise for a two-terminal
mesoscopic device to the multichannel case with differing weight factors and
examine zero-frequency shot noise for two special cases: (i) a single-molecule
QD and (ii) coupled semiconductor QDs. The nonequilibrium Green's function
method facilitates calculation of single-electron transmission and reflection
amplitudes for inelastic processes under nonequilibrium conditions in the
mapping model. For the single-molecule QD we find that, in the presence of the
electron-phonon interaction, both differential conductance and differential
shot noise display additional peaks as bias-voltage increases due to
phonon-assisted processes. In the case of coupled QDs, our nonperturbative
calculations account for the electron-phonon interaction on an equal footing
with couplings to the leads, as well as the coupling between the two dots. Our
results exhibit oscillations in both the current and shot noise as functions of
the energy difference between the two QDs, resulting from the spontaneous
emission of phonons in the nonlinear transport process. In the "zero-phonon"
resonant tunneling regime, the shot noise exhibits a double peak, while in the
"one-phonon" region, only a single peak appears.Comment: 10 pages, 6 figures, some minor changes, accepted by Phys. Rev.
Nodal/Antinodal Dichotomy and the Two Gaps of a Superconducting Doped Mott Insulator
We study the superconducting state of the hole-doped two-dimensional Hubbard
model using Cellular Dynamical Mean Field Theory, with the Lanczos method as
impurity solver. In the under-doped regime, we find a natural decomposition of
the one-particle (photoemission) energy-gap into two components. The gap in the
nodal regions, stemming from the anomalous self-energy, decreases with
decreasing doping. The antinodal gap has an additional contribution from the
normal component of the self-energy, inherited from the normal-state pseudogap,
and it increases as the Mott insulating phase is approached.Comment: Corrected typos, 4.5 pages, 4 figure
Dynamical Mean-Field Theory for Molecular Electronics: Electronic Structure and Transport Properties
We present an approach for calculating the electronic structure and transport
properties of nanoscopic conductors that takes into account the dynamical
correlations of strongly interacting d- or f-electrons by combining density
functional theory calculations with the dynamical mean-field theory. While the
density functional calculation yields a static mean-field description of the
weakly interacting electrons, the dynamical mean-field theory explicitly takes
into account the dynamical correlations of the strongly interacting d- or
f-electrons of transition metal atoms. As an example we calculate the
electronic structure and conductance of Ni nanocontacts between Cu electrodes.
We find that the dynamical correlations of the Ni 3d-electrons give rise to
quasi-particle resonances at the Fermi-level in the spectral density. The
quasi-particle resonances in turn lead to Fano lineshapes in the conductance
characteristics of the nanocontacts similar to those measured in recent
experiments of magnetic nanocontacts.Comment: replaced with revised version; 11 pages; 9 figure
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
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