19 research outputs found
Solution of the Holstein polaron anisotropy problem
We study Holstein polarons in three-dimensional anisotropic materials. Using
a variational exact diagonalization technique we provide highly accurate
results for the polaron mass and polaron radius. With these data we discuss the
differences between polaron formation in dimension one and three, and at small
and large phonon frequency. Varying the anisotropy we demonstrate how a polaron
evolves from a one-dimensional to a three-dimensional quasiparticle. We thereby
resolve the issue of polaron stability in quasi-one-dimensional substances and
clarify to what extent such polarons can be described as one-dimensional
objects. We finally show that even the local Holstein interaction leads to an
enhancement of anisotropy in charge carrier motion.Comment: 6 pages, 7 figures; extended version accepted for publication in
Phys. Rev.
Polarons and slow quantum phonons
We describe the formation and properties of Holstein polarons in the entire
parameter regime. Our presentation focuses on the polaron mass and radius,
which we obtain with an improved numerical technique. It is based on the
combination of variational exact diagonalization with an improved construction
of phonon states, providing results even for the strong coupling adiabatic
regime. In particular we can describe the formation of large and heavy
adiabatic polarons. A comparison of the polaron mass for the one and three
dimensional situation explains how the different properties in the static
oscillator limit determine the behavior in the adiabatic regime. The transport
properties of large and small polarons are characterized by the f-sum rule and
the optical conductivity. Our calculations are approximation-free and have
negligible numerical error. This allows us to give a conclusive and impartial
description of polaron formation. We finally discuss the implications of our
results for situations beyond the Holstein model.Comment: Final version, 10 pages, 10 figure
Nonlinear high-temperature superconducting terahertz metamaterials
We report the observation of a nonlinear terahertz response of split-ring resonator arrays made of high-temperature superconducting films. Intensity-dependent transmission measurements indicate that the resonance strength decreases dramatically (i.e. transient bleaching) and the resonance frequency shifts as the intensity is increased. Pumpāprobe measurements confirm this behaviour and reveal dynamics on the few-picosecond timescale.Los Alamos National Laboratory. Laboratory Directed Research and Development ProgramUnited States. Office of Naval Research (Grant N00014-09-1-1103)National Science Foundation (U.S.) (American Competitiveness in Chemistry Fellowship 1041979
Magnetic, electronic, and optical properties of double perovskite Bi2FeMnO6
Double perovskite Bi2FeMnO6 is a potential
candidate for the single-phase multiferroic system. In this work, we study the
magnetic, electronic, and optical properties in BFMO by performing the density functional theory
calculations and experimental measurements of magnetic moment. We also
demonstrate the strain dependence of magnetization. More importantly, our calculations of
electronic and optical properties reveal that the onsite local correlation on Mn and
Fe sites is critical to the gap opening in BFMO, which is a prerequisite condition
for the ferroelectric ordering. Finally, we calculate the x-ray magnetic circular
dichroism spectra of Fe and Mn ions (L2 and L3 edges) in
BFMO