12 research outputs found
Surface Effects on Anisotropic Photoluminescence in One-Dimensional Organic Metal Halide Hybrids
One-dimensional (1D) organic metal halide hybrids exhibit strongly
anisotropic optical properties, highly efficient light emission, and large
Stokes shift, holding promises for novel photodetection and lighting
applications. However, the fundamental mechanisms governing their unique
optical properties and in particular the impacts of surface effects are not
understood. Here, we investigate 1D C4N2H14PbBr4 by polarization-dependent
time-averaged and time-resolved photoluminescence (TRPL) spectroscopy, as a
function of photoexcitation energy. Surprisingly, we find that the emission
under photoexcitation polarized parallel to the 1D metal halide chains can be
either stronger or weaker than that under perpendicular polarization, depending
on the excitation energy. We attribute the excitation-energy-dependent
anisotropic emission to fast surface recombination, supported by
first-principles calculations of optical absorption in this material. The fast
surface recombination is directly confirmed by TRPL measurements, when the
excitation is polarized parallel to the chains. Our comprehensive studies
provide a more complete picture for a deeper understanding of the optical
anisotropy in 1D organic metal halide hybrids
Manipulating Multiple Order Parameters via Oxygen Vacancies: The case of Eu0.5Ba0.5TiO3-{\delta}
Controlling functionalities, such as magnetism or ferroelectricity, by means
of oxygen vacancies (VO) is a key issue for the future development of
transition metal oxides. Progress in this field is currently addressed through
VO variations and their impact on mainly one order parameter. Here we reveal a
new mechanism for tuning both magnetism and ferroelectricity simultaneously by
using VO. Combined experimental and density-functional theory studies of
Eu0.5Ba0.5TiO3-{\delta}, we demonstrate that oxygen vacancies create Ti3+ 3d1
defect states, mediating the ferromagnetic coupling between the localized Eu
4f7 spins, and increase an off-center displacement of Ti ions, enhancing the
ferroelectric Curie temperature. The dual function of Ti sites also promises a
magnetoelectric coupling in the Eu0.5Ba0.5TiO3-{\delta}.Comment: Accepted by Physical Review B, 201
Prediction of spin polarized Fermi arcs in quasiparticle interference in CeBi
We predict that CeBi in the ferromagnetic state is a Weyl semimetal. Our calculations within density functional theory show the existence of two pairs of Weyl nodes on the momentum path (0,0,kz) at 15meV above and 100meV below the Fermi level. Two corresponding Fermi arcs are obtained on surfaces of mirror-symmetric (010)-oriented slabs at E=15meV and both arcs are interrupted into three segments due to hybridization with a set of trivial surface bands. By studying the spin texture of surface states, we find the two Fermi arcs are strongly spin polarized but in opposite directions, which can be detected by spin-polarized ARPES measurements. Our theoretical study of quasiparticle interference (QPI) for a nonmagnetic impurity at the Bi site also reveals several features related to the Fermi arcs. Specifically, we predict that the spin polarization of the Fermi arcs leads to a bifurcation-shaped feature only in the spin-dependent QPI spectrum, serving as a fingerprint of the Weyl nodes.</p
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Surface Effects on Anisotropic Photoluminescence in One‐Dimensional Organic Metal Halide Hybrids
High Entropy Oxide Relaxor Ferroelectrics
Relaxor ferrolectrics are important in technological applications due to a
strong electromechanical response, energy storage capacity, electrocaloric
effect, and pyroelectric energy conversion properties. Current efforts to
discover and design new materials in this class generally rely on
substitutional doping of known ferroelectrics, as slight changes to local
compositional order can significantly affect the Curie temperature,
morphotropic phase boundary, and electromechanical responses. In this work, we
demonstrate that moving to the strong limit of compositional complexity in an
ABO3 perovskite allows stabilization of novel relaxor responses that do not
rely on a single narrow phase transition region. Entropy-assisted synthesis
approaches are used to create single crystal Ba(Ti0.2Sn0.2Zr0.2Hf0.2Nb0.2)O3
[Ba(5B)O] films. The high levels of configurational disorder present in this
system is found to influence dielectric relaxation, phase transitions,
nano-polar domain formation, and Curie temperature. Temperature-dependent
dielectric, Raman spectroscopy and second-harmonic generation measurements
reveal multiple phase transitions, a high Curie temperature of 570 K, and the
relaxor ferroelectric nature of Ba(5B)O films. The first principles theory
calculations are used to predict possible combinations of cations to quantify
the relative feasibility of formation of highly disordered single-phase
perovskite systems. The ability to stabilize single-phase perovskites with such
a large number of different cations on the B-sites offers new possibilities for
designing high-performance materials for piezoelectric, pyroelectric and
tunable dielectric applications