3,369 research outputs found
Magnetic exchange interaction between rare-earth and Mn ions in multiferroic hexagonal manganites
We report a study of magnetic dynamics in multiferroic hexagonal manganite
HoMnO3 by far-infrared spectroscopy. Low-temperature magnetic excitation
spectrum of HoMnO3 consists of magnetic-dipole transitions of Ho ions within
the crystal-field split J=8 manifold and of the triangular antiferromagnetic
resonance of Mn ions. We determine the effective spin Hamiltonian for the Ho
ion ground state. The magnetic-field splitting of the Mn antiferromagnetic
resonance allows us to measure the magnetic exchange coupling between the
rare-earth and Mn ions.Comment: accepted for publication in Physical Review Letter
Reconsidering the interpretation of quantum oscillation experiments on underdoped YBa(2)Cu(3)O(6+x)
On the basis of negative transport coefficients, it has been argued that the
quantum oscillations observed in underdoped YBa(2)Cu(3)O(6+x) in high magnetic
fields must be due to antinodal electron pockets. We point out a counter
example in which electron-like transport in a hole-doped cuprate is associated
with Fermi-arc states. We also present evidence that the antinodal gap in
YBa(2)Cu(3)O(6+x) is robust to modest applied magnetic fields. We suggest that
these observations should be taken into account when interpreting the results
of the quantum oscillation experiments.Comment: 3+eps pages, 2 figures; final version, accepted in PRB, has new
title, completely rewritten and simplified tex
Fabrication and Characterization of Topological Insulator BiSe Nanocrystals
In the recently discovered class of materials known as topological
insulators, the presence of strong spin-orbit coupling causes certain
topological invariants in the bulk to differ from their values in vacuum. The
sudden change of invariants at the interface results in metallic, time reversal
invariant surface states whose properties are useful for applications in
spintronics and quantum computation. However, a key challenge is to fabricate
these materials on the nanoscale appropriate for devices and probing the
surface. To this end we have produced 2 nm thick nanocrystals of the
topological insulator BiSe via mechanical exfoliation. For crystals
thinner than 10 nm we observe the emergence of an additional mode in the Raman
spectrum. The emergent mode intensity together with the other results presented
here provide a recipe for production and thickness characterization of
BiSe nanocrystals.Comment: 4 pages, 3 figures (accepted for publication in Applied Physics
Letters
Ion-lithium collision dynamics studied with an in-ring MOTReMi
We present a novel experimental tool allowing for kinematically complete
studies of break-up processes of laser-cooled atoms. This apparatus, the
'MOTReMi', is a combination of a magneto-optical trap (MOT) and a Reaction
Microscope (ReMi). Operated in an ion-storage ring, the new setup enables to
study the dynamics in swift ion-atom collisions on an unprecedented level of
precision and detail. In first experiments on collisions with 1.5 MeV/amu
O-Li the pure ionization of the valence electron as well as
ionization-excitation of the lithium target has been investigated
Real-time dynamics of the formation of hydrated electrons upon irradiation of water clusters with extreme ultraviolet light
Free electrons in a polar liquid can form a bound state via interaction with the molecular environment. This so-called hydrated electron state in water is of fundamental importance e.g.~in cellular biology or radiation chemistry. Hydrated electrons are highly reactive radicals that can either directly interact with DNA or enzymes, or form highly excited hydrogen (H∗) after being captured by protons. Here, we investigate the formation of the hydrated electron in real-time employing XUV femtosecond pulses from a free electron laser, in this way observing the initial steps of the hydration process. Using time-resolved photoelectron spectroscopy we find formation timescales in the low picosecond range and resolve the prominent dynamics of forming excited hydrogen states
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
Matter-gravity interaction in a multiply warped braneworld,
The role of a bulk graviton in predicting the signature of extra dimensions
through collider-based experiments is explored in the context of a multiply
warped spacetime. In particular it is shown that in a doubly warped braneworld
model, the presence of the sixth dimension, results in enhanced concentration
of graviton Kaluza Klein (KK) modes compared to that obtained in the usual
5-dimensional Randall-Sundrum model. Also, the couplings of these massive
graviton KK modes with the matter fields on the visible brane turn out to be
appreciably larger than that in the corresponding 5- dimensional model. The
significance of these results are discussed in the context of KK graviton
search at the Large Hadron Collider (LHC).Comment: 13 pages, 2 table
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