61 research outputs found
Electromagnon and phonon excitations in multiferroic TbMnO3
We have performed Raman measurements on TbMnO3 single crystal under magnetic
field along the three crystallographic directions. The flip of the spin spiral
plane creates an electromagnon excitation. In addition to the electromagnons
induced by the Heisenberg coupling, we have detected the electromagnon created
by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified
all the vibrational modes of TbMnO3. Their temperature dependences show that
only one phonon observed along the polarization axis is sensitive to the
ferroelectric transition. This mode is tied to the Tb3+ ion displacements that
contribute to the ferroelectric polarization
Magneto-electric excitations in multiferroic TbMnO3 by Raman scattering
Low energy excitations in the multiferroic material TbMnO3 have been
investigated by Raman spectroscopy. Our observations reveal the existence of
two peaks at 30 cm-1 and 60 cm-1. They are observed in the cycloidal phase
below the Curie temperature but not in the sinusoidal phase, suggesting their
magnetoelectric origin. While the peak energies coincide with the frequencies
of electromagnons measured previously by transmission spectroscopy, they show
surprisingly different selection rules, with the 30 cm-1 excitation enhanced by
the electric field of light along the spontaneous polarization. The origins of
the modes are discussed under Raman and infrared selection rules
considerations
Magnetic field induced dehybridization of the electromagnons in multiferroic TbMnO3
We have studied the impact of the magnetic field on the electromagnon
excitations in TbMnO3 crystal. Applying magnetic field along the c axis, we
show that the electromagnons transform into pure antiferromagnetic modes,
losing their polar character. Entering in the paraelectric phase, we are able
to track the spectral weight transfer from the electromagnons to the magnon
excitations and we discuss the magnetic excitations underlying the
electromagnons. We also point out the phonons involved in the phase transition
process. This reveals that the Mn-O distance plays a key role in understanding
the ferroelectricity and the polar character of the electromagnons. Magnetic
field measurements along the b axis allow us to detect a new electromagnon
resonance in agreement with a Heisenberg model
Polar phonons and spin excitations coupling in multiferroic BiFeO3 crystals
Raman scattering measurements on BiFeO3 single crystals show an important
coupling between the magnetic order and lattice vibrations. The temperature
evolution of phonons shows that the lowest energy E and A1 phonon modes are
coupled to the spin order up to the Neel temperature. Furthermore, low
temperature anomalies associated with the spin re-orientation are observed
simultaneously in both the E phonon and the magnon. These results suggest that
magnetostriction plays an important role in BiFeO3
Electric-field control of spin waves at room temperature in multiferroic BiFeO3
To face the challenges lying beyond current CMOS-based technology, new
paradigms for information processing are required. Magnonics proposes to use
spin waves to carry and process information, in analogy with photonics that
relies on light waves, with several advantageous features such as potential
operation in the THz range and excellent coupling to spintronics. Several
magnonic analog and digital logic devices have been proposed, and some
demonstrated. Just as for spintronics, a key issue for magnonics is the large
power required to control/write information (conventionally achieved through
magnetic fields applied by strip lines, or by spin transfer from large
spin-polarized currents). Here we show that in BiFeO3, a room-temperature
magnetoelectric material, the spin wave frequency (>600 GHz) can be tuned
electrically by over 30%, in a non-volatile way and with virtually no power
dissipation. Theoretical calculations indicate that this effect originates from
a linear magnetoelectric effect related to spin-orbit coupling induced by the
applied electric field. We argue that these properties make BiFeO3 a promising
medium for spin wave generation, conversion and control in future magnonics
architectures.Comment: 3 figure
Strong reduction of the coercivity by a surface acoustic wave in an out-of-plane magnetized epilayer
The 2019 surface acoustic waves roadmap
Today, surface acoustic waves (SAWs) and bulk acoustic waves are already two of the very few phononic technologies of industrial relevance and can been found in a myriad of devices employing these nanoscale earthquakes on a chip. Acoustic radio frequency filters, for instance, are integral parts of wireless devices. SAWs in particular find applications in life sciences and microfluidics for sensing and mixing of tiny amounts of liquids. In addition to this continuously growing number of applications, SAWs are ideally suited to probe and control elementary excitations in condensed matter at the limit of single quantum excitations. Even collective excitations, classical or quantum are nowadays coherently interfaced by SAWs. This wide, highly diverse, interdisciplinary and continuously expanding spectrum literally unites advanced sensing and manipulation applications. Remarkably, SAW technology is inherently multiscale and spans from single atomic or nanoscopic units up even to the millimeter scale. The aim of this Roadmap is to present a snapshot of the present state of surface acoustic wave science and technology in 2019 and provide an opinion on the challenges and opportunities that the future holds from a group of renown experts, covering the interdisciplinary key areas, ranging from fundamental quantum effects to practical applications of acoustic devices in life science
Chirality of Matter Shows Up via Spin Excitations
Right- and left-handed circularly polarized light interact differently with
electronic charges in chiral materials. This asymmetry generates the natural
circular dichroism and gyrotropy, also known as the optical activity. Here we
demonstrate that optical activity is not a privilege of the electronic charge
excitations but it can also emerge for the spin excitations in magnetic matter.
The square-lattice antiferromagnet BaCoGeO offers an ideal arena to
test this idea, since it can be transformed to a chiral form by application of
external magnetic fields. As a direct proof of the field-induced chiral state,
we observed large optical activity when the light is in resonance with spin
excitations at sub-terahertz frequencies. In addition, we found that the
magnetochiral effect, the absorption difference for the light beams propagating
parallel and anti-parallel to the applied magnetic field, has an exceptionally
large amplitude close to 100%. All these features are ascribed to the
magnetoelectric nature of spin excitations as they interact both with the
electric and magnetic components of light
Cell-based screen for altered nuclear phenotypes reveals senescence progression in polyploid cells after Aurora kinase B inhibition.
Cellular senescence is a widespread stress response and is widely considered to be an alternative cancer therapeutic goal. Unlike apoptosis, senescence is composed of a diverse set of subphenotypes, depending on which of its associated effector programs are engaged. Here we establish a simple and sensitive cell-based prosenescence screen with detailed validation assays. We characterize the screen using a focused tool compound kinase inhibitor library. We identify a series of compounds that induce different types of senescence, including a unique phenotype associated with irregularly shaped nuclei and the progressive accumulation of G1 tetraploidy in human diploid fibroblasts. Downstream analyses show that all of the compounds that induce tetraploid senescence inhibit Aurora kinase B (AURKB). AURKB is the catalytic component of the chromosome passenger complex, which is involved in correct chromosome alignment and segregation, the spindle assembly checkpoint, and cytokinesis. Although aberrant mitosis and senescence have been linked, a specific characterization of AURKB in the context of senescence is still required. This proof-of-principle study suggests that our protocol is capable of amplifying tetraploid senescence, which can be observed in only a small population of oncogenic RAS-induced senescence, and provides additional justification for AURKB as a cancer therapeutic target.This work was supported by the University of Cambridge, Cancer Research UK, Hutchison Whampoa; Cancer Research UK grants A6691 and A9892 (M.N., N.K., C.J.T., D.C.B., C.J.C., L.S.G, and M.S.); a fellowship from the Uehara Memorial Foundation (M.S.).This is the author accepted manuscript. The final version is available from the American Society for Cell Biology via http://dx.doi.org/10.1091/mbc.E15-01-000
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