1,194 research outputs found
Ultrafast and reversible control of the exchange interaction in Mott insulators
The strongest interaction between microscopic spins in magnetic materials is
the exchange interaction . Therefore, ultrafast control of
holds the promise to control spins on ultimately fast timescales.
We demonstrate that time-periodic modulation of the electronic structure by
electric fields can be used to reversibly control on ultrafast
timescales in extended antiferromagnetic Mott insulators. In the regime of weak
driving strength, we find that can be enhanced and reduced for
frequencies below and above the Mott gap, respectively. Moreover, for strong
driving strength, even the sign of can be reversed and we show
that this causes time reversal of the associated quantum spin dynamics. These
results suggest wide applications, not only to control magnetism in condensed
matter systems, for example, via the excitation of spin resonances, but also to
assess fundamental questions concerning the reversibility of the quantum
many-body dynamics in cold atom systems.Comment: 9 pages, 4 figure
Kondo Screening and Magnetic Ordering in Frustrated UNi4B
UNi4B exhibits unusual properties and, in particular, a unique
antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the
low temperature behavior of this compound, we propose that the remaining 1/3 U
sites are nonmagnetic due to the Kondo effect. We derive a model in which the
coexistence of magnetic and nonmagnetic U sites is the consequence of the
competition between frustration of the crystallographic structure and
instability of the 5f moments.Comment: 4 pages, 2 figure
Supervised learning of an opto-magnetic neural network with ultrashort laser pulses
The explosive growth of data and its related energy consumption is pushing
the need to develop energy-efficient brain-inspired schemes and materials for
data processing and storage. Here, we demonstrate experimentally that Co/Pt
films can be used as artificial synapses by manipulating their magnetization
state using circularly-polarized ultrashort optical pulses at room temperature.
We also show an efficient implementation of supervised perceptron learning on
an opto-magnetic neural network, built from such magnetic synapses.
Importantly, we demonstrate that the optimization of synaptic weights can be
achieved using a global feedback mechanism, such that the learning does not
rely on external storage or additional optimization schemes. These results
suggest there is high potential for realizing artificial neural networks using
optically-controlled magnetization in technologically relevant materials, that
can learn not only fast but also energy-efficient.Comment: 9 pages, 4 figure
Inflection point in the magnetic field dependence of the ordered moment of URu2Si2 observed by neutron scattering in fields up to 17 T
We have measured the magnetic field dependence of the ordered
antiferromagnetic moment and the magnetic excitations in the heavy-fermion
superconductor URu2Si2 for fields up to 17 Tesla applied along the tetragonal c
axis, using neutron scattering. The decrease of the magnetic intensity of the
tiny moment with increasing field does not follow a simple power law, but shows
a clear inflection point, indicating that the moment disappears first at the
metamagnetic transition at ~40 T. This suggests that the moment m is connected
to a hidden order parameter Phi which belongs to the same irreducible
representation breaking time-reversal symmetry. The magnetic excitation gap at
the antiferromagnetic zone center Q=(1,0,0) increases continuously with
increasing field, while that at Q=(1.4,0,0) is nearly constant. This field
dependence is opposite to that of the gap extracted from specific-heat data.Comment: 10 pages, 5 figures, submitted to PR
Simultaneous power transfer and bidirectional serial communication for implantable electronics
Specific Heat of URuSi in Fields to 42 T: Clues to the 'Hidden Order'
The large C observed at 17.5 K in URuSi is inconsistent
with the small, 0.04 moment measured for the antiferromagnetism
observed starting (perhaps coincidentally) at the same temperature. We report
measurements of this specific heat transition, thought to be due to some
'hidden order', in magnetic fields between 24 and 42 T, i. e. through the field
region where three metamagnetic transtions are known to occur at 35.8, 37.3,
and 39.4 T. The response of C in single crystal URuSi to
magnetic field, which includes a change to C being possibly associated
with a first order phase transition for high fields, is analyzed to shed
further light on the possible explanations of this unknown ordering process. At
fields above 35 T, a new high field phase comes into being; the connection
between this high field phase revealed by the specific heat and earlier
magnetization data is discussed
Characterisation of a multi-channel multiplexed EMG recording system: towards realising variable electrode configurations
First steps towards osseointegrated myoelec-trically-controlled prostheses: Bone anchor conduit conveys EMG signals from implanted electrodes [1]. In vivo selection of electrode configurations would improve signal-to-noise ratio (SNR) of EMG recordings [2]; optimal electrode config-urations are not known before implantation. The CAPITel system: Control of Active Prostheses using Implant-able Telemetry [3,4]. Implantable EMG amplifier with a novel multi-plexed frontend. In vivo selection of monopolar, bipolar or tripolar configurations. Designed using commercially available com-ponents for use in animal models. After further research design will be imple-mented as an ASIC
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