13 research outputs found
Persistence of structural distortion and bulk band Rashba splitting in SnTe above its ferroelectric critical temperature
The ferroelectric semiconductor -SnTe has been regarded as a
topological crystalline insulator and the dispersion of its surface states has
been intensively measured with angle-resolved photoemission spectroscopy
(ARPES) over the last decade. However, much less attention has been given to
the impact of the ferroelectric transition on its electronic structure, and in
particular on its bulk states. Here, we investigate the low-energy electronic
structure of -SnTe with ARPES and follow the evolution of the
bulk-state Rashba splitting as a function of temperature, across its
ferroelectric critical temperature of about K. Unexpectedly, we
observe a persistent band splitting up to room temperature, which is consistent
with an order-disorder contribution to the phase transition that requires the
presence of fluctuating local dipoles above . We conclude that no
topological surface state can occur at the (111) surface of SnTe, at odds with
recent literature.Comment: 26 pages, 8 figure
Field-induced ultrafast modulation of Rashba coupling at room temperature in ferroelectric -GeTe(111)
Rashba materials have appeared as an ideal playground for spin-to-charge
conversion in prototype spintronics devices. Among them, -GeTe(111) is
a non-centrosymmetric ferroelectric (FE) semiconductor for which a strong
spin-orbit interaction gives rise to giant Rashba coupling. Its room
temperature ferroelectricity was recently demonstrated as a route towards a new
type of highly energy-efficient non-volatile memory device based on switchable
polarization. Currently based on the application of an electric field, the
writing and reading processes could be outperformed by the use of femtosecond
(fs) light pulses requiring exploration of the possible control of
ferroelectricity on this timescale. Here, we probe the room temperature
transient dynamics of the electronic band structure of -GeTe(111) using
time and angle-resolved photoemission spectroscopy (tr-ARPES). Our experiments
reveal an ultrafast modulation of the Rashba coupling mediated on the fs
timescale by a surface photovoltage (SPV), namely an increase corresponding to
a 13 % enhancement of the lattice distortion. This opens the route for the
control of the FE polarization in -GeTe(111) and FE semiconducting
materials in quantum heterostructures.Comment: 31 pages, 12 figure
Collective topological spin dynamics in a correlated spin glass
The interplay between spin-orbit interaction (SOI) and magnetic order is
currently one of the most active research fields in condensed matter physics
and leading the search for materials with novel and tunable magnetic and spin
properties. Here we report on a variety of unexpected and unique observations
in thin multiferroic \GeMnTe films. The ferrimagnetic order in this
ferroelectric semiconductor is found to reverse with current pulses six orders
of magnitude lower as for typical spin-orbit torque systems. Upon a switching
event, the magnetic order spreads coherently and collectively over macroscopic
distances through a correlated spin-glass state. Lastly, we present a novel
methodology to controllably harness this stochastic magnetization dynamics,
allowing us to detect spatiotemporal nucleation of topological spin textures we
term ``skyrmiverres''.Comment: 26 pages, 10 figures, 2 table
Field-induced ultrafast modulation of Rashba coupling at room temperature in ferroelectric alpha-GeTe(111)
Rashba materials have appeared as an ideal playground for spin-to-charge conversion in prototype spintronics devices. Among them, α-GeTe(111) is a non-centrosymmetric ferroelectric semiconductor for which a strong spin-orbit interaction gives rise to giant Rashba coupling. Its room temperature ferroelectricity was recently demonstrated as a route towards a new type of highly energy-efficient non-volatile memory device based on switchable polarization. Currently based on the application of an electric field, the writing and reading processes could be outperformed by the use of femtosecond light pulses requiring exploration of the possible control of ferroelectricity on this timescale. Here, we probe the room temperature transient dynamics of the electronic band structure of α-GeTe(111) using time and angle-resolved photoemission spectroscopy. Our experiments reveal an ultrafast modulation of the Rashba coupling mediated on the fs timescale by a surface photovoltage, namely an increase corresponding to a 13% enhancement of the lattice distortion. This opens the route for the control of the ferroelectric polarization in α-GeTe(111) and ferroelectric semiconducting materials in quantum heterostructures.Rashba materials have appeared as an ideal playground for spin-to-charge conversion in prototype spintronics devices. Among them, α-GeTe(111) is a non-centrosymmetric ferroelectric semiconductor for which a strong spin-orbit interaction gives rise to giant Rashba coupling. Its room temperature ferroelectricity was recently demonstrated as a route towards a new type of highly energy-efficient non-volatile memory device based on switchable polarization. Currently based on the application of an electric field, the writing and reading processes could be outperformed by the use of femtosecond light pulses requiring exploration of the possible control of ferroelectricity on this timescale. Here, we probe the room temperature transient dynamics of the electronic band structure of α-GeTe(111) using time and angle-resolved photoemission spectroscopy. Our experiments reveal an ultrafast modulation of the Rashba coupling mediated on the fs timescale by a surface photovoltage, namely an increase corresponding to a 13% enhancement of the lattice distortion. This opens the route for the control of the ferroelectric polarization in α-GeTe(111) and ferroelectric semiconducting materials in quantum heterostructures
X-Treme beamline at SLS: X-ray magnetic circular and linear dichroism at high field and low temperature
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Ferroelectric Self-Poling in GeTe Films and Crystals
Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for spintronics applications. Typically, ferroelectric materials possess random oriented domains that need poling to achieve macroscopic polarization. By using X-ray absorption fine structure spectroscopy complemented with anomalous diffraction and piezo-response force microscopy, we investigated the bulk ferroelectric structure of GeTe crystals and thin films. Both feature multi-domain structures in the form of oblique domains for films and domain colonies inside crystals. Despite these multi-domain structures which are expected to randomize the polarization direction, our experimental results show that at room temperature there is a preferential ferroelectric order remarkably consistent with theoretical predictions from ideal GeTe crystals. This robust self-poled state has high piezoelectricity and additional poling reveals persistent memory effects. © 2019 by the authors. Licensee MDPI, Basel, Switzerland
Ferroelectric Self-Poling in GeTe Films and Crystals
Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for spintronics applications. Typically, ferroelectric materials possess random oriented domains that need poling to achieve macroscopic polarization. By using X-ray absorption fine structure spectroscopy complemented with anomalous diffraction and piezo-response force microscopy, we investigated the bulk ferroelectric structure of GeTe crystals and thin films. Both feature multi-domain structures in the form of oblique domains for films and domain colonies inside crystals. Despite these multi-domain structures which are expected to randomize the polarization direction, our experimental results show that at room temperature there is a preferential ferroelectric order remarkably consistent with theoretical predictions from ideal GeTe crystals. This robust self-poled state has high piezoelectricity and additional poling reveals persistent memory effects