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Dennis Valbjørn
Christensen
,
Urs
Staub
,
T. R.
Devidas
,
Beena
Kalisky
,
Katja
Nowack
,
James Luke
Webb
,
Ulrik L.
Andersen
,
Alexander
Huck
,
David Aaron
Broadway
,
Kai
Wagner
,
Patrick
Maletinsky
,
Toeno
Van Der Sar
,
Chunhui
Du
,
Amir
Yacoby
,
David
Collomb
,
Simon J.
Bending
,
Ahmet
Oral
,
Hans Josef
Hug
,
Andrada Oana
Mandru
,
Volker
Neu
,
Hans Werner
Schumacher
,
Sibylle
Sievers
,
Hitoshi
Saito
,
Alexander Ako
Khajetoorians
,
Nadine
Hauptmann
,
Susanne
Baumann
,
Alexander
Eichler
,
Christian
Degen
,
Jeffrey
Mccord
,
Michael
Vogel
,
Manfred
Fiebig
,
Peter
Fischer
,
Aurelio
Hierro-Rodriguez
,
Simone
Finizio
,
Sarnjeet
Dhesi
,
Claire
Donnelly
,
Felix
Buttner
,
Ofer
Kfir
,
Wen
Hu
,
Sergey
Zayko
,
Stefan
Eisebitt
,
Bastian
Pfau
,
Robert
Frömter
,
Mathias
Klaui
,
Fehmi
Yasin
,
Benjamin J.
Mcmorran
,
Shinichiro
Seki
,
Xiuzhen
Yu
,
Axel
Lubk
,
Daniel
Wolf
,
Nini
Pryds
,
Denys
Makarov
,
Martino
Poggio
Open Access
Abstract: Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetization patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using SQUIDs, spin center and Hall effect magnetometries, scanning probe microscopies, x-ray- and electron-based methods as well as magnetooptics and nanoMRI. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, 3D and geometrically curved objects of different material classes including 2D materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials.
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Mar 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[28375]
Open Access
Abstract: The concept of chirality is of great relevance in nature, from chiral molecules such as sugar to parity transformations in particle physics. In condensed matter physics, recent studies have demonstrated chiral fermions and their relevance in emergent phenomena closely related to topology1,2,3. The experimental verification of chiral phonons (bosons) remains challenging, however, despite their expected strong impact on fundamental physical properties4,5,6. Here we show experimental proof of chiral phonons using resonant inelastic X-ray scattering with circularly polarized X-rays. Using the prototypical chiral material quartz, we demonstrate that circularly polarized X-rays, which are intrinsically chiral, couple to chiral phonons at specific positions in reciprocal space, allowing us to determine the chiral dispersion of the lattice modes. Our experimental proof of chiral phonons demonstrates a new degree of freedom in condensed matter that is both of fundamental importance and opens the door to exploration of new emergent phenomena based on chiral bosons.
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Jun 2023
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I16-Materials and Magnetism
|
Hiroki
Ueda
,
Michael
Porer
,
Jose R. L.
Mardegan
,
Sergii
Parchenko
,
Namrata
Gurung
,
Federica
Fabrizi
,
Mahesh
Ramakrishnan
,
Larissa
Boie
,
Martin Josef
Neugebauer
,
Bulat
Burganov
,
Max
Burian
,
Steven Lee
Johnson
,
Kai
Rossnagel
,
Urs
Staub
Diamond Proposal Number(s):
[15742]
Open Access
Abstract: The correlation between electronic and crystal structures of
1T − TiSe2
in the charge-density wave (CDW) state is studied by x-ray diffraction in order to clarify basic properties in the CDW state, transport properties, and chirality. Three families of reflections are used to probe atomic displacements and the orbital asymmetry in Se. Two distinct onset temperatures are found:
T
CDW
and a lower
T
∗
indicative for an onset of Se out-of-plane atomic displacements.
T
∗
coincides with a DC resistivity maximum and the onset of the proposed gyrotropic (chiral) electronic structure. However, no indication for chirality is found. The relation between the atomic displacements and the transport properties is discussed in terms of Ti
3
d
and Se
4
p
states that only weakly couple to the CDW order.
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Apr 2021
|
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I16-Materials and Magnetism
|
Max
Burian
,
Michael
Porer
,
Jose R. L.
Mardegan
,
Vincent
Esposito
,
Sergii
Parchenko
,
Bulat
Burganov
,
Namrata
Gurung
,
Mahesh
Ramakrishnan
,
Valerio
Scagnoli
,
Hiroki
Ueda
,
Sonia
Francoual
,
Federica
Fabrizi
,
Yoshikazu
Tanaka
,
Tadashi
Togashi
,
Yuya
Kubota
,
Makina
Yabashi
,
Kai
Rossnagel
,
Steven L.
Johnson
,
Urs
Staub
Diamond Proposal Number(s):
[15742]
Open Access
Abstract: In this work, we use ultrafast pump-probe nonresonant and resonant x-ray diffraction to track the periodic lattice distortion and the electronic charge density wave in
1
T
−
TiSe
2
upon optical excitation. We observe a fluence regime in which the periodic lattice deformation is strongly suppressed but the charge density wave related Se
4
p
orbital order remains mostly intact. Complete melting of both structural and electronic order occurs four to five times faster than expected from a purely electronic charge-screening process, strongly suggesting a structurally assisted weakening of excitonic correlations. Our experimental data provide insight on the intricate coupling between structural and electronic order in stabilizing the periodic-lattice-distortion/charge-density-wave state in
1
T
−
TiSe
2
. The results further show that electron-phonon coupling can lead to different, energy dependent phase-transition pathways in condensed matter systems, opening different possibilities in the conception of nonequilibrium phenomena at the ultrafast scale.
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Feb 2021
|
|
|
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Saumya
Mukherjee
,
Kenta
Shimamoto
,
Yoav William
Windsor
,
Mahesh
Ramakrishnan
,
Sergii
Parchenko
,
Urs
Staub
,
Laurent
Chapon
,
Bachir
Ouladdiaf
,
Marisa
Medarde
,
Tian
Shang
,
Elisabeth A.
Müller
,
Michel
Kenzelmann
,
Thomas
Lippert
,
Christof W.
Schneider
,
Christof
Niedermayer
Abstract: We present a generalized multiferroic phase diagram for orthorhombic RMnO3(R=Gd–Lu) based on coherently grown thin films. The magnetic order was identified by neutron-diffraction and resonant soft x-ray scattering experiments. For large R-ions (R=Gd–Dy), the transition temperature to a long-range ordered antiferromagnetic phase is only weakly dependent on the R-ion radius, but decreases monotonically with decreasing R-ion radius for films with R=Ho–Lu. The antiferromagnetic phase is characterized by an incommensurate order of the Mn3+ spins, which successively locks into a commensurate E-type state. These findings confirm a uniform multiferroic ground state independent of the R ion and are in excellent agreement with predicted properties of strain-induced multiferroicity in these materials. In particular, strong variation of multiferroic properties in these epitaxial films compared to bulk highlights the tuning ability of strain.
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Nov 2018
|
|
I16-Materials and Magnetism
|
N.
Gurung
,
N.
Leo
,
S. P.
Collins
,
G.
Nisbet
,
G.
Smolentsev
,
M.
Garcia-Fernandez
,
K.
Yamaura
,
L. J.
Heyderman
,
U.
Staub
,
Y.
Joly
,
D. D.
Khalyavin
,
S. W.
Lovesey
,
V.
Scagnoli
Diamond Proposal Number(s):
[12459, 14853]
Abstract: The 5d transition-metal oxides offer further opportunities to test our understanding of the interplay of correlation effects and spin-orbit interactions in materials in the absence of a single dominant interaction. The subtle balance between solid-state interactions can result in mechanisms that minimize the interaction energy, and in material properties of potential use for applications. We focus here on the 5d transition-metal oxide NaOsO3, a strong candidate for the realization of a magnetically driven transition from a metallic to an insulating state exploiting the so-called Slater mechanism. Experimental results are derived from nonresonant and resonant x-ray single-crystal diffraction at the Os L edges. A change in the crystallographic symmetry does not accompany the metal-insulator transition in the Slater mechanism and, indeed, we find no evidence of such a change in NaOsO3. An equally important experimental observation is the emergence of the (300) Bragg peak in the resonant condition with the onset of magnetic order. The intensity of this space-group-forbidden Bragg peak continuously increases with decreasing temperature in line with the square of intensity observed for an allowed magnetic Bragg peak. Our main experimental results, the absence of crystal symmetry breaking, and the emergence of a space-group-forbidden Bragg peak with developing magnetic order, support the use of the Slater mechanism to interpret the metal-insulator transition in NaOsO3. We successfully describe our experimental results with simulations of the electronic structure and with an atomic model based on the established symmetry of the crystal and magnetic structure.
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Sep 2018
|
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I06-Nanoscience (XPEEM)
|
Elisabeth M.
Bothschafter
,
Elsa
Abreu
,
Laurenz
Rettig
,
Teresa
Kubacka
,
Sergii
Parchenko
,
Michael
Porer
,
Christian
Dornes
,
Yoav William
Windsor
,
Mahesh
Ramakrishnan
,
Aurora
Alberca
,
Sebastian
Manz
,
Jonathan
Saari
,
Seyed M.
Koohpayeh
,
Manfred
Fiebig
,
Thomas
Forrest
,
Philipp
Werner
,
Sarnjeet S.
Dhesi
,
Steven L.
Johnson
,
Urs
Staub
Diamond Proposal Number(s):
[13355, 13926]
Abstract: We investigate the demagnetization dynamics of the cycloidal and sinusoidal phases of multiferroic TbMnO3 by means of time-resolved resonant soft x-ray diffraction following excitation by an optical pump. The use of orthogonal linear x-ray polarizations provides information on the contribution from the different magnetic moment directions, which can be interpreted as signatures from multiferroic cycloidal spin order and sinusoidal spin order. Tracking these signatures in the time domain enables us to identify the transient magnetic phase created by intense photoexcitation of the electrons and subsequent heating of the spin system on a picosecond time scale. The transient phase is shown to exhibit mostly spin density wave character, as in the adiabatic case, while nevertheless retaining the wave vector of the cycloidal long-range order. Two different pump photon energies, 1.55 and 3.1 eV, lead to population of the conduction band predominantly via intersite d−d or intrasite p−d transitions, respectively. We find that the nature of the optical excitation does not play an important role in determining the dynamics of magnetic order melting. Further, we observe that the orbital reconstruction, which is induced by the spin ordering, disappears on a time scale comparable to that of the cycloidal order, attesting to a direct coupling between magnetic order and orbital reconstruction. Our observations are discussed in the context of recent theoretical models of demagnetization dynamics in strongly correlated systems, revealing the potential of this type of measurement as a benchmark for such theoretical studies.
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Nov 2017
|
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Theoretical Physics
|
Abstract: There is general agreement within the community of researchers that investigate high-Tc
materials that it is most important to understand the pseudo-gap phase. To this end, many
experiments on various cuprates have been reported. Two prominent investigations—Kerr
effect and neutron Bragg diffraction—imply that underdoped YBCO samples possess longrange
magnetic order of an unusual kind. However, other measurements do not support the
existence of magnetic order. Here we show that the Kerr effect and magnetic Bragg diffraction
data are individual manifestations of ordered magneto-electric quadrupoles at Cu sites.
While the use of magneto-electric multipoles is new in studies of the electronic properties
of cuprates, they are not unknown in other materials, including an investigation with x-rays
of the parent compound CuO. We exploit the recent prediction that neutrons are deflected by
magneto-electric multipoles. The outcome of our study is a theory for the order-parameter
of the pseudo-gap phase without the aforementioned conflict with other measurements, and
the first experimental evidence that neutrons interact with multipoles belonging to a state of
magnetic charge.
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Jul 2015
|
|
|
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Abstract: The absence of spatial inversion symmetry at both local (point group (4) over bar) and global (crystal class (4) over bar 2m) levels greatly influences the electronic properties of chalcopyrite (CuFeS2). The predicted dichroic signals (natural circular, non-reciprocal and magneto-chiral) and resonant, parity-odd Bragg diffraction patterns at space-group forbidden reflections portray the uncommon, acentric symmetry. Despite extensive experimental investigations over several decades, by mineralogists, chemists and physicists, there is no consensus view about the electrical and magnetic properties of chalcopyrite. New spectroscopic and diffraction data, gathered at various temperatures in the vicinity of the copper and iron L-2,L-3 edges, provide necessary confidence in the magnetic motif used in our analytic simulations of x-ray scattering. With the sample held at 10 and 65 K, our data establish beyond reasonable doubt that there is no valence transition, and ordering of the copper moments as the origin of the low-temperature phase (T-c approximate to 53 K) is ruled out.
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May 2012
|
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I16-Materials and Magnetism
|
Abstract: Resonant x-ray Bragg diffraction by gallium ferrate (GaFeO3) at Friedel pairs of charge allowed reflections in the vicinity of the Fe K edge are presented. By use of the magnetization difference, the interference of charge diffraction with the magnetic diffraction is extracted. The study of Friedel pairs and concentrating at the pre-edge allows us to extract the effect of inversion symmetry breaking on the magnetic Fe 3d shell. The data are analyzed using a model based on atomic multipole moments which are magnetic and have no space inversion symmetry (magnetoelectric) interfering with the charge scattering. This model successfully describes data as a function of azimuthal angle and for different incident polarization and it shows that data can be directly related to the magnetoelectric dipole (toroidal) and quadrupole moments. Though the model describes most of the observations successfully, how to correctly describe the observed magnetic nonresonant intensity below the edge remains an open question.
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Apr 2012
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