B23-Circular Dichroism
|
Karl
Frontzek
,
Marco
Bardelli
,
Assunta
Senatore
,
Anna
Henzi
,
Regina R.
Reimann
,
Seden
Bedir
,
Marika
Marino
,
Rohanah
Hussain
,
Simon
Jurt
,
Georg
Meisl
,
Mattia
Pedotti
,
Federico
Mazzola
,
Giuliano
Siligardi
,
Oliver
Zerbe
,
Marco
Losa
,
Tuomas
Knowles
,
Asvin
Lakkaraju
,
Caihong
Zhu
,
Petra
Schwarz
,
Simone
Hornemann
,
Matthew G.
Holt
,
Luca
Simonelli
,
Luca
Varani
,
Adriano
Aguzzi
Diamond Proposal Number(s):
[19680]
Open Access
Abstract: Prion infections cause conformational changes of the cellular prion protein (PrPC) and lead to progressive neurological impairment. Here we show that toxic, prion-mimetic ligands induce an intramolecular R208-H140 hydrogen bond (‘H-latch’), altering the flexibility of the α2–α3 and β2–α2 loops of PrPC. Expression of a PrP2Cys mutant mimicking the H-latch was constitutively toxic, whereas a PrPR207A mutant unable to form the H-latch conferred resistance to prion infection. High-affinity ligands that prevented H-latch induction repressed prion-related neurodegeneration in organotypic cerebellar cultures. We then selected phage-displayed ligands binding wild-type PrPC, but not PrP2Cys. These binders depopulated H-latched conformers and conferred protection against prion toxicity. Finally, brain-specific expression of an antibody rationally designed to prevent H-latch formation prolonged the life of prion-infected mice despite unhampered prion propagation, confirming that the H-latch is an important reporter of prion neurotoxicity.
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Aug 2022
|
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I05-ARPES
|
F.
Mazzola
,
C.-M.
Yim
,
V.
Sunko
,
S.
Khim
,
P.
Kushwaha
,
O. J.
Clark
,
L.
Bawden
,
I.
Markovic
,
D.
Chakraborti
,
T. K.
Kim
,
M.
Hoesch
,
A. P.
Mackenzie
,
P.
Wahl
,
P. D. C.
King
Diamond Proposal Number(s):
[12469, 14927, 1626]
Open Access
Abstract: Controlling spin wave excitations in magnetic materials underpins the burgeoning field of magnonics. Yet, little is known about how magnons interact with the conduction electrons of itinerant magnets, or how this interplay can be controlled. Via a surface-sensitive spectroscopic approach, we demonstrate a strong electron–magnon coupling at the Pd-terminated surface of the delafossite oxide PdCoO2, where a polar surface charge mediates a Stoner transition to itinerant surface ferromagnetism. We show how the coupling is enhanced sevenfold with increasing surface disorder, and concomitant charge carrier doping, becoming sufficiently strong to drive the system into a polaronic regime, accompanied by a significant quasiparticle mass enhancement. Our study thus sheds light on electron–magnon interactions in solid-state materials, and the ways in which these can be controlled.
|
Feb 2022
|
|
I09-Surface and Interface Structural Analysis
|
Gian Marco
Pierantozzi
,
Alessandro
De Vita
,
Chiara
Bigi
,
Xin
Gui
,
Hung-Ju
Tien
,
Debashis
Mondal
,
Federico
Mazzola
,
Jun
Fujii
,
Ivana
Vobornik
,
Giovanni
Vinai
,
Alessandro
Sala
,
Cristina
Africh
,
Tien-Lin
Lee
,
Giorgio
Rossi
,
Tay-Rong
Chang
,
Weiwei
Xie
,
Robert J.
Cava
,
Giancarlo
Panaccione
Diamond Proposal Number(s):
[24968]
Open Access
Abstract: We unravel the interplay of topological properties and the layered (anti)ferromagnetic ordering in EuSn2P2, using spin and chemical selective electron and X-ray spectroscopies supported by first-principle calculations. We reveal the presence of in-plane long-range ferromagnetic order triggering topological invariants and resulting in the multiple protection of topological Dirac states. We provide clear evidence that layer-dependent spin-momentum locking coexists with ferromagnetism in this material, a cohabitation that promotes EuSn2P2 as a prime candidate axion insulator for topological antiferromagnetic spintronics applications.
|
Jan 2022
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[18705]
Open Access
Abstract: We report a combined experimental and theoretical study of the surface and bulk electronic structure of aluminium diboride, a nonsuperconducting sister compound of the superconductor
MgB
2
. We perform angle-resolved photoemission measurements with variable photon energy, and compare them to density functional theory calculations to disentangle the surface and bulk contributions to the measured spectra. Aluminium diboride is known to be aluminium deficient,
Al
1
−
δ
B
2
, which would be expected to lead to a hole doping as compared to the nominally stoichimoetric compound. Nonetheless, we find that the bulk
σ
states, which mediate superconductivity in
MgB
2
, remain more than
600
meV
below the Fermi level. However, we also observe
σ
states originating from the boron terminated surface, with an order of magnitude smaller binding energy of
70
meV
, and demonstrate how surface hole-doping can bring these across the Fermi level.
|
Jul 2020
|
|
I05-ARPES
|
Igor
Markovic
,
Matthew D.
Watson
,
Oliver J.
Clark
,
Federico
Mazzola
,
Edgar
Abarca Morales
,
Chris A.
Hooley
,
Helge
Rosner
,
Craig M.
Polley
,
Thiagarajan
Balasubramanian
,
Saumya
Mukherjee
,
Naoki
Kikugawa
,
Dmitry A.
Sokolov
,
Andrew P.
Mackenzie
,
Phil D. C.
King
Diamond Proposal Number(s):
[21986, 25040]
Abstract: The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca3Ru2O7
, a 4d
oxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spin-reorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin–orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.
|
Jun 2020
|
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I05-ARPES
I10-Beamline for Advanced Dichroism
|
Matthew D.
Watson
,
Igor
Markovic
,
Federico
Mazzola
,
Akhil
Rajan
,
Edgar A.
Morales
,
David
Burn
,
Thorsten
Hesjedal
,
Gerrit
Van Der Laan
,
Saumya
Mukherjee
,
Timur K.
Kim
,
Chiara
Bigi
,
Ivana
Vobornik
,
Monica
Ciomaga Hatnean
,
Geetha
Balakrishnan
,
Philip D. C.
King
Diamond Proposal Number(s):
[21986, 22794, 23785]
Abstract: We investigate the temperature-dependent electronic structure of the van der Waals ferromagnet, CrGeTe3. Using angle-resolved photoemission spectroscopy, we identify atomic- and orbital-specific band shifts upon cooling through TC. From these, together with x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we identify the states created by a covalent bond between the Te 5p and the Cr eg orbitals as the primary driver of the ferromagnetic ordering in this system, while it is the Cr t2g states that carry the majority of the spin moment. The t2g states furthermore exhibit a marked bandwidth increase and a remarkable lifetime enhancement upon entering the ordered phase, pointing to a delicate interplay between localized and itinerant states in this family of layered ferromagnets.
|
May 2020
|
|
I05-ARPES
I09-Surface and Interface Structural Analysis
|
Veronika
Sunko
,
F.
Mazzola
,
S.
Kitamura
,
S.
Khim
,
P.
Kushwaha
,
O. J.
Clark
,
M. D.
Watson
,
I.
Markovic
,
D.
Biswas
,
L.
Pourovskii
,
T. K.
Kim
,
T.-L.
Lee
,
P. K.
Thakur
,
H.
Rosner
,
A.
Georges
,
R.
Moessner
,
T.
Oka
,
A. P.
Mackenzie
,
P. D. C.
King
Diamond Proposal Number(s):
[19479, 17699]
Open Access
Abstract: A nearly free electron metal and a Mott insulating state can be thought of as opposite ends of the spectrum of possibilities for the motion of electrons in a solid. Understanding their interaction lies at the heart of the correlated electron problem. In the magnetic oxide metal PdCrO2, nearly free and Mott-localized electrons exist in alternating layers, forming natural heterostructures. Using angle-resolved photoemission spectroscopy, quantitatively supported by a strong coupling analysis, we show that the coupling between these layers leads to an “intertwined” excitation that is a convolution of the charge spectrum of the metallic layer and the spin susceptibility of the Mott layer. Our findings establish PdCrO2 as a model system in which to probe Kondo lattice physics and also open new routes to use the a priori nonmagnetic probe of photoemission to gain insights into the spin susceptibility of correlated electron materials.
|
Feb 2020
|
|
I09-Surface and Interface Structural Analysis
|
G.
Vinai
,
C.
Bigi
,
A.
Rajan
,
M. D.
Watson
,
T.-L.
Lee
,
F.
Mazzola
,
S.
Modesti
,
S.
Barua
,
M.
Ciomaga Hatnean
,
G.
Balakrishnan
,
P. D. C.
King
,
P.
Torelli
,
G.
Rossi
,
G.
Panaccione
Diamond Proposal Number(s):
[21429]
Abstract: Among transition-metal dichalcogenides, mono and few-layers thick
VSe
2
has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of
Fe
/
VSe
2
heterostructure by combining element sensitive x-ray absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk
VSe
2
do not show intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the
Fe
/
VSe
2
interface and its relation with interfacial magnetic coupling.
|
Jan 2020
|
|
I05-ARPES
|
Veronika
Sunko
,
Edgar
Abarca Morales
,
Igor
Markovic
,
Mark E.
Barber
,
Dijana
Milosavljević
,
Federico
Mazzola
,
Dmitry A.
Sokolov
,
Naoki
Kikugawa
,
Cephise
Cacho
,
Pavel
Dudin
,
Helge
Rosner
,
Clifford
Hicks
,
Philip D. C.
King
,
Andrew P.
Mackenzie
Diamond Proposal Number(s):
[20427]
Open Access
Abstract: Pressure represents a clean tuning parameter for traversing the complex phase diagrams of interacting electron systems, and as such has proved of key importance in the study of quantum materials. Application of controlled uniaxial pressure has recently been shown to more than double the transition temperature of the unconventional superconductor Sr2RuO4, leading to a pronounced peak in Tc versus strain whose origin is still under active debate. Here we develop a simple and compact method to passively apply large uniaxial pressures in restricted sample environments, and utilise this to study the evolution of the electronic structure of Sr2RuO4 using angle-resolved photoemission. We directly visualise how uniaxial stress drives a Lifshitz transition of the γ-band Fermi surface, pointing to the key role of strain-tuning its associated van Hove singularity to the Fermi level in mediating the peak in Tc. Our measurements provide stringent constraints for theoretical models of the strain-tuned electronic structure evolution of Sr2RuO4. More generally, our experimental approach opens the door to future studies of strain-tuned phase transitions not only using photoemission but also other experimental techniques where large pressure cells or piezoelectric-based devices may be difficult to implement.
|
Dec 2019
|
|
I05-ARPES
|
O. J.
Clark
,
F.
Mazzola
,
I.
Markovic
,
J. M.
Riley
,
J.
Feng
,
B.-J.
Yang
,
K.
Sumida
,
T.
Okuda
,
J.
Fujii
,
I.
Vobornik
,
T. K.
Kim
,
K.
Okawa
,
T.
Sasagawa
,
M. S.
Bahramy
,
P. D. C.
King
Diamond Proposal Number(s):
[14927, 16262]
Abstract: The band inversions that generate the topologically non-trivial band gaps of topological insulators and the isolated Dirac touching points of three-dimensional Dirac semimetals generally arise from the crossings of electronic states derived from different orbital manifolds. Recently, the concept of single orbital-manifold band inversions occurring along high-symmetry lines has been demonstrated, stabilising multiple bulk and surface Dirac fermions. Here, we discuss the underlying ingredients necessary to achieve such phases, and discuss their existence within the family of transition metal dichalcogenides. We show how their three-dimensional band structures naturally produce only small k z projected band gaps, and demonstrate how these play a significant role in shaping the surface electronic structure of these materials. We demonstrate, through spin- and angle-resolved photoemission and density functional theory calculations, how the surface electronic structures of the group-X TMDs PtSe2 and PdTe2 are host to up to five distinct surface states, each with complex band dispersions and spin textures. Finally, we discuss how the origin of several recently-realised instances of topological phenomena in systems outside of the TMDs, including the iron-based superconductors, can be understood as a consequence of the same underlying mechanism driving k z -mediated band inversions in the TMDs.
|
Mar 2019
|
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