I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Zubia
Hasan
,
Grace A.
Pan
,
Harrison
Labollita
,
Austin
Kaczmarek
,
Suk Hyun
Sung
,
Shekhar
Sharma
,
Purnima P.
Balakrishnan
,
Edward
Mercer
,
Vivek
Bhartiya
,
Alpha T.
N'Diaye
,
Zaher
Salman
,
Thomas
Prokscha
,
Andreas
Suter
,
Alexander J.
Grutter
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Ismail
El Baggari
,
Darrell G.
Schlom
,
Matthew R.
Barone
,
Charles M.
Brooks
,
Katja C.
Nowack
,
Antia S.
Botana
,
Brendan D.
Faeth
,
Alberto
De La Torre
,
Julia A.
Mundy
Diamond Proposal Number(s):
[34236]
Open Access
Abstract: Geometrically frustrated lattices can display a range of correlated phenomena, ranging from spin frustration and charge order to dispersionless flat bands due to quantum interference. One particularly compelling family of such materials is the half-valence spinel LiB2O4 materials. On the B-site frustrated pyrochlore sublattice, the interplay of correlated metallic behavior and charge frustration leads to a superconducting state in LiTi2O4 and heavy fermion behavior in LiV2O4. To date, however, LiTi2O4 has primarily been understood as a conventional BCS superconductor despite a lattice structure that could host more exotic ground states. Here, we present a multimodal investigation of LiTi2O4, combining ARPES, RIXS, proximate magnetic probes, and ab-initio many-body theoretical calculations. Our data reveals a novel mobile polaronic ground state with spectroscopic signatures that underlie co-dominant electron-phonon coupling and electron-electron correlations also found in the lightly doped cuprates. The cooperation between the two interaction scales distinguishes LiTi2O4 from other superconducting titanates, suggesting an unconventional origin to superconductivity in LiTi2O4. Our work deepens our understanding of the rare interplay of electron-electron correlations and electron-phonon coupling in unconventional superconducting systems. In particular, our work identifies the geometrically frustrated, mixed-valence spinel family as an under-explored platform for discovering unconventional, correlated ground states.
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Jan 2026
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I06-Nanoscience (XPEEM)
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Purnima P.
Balakrishnan
,
Hemian
Yi
,
Zi-Jie
Yan
,
Wei
Yuan
,
Andreas
Suter
,
Christopher J.
Jensen
,
Pascal
Manuel
,
Fabio
Orlandi
,
Takayasu
Hanashima
,
Christy J.
Kinane
,
Andrew J.
Caruana
,
Dirk
Backes
,
Padraic
Shafer
,
Brian B.
Maranville
,
Zaher
Salman
,
Thomas
Prokscha
,
Cui-Zu
Chang
,
Alexander J.
Grutter
Diamond Proposal Number(s):
[42224]
Abstract: The search for chiral topological superconductivity in magnetic topological insulator (TI)-FeTe heterostructures is a key frontier in condensed matter physics, with potential applications in topological quantum computing. The combination of ferromagnetism, superconductivity, and topologically nontrivial surface states brings together the key elements required for chiral Majorana physics. In this work, we examine the interplay between magnetism and superconductivity at the interfaces between FeTe and a series of Te-based TI overlayers. In both Te/FeTe and superconducting MnBi2Te4/FeTe, any interfacial suppression of antiferromagnetism must affect at most a few nanometers. On the other hand, (Bi,Sb)2Te3/FeTe layers exhibit near-total suppression of antiferromagnetic ordering. Ferromagnetic Cr𝑥(Bi,Sb)2−𝑥Te3 (CBST)/FeTe bilayers exhibit net magnetization in both CBST and FeTe layers, with evidence of interactions between superconductivity and ferromagnetism. These observations identify magnetic TI/FeTe interfaces as an exceptionally robust platform to realize chiral topological superconductivity.
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Oct 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Teguh Citra
Asmara
,
Robert J.
Green
,
Andreas
Suter
,
Yuan
Wei
,
Wenliang
Zhang
,
Daniel
Knez
,
Grant
Harris
,
Yi
Tseng
,
Tianlun
Yu
,
Davide
Betto
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Yannick Maximilian
Klein
,
Neeraj
Kumar
,
Carlos W.
Galdino
,
Zaher
Salman
,
Thomas
Prokscha
,
Marisa
Medarde
,
Elisabeth
Müller
,
Yona
Soh
,
Nicholas B.
Brookes
,
Ke-Jin
Zhou
,
Milan
Radovic
,
Thorsten
Schmitt
Diamond Proposal Number(s):
[28665]
Open Access
Abstract: Strongly-correlated transition-metal oxides are widely known for their various exotic phenomena. This is exemplified by rare-earth nickelates such as LaNiO3, which possess intimate interconnections between their electronic, spin, and lattice degrees of freedom. Their properties can be further enhanced by pairing them in hybrid heterostructures, which can lead to hidden phases and emergent phenomena. An important example is the LaNiO3/LaTiO3 superlattice, where an interlayer electron transfer has been observed from LaTiO3 into LaNiO3 leading to a high-spin state. However, macroscopic emergence of magnetic order associated with this high-spin state has so far not been observed. Here, by using muon spin rotation, x-ray absorption, and resonant inelastic x-ray scattering, direct evidence of an emergent antiferromagnetic order with high magnon energy and exchange interactions at the LaNiO3/LaTiO3 interface is presented. As the magnetism is purely interfacial, a single LaNiO3/LaTiO3 interface can essentially behave as an atomically thin strongly-correlated quasi-2D antiferromagnet, potentially allowing its technological utilization in advanced spintronic devices. Furthermore, its strong quasi-2D magnetic correlations, orbitally-polarized planar ligand holes, and layered superlattice design make its electronic, magnetic, and lattice configurations resemble the precursor states of superconducting cuprates and nickelates, but with an S→1 spin state instead.
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Aug 2024
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I10-Beamline for Advanced Dichroism - scattering
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T. J.
Hicken
,
M. N.
Wilson
,
Z.
Salman
,
S. L.
Zhang
,
S. J. R.
Holt
,
T.
Prokscha
,
A.
Suter
,
F. L.
Pratt
,
G.
Van Der Laan
,
T.
Hesjedal
,
T.
Lancaster
Diamond Proposal Number(s):
[18898]
Open Access
Abstract: Skyrmion-hosting multilayer stacks are promising avenues for applications, although little is known about the depth dependence of the magnetism. We address this by reporting the results of circular dichroic resonant elastic x-ray scattering (CD-REXS), micromagnetic simulations, and low-energy muon-spin rotation (LE-
μ
+
SR
) measurements on a stack comprising
[
Ta
/CoFeB/
MgO
]
16
/Ta on a Si substrate. Energy-dependent CD-REXS shows a continuous, monotonic evolution of the domain-wall helicity angle with incident energy, consistent with a three-dimensional hybrid domain-wall-like structure that changes from Néel-like near the surface to Bloch-like deeper within the sample. LE-
μ
+
SR
reveals that the magnetic field distribution in the trilayers near the surface of the stack is distinct from that in trilayers deeper within the sample. Our micromagnetic simulations support a quantitative analysis of the
μ
+
SR
results. By increasing the applied magnetic field, we find a reduction in the volume occupied by domain walls at all depths, consistent with a crossover into a region dominated by skyrmions above approximately 180 mT.
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Apr 2024
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I10-Beamline for Advanced Dichroism - scattering
|
N.-J.
Steinke
,
S. L.
Zhang
,
P. J.
Baker
,
L. B.
Duffy
,
F.
Kronast
,
J.
Krieger
,
Z.
Salman
,
T.
Prokscha
,
A.
Suter
,
S.
Langridge
,
Gerrit
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[11503]
Abstract: Chromium-doped
Sb
2
Te
3
is a magnetic topological insulator (MTI), which belongs to the
(
Sb
,
Bi
)
2
(
Se
,
Te
)
3
family. When doped with the transition metals V, Cr, and Mn this family displays long-range ferromagnetic order above liquid nitrogen temperature and is currently intensely explored for quantum device applications. Despite the large magnetic ordering temperature, the experimental observation of dissipationless electrical transport channels, i.e., the quantum anomalous Hall effect, is limited in these materials to temperatures below
≈
2
K. Inhomogeneities in the MTI have been identified as a major concern, affecting the coupling between the Dirac states and the magnetic dopants. Nevertheless, details on the local magnetic order in these materials are not well understood. Here, we report the study of the magnetic correlations in thin films using a combination of muon spin relaxation
(
μ
SR
)
, and magnetic soft x-ray spectroscopy and imaging.
μ
SR
provides two key quantities for understanding the microscopic magnetic behavior: The magnetic volume fraction, i.e., the percentage of the material that is ferromagnetically ordered, and the relaxation rate, which is sensitive to the magnetic static
(
≈
μ
s
)
and dynamic disorder. By choosing different implantation depths for the muons, one can further discriminate between near-surface and bulk properties. No evidence for a surface enhancement of the magnetic ordering is observed, but, instead, we find evidence of small magnetically ordered clusters in a paramagnetic background, which are coupled. The significant magnetic field shift that is present in all samples indicates a percolation transition that proceeds through the formation and growth of magnetically ordered spin clusters. We further find that fluctuations are present even at low temperatures, and that there appears to be a transition between superparamagnetism and superferromagnetism.
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Dec 2022
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|
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L. B.
Duffy
,
N.-J.
Steinke
,
J. A.
Krieger
,
A. I.
Figueroa
,
K.
Kummer
,
T.
Lancaster
,
S. R.
Giblin
,
F. L.
Pratt
,
S. J.
Blundell
,
T.
Prokscha
,
A.
Suter
,
Sean
Langridge
,
V. N.
Strocov
,
Z.
Salman
,
G.
Van Der Laan
,
T.
Hesjedal
Abstract: Magnetic doping with transition metal ions is the most widely used approach to break time-reversal symmetry in a topological insulator (TI)—a prerequisite for unlocking the TI’s exotic potential. Recently, we reported the doping of Bi2Te3 thin films with rare-earth ions, which, owing to their large magnetic moments, promise commensurately large magnetic gap openings in the topological surface states. However, only when doping with Dy has a sizable gap been observed in angle-resolved photoemission spectroscopy, which persists up to room temperature. Although disorder alone could be ruled out as a cause of the topological phase transition, a fundamental understanding of the magnetic and electronic properties of Dy-doped Bi2Te3 remained elusive.Here, we present an x-ray magnetic circular dichroism, polarized neutron reflectometry, muon-spin rotation, and resonant photoemission study of the microscopic magnetic and electronic properties. We find that the films are not simply paramagnetic but that instead the observed behavior can be well explained by the assumption of slowly fluctuating, inhomogeneous, magnetic patches with increasing volume fraction as the temperature decreases. At liquid helium temperatures, a large effective magnetization can be easily introduced by the application of moderate magnetic fields, implying that this material is very suitable for proximity coupling to an underlying ferromagnetic insulator or in a heterostructure with transition-metal-doped layers. However, the introduction of some charge carriers by the Dy dopants cannot be excluded at least in these highly doped samples. Nevertheless, we find that the magnetic order is not mediated via the conduction channel in these samples and therefore magnetic order and carrier concentration are expected to be independently controllable. This is not generally the case for transition-metal-doped topological insulators, and Dy doping should thus allow for improved TI quantum devices.
|
May 2018
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I10-Beamline for Advanced Dichroism - scattering
|
S. L.
Zhang
,
I.
Stasinopoulos
,
T.
Lancaster
,
F.
Xiao
,
A.
Bauer
,
F.
Rucker
,
A. A.
Baker
,
A. I.
Figueroa
,
Z.
Salman
,
F. L.
Pratt
,
S. J.
Blundell
,
T.
Prokscha
,
A.
Suter
,
J.
Waizner
,
M.
Garst
,
D.
Grundler
,
G.
Van Der Laan
,
C.
Pfleiderer
,
T.
Hesjedal
Diamond Proposal Number(s):
[8703, 9595]
Open Access
Abstract: Chiral magnets are promising materials for the realisation of high-density and low-power spintronic memory devices. For these future applications, a key requirement is the synthesis of appropriate materials in the form of thin films ordering well above room temperature. Driven by the Dzyaloshinskii-Moriya interaction, the cubic compound FeGe exhibits helimagnetism with a relatively high transition temperature of 278 K in bulk crystals. We demonstrate that this temperature can be enhanced significantly in thin films. Using x-ray scattering and ferromagnetic resonance techniques, we provide unambiguous experimental evidence for long-wavelength helimagnetic order at room temperature and magnetic properties similar to the bulk material. We obtain αintr = 0.0036 ± 0.0003 at 310 K for the intrinsic damping parameter. We probe the dynamics of the system by means of muon-spin rotation, indicating that the ground state is reached via a freezing out of slow dynamics. Our work paves the way towards the fabrication of thin films of chiral magnets that host certain spin whirls, so-called skyrmions, at room temperature and potentially offer integrability into modern electronics.
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Mar 2017
|
|
I06-Nanoscience (XPEEM)
I10-Beamline for Advanced Dichroism - scattering
|
M. D.
Watson
,
L. J.
Collins-Mcintyre
,
L. R.
Shelford
,
A. I.
Coldea
,
D.
Prabhakaran
,
S. C.
Speller
,
T.
Mousavi
,
C. R. M.
Grovenor
,
Z.
Salman
,
S. R.
Giblin
,
G.
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[7345]
Open Access
Abstract: Breaking the time reversal symmetry of a topological insulator, for example by the presence of magnetic ions, is a prerequisite for spin-based electronic applications in the future. In this regard Mn-doped Bi2Te3 is a prototypical example that merits a systematic investigation of its magnetic properties. Unfortunately, Mn doping is challenging in many host materials—resulting in structural or chemical inhomogeneities affecting the magnetic properties. Here, we present a systematic study of the structural, magnetic and magnetotransport properties of Mn-doped Bi2Te3 single crystals using complimentary experimental techniques. These materials exhibit a ferromagnetic phase that is very sensitive to the structural details, with TC varying between 9 and 13 K (bulk values) and a saturation moment that reaches 4.4(5) μB per Mn in the ordered phase. Muon spin rotation suggests that the magnetism is homogeneous throughout the sample. Furthermore, torque measurements in fields up to 33 T reveal an easy axis magnetic anisotropy perpendicular to the ab-plane. The electrical transport data show an anomaly around TC that is easily suppressed by an applied magnetic field, and also anisotropic behavior due to the spin-dependent scattering in relation to the alignment of the Mn magnetic moment. Hall measurements on different crystals established that these systems are n-doped with carrier concentrations of ~ 0.5–3.0 × 1020 cm−3. X-ray magnetic circular dichroism (XMCD) at the Mn L2,3 edge at 1.8 K reveals a large spin magnetic moment of 4.3(3) μB/Mn, and a small orbital magnetic moment of 0.18(2) μB/Mn. The results also indicate a ground state of mixed d4–d5–d6 character of a localized electronic nature, similar to the diluted ferromagnetic semiconductor Ga1−xMnxAs. XMCD measurements in a field of 6 T give a transition point at T ≈ 16 K, which is ascribed to short range magnetic order induced by the magnetic field. In the ferromagnetic state the easy direction of magnetization is along the c-axis, in agreement with bulk magnetization measurements. This could lead to gap opening at the Dirac point, providing a means to control the surface electric transport, which is of great importance for applications.
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Oct 2013
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