I16-Materials and Magnetism
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Diamond Proposal Number(s):
[24570]
Open Access
Abstract: Although there have been several studies on the powder form, there has yet to be a report on the bulk crystal growth and its property studies of LiNiO2. In the present study, we report the first successful growth of a LiNiO2 single crystal by employing the optical floating-zone technique. Structural properties have been studied using single-crystal X-ray diffraction (XRD). The structural refinement of the single-crystal XRD data, along with the Laue diffraction patterns, confirms that this system crystallizes in a rhombohedral unit cell in space group R3m and the presence of a single grain along the length of the grown crystal. Furthermore, for the first time, we have observed and determined their superstructures as a function of temperature using single-crystal XRD. We have also conducted a study using the high flux of synchrotron X-rays to demonstrate the mechanism which drives the superstructure witnessed by the single-crystal XRD. Resonant elastic X-ray scattering was used to confirm the superstructure and the mixed valence state of different Ni sites. No additional ordering phenomena were observed, including magnetic or electronic ordering. Our study demonstrates the optimization of LiNiO2 growth parameters and provides information about atomic and electronic ordering in the system, including the onset of a superstructure phase. This will provide a basis for further work in developing improved cathode materials and understanding quantum spin liquids.
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Apr 2026
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I05-ARPES
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Xian
Yang
,
Chia-Hsiu
Hsu
,
Gokul
Acharya
,
Junyi
Zhang
,
Md shafayat
Hossain
,
Tyler A.
Cochran
,
Bimal
Neupane
,
Zi-Jia
Cheng
,
Santosh Karki
Chhetri
,
Byunghoon
Kim
,
Shiyuan
Gao
,
Yu-Xiao
Jiang
,
Maksim
Litskevich
,
Jian
Wang
,
Yuanxi
Wang
,
Jin
Hu
,
M. Zahid
Hasan
Abstract: Topological materials hold immense promise for exhibiting exotic quantum phenomena, yet achieving controllable topological phase transitions remains challenging. Here, we demonstrate a structurally driven, reversible topological phase transition in the distorted square net material GdPS, induced via in situ potassium dosing. Using angle-resolved photoemission spectroscopy and first principles calculations, we demonstrate a cascade of topological phases in the subsurface P layer: from a large, topologically trivial band gap to a gapless Dirac cone state with a 2 eV dispersion, and finally to a two-dimensional topological insulator as inferred from theory. This evolution is driven by subtle structural distortions in the first P layer caused by potassium adsorption, which in turn contribute to the band gap closure and topological phase transition. Furthermore, the ability to manipulate the topology of a subsurface layer in GdPS offers a unique route for exploring and controlling topological states in bulk materials.
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Mar 2026
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[36210]
Open Access
Abstract: Quasiparticles describe collective excitations in many-body systems, and their symmetry classification is of fundamental importance for physical processes such as excited states, transport phenomena, and phase transitions. Recent studies have introduced chirality as an additional degree of freedom in condensed matter physics, leading to a range of novel phenomena. Among these, chiral phonons are of special interest because they carry angular momentum and therefore intrinsically break time reversal symmetry, which non-trivially bridges the spin system with the lattice. Here, we directly prove the presence of chiral phonons in a prototypical polar LiNbO3 crystal. Our demonstration of chiral phonons in a ferroelectric enables in-situ electrical control of momentum-dependent “magnetic” polarization with the reversible phonon handedness. This ferroic control of phonon chirality has substantial potential in the emerging field of chiral phononics, particularly along the associated control of its phonon angular momentum.
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Dec 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Maryia
Zinouyeva
,
Martina
Fracchia
,
Giulia
Maranini
,
Davide
Impelluso
,
Nicholas B.
Brookes
,
Lorenzo
Grilli
,
Kurt
Kummer
,
Francesco
Rosa
,
Matteo
Aramini
,
Giacomo
Ghiringhelli
,
Paolo
Ghigna
,
Marco
Moretti Sala
,
Mauro
Coduri
Open Access
Abstract: We employ several X-ray based techniques, including X-ray diffraction, X-ray absorption spectroscopy and resonant inelastic X-ray scattering, to disentangle the contributions of individual chemical species to the structural, electronic and magnetic properties of high-entropy oxides. In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related systems, we unambiguously resolve a sizable Jahn–Teller distortion at the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, suggesting that these ions promote positional order, whereas Cu2+ ions act to destabilize it. Moreover, we detect magnetic excitations and estimate the strength of the interactions between pairs of different magnetic elements. Our results provide valuable insights into the role of various chemical species in shaping the physical properties of high-entropy oxides.
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Nov 2025
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I09-Surface and Interface Structural Analysis
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C.-H.
Min
,
M.
Scholz
,
T.-L.
Lee
,
C.
Schlueter
,
A.
Gloskovskii
,
E. D. L.
Rienks
,
V.
Hinkov
,
H.
Bentmann
,
Y. S.
Kwon
,
F.
Reinert
,
H.-D.
Kim
,
K.
Rossnagel
,
S.
Müller
,
W. J.
Choi
,
V.
Zabolotnyy
,
M.
Heber
,
J. D.
Denlinger
,
C.-J.
Kang
,
M.
Kalläne
,
N.
Wind
,
L.
Dudy
Diamond Proposal Number(s):
[22630]
Abstract: Exotic quasiparticle states have been proposed in mixed-valent compounds exhibiting valence transitions. However, clear spectroscopic evidence identifying these states has remained elusive. Using synchrotron-based hard x-ray and extreme ultraviolet photoemission spectroscopy, we have probed the Tm 3𝑑 and 4𝑓 emissions in TmSe1−𝑥Te𝑥, where a Te concentration-dependent semimetal–insulator transition occurs alongside the valence transition. Our photoemission results, which are characteristic of the bulk, track this combined transition across the critical concentration (𝑥𝑐 =0.29). Notably, our results reveal a noninteger valence for the insulating phase and a novel quasiparticle excitation in the semimetallic phase: a Holstein polaron that extends beyond the standard periodic Anderson model.
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Oct 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Abstract: Mott-insulating 5d double perovskites (DPs) have recently emerged as strongly correlated electron systems of interest due to the novel multipolar physics they display. Key to understanding these properties is proper identification of the energy scales in the electronic Hamiltonian, for which resonant inelastic X-ray scattering (RIXS) is an ideal tool. In the A2MgReO6 (A = Ca, Sr, Ba) 5d1 DPs, Re L3 edge RIXS reveals that the 5d shell is split at a high level by the crystalline electric field (CEF) and at a low level by strong spin-orbit coupling (SOC). Unexpectedly, the SOC excitations are dressed by Jahn-Teller (JT) active phonon modes, implying the presence of a dynamic JT effect. This dynamic JT effect couples the electronic and lattice degrees of freedom, resulting in a spin-orbit-lattice entangled ground state. Vibronic RIXScalculations support these findings and estimate the dynamic JT effect to be one order of magnitude weaker than the SOC. Higher resolution O K edge RIXS measurements of the A2MgReO6 DPs are also presented, wherein the 5d1 ground state is probed via Re 5d - O 2p orbital hybridization. This higher resolution resolves the individual vibronic modes dressing the SOC excitations, and expanded temperature dependence measurements reveal systematic evolution of the dynamic JT effect. Significant enhancement of low energy phononic features is observed at the O K edge as predicted theoretically.Intermediate state effects are believed to imprint the spectra in O K edge RIXS due to the longer core-hole lifetime. In the 5d2 DPs Ba2YReO6 and Sr2CrReO6, Re L2 and L3 edge RIXS reveals that the 5d levels are split at a high level by the CEF as in the 5d1 case. The 5d2 and 5d1 cases diverge at lower energy where the 5d2 levels are split into several multiplets by the interplay of SOC and Hund’s coupling introduced by the presence of a second electron. Computational methods are used to successfully untangle the individual energy scales of the Hund’s and spin-orbit couplings. Differences between the L2 and L3 spectra reflective of dipole selection rules prove key to being able to unambiguously separate these energy scales.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Wenjing
Xu
,
Hailing
Guo
,
Zhenni
Yang
,
Yihong
Chen
,
Xiangyu
Xu
,
Tien-Lin
Lee
,
Duanyang
Chen
,
Xinxin
Yu
,
Yuzheng
Guo
,
Zhaofu
Zhang
,
Hongji
Qi
,
Kelvin H. I.
Zhang
Diamond Proposal Number(s):
[37428]
Abstract: In this work, we investigate the electronic structure and interfacial band alignment of β-(Al𝑥Ga1−𝑥)2O3/Ga2O3 heterojunctions using a combination of synchrotron-based hard x-ray photoemission spectroscopy (HAXPES) and first-principles hybrid density functional theory calculations. β-(Al𝑥Ga1−𝑥)2O3 films with Al compositions of x = 0.12, 0.19, and 0.29 were grown on Fe-doped β-Ga2O3 (010) substrates via pulsed laser deposition. The band gap of β-(Al𝑥Ga1−𝑥)2O3 increases from (4.83 ± 0.05) eV (x = 0) to (5.37 ± 0.08) eV (x = 0.29), primarily driven by an upward shift of the conduction band edge due to hybridization between Al 3s and Ga 4s states, while the valence band edge exhibits a slight downward shift. Both experimental HAXPES data and theoretical calculations confirmed the formation of a “type I” (straddling) band alignment in the β-(Al𝑥Ga1−𝑥)2O3/Ga2O3 heterojunctions. For instance, at x = 0.29, the conduction band offset and valence band offset are approximately 0.33 and 0.21 eV, respectively. These findings provide valuable insights for designing modulation-doped β-(Al𝑥Ga1−𝑥)2O3/Ga2O3 heterostructures, enabling the realization of a two-dimensional electron gas and its application in high-frequency electronic devices.
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Oct 2025
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I07-Surface & interface diffraction
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Dario
Mastrippolito
,
Ashkan
Shahmanesh
,
Mariarosa
Cavallo
,
Erwan
Bossavit
,
Iman
Laqchaa El Abed
,
Corentin
Dabard
,
Shalini
Singh
,
Mathieu
Silly
,
Francesco
Capitani
,
Nemanja
Peric
,
Louis
Biadala
,
Andrea
Zitolo
,
Jose
Avila
,
Francesco
Carla
,
Cesare
Tresca
,
Emmanuel
Lhuillier
,
Benoit
Mahler
,
Debora
Pierucci
Diamond Proposal Number(s):
[38497]
Abstract: Controlling the crystal phase of two-dimensional transition metal dichalcogenides (TMDs) is essential for tailoring their electronic and optical properties. Among the polymorphs of WS2, the metastable 1T′ phase exhibits semimetallic or narrow-bandgap character and hosts quantum functionalities distinct from the semiconducting 1H phase. Here, we investigate the temperature-induced 1T′/1H phase transition in colloidally synthesized monolayer WS2 nanosheets functionalized with organic ligands. The reducing conditions of the synthesis stabilize the 1T′ phase via electron doping. Through in situ analyses of both the structural and electronic properties, we monitor the phase evolution during annealing and find that the 1T′ phase remains stable up to 300 °C, accompanied by a relative lattice contraction. Between 300 and 350 °C, a mixed 1T′/1H regime appears, where the 1H content can be finely tuned by controlling the annealing time. Above 350 °C, a rapid and complete transformation to the 1H phase occurs. We demonstrate that the decomposition of the reducing ligand serves as the primary trigger of the structural transition, revealing a strong interplay among doping, surface chemistry, and lattice structure. Notably, nanosheets with smaller lateral dimensions exhibit slower phase transition kinetics, suggesting that finite size could influence the structural rearrangement underlying the phase transformation.
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Oct 2025
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I06-Nanoscience (XPEEM)
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Diamond Proposal Number(s):
[12893, 5888]
Open Access
Abstract: The elastic degree of freedom is widely exploited to mediate magnetoelectric coupling between ferromagnetic films and ferroelectric substrates. For epitaxial Fe films grown on clean BaTiO3 substrates, shear strain can determine the underlying magnetoelastic coupling. Here, we use PhotoEmission Electron Microscopy of ferroic Fe and BaTiO3 domains, combined with micromagnetic simulations, to directly reveal an inverted interfacial magnetoelastic coupling in the low-dimensional limit. We show that the magnetocrystalline anisotropy competes with the epitaxial shear strain to align the local magnetization of ultrathin Fe films close to the local polarization direction of the ferroelectric BaTiO3 in-plane domains. Poling the BaTiO3 substrate creates c-domains with no shear strain contribution with the local magnetization rotated by ~45°. Tuning shear strain magnetoelastic contributions suggests new routes for designing magnetoelectric devices.
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Sep 2025
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I05-ARPES
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Nicolai
Taufertshöfer
,
Corinna
Burri
,
Rok
Venturini
,
Iason
Giannopoulos
,
Sandy Adhitia
Ekahana
,
Enrico
Della Valle
,
Anže
Mraz
,
Yevhenii
Vaskivskyi
,
Jan
Lipič
,
Alexei
Barinov
,
Dimitrios
Kazazis
,
Yasin
Ekinci
,
Dragan
Mihailovic
,
Simon
Gerber
Open Access
Abstract: In-operando characterization of van der Waals (vdW) devices using surface-sensitive methods provides critical insights into phase transitions and correlated electronic states. Yet, integrating vdW materials in functional devices while maintaining pristine surfaces is a key challenge for combined transport and surface-sensitive experiments. Conventional lithographic techniques introduce surface contamination, limiting the applicability of state-of-the-art spectroscopic probes. We present a stencil lithography-based approach for fabricating vdW devices, producing micron-scale electrical contacts, and exfoliation in ultra-high vacuum. The resist-free patterning method utilizes a shadow mask to define electrical contacts and yields thin flakes down to the single-layer regime via gold-assisted exfoliation. As a demonstration, we fabricate devices from 1T-TaS2 flakes, achieving reliable contacts for application of electrical pulses and resistance measurements, as well as clean surfaces allowing for angle-resolved photoemission spectroscopy. The approach provides a platform for studying the electronic properties of vdW systems with surface-sensitive probes in well-defined device geometries.
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Aug 2025
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