I16-Materials and Magnetism
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Diamond Proposal Number(s):
[34820]
Open Access
Abstract: We present results of an experimental study on single crystals of a 5d
double perovskite Ba2CaReO6. Magnetization measurements reveal a weak splitting between zero-field-cooled and field-cooled protocols below 12 K. At magnetic fields above 1 T the splitting is absent and the magnetic susceptibility is featureless. A detailed specific heat study in a wide temperature range and comprising different heat pulses did not reveal any indication of a thermodynamic phase transition. At low temperatures we do observe specific heat deviating from a phonon background, leading to a total electronic entropy release of
. Resonant and non-resonant x-ray diffraction of characteristic Bragg peaks indicates a significant presence of disorder, potentially related to random tilts and rotations of rigid ReO6 octahedra.
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Nov 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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I11-High Resolution Powder Diffraction
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Open Access
Abstract: The first reported phase in the Y2O3–NiO–TiO2 chemical space, the Y2NiTiO6 perovskite undergoes a temperature-induced order–disorder transition. Above ∼1700 K, it adopts the structure of a disordered CaTiO3-type orthorhombic perovskite with a = 5.26939(2), b = 5.60367(2), and c = 7.58137(3) Å, with the B site uniformly occupied by 0.5Ni+0.5Ti. Below this temperature, Y2NiTiO6 adopts rock-salt ordering of the transition metals in a monoclinic unit cell (a = 5.26695(2), b = 5.60164(2), c = 7.57493(2) Å, β = 90.4940(2)°) with 0.9/0.1 ordering of the B site. Ordering of Ni and Ti changes the magnetic properties from spin-glass behavior in the orthorhombic phase to antiferromagnetic order (TN = 17 K) for the monoclinic phase, while the optical properties of both phases remain unchanged across the transition.
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Oct 2025
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I05-ARPES
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Qun
Wang
,
Yifang
Jiang
,
Songyuan
Geng
,
Hanpu
Liang
,
Yunbo
Wu
,
Risi
Guo
,
Fangjie
Chen
,
Kangjie
Li
,
Xin
Wang
,
Bin
Cao
,
Keyu
An
,
Shengtao
Cui
,
Zhe
Sun
,
Mao
Ye
,
Zhengtai
Liu
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Changming
Yue
,
Shiming
Lei
,
Haoxiang
Li
Abstract: Engineering narrow-bandgap semiconductors remains a pivotal challenge for next-generation electronic and energy devices. Charge density wave (CDW) systems offer a promising platform for bandgap engineering. However, most 2D and 3D CDW systems remain metallic despite exhibiting Fermi surface nesting. Here, a doping-dependent metal-insulator transition (MIT) with tunable bandgaps is reported in square-net materials GdSbxTe2-x-δ and a cooperative interaction between CDWs and vacancies that drives the MIT is discovered. Angle-resolved photoemission spectroscopy (ARPES) reveals the MIT in the low Sb-content regime of GdSbxTe2-x-δ, with a maximum energy gap of Δ ≈ 98 meV at x = 0.16, corroborated by electrical transport measurements. Following the MIT, X-ray diffraction reveals a doping-dependent shift of the CDW wavevector toward a commensurate structure with q = 0.25 a*, concurrent with the appearance of Te vacancies in the square-net layers. Density functional theory (DFT) calculations attribute the gap formation to the ordered Te vacancies modulated by the 4×1×1 CDW superstructure, which suppresses the electronic states near the Fermi level. Contrasting with the partial gap scenarios in conventional CDW systems, this synergy between the CDW and the vacancy stabilizes the insulating phase, offering a distinct avenue for narrow bandgap engineering in electronic materials.
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Oct 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[38040]
Open Access
Abstract: Altermagnets, a unique class of magnetic materials that combines features of both ferromagnets and antiferromagnets, have garnered attention for their potential in spintronics and magnonics. While the electronic properties of altermagnets have been well studied, characterizing their magnon excitations is essential for fully understanding their behavior and enabling practical device applications. In this work, we introduce a measurement protocol combining resonant inelastic X-ray scattering with circular polarization and azimuthal scanning to probe the chiral nature of the altermagnetic split magnon modes in CrSb. This approach circumvents the challenges posed by domain averaging in macroscopic samples, allowing for precise measurements of the polarization and energy of the magnons in individual antiferromagnetic domains. Our findings demonstrate a pronounced circular dichroism in the magnon peaks, with an azimuthal dependence that is consistent with the theoretical predictions and the g-wave symmetry. By establishing a reliable and accessible method for probing altermagnetic magnons, this work opens new avenues for fundamental studies of these collective excitations and for developing next-generation magnonic device applications.
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Oct 2025
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Open Access
Abstract: A material in possession of localized 4𝑓-electron magnetism and delocalized 3𝑑-electron or band magnetism can often present enigmatic physical phenomena, and there has been a longstanding interest in the kagome metal YbFe6Ge6. More recently, because of an investigation of a so-called anomalous Hall effect, or topological Hall effect, and magnetic neutron Bragg diffraction [Yao et al., Phys. Rev. Lett. 134, 186501 (2025)]. Iron moments in the two-dimensional layers of a hexagonal nuclear structure undergo collinear antiferromagnetic order below a temperature ≈500 K. The moments depart from the 𝑐 axis in a spontaneous transition at ≈63 K to an orthorhombic structure. The magnetism of Yb ions appears to behave independently, which can be confirmed using resonant x-ray Bragg diffraction enhanced by a Fe atomic resonance. The inferred magnetic structure is P(parity)T(time)-symmetric (anti-inversion Math output error) collinear antiferromagnetism that does not couple to circular polarization (helicity) in primary x-rays, unlike altermagnetism. A linear magnetoelectric effect is allowed, and Kerr rotation and the piezomagnetic effect are forbidden. Symmetry informed Bragg diffraction patterns for future x-ray and neutron experiments are shown to be rich in Fe magnetic properties of orthorhombic YbFe6Ge6, including space-spin correlations, anapoles, and Dirac quadrupoles familiar in high-Tc ceramic superconductors.
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Oct 2025
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I10-Beamline for Advanced Dichroism - scattering
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Andrey D.
Poletayev
,
Robert J.
Green
,
Jack E. N.
Swallow
,
Lijin
An
,
Leanne
Jones
,
Grant
Harris
,
Peter
Bencok
,
Ronny
Sutarto
,
Jonathon P.
Cottom
,
Benjamin J.
Morgan
,
Robert A.
House
,
Robert S.
Weatherup
,
M. Saiful
Islam
Diamond Proposal Number(s):
[33062, 30644]
Open Access
Abstract: Nickelate materials offer diverse functionalities for energy and computing applications. Lithium nickel oxide (LiNiO2) is an archetypal layered nickelate, but the electronic structure of this correlated material is not yet fully understood. Here we investigate the temperature-dependent speciation and spin dynamics of Ni ions in LiNiO2. Ab initio simulations predict that Ni ions disproportionate into three states, which dynamically interconvert and whose populations vary with temperature. These predictions are verified using x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and resonant inelastic x-ray scattering at the Ni L3,2-edge. Charge-transfer multiplet calculations consistent with disproportionation reproduce all experimental features. Our results support a model of dynamic disproportionation that explains diverse physical observations of LiNiO2, including magnetometry, thermally activated electronic conduction, diffractometry, core-level spectroscopies, and the stability of ubiquitous antisite defects. This unified understanding of the material properties of LiNiO2 is important for applications of nickelate materials as battery cathodes, catalysts, and superconductors.
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Oct 2025
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Yafei
Chu
,
Chaocheng
Liu
,
Ruiqi
Liu
,
Weican
Lan
,
Lu
Cheng
,
Huijuan
Wang
,
Minghui
Fan
,
Hengli
Duan
,
Chao
Wang
,
Yajuan
Feng
,
Wensheng
Yan
Abstract: Twisted bilayer transition metal dichalcogenides (TMDs) have generated diverse unusual electrical and optical phenomena and can provide a powerful platform for designing nanodevices with tunable interlayer interaction. Striving to explore novel excitons with spin response in these semiconductor systems is highly desirable, as they highlight the possibility to access complex electronic band structure and magneto-exciton effect, thereby facilitating efficient spin-based information storage via exciton degrees of freedom. Here, fabrication of bilayer WSe2/Fe5GeTe2 (FGT) heterostructures with different stacking phases is reported, and a new hybridized excitonic state T* is defined in both 3R and 2H bilayer WSe2, which exhibits strong correlations dependent on the FGT spin order. This spin-dependent hybridized exciton is demonstrated to originate from the coupling between injected spin-polarized electrons and neutral excitons, because of the spin-cross-polarized band that obstructs the normal electron–hole annihilation process. Besides, the difference in the coupling strength of the T* exciton attributed to the distinct stacking symmetries in twisted bilayer WSe2 is further unveiled. These findings open an accessible avenue for designing tailored excitonic states in twisted bilayers, thus offering prospects for the future applications of stacking-engineered opto-spintronics at the integration level.
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Oct 2025
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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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I05-ARPES
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Cong
Li
,
Yang
Wang
,
Jianfeng
Zhang
,
Hongxiong
Liu
,
Wanyu
Chen
,
Guowei
Liu
,
Hanbin
Deng
,
Timur K.
Kim
,
Craig
Polley
,
Balasubramanian
Thiagarajan
,
Jiaxin
Yin
,
Youguo
Shi
,
Tao
Xiang
,
Oscar
Tjernberg
Diamond Proposal Number(s):
[34265, 39652]
Open Access
Abstract: For several decades, it was widely believed that a noninteracting disordered electronic system could only undergo an Anderson metal–insulator transition due to Anderson localization. However, numerous recent theoretical works have predicted the existence of a disorder-driven non-Anderson phase transition that differs from Anderson localization. The frustration lies in the fact that this non-Anderson disorder-driven transition has not yet been experimentally demonstrated in any system. Here, using angle-resolved photoemission spectroscopy, we present a case study of observing the non-Anderson disorder-driven transition by visualizing the electronic structure of the Weyl semimetal NdAlSi on surfaces with varying amounts of disorder. Our observations reveal that strong disorder can effectively suppress all surface states in the Weyl semimetal NdAlSi, including the topological surface Fermi arcs. This disappearance of surface Fermi arcs is associated with the vanishing of the topological invariant, indicating a quantum phase transition from a Weyl semimetal to a diffusive metal. These observations provide direct experimental evidence of the non-Anderson disorder-driven transition occurring in real quantum systems, a finding long anticipated by theoretical physicists.
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Oct 2025
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