I15-Extreme Conditions
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Diamond Proposal Number(s):
[7758, 8615]
Open Access
Abstract: The β′-Gd2(MoO4)3 phase is one of the most well-known multiferroic materials, exhibiting both ferroelectricity and ferroelasticity under ambient conditions, with a complex temperature-pressure phase diagram. In this study, we review the pressure-dependent behavior of the RE2(MoO4)3 compound family (where RE ≡ Pr–Ho), which crystallizes in the β′-phase, with the β-phase being the paraelectric parent structure. Eu, Tb, and Ho molybdates were synthesized via solid-state reactions, ensuring the absence of impurities. High-pressure experiments at DIAMOND synchrotron revealed that the β′-phase persists at low-pressures. At approximately 2 GPa, new peaks emerged, which were refined as a mixture of the β′-phase, other rare-earth molybdates, and oxides, some of which have been detected in earlier stages of synthesis. The β′-phase became distorted with increasing pressure while coexisting with these new phases, whose average unit cell volume was found to lie between that of the β′-phase and the formed distorted phase. Ultimately, this multiphase crystalline decomposition acts as a precursor to pressure-induced amorphization, leading to a loss of long-range periodicity without complete loss of local order. The onsets of pressure-induced decomposition, distortion of the β′-phase and apparent amorphization increase as the ionic radius of the rare-earth element decreases. This scenario of irreversible structural disorder accumulated through phase coexistence is consistent with previous studies and resolves a debate persisting for over half a century.
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Aug 2026
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[25166]
Abstract: Layered perovskite oxides continue to be the subject of intense research efforts due to their highly tunable crystal structures, which often arise from the competition between various lattice, spin, charge and orbital degrees of freedom. In particular, a number of recent works have focused on the mechanisms through which polar phases (those with globally broken inversion symmetry) emerge through the coupling of different structural distortions. The so-called hybrid improper mechanism, in which nonpolar structural distortions couple to break inversion symmetry, has been invoked to explain the appearance of polar structures in many different layered perovskite oxides. We use a combined experimental and computational approach to investigate the pseudo-Ruddlesden–Popper system Li2SrxCa1–xTa2O7 (0 < x < 1), which exhibits multiple competing polar phases that arise through distinct mechanisms. We untangle the complex interactions between various structural modes and find that, in contrast with previous work, the hybrid improper mechanism cannot by itself account for the observed polar phases. Our work demonstrates that there are significant differences in the mechanisms through which polar phases emerge in even nominally the same family of layered perovskites, suggesting a rich playground for further exploration and functional materials design.
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Jun 2026
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I05-ARPES
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Junhyeok
Jeong
,
Yamato
Enomoto
,
Yoshimitsu
Kohama
,
Tomotaka
Nakayama
,
Kotaro
Ando
,
Kifu
Kurokawa
,
Soonsang
Huh
,
Zhuo
Yang
,
Toshihiro
Nomura
,
Matthew D.
Watson
,
Timur K.
Kim
,
Cephise
Cacho
,
Chun
Lin
,
Makoto
Hashimoto
,
Donghui
Lu
,
Shiro
Sakai
,
Takami
Tohyama
,
Kazuyasu
Tokiwa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[36822, 30646, 28930, 25416]
Open Access
Abstract: Fermi arcs observed in underdoped cuprates have sparked debate over whether they represent segments of a large Fermi surface or small Fermi pockets. This ambiguity has long hindered their classification as either the conventional Bardeen-Cooper-Schrieffer (BCS) regime or the strongly coupled Bose-Einstein condensation (BEC) crossover limit. Here, using angle-resolved photoemission spectroscopy and quantum oscillations, we demonstrate the coexistence of a small Fermi pocket and a large superconducting gap in the clean inner CuO2 layers of the four-layer cuprate Ba2Ca3Cu4O8(F,O)2. This coexistence constitutes a hallmark of the BCS-BEC crossover and has remained elusive for decades. Despite the presence of antiferromagnetic (AF) order, the superconducting gap in the small pocket is remarkably large, yielding a gap-to-Fermi energy ratio (Δpocket/εF ~ 0.6) and a critical-to-Fermi temperature ratio (Tc/TF ~ 0.13) that reach the theoretical upper bound for two-dimensional superconductivity. Unexpectedly, this BCS-BEC crossover emerges not as the carrier density decreases but as it increases, abruptly within a narrow doping range of less than 1%. These results provide a long-sought microscopic foundation for the d-wave pairing mechanism in doped AF-Mott insulators.
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Jun 2026
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I15-Extreme Conditions
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Huixin
Hu
,
Israel
Osmond
,
Calum
Strain
,
Hannah A.
Shuttleworth
,
Callum R.
Stevens
,
Andrew
Huxley
,
Mikhail A.
Kuzovnikov
,
Federico A.
Gorelli
,
Eugene
Gregoryanz
,
Miriam
Pena-Alvarez
,
Philip
Dalladay-Simpson
,
Ross T.
Howie
Open Access
Abstract: Sulfur and selenium demonstrate one of the most complex behavior under high pressure among all elements of the periodic table. Despite being known to form interchalcogens, the properties of these compounds have not been widely explored in the dense state. Through a series of diamond anvil experiments combined with x-ray diffraction, optical spectroscopy, and electrical resistance measurements, we explore the properties of selenium disulfide (SeS2) up to pressures of 150 GPa. At ambient pressure, SeS2-I represents a substitutional solid solution of S and Se atoms, forming an eight-membered molecular ring arrangement analogous to γ -S. The band gap of SeS2-I rapidly closes upon compression, and above 27 GPa, there is a transformation to a metallic tetragonal phase (SeS2-III), in which atoms form square helical chains. Upon further compression, we observe a phase sequence from incommensurate modulated SeS2-IV above 59 GPa, transforming to rhombohedral SeS2-V by 116 GPa.
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Jun 2026
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I06-Nanoscience (XPEEM)
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Diamond Proposal Number(s):
[6230, 1771]
Open Access
Abstract: Epitaxial films of the ferromagnetic manganite La0.7Sr0.3MnO3 on substrates of the ferroelectric perovskite BaTiO3 are known to display sharp magnetic changes and large magnetoelectric effects when the film is strained by the substrate undergoing thermally driven structural transitions and ferroelectric domain switching, respectively. However, only a single component of the in-plane magnetization has been hitherto imaged. Here we present magnetic vector maps—obtained from photoemission electron microscopy images with magnetic contrast from x-ray magnetic circular dichroism—to show that the electrically and thermally driven changes of local and global magnetization are deterministically influenced by the state of the substrate while also being complex and sample dependent. Our findings, supported by ferromagnetic resonance data and vibrating sample magnetometry, reveal that the behavior of La0.7Sr0.3MnO3 films on BaTiO3 substrates is not well predicted from knowledge of each system, probably due to long-range strain between BaTiO3 domains. In the future, it would be interesting to reduce complexity by patterning the film into regions between which magnetic communication is negligible.
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May 2026
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[29150]
Open Access
Abstract: Cuprate superconductors show various collective charge correlations that are intimately connected with their electronic properties. In particular, charge order in the form of an incommensurate charge density wave (CDW) order with an in-plane wave vector 𝛿CDW≈0.23–0.35 reciprocal lattice units appears to be universally present. In addition to CDW, dynamic charge density fluctuations (CDFs) are also present with wave vectors comparable to 𝛿CDW. CDFs are present up to ≈300K and have relatively short correlation lengths of 𝜉≈20Å. Here we use Cu-𝐿3 and O-𝐾 resonant inelastic x-ray scattering (RIXS) to study the doping dependence of CDW and CDFs in La2−𝑥Sr𝑥CuO4. We fit our data with (quasi)elastic peaks resulting from the CDW and up to four inelastic modes associated with oxygen phonons that can be strongly coupled to the CDFs. Our analysis allows us to separate the charge correlations into three components: the CDW with wave vector 𝛿4𝑎-CDW≈0.24 and two CDF components with 𝛿4𝑎-CDF≈0.24 and 𝛿3𝑎-CDF≈0.30. We find that for 𝑇≈𝑇𝑐 the CDW coexists with the CDFs for dopings near 𝑥=𝑝≈1/8. The 4𝑎-CDW disappears beyond 𝑥=0.16 and the 4𝑎-CDF beyond 𝑥=0.19, leaving only a weak 3𝑎-CDF at the highest doping studied, 𝑥=0.22. Our data suggest that low-energy charge fluctuations exist up to doping 𝑥=0.19=𝑝★, where the pseudogap disappears; however, we find no evidence that they are associated with a quantum critical point.
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May 2026
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E02-JEM ARM 300CF
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Christopher J. H.
Smalley
,
Colan E.
Hughes
,
Tom
Willhammar
,
Raj
Pandya
,
Semion K.
Saikin
,
Duncan N.
Johnstone
,
Jeffrey
Gorman
,
Jooyoung
Sung
,
Gianni
Jacucci
,
Paul A.
Midgley
,
Demie M.
Kepaptsoglou
,
Quentin M.
Ramasse
,
Akshay
Rao
,
Kenneth D. M.
Harris
,
Sean M.
Collins
Diamond Proposal Number(s):
[20527]
Open Access
Abstract: Organic semiconductors continue to make substantial performance gains from photovoltaics to electronics. However, understanding how differences in solid-state structure give rise to large differences in energy transport properties remains unresolved. We report that microcrystals of two perylene diimide (PDI) derivatives differing only in their terminal groups [cyclohexyl (CH) and 4-heptyl (ST)] have exciton diffusion coefficients differing by more than two orders of magnitude. Applying state-of-the-art techniques for microcrystal structure determination, we report the crystal structures of CH-PDI and two polymorphs of ST-PDI. Scanning electron diffraction reveals a range of crystallographic defects in ST-PDI microcrystals, attributed to polymorph intergrowths, while electron energy loss spectroscopy links these defects to nanoscale electronic structure changes. Computational modeling demonstrates that rotational disorder explains the difference in exciton diffusion coefficients. Our observations establish the importance of defect-induced orientational disorder as a source of extrinsic energetic disorder, highlighting the need for defect management in organic semiconductor technologies.
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May 2026
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I05-ARPES
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Xingtian
Sun
,
Suppanut
Sangphet
,
Nan
Guo
,
Yu
Fan
,
Yutong
Chen
,
Minyinan
Lei
,
Xue
Ming
,
Xiyu
Zhu
,
Hai-Hu
Wen
,
Haichao
Xu
,
Rui
Peng
,
Donglai
Feng
Diamond Proposal Number(s):
[39544]
Abstract: The superconducting transition temperatures (𝑇c’s) of trilayer or quadruple-layer cuprates typically surpass those of single-layer or bilayer systems. However, the lack of direct electronic-structure and superconducting-gap measurements in optimal-𝑇c quadruple-layer cuprates has impeded a comprehensive understanding of the origin of the enhanced 𝑇c in multilayer systems. In this Letter, using angle-resolved photoemission spectroscopy, we investigate the quadruple-layer cuprate (Cu,C)Ba2Ca3Cu4O11+𝛿 (CuC-1234) with a high 𝑇c of 110 K, and resolved distinct superconducting-gap behaviors between the inner CuO2 planes and outer CuO2 planes, in contrast to that reported for trilayer cuprates. Outer CuO2 planes develop their own superconducting gap and superconducting coherence peak at a temperature much lower than the 𝑇c of the material, while the large pairing strength and phase coherence concurrently emerge at the underdoped inner CuO2 planes at 𝑇c. Our findings suggest that CuO2 planes free of apical oxygen can have significant contribution to superconductivity up to 110 K in multilayer cuprates, even at a doping level of 0.07 holes per Cu, a level that lies deep in the underdoped regime of single- and bilayer cuprates. These findings provide new insights into the origin of high 𝑇c in multilayer cuprates.
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May 2026
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I19-Small Molecule Single Crystal Diffraction
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S. D.
Nabi
,
L.
Facheris
,
V.
Romerio
,
V.
Kocsis
,
K. Yu.
Povarov
,
D.
Sheptyakov
,
J.
Lass
,
D. G.
Mazzone
,
H.
Kikuchi
,
T.
Masuda
,
S. A.
Barnett
,
D. R.
Allan
,
Z.
Yan
,
S.
Gvasaliya
,
A.
Zheludev
Diamond Proposal Number(s):
[37825]
Abstract: We report comprehensive thermodynamic and neutron scattering measurements on the 𝑆=3/2 antiferromagnet Cs2CoI4, a member of the thoroughly studied family of frustrated magnets Cs2𝑀𝑋4 (𝑀=Cu, Co, Ru, 𝑋=Br, Cl, I, O). Unlike previously studied members, Cs2CoI4 undergoes a structural phase transition, for which we determine the low-temperature crystallographic structure. The resulting symmetry reduction strongly affects both the magnetic exchange interactions and single-ion anisotropy. Despite the large parameter space, we propose a minimal magnetic Hamiltonian that reasonably captures the observed excitation spectrum, analyzed using extended SU(4) linear spin-wave theory.
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May 2026
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I05-ARPES
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Roni Anna
Gofman
,
Abigail
Dishi
,
Hyeonhu
Bae
,
Yuval
Nitzav
,
Ilay
Mangel
,
Nitzan
Ragoler
,
K. P.
Sajilesh
,
Alex
Louat
,
Matthew D.
Watson
,
Cephise
Cacho
,
Dmitry
Marchenko
,
Andrei
Varykhalov
,
Irena
Feldman
,
Binghai
Yan
,
Amit
Kanigel
Open Access
Abstract: We use micro-angle-resolved photoemission spectroscopy (micro-ARPES) to investigate chiral charge density waves (CDWs) in 4Hb-TaS2 with micron-scale spatial resolution. In the 1T layers of 4Hb-TaS2, we uncover coexisting left- and right-handed CDW domains and resolve four distinct spectral patterns arising from the interplay of chirality and rotational stacking. In contrast, bulk 1T-TaS2 exhibits uniform chirality. In addition, 4Hb-TaS2 shows negligible out-of-plane dispersion of the 1T-derived bands, in contrast to the large interlayer coupling observed in bulk 1T-TaS2. Density Functional Theory (DFT) calculations corroborate this picture, revealing that the interlayer interaction of the chiral order in 4Hb-TaS2 is nearly two orders of magnitude weaker than in the 1T polytype. Our findings establish 4Hb-TaS2 as a quasi-two-dimensional platform for exploring tunable chiral CDW phenomena.
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May 2026
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