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Yidian
Li
,
Mingxin
Zhang
,
Xian
Du
,
Cuiying
Pei
,
Jieyi
Liu
,
Houke
Chen
,
Wenxuan
Zhao
,
Kaiyi
Zhai
,
Yinqi
Hu
,
Senyao
Zhang
,
Jiawei
Shao
,
Mingxin
Mao
,
Yantao
Cao
,
Jinkui
Zhao
,
Zhengtai
Liu
,
Dawei
Shen
,
Yaobo
Huang
,
Makoto
Hashimoto
,
Donghui
Lu
,
Zhongkai
Liu
,
Yulin
Chen
,
Hanjie
Guo
,
Yilin
Wang
,
Yanpeng
Qi
,
Lexian
Yang
Abstract: The interplay among orbital-selective electron correlation, Hund's coupling, tunable structural motifs, and Kondo-like scattering establishes a compelling paradigm for understanding and engineering correlated multiorbital systems, as vividly exemplified by nickelate superconductors. Here, using high-resolution angle-resolved photoemission spectroscopy combined with theoretical calculations, we systematically investigate the electronic properties of trilayer nickelates. In La4Ni3O10, we observe pronounced interorbital hybridization, whereas in Pr4Ni3O10, the flat 𝑑𝑧2 band becomes markedly incoherent and diminishes in spectral weight. By contrast, the dispersive 𝑑𝑥2−𝑦2 bands retain coherence in both compounds. This striking incoherence/coherence dichotomy identifies an orbital differentiation modulated by the interlayer Ni-O-Ni bonding angle. The depletion of the 𝑑𝑧2 orbitals further suppresses the interorbital hybridization and influences the density-wave transition in Pr4Ni3O10. Moreover, the density-wave gap is substantially reduced in Pr4Ni3O10, likely due to extra scattering channels provided by the local moments of Pr3+ cations. Our findings reveal a structural control parameter for the multiorbital correlated state in trilayer nickelates, providing important insights into the emergence of superconductivity under high pressure.
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Aug 2026
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Xiaoyang
Chen
,
Wenliang
Zhang
,
Fei
Peng
,
Ting
Cui
,
Guangdi
Zhou
,
Zezhong
Li
,
Jaewon
Choi
,
Lizhi
Xu
,
Yiu-Fung
Chiu
,
Stefano
Agrestini
,
Sahil
Tippireddy
,
Haoliang
Huang
,
Heng
Wang
,
Xianfeng
Wu
,
Peng
Li
,
Jin-Feng
Jia
,
Mirian
Garcia-Fernandez
,
Yi
Lu
,
Er-Jia
Guo
,
Qi-Kun
Xue
,
Zhuoyu
Chen
,
Donglai
Feng
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[42637]
Open Access
Abstract: The recent discovery of Ruddlesden-Popper (RP) nickelate thin-film superconductors has opened a new frontier in unconventional superconductivity. Its realization requires both compressive epitaxial strain and highly oxidative growth conditions, yet the microscopic pathway from the parent phase to the superconducting phase remains elusive. Here, X-ray absorption spectra and resonant inelastic X-ray scattering are employed to track this evolution by independently tuning strain and oxygen content in (La,Pr)3Ni2O7 − δ thin films. We uncover a remarkable two-step narrative. First, signatures of delocalization emerge: Spectral weight transfers from a “Upper Hubbard”-like peak to the hole-like peak associated with O 2pz state, and in parallel, the initially localized Ni
orbital becomes more itinerant followed by the broadening and weakening of dd orbital excitations. Second, as itinerancy increases, long-range spin-density-wave (SDW) order is suppressed in both intensity and correlation length, indicating direct competition with superconductivity. Yet, short-range magnons persist: they become damped but their bandwidth stays unchanged. Our results paint a coherent picture that both strain and oxygenation drive the RP bilayer nickelates towards the superconducting instability, where the O 2pz and Ni
orbitals become delocalized. Concomitantly, the long-range magnetic order loses coherence and gets suppressed. These findings establish an orbital-selective route to RP nickelate superconductivity, in which the emergence and progressive delocalization of the interlayer
-2pz-
channel and the robust short-range magnons upon the melting of SDW order are prerequisites, providing strong constraints for theory and the roadmap for designing nickelate superconductors.
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Aug 2026
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I05-ARPES
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Junhyeok
Jeong
,
Kifu
Kurokawa
,
Shiro
Sakai
,
Tomotaka
Nakayama
,
Kotaro
Ando
,
Naoshi
Ogane
,
Soonsang
Huh
,
Matthew D.
Watson
,
Timur K.
Kim
,
Cephise
Cacho
,
Chun
Lin
,
Makoto
Hashimoto
,
Donghui
Lu
,
Takami
Tohyama
,
Kazuyasu
Tokiwa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[36822, 30646, 28930, 25416]
Open Access
Abstract: In multilayered high-Tc cuprates, the inner CuO2 planes (IPs) are spatially separated from dopant layers and thus remain cleaner than the outer planes (OPs). Here, we investigate five-layer (Cu,C)Ba2Ca4Cu5Oy (Cu1245) and three-layer Ba2Ca2Cu3O6(F,O)2 (F0223) using angle-resolved photoemission spectroscopy (ARPES) and uncover an unprecedented situation, in which only the IPs become superconducting while the OPs remain metallic at low temperatures. Our model calculations indicate that over 95% of the OP wavefunction remains confined to OP itself, rendering superconducting proximity negligible. This interlayer decoupling realizes an ideal configuration—a single superconducting CuO2 layer screened from the dopant layer-induced disorder by heavily overdoped metallic OPs. The clean CuO2 layer exhibits a large superconducting gap with coherent Bogoliubov peaks extending beyond the antiferromagnetic zone boundary, and a widely extended coherent flat band at the Brillouin zone edge. These findings introduce the “degree of screening” as a physical parameter for probing competition between pseudogap and superconductivity, and for bridging typically disordered real materials with the idealized theoretical models.
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Jul 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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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Kunhao
Li
,
Qizhi
Li
,
Changwei
Zou
,
Jaewon
Choi
,
Chaohui
Yin
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Shilong
Zhang
,
Chengtian
Lin
,
Xingjiang
Zhou
,
Ke-Jin
Zhou
,
Yi
Lu
,
Yingying
Peng
Diamond Proposal Number(s):
[30361]
Abstract: The superconducting gap is a characteristic feature of high-𝑇c superconductors and provides crucial information on the pairing mechanism underlying high-temperature superconductivity. Here, we employ high-resolution resonant inelastic x-ray scattering (RIXS) at the Cu 𝐿3 edge to investigate the superconducting gap in the overdoped cuprate Bi2Sr2Ca2Cu3O10+𝛿 (𝑇c=107K). By analyzing antisymmetrized, temperature-dependent RIXS spectra over a range of in-plane momentum transfers, we observe a clear suppression of low-energy spectral weight below 𝑇c, indicative of superconducting-gap formation. This suppression is most pronounced at small momentum transfers [
| | |
𝒒∥
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≤0.18 r.l.u. (reciprocal lattice units)] and corresponds to a gap size of approximately 2Δ0∼130 meV. Comparison with theoretical calculations of the momentum-dependent charge susceptibility supports a 𝑑-wave symmetry of the superconducting gap, while an isotropic 𝑠-wave gap fails to reproduce key experimental features. These findings establish RIXS as a powerful, bulk-sensitive probe of superconducting-gap symmetry and highlight its utility for studying materials beyond the reach of surface-sensitive techniques such as ARPES and STM.
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Jun 2026
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I15-Extreme Conditions
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Abstract: Pressure is an important thermodynamic variable that can manipulate interatomic distances and electronic band structures of materials. One can induce phase transitions by experimentally varying pressure-temperature conditions, revealing exotic properties and structures that cannot be attained under ambient conditions. The study of binary metal hydrides has garnered significant attention over the past decade due to their diverse physical and chemical behaviours. At sufficiently high pressures, the chemical potential of hydrogen increases and may eventually overcome the dissociation barrier at the surface of a metal, forming metal alloys with atomic hydrogen occupying interstitial sites. These metal hydrides have been demonstrated to exhibit remarkable phenomena such as superionicity, hydrogen storage potential and conventional high-temperature superconductivity. Currently, there exists a plethora of theoretical calculations predicting novel stoichiometries, structures and electronic states of various binary metal-hydrogen systems. More recently, theoretical work has gradually moved towards predictions in ternary and even quaternary systems. Despite this, there is still much to learn from binary hydrides, such as how hydrogen content affects electronic properties in specific systems and how the addition of f -electrons may influence superconducting transitions. This PhD thesis covers a total of five highpressure binary heavy metal hydride systems extensively studied in diamond anvil cell experiments. Firstly, the pressure-induced metallisation of BaH2 and the effect of hydrogenation are presented, followed by studies that reveal complexity and distinct structural analogies of novel heavy lanthanide polyhydrides up to 180 GPa (namely ytterbium, thulium, and erbium hydrides). Finally, structural phase transitions, recoverability and predicted superconductivity are explored in the uranium-hydrogen system below 100 GPa.
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Jun 2026
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Grace A.
Pan
,
Dan Ferenc
Segedin
,
Sophia F. R.
Tenhuisen
,
Lopa
Bhatt
,
Harrison
Labollita
,
Abigail Y.
Jiang
,
Qi
Song
,
Ari B.
Turkiewicz
,
Denitsa R.
Baykusheva
,
Abhishek
Nag
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Hua
Zhou
,
Mark P. M.
Dean
,
Hanjong
Paik
,
David A.
Muller
,
Lena F.
Kourkoutis
,
Charles M.
Brooks
,
Matteo
Mitrano
,
Antia S.
Botana
,
Berit H.
Goodge
,
Julia A.
Mundy
Diamond Proposal Number(s):
[27484]
Abstract: The discovery of superconductivity in square-planar nickelates has offered a rich materials platform to explore the origins of high-temperature superconductivity. However, experimental investigations have largely been limited to the infinite-layer RNiO2 (R, rare earth) nickelates. We constructed a phase diagram of multilayer square-planar Ndn+1NinO2n+2 compounds and found signatures of superconductivity for dimensionality n = 4 to 8. Upon decreasing n, the superconducting anisotropy evolves owing to 4f electron effects, and electronic structure characteristics approach cuprate-like behavior. Magnetic fluctuations persist from within the superconducting regime and into the overdoped, nonsuperconducting regime. The superconducting regime overlaps with that of chemically doped infinite-layer nickelates, demonstrating underlying commonalities as well as differences across varying structural realizations of square-planar nickelates. Our work establishes this layered template for creating new nickel-based superconductors.
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Jun 2026
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Abstract: The Remeika stannides (𝑅3T4Sn13, with R = rare earth/alkaline metals, T = transition metal, and X = p-block elements) have been extensively studied due to the interplay between the charge-density-wave (CDW) ordering and superconductivity often found in these materials. Here, we explore the relationship between these two orders in cubic La3Co4Sn13 by conducting electrical transport measurements under uniaxial stress along different crystallographic directions ([100], [110], and [111]). We find that the superconducting transition temperature (𝑇c) is suppressed under compression for all directions measured, in contrast to previous measurements under hydrostatic pressure. This indicates 𝑠-wave superconductivity. The CDW transition temperature is also suppressed under compression for all measured directions. The simultaneous suppression of superconductivity and CDW order suggests that changes in 𝑇c with uniaxial stress are mainly driven by changes in the electronic density of states and not a competition between these two orders.
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Jun 2026
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I05-ARPES
|
Diamond Proposal Number(s):
[28484, 31262]
Open Access
Abstract: We report pressure-induced metallization in BaMn2P2 based on resistivity measurements in a diamond anvil cell. At ambient pressure, the temperature-dependent resistivity is well described by a two-gap Arrhenius model, yielding intrinsic and extrinsic activation energies of approximately 0.2 and 0.04 eV, respectively. Angle-resolved photoemission spectroscopy (ARPES) shows no detectable spectral weight at the Fermi level within the measured momentum window. The growth of spectral weight at higher binding energies is consistent with the energy scales inferred from transport measurements. Under pressure, the temperature dependence of the resistivity evolves from insulatinglike to mixed-slope behavior and becomes metallic above Pc ≈ 7 GPa, with no low-temperature upturn. The resistivity ratio R(P) = ρ(100 K)/ρ(300 K) also drops abruptly near Pc. A baseline transport model combining Bloch-Grüneisen phonon scattering with a thermally activated carrier density fails to reproduce this sharp change for any smoothly varying activation energy. Temperature- and pressure-dependent x-ray diffraction shows smooth evolution of V with no symmetry change and no resolvable discontinuity at Pc . Taken together, these results indicate an abrupt pressure-driven metallization near Pc, with no evidence for a structural phase transition within our experimental resolution.
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May 2026
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