I05-ARPES
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Diamond Proposal Number(s):
[34246]
Open Access
Abstract: Magnetic van der Waals materials are an important building block to realize spintronic functionalities in heterostructures of two-dimensional (2D) materials. However, establishing their magnetic and electronic properties and the interrelationship between the magnetic ground state and electronic structure is often challenging because only a limited number of techniques can probe magnetism and electronic structure on length scales of tens to hundreds of nanometers. Chromium chalcogenides are a class of 2D magnetic materials for which a rich interplay between structure and magnetism has been predicted. Here, we combine angle-resolved photoemission and quasiparticle interference imaging to establish the electronic structure of a monolayer of CrTe2 on graphite. From a comparison of model calculations with spectroscopic mapping using angle-resolved photoemission spectroscopy and scanning tunneling microscopy we establish the magnetic ground state and the low-energy electronic structure. We demonstrate that the band structure of monolayer CrTe2 is captured well by density functional theory (DFT) in a DFT+𝑈 framework when a Coulomb repulsion of 𝑈=2.5eV is accounted for.
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Dec 2025
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I05-ARPES
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Gabriele
Domaine
,
Moritz M.
Hirschmann
,
Kirill
Parshukov
,
Mihir
Date
,
Holger L.
Meyerheim
,
Matthew D.
Watson
,
Katayoon
Mohseni
,
Sydney K. Y.
Dufresne
,
Shigemi
Terakawa
,
Marcin
Rosmus
,
Natalia
Olszowska
,
Stuart S. P.
Parkin
,
Andreas P.
Schnyder
,
Niels B. M.
Schroeter
Diamond Proposal Number(s):
[39232]
Open Access
Abstract: Kramers nodal lines are doubly degenerate band crossings in achiral non-centrosymmetric crystals, arising from spin-orbit coupling and connecting time-reversal invariant momenta. When intersecting the Fermi level, they generate exotic three-dimensional Fermi surfaces, in some cases described by two-dimensional massless Dirac fermions, enabling enhanced graphene-like physics such as quantized optical conductivity and large anomalous Hall effects. However, no experimental realization of such materials has been reported. Here, we identify Kramers nodal line metals beyond the case of Fermi surfaces enclosing a single time-reversal invariant momentum. Using angle-resolved photoemission spectroscopy and first-principles calculations, we show that 3R-TaS2 and 3R-NbS2 host open Octdong and Spindle-torus Fermi surfaces, respectively. We observe a filling-controlled transition between these configurations and evidence of size quantization in 3R-TaS2 inclusions within 2H-TaS2. We further predict a strain- or pressure-driven transition to a conventional metal. Our results establish 3R transition-metal dichalcogenides as a tunable platform for Kramers nodal line physics.
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Dec 2025
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I05-ARPES
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Shu
Mo
,
Ksenija
Kovalenka
,
Sebastian
Buchberger
,
Bruno K.
Saika
,
Anugrah
Azhar
,
Akhil
Rajan
,
Andela
Zivanovic
,
Yu-Chi
Yao
,
Rodion V.
Belosludov
,
Matthew D.
Watson
,
M. Saeed
Bahramy
,
Phil D. C.
King
Diamond Proposal Number(s):
[36192]
Open Access
Abstract: Moiré heterostructures, created by stacking 2D materials together with a finite lattice mismatch or rotational twist, represent a new frontier of designer quantum materials. Typically, however, this requires the painstaking manual assembly of heterostructures formed from exfoliated materials. Here, clear spectroscopic signatures of moiré lattice formation in epitaxial heterostructures of monolayer (ML) NbSe2 grown on graphite substrates are observed. Angle-resolved photoemission measurements and theoretical calculations of the resulting electronic structure reveal moiré replicas of the graphite π states forming pairs of interlocking Dirac cones. Interestingly, these intersect the NbSe2 Fermi surface at the -space locations where NbSe2's charge-density wave (CDW) gap is maximal in the bulk. This provides a natural route to understand the lack of CDW enhancement for ML-NbSe2/graphene as compared to a more than fourfold enhancement for NbSe2 on insulating support substrates, and opens new prospects for using moiré engineering for controlling the collective states of 2D materials.
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Dec 2025
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I05-ARPES
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I.
Biało
,
Qisi
Wang
,
J.
Küspert
,
X.
Hong
,
L.
Martinelli
,
O.
Gerguri
,
Y.
Chan
,
K.
Von Arx
,
O. K.
Forslund
,
W. R.
Pudełko
,
C.
Lin
,
N. C.
Plumb
,
Y.
Sassa
,
D.
Betto
,
N. B.
Brookes
,
M.
Rosmus
,
N.
Olszowska
,
Ma. D.
Watson
,
T. K.
Kim
,
C.
Cacho
,
M.
Horio
,
M.
Ishikado
,
H. M.
Rønnow
,
J.
Chang
Diamond Proposal Number(s):
[32147]
Open Access
Abstract: Strong electron correlations drive Mott insulator transitions. Yet, there exists no framework to classify Mott insulators by their degree of correlation. Cuprate superconductors, with their tunable doping and rich phase diagrams, offer a unique platform to investigate the evolution of these interactions. However, spectroscopic access to a clean half-filled Mott-insulating state is lacking in compounds with the highest superconducting onset temperature. To fill this gap, we introduce a pristine, half-filled thallium-based cuprate system, Tl2Ba5Cu4Ox. Using high-resolution resonant inelastic x-ray scattering, we probe long-lived magnon excitations and uncover a pronounced kink in the magnon dispersion, marked by a simultaneous change in group velocity and lifetime broadening. Modeling the dispersion within a Hubbard-Heisenberg approach, we extract the interaction strength and compare it with other cuprate systems. Our results establish a cuprate universal relation between electron-electron interaction and magnon zone-boundary dispersion. Superconductivity seems to be optimal at intermediate correlation strength, suggesting an optimal balance between localization and itinerancy.
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Dec 2025
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I05-ARPES
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Hongyun
Zhang
,
Jinxi
Lu
,
Kai
Liu
,
Yijie
Wang
,
Size
Wu
,
Wanying
Chen
,
Xuanxi
Cai
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Jose
Avila
,
Pavel
Dudin
,
Matthew D.
Watson
,
Alex
Louat
,
Takafumi
Sato
,
Pu
Yu
,
Wenhui
Duan
,
Zhida
Song
,
Guorui
Chen
,
Shuyun
Zhou
Diamond Proposal Number(s):
[37939]
Abstract: The fractional quantum anomalous Hall effect (FQAHE) is a fascinating emergent quantum state characterized by fractionally charged excitations in the absence of a magnetic field. Recently, the FQAHE has been observed in aligned rhombohedral pentalayer graphene on BN (aligned R5G/BN)1 with moiré potential. Intriguingly, the FQAHE preferably emerges when carriers are displaced away from the moiré interface1,2,3, raising debates about the role of moiré potential4,5,6,7,8,9,10,11,12,13,14,15,16,17. Here, by performing nanospot angle-resolved photoemission spectroscopy, we directly visualize the topological flat band in both aligned and non-aligned R5G/BN. The moiré potential in the aligned sample generates moiré bands and enhances the topological flat band as compared to non-aligned sample. Combined with theoretical calculations, we propose that the moiré bands on the top surface arise through the interlayer Coulomb interaction with the moiré-modulated bottom layer. Our results provide direct experimental evidence for the role of moiré potential in aligned rhombohedral graphene, and establish a foundation for understanding its emergent quantum phenomena.
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Nov 2025
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I05-ARPES
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Jiabao
Yang
,
Mihir
Date
,
Irián Sánchez
Ramírez
,
Vicky
Hasse
,
Deepnarayan
Biswas
,
Stuart S. P.
Parkin
,
Maia G.
Vergniory
,
Fernando
De Juan
,
Claudia
Felser
,
Matthew D.
Watson
,
Niels B. M.
Schroeter
Diamond Proposal Number(s):
[33319]
Open Access
Abstract: Recent work suggests that crystal structures with two sublattice pairs per primitive cell can host “dark states”, electronic states that barely interact with light due to destructive interference, which makes them invisible in photoemission. In practice, however, dark states are only approximately dark, arising from near but imperfect translation symmetries. Here, we demonstrate a practical consequence of this in the semiconductor (NbSe4)3I: Although its band structure indicates an almost direct gap, the material behaves optically like an indirect-gap semiconductor. Angle-resolved photoemission spectroscopy uncovers weak spectral-weight bands folded from a larger Brillouin zone, reflecting approximate intra-unit-cell symmetry. These states form a small direct band gap consistent with transport data but exhibit very low optical transition probability. Instead, optical absorption is dominated by higher-energy transitions involving bands with stronger spectral weight, effectively enlarging the observed optical gap. Our results show that dark states are approximate phenomena with significant consequences for optoelectronic properties.
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Nov 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
,
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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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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I05-ARPES
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Y.
Alexanian
,
A.
De La Torre
,
S.
Mckeown Walker
,
M.
Straub
,
G.
Gatti
,
A.
Hunter
,
S.
Mandloi
,
E.
Cappelli
,
S.
Riccò
,
F. Y.
Bruno
,
M.
Radovic
,
N. C.
Plumb
,
M.
Shi
,
J.
Osiecki
,
C.
Polley
,
T. K.
Kim
,
P.
Dudin
,
M.
Hoesch
,
R. S.
Perry
,
A.
Tamai
,
F.
Baumberger
Diamond Proposal Number(s):
[10348, 12404, 17381]
Open Access
Abstract: The fate of the Fermi surface in bulk electron-doped Sr2IrO4 remains elusive, as does the origin and extension of its pseudogap phase. Here, we use high-resolution angle-resolved photoelectron spectroscopy (ARPES) to investigate the electronic structure of Sr2−xLaxIrO4 up to x = 0.2, a factor of two higher than in previous work. We find that the antinodal pseudogap persists up to the highest doping level, and thus beyond the sharp increase in Hall carrier density to ≃ 1 + x recently observed above x* ≃ 0.161. This suggests that doped iridates host a unique phase of matter in which a large Hall density coexists with an anisotropic pseudogap, breaking up the Fermi surface into disconnected arcs. The temperature boundary of the pseudogap is T* ≃ 200 K for x = 0.2, comparable to cuprates and to the energy scale of short range antiferromagnetic correlations in cuprates and iridates.
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Oct 2025
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I05-ARPES
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Diamond Proposal Number(s):
[34479, 33317, 35210]
Open Access
Abstract: Understanding the interface between metals and two-dimensional materials is critical for their application in electronics and for the development of metal-mediated exfoliation of large area monolayers. Studying the intricate interactions at the interface requires model systems that enable control of the roughness, purity, and crystallinity of the metal surface. Here, we use angle-resolved photoemission spectroscopy to investigate the layer-dependent electronic structure of WSe\textsubscript{2}~on template-stripped gold substrates fabricated using both silicon and mica templates, giving crystallographically disordered and Au(111) ordered surfaces, respectively, and contrast these findings with \textit{ab initio} predictions. We observe strong hybridization around the Brillouin zone centre at $\overline{\Gamma}$, indicating a covalent admixture in the gold-WSe\textsubscript{2}~interaction, and band shifts that suggest charge rearrangement at the Au(111) / WSe\textsubscript{2}~interface. Core-level spectroscopy shows a single chemical environment for the interfacial WSe\textsubscript{2}~layer on the template-stripped gold, distinct from the subsequent layers. These results reveal a mixture of van der Waals and covalent interactions, best described as a covalent-like quasi-bonding with intermediate interaction strength.
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Oct 2025
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