I05-ARPES
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Cedric
Schmitt
,
Lukas
Gehrig
,
Kilian
Strauß
,
Jonas
Erhardt
,
Merit
Spring
,
Bing
Liu
,
Matthew D.
Watson
,
Han
Gao
,
Hanbo
Xiao
,
Zhongkai
Liu
,
Gang
Li
,
Giorgio
Sangiovanni
,
Jörg
Schäfer
,
Ralph
Claessen
,
Simon
Moser
Diamond Proposal Number(s):
[41909]
Abstract: Circular dichroism in angle-resolved photoemission spectroscopy (CD-ARPES) is widely used to probe orbital angular momentum (OAM) and Berry-curvature-related phenomena in two-dimensional quantum materials. However, in many materials, conventional micron-scale measurements often average over domains with opposite OAM polarization, canceling intrinsic dichroic signals and leaving spectra dominated by extrinsic asymmetries arising from photoelectron final-state interference. Here, we combine circularly polarized light with NanoARPES to achieve spatially resolved CD-ARPES with sub-800 nm resolution. By isolating individual domains, this approach enables direct access to the intrinsic OAM texture. As a model system, we investigate the K/K′ point valley states of the quantum spin Hall insulator indenene─a triangular indium monolayer epitaxially grown on SiC(0001)─where substrate-induced terraces host alternating valley configurations whose dichroic response is averaged out in conventional measurements. Terrace-resolved NanoARPES disentangles these contributions, allowing direct visualization of oppositely polarized domains and revealing the OAM texture associated with a topological band inversion. Our results establish spatially resolved CD-ARPES as a robust approach for isolating intrinsic OAM contrast by eliminating domain averaging and correcting for extrinsic geometry-dependent contributions. This enables direct access to the Berry curvature near the Fermi level, providing a powerful probe of the system’s intrinsic topological character.
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Oct 2026
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I05-ARPES
|
Wanying
Chen
,
Hongyun
Zhang
,
Jinxi
Lu
,
Yu
Gu
,
Qiyun
Xu
,
Fei
Wang
,
Xuanxi
Cai
,
Jiansong
Li
,
Jiayong
Xiao
,
Rui
Chen
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Jose
Avila
,
Pavel
Dudin
,
Matthew D.
Watson
,
Pu
Yu
,
Shengwei
Jiang
,
Wenhui
Duan
,
Tingxin
Li
,
Chong
Wang
,
Shuyun
Zhou
Diamond Proposal Number(s):
[39762]
Abstract: Twisted MoTe2 hosts intriguing correlated quantum phenomena including the fractional quantum anomalous Hall effect in twisted bilayer (t-BL) MoTe2 near 3.7°, which is sensitive to the twist angle and moiré superlattices. Here, we directly visualize the twist-angle-modulated electronic structure of t-BL and twisted double-bilayer (t-DBL) MoTe2 near this critical angle. We find that the moiré superlattice not only modifies the relative energy between the Γ and 𝐾 valleys in t-BL MoTe2, but also strongly reconstructs the Γ valley for both t-BL and t-DBL MoTe2. Specifically, the deep 𝑝𝑧-derived band at Γ exhibits a distinct splitting that systematically varies with increasing twist angle. Theoretical analysis suggests that this modulation arises from the twist-angle-dependent lattice relaxation, especially interfacial corrugations. Our work directly visualizes the moiré-modulated electronic structure and provides key spectroscopic information of lattice relaxation and interlayer interactions underlying the physics of twisted MoTe2.
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Sep 2026
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I05-ARPES
|
Gianmarco
Gatti
,
Amalie H.
Svaneborg
,
Wu
Bing
,
Gesa-R.
Siemann
,
Anders S.
Mortensen
,
Naina
Kushwaha
,
Jennifer
Rigden
,
Jakob K.
Svaneborg
,
Matthew D.
Watson
,
Timur K.
Kim
,
Charlotte
Sanders
,
Kristian S.
Thygesen
,
Zdenek
Sofer
,
Philip
Hofmann
Diamond Proposal Number(s):
[39998]
Abstract: The bulk and surface electronic structure of MoAlB(010) is studied by a combination of angle-resolved photoemission spectroscopy and density functional calculations. The observed bulk Fermi-level crossings agree with the previously reported bulk Fermi surface of the material. Additionally, we find several surface states in the wide projected bulk band gaps around the Fermi energy. The surface states differ in their stability under residual-gas exposure in the vacuum system and in the magnitude of their Rashba-type spin-orbit splitting. We explain this in terms of their elemental and orbital character. A surface state arising from Al dangling bonds is sensitive to surface contamination, whereas a mainly Mo-derived surface state exhibits the stronger spin-orbit splitting.
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Sep 2026
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I05-ARPES
|
Cong
Li
,
Zhilong
Yang
,
Hongxiong
Liu
,
Magnus H.
Berntsen
,
Francesco
Scali
,
Dibya
Phuyal
,
Jianfeng
Zhang
,
Timur K.
Kim
,
Jacek
Osiecki
,
Balasubramanian
Thiagarajan
,
Youguo
Shi
,
Tao
Xiang
,
Quansheng
Wu
,
Oscar
Tjernberg
Diamond Proposal Number(s):
[39652, 41048]
Open Access
Abstract: Topological materials are defined by the correspondence between bulk topology and boundary states, yet this correspondence becomes enigmatic on low-symmetry surfaces where bulk and surface periodicities may not coincide within a conventional first bulk Brillouin zone projection. Here we study the (103) surface of the Weyl semimetal NdAlSi and identify Fermi arc interference in the boundary spectrum. Angle-resolved photoemission spectroscopy uncovers loop-like Fermi-arc connectivity and characteristic replica modulations that are not observed on high symmetry surfaces. Crucially, the topological surface states themselves are reconstructed because Fermi arcs from phase-shifted bulk-zone projections overlap and hybridize, producing connectivity patterns unique to low-symmetry facets. We show that these emerge from incomplete bulk projection and multi-cell interference governed by a least-common-multiple framework. Least-common-multiple guided density functional theory and Green’s-function calculations reproduce the reconstructed periodicity and dominant replica structure in the spectra, providing a broadly applicable commensuration guideline. These findings resolve the apparent bulk-boundary correspondence paradox on low-symmetry surfaces and provide an operational route to model and interpret boundary spectra on complex facets.
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Aug 2026
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I05-ARPES
|
S. K.
Mahatha
,
A.
Kar
,
J.
Corral-Sertal
,
J.
Diego
,
A.
Korshunov
,
C.-Y.
Lim
,
F. K.
Diekmann
,
D.
Subires
,
J.
Phillips
,
T. K.
Kim
,
D.
Ishikawa
,
G.
Marini
,
I.
Vobornik
,
I.
Errea
,
S.
Rohlf
,
M.
Kalläne
,
V.
Bellini
,
A. Q. R.
Baron
,
Adolfo O.
Fumega
,
A.
Bosak
,
V.
Pardo
,
K.
Rossnagel
,
S.
Blanco-Canosa
Diamond Proposal Number(s):
[36505]
Abstract: First-order phase transitions, characterized by a discontinuous change in the order parameter, are intriguing phenomena in condensed matter physics. However, the underlying, material-specific, microscopic mechanisms often remain unclear. Here, we unveil a high-temperature incommensurate charge-order precursor with the wave vector 𝐪*=(0,
1
4
+𝛿,
1
2
) in the 1T' phase of TaTe2, which competes with fluctuating high-temperature Ta trimer bonding states at 𝐪CO=(0,
1
3
,0). The precursor state follows the temperature dependence of the hidden incommensurability of the quasi-1D nested Fermi surface. In contrast, the low-temperature commensurate charge order at 𝐪CO, characterized by a charge disproportionation of the inequivalent Ta sites, appears to be driven by local chemical bonding. Dynamical lattice calculations identify an imaginary optical mode at 𝐪*, involving an in-plane vibration of the Ta atoms forming a chainlike structure that renormalizes below 𝑇CO. Our experimental and theoretical observations suggest that the controversial first-order phase transition, as captured by phenomenological Ginzburg-Landau theory, results from the competition between two order parameters: one involving Fermi surface nesting and the other involving local chemical bonding.
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Jul 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
|
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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I05-ARPES
|
Chan-Young
Lim
,
Francesc
Ballester
,
Arunava
Kar
,
Manex
Alkorta
,
David
Subires
,
Ji
Dai
,
Massimo
Tallarida
,
Elio
Vescovo
,
Timur K.
Kim
,
Cephise
Cacho
,
Changjiang
Yi
,
Subhajit
Roychowdhury
,
Avdhesh Kumar
Sharma
,
Yongseong
Choi
,
Gilberto
Fabbris
,
Joerg
Strempfer
,
Pierluigi
Gargiani
,
Chandra
Shekhar
,
Claudia
Felser
,
Ion
Errea
,
Maia G.
Vergniory
,
Santiago
Blanco-Canosa
Diamond Proposal Number(s):
[36505]
Abstract: Kagome materials are known for hosting emergent quantum phenomena driven by the interaction between different lattice, charge, and spin orders. Here, we present a detailed angle-resolved photoemission (ARPES), density functional theory (DFT), and x-ray magnetic circular dichroism (XMCD) study of the electronic and magnetic structure of 𝑅Ti3Bi4 (𝑅=Nd, Sm, Gd). ARPES and DFT demonstrate that the bulk electronic band structure is dominated by the hybridization of the Ti bands, and the weak electron-like pocket at Γ is identified as a surface state. The isotropic XAS profile of the 𝑀4,5 edge of the rare earth is consistent with the presence of the 𝑅3+ oxidation state. Using the XMCD sum rules, backed by the atomic-multiplet-theory calculations, we obtain the spin and orbital magnetic moments. The Ti 𝐿2,3-edge XMCD reveals the presence of a small magnetic moment in GdTi3Bi4, presumably driven by the proximity of the Ti kagome layers to the zigzag chains of Gd, while the total magnetic moment of Gd is shared by the 𝑓 and 𝑑 electrons. Our combined XMCD, ARPES, and DFT study provides an important piece of information to understand the spin-flip transitions and anomalous Hall effect observed in the 𝑅Ti3Bi4 kagome metals.
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Jun 2026
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I05-ARPES
|
Y.
Morita
,
K.
Nakayama
,
N.
Ito
,
T.
Kato
,
T.
Nakamura
,
H.
Zhang
,
X.
Tang
,
T.
Lin
,
K.
Yanagizawa
,
S.
Souma
,
S.
Masaki
,
T.
Ikushima
,
Y.
Moriyasu
,
K.
Hagiwara
,
F.
Matsui
,
K.
Tanaka
,
K.
Ozawa
,
D.
Shiga
,
H.
Kumigashira
,
M.
Maeda
,
Y.
Niimi
,
T.
Kida
,
M.
Hagiwara
,
T. K.
Kim
,
C.
Cacho
,
T.
Takahashi
,
Y.
Okada
,
S.
Zhou
,
T.
Koretsune
,
K.
Kudo
,
T.
Sato
Diamond Proposal Number(s):
[38107]
Open Access
Abstract: Exploiting electronic singularities to drive emergent quantum phenomena is a key basis in condensed matter physics, yet this powerful strategy has been largely limited to two dimensions, leaving the potential of three-dimensional materials often inaccessible. A “saddle-loop” singularity—a one-dimensional ring of saddle points—has been proposed as a way to extend the concept of van Hove singularities to three-dimensional electron systems, but has remained experimentally elusive. Here, we provide the direct experimental evidence for the saddle‑loop singularity in Pt(Bi1−xSex)2, using angle‑resolved photoemission spectroscopy. We also show that the saddle loop is positioned closer to the Fermi level at low x values where the superconducting critical temperature is higher. Furthermore, our advanced theoretical calculations reveal that the saddle loop originates from inter-orbital hybridization, establishing a generalizable design concept. Our findings demonstrate a viable mechanism for realizing singular electronic states in three-dimensional electron systems, providing a platform to investigate correlation-driven phenomena in three dimensions.
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Jun 2026
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I05-ARPES
|
Z. W.
Riedel
,
P. A. E.
Murgatroyd
,
C. S.
Kengle
,
P. M. T.
Trocado Vianez
,
A.
Schmidt
,
X.
Du
,
K.
Allen
,
Ti. K.
Kim
,
C.
Lane
,
Y. W.
Li
,
J.-X.
Zhu
,
J. D.
Thompson
,
F.
Ronning
,
S. M.
Thomas
,
P. F. S.
Rosa
,
E. D.
Bauer
Diamond Proposal Number(s):
[41855]
Abstract: The chemical flexibility of the 𝑅𝑀6𝑋6 stoichiometry, where an 𝑓-block element is intercalated in the CoSn structure type, allows for the tuning of flatbands associated with kagome lattices to the Fermi level and for emergent phenomena due to interactions between the 𝑓- and 𝑑-electron lattices. Yet, 5𝑓 members of the “166” compounds are underrepresented compared with 4𝑓 members. Here, we report single-crystal growth of UCr6Ge6, which crystallizes in a monoclinically distorted Y0.5Co3Ge3-type structure. The real-space character of the modulation, which is unique within the 𝑅𝑀6𝑋6 family, is approximated by a 3×1×2 supercell of the average monoclinic cell. The compound has kagome-lattice flatbands near the Fermi level and a moderately enhanced electronic heat capacity, as evidenced by its low-temperature Sommerfeld coefficient (𝛾=86.5 mJ mol−1 K−2) paired with band structure calculations. The small, isotropic magnetization and featureless resistivity of UCr6Ge6 suggest itinerant uranium 5𝑓 electrons and Pauli paramagnetism. Angle-resolved photoemission spectroscopy results provide evidence for uranium 5𝑓 weight at the Fermi level and for a flatband near the Fermi level associated with the chromium 3𝑑 kagome lattice. The isotropic magnetic behavior of the uranium 5𝑓 electrons starkly contrasts with localized behavior in other uranium 166 compounds, highlighting the high tunability of the magnetic ground state across the material family.
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May 2026
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