I05-ARPES
|
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.
|
Jul 2026
|
|
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.
|
Jun 2026
|
|
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.
|
Jun 2026
|
|
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.
|
Jun 2026
|
|
I05-ARPES
|
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.
|
May 2026
|
|
I05-ARPES
|
Chakradhar
Sahoo
,
Suman Kumar
Chakraborty
,
Anbalagan
Kousika
,
Alfred J. H.
Jones
,
Manas
Sharma
,
Thomas S.
Nielsen
,
Zhihao
Jiang
,
Ihsan A.
Kolasseri
,
Subhadip
Das
,
Matthew D.
Watson
,
Cephise
Cacho
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Yong P.
Chen
,
Tony F.
Heinz
,
Ananth
Govind Rajan
,
Prasana K.
Sahoo
,
Søren
Ulstrup
Diamond Proposal Number(s):
[36290, 38414]
Abstract: Atomic-scale control over band alignment in single-layer lateral heterostructures (LHSs) of dissimilar transition metal dichalcogenides (TMDCs) is critical for next-generation electronic, optoelectronic, and quantum technologies. However, direct experimental access to interfacial electronic states with nanometer precision remains a significant challenge. Here, we employ angle-resolved photoemission spectroscopy with nanoscale spatial resolution (nanoARPES) to directly map the epitaxial alignment and valence band evolution across the MoSe2–WSe2 LHSs. By combining nanoARPES with spatially resolved photoluminescence, we correlate the evolution of the valence band maximum and exciton features across both atomically sharp and compositionally graded diffusive interfaces. We identified type-II band alignments governed by both material composition and interstitial-induced modifications of band offsets in close agreement with density functional theory calculations. These results reveal fundamental mechanisms of electronic structure modulation at 1D TMDC heterointerfaces and provide a robust platform for tailored band engineering in van der Waals materials.
|
Apr 2026
|
|
I05-ARPES
|
Aymeric
Saunot
,
Vesna
Mikšić Trontl
,
Ilya I.
Klimovskikh
,
Denis V.
Vyalikh
,
Alex
Louat
,
Cephise
Cacho
,
Asish K.
Kundu
,
Elio
Vescovo
,
Ivana
Vobornik
,
Alexander
Fedorov
,
Cedomir
Petrovic
,
Tonica
Valla
Diamond Proposal Number(s):
[36637]
Abstract: CeTe3 is a 2-dimensional (2D) Van der Waals (VdW) material with incommensurate charge density waves (CDW), extremely high transition temperature ( ), and a large momentum-dependent CDW gap that leaves a significant portion of the Fermi surface intact. It is also considered to be a weak Kondo system, a property unexpected for a material with incommensurate CDW, where each atomic site is slightly different. Here, we study the properties of the CDW state in several RTe3 (R is rare earth) materials and examine the hybridization of itinerant states with the localized Ce 4f multiplet in CeTe3 by using angle resolved photoemission spectroscopy. We find that the renormalization of the itinerant states originating from the hybridization with the deeper localized 4f states at meV is dependent and extends to the Fermi level. As these localized states are far from the Fermi level, the observed hybridization affects the effective masses only marginally and does not lead to heavy fermions. However, since the same renormalizing mechanism normally leads to the heavy fermion physics when the localized 4f states are near the Fermi level, our observation of its strong dependence suggests that this could be the reason for discrepancy between the heavy masses in specific heat and light ones in Shubnikov de Haas oscillations, often observed in heavy fermions.
|
Mar 2026
|
|
E02-JEM ARM 300CF
I05-ARPES
|
Amy
Carl
,
Nicholas
Clark
,
David G.
Hopkinson
,
Matthew
Hamer
,
Matthew
Watson
,
Laxman
Nagireddy
,
James E.
Nunn
,
Alexei
Barinov
,
Yichao
Zou
,
William
Thornley
,
Casey
Cheung
,
Wendong
Wang
,
Sam
Sullivan-Allsop
,
Xiao
Li
,
Astrid
Weston
,
Eli G.
Castanon
,
Andrey V.
Kretinin
,
Cephise
Cacho
,
Neil R.
Wilson
,
Sarah J.
Haigh
,
Roman
Gorbachev
Diamond Proposal Number(s):
[21597, 21981, 24290, 24338]
Open Access
Abstract: Magnetic two-dimensional materials are a promising platform for novel nano-electronic device architectures. One such layered crystal is the ferromagnetic semiconductor chromium germanium telluride (Cr2Ge2Te6) which recently attracted interest due to its potential for spintronics and memory applications. Here we investigate its properties from the structural standpoint using atomic resolution Scanning Transmission Electron Microscopy (STEM) and present the first atomic resolution images down to its monolayer limit. We develop a novel technique that allows one to map the local tilt with unprecedented spatial resolution using only high-resolution images, enabling mapping of the topography and morphological variation of atomically thin crystals. Using it, we show that the Cr2Ge2Te6 monolayer has an unusually large out-of-plane rippling, with local tilt variation reaching 20° over few nm length scales. We hypothesize that such a strongly buckled structure originates from both point and extended lattice defects which are more prevalent in monolayer crystals. In addition, we correlate the structural observations with the band structure measurements using Angle-Resolved Photoemission Spectroscopy (ARPES). We believe that both the atomic scale insights we have gained on Cr2Ge2Te6 and our novel approach to nanoscale topography mapping will benefit the development of van der Waals heterostructures in both fundamental and applied research.
|
Feb 2026
|
|
I05-ARPES
|
Yuval
Nitzav
,
Roni A.
Kiassi Gofman
,
Ilay
Mangel
,
Abigail
Dishi
,
Nitzan
Ragoler
,
K. P.
Sajilesh
,
Yaron
Jarach
,
Alex
Louat
,
Matthew D.
Watson
,
Cephise
Cacho
,
Irena
Feldman
,
Amit
Kanigel
Diamond Proposal Number(s):
[33131]
Abstract: The origin of the insulating state in 1𝑇 −TaS2 has long been a subject of debate. A short current pulse transforms this insulating state into a metastable metallic phase. Using micro–angle-resolved photoemission spectroscopy, we investigate the electronic structure of this phase and uncover spatially dependent modifications caused by the current pulse. In some regions of the sample, a Fermi surface emerges, while others remain gapped. Detailed band structure analysis reveals that the metallic regions exhibit an electronic structure similar to that observed in the high-temperature phase of 1𝑇 −TaS2, characterized by suppressed energy gaps and bands crossing the Fermi level. Furthermore, the metallic and insulating regions display distinct out of plane dispersions, consistent with the current pulse influencing the Star of David dimers that characterize the insulating phase.
|
Feb 2026
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[37658, 36215, 39549]
Open Access
Abstract: We report the electronic structure of monolayer CrSBr exfoliated onto mica template-stripped gold substrates. Angle-resolved photoemission spectroscopy reveals charge transfer from the substrate, populating the conduction band of monolayer CrSBr, accompanied by a pronounced reduction in the quasiparticle band gap. Furthermore, we observe two separate conduction bands that exhibit a splitting at the X point. This indicates a breaking of glide-mirror symmetry, which in the bulk or in a free-standing monolayer protects the band degeneracies at the Brillouin zone boundary. Our results demonstrate that ultraflat gold substrates do more than modify carrier densities and screening: they can lift symmetry-protected degeneracies and thus fundamentally reshape the band topology of 2D materials.
|
Jan 2026
|
|
