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
|
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
|
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
|
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.
|
May 2026
|
|
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.
|
May 2026
|
|
I05-ARPES
|
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.
|
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
|
|
I05-ARPES
|
Xian
Yang
,
Chia-Hsiu
Hsu
,
Gokul
Acharya
,
Junyi
Zhang
,
Md shafayat
Hossain
,
Tyler A.
Cochran
,
Bimal
Neupane
,
Zi-Jia
Cheng
,
Santosh Karki
Chhetri
,
Byunghoon
Kim
,
Shiyuan
Gao
,
Yu-Xiao
Jiang
,
Maksim
Litskevich
,
Jian
Wang
,
Yuanxi
Wang
,
Jin
Hu
,
M. Zahid
Hasan
Abstract: Topological materials hold immense promise for exhibiting exotic quantum phenomena, yet achieving controllable topological phase transitions remains challenging. Here, we demonstrate a structurally driven, reversible topological phase transition in the distorted square net material GdPS, induced via in situ potassium dosing. Using angle-resolved photoemission spectroscopy and first principles calculations, we demonstrate a cascade of topological phases in the subsurface P layer: from a large, topologically trivial band gap to a gapless Dirac cone state with a 2 eV dispersion, and finally to a two-dimensional topological insulator as inferred from theory. This evolution is driven by subtle structural distortions in the first P layer caused by potassium adsorption, which in turn contribute to the band gap closure and topological phase transition. Furthermore, the ability to manipulate the topology of a subsurface layer in GdPS offers a unique route for exploring and controlling topological states in bulk materials.
|
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
|
|
