I05-ARPES
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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.
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Apr 2026
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I09-Surface and Interface Structural Analysis
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Lixin
Liu
,
Han
Yan
,
Leyi
Loh
,
Kamal Kumar
Paul
,
Soumya
Sarkar
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Takashi
Taniguchi
,
Kenji
Watanabe
,
Manish
Chhowalla
,
Yan
Wang
Diamond Proposal Number(s):
[38012, 39914]
Open Access
Abstract: Excellent gate electrostatics in field effect transistors (FETs) based on 2D transition metal dichalcogenide (2D TMD) channels can dramatically decrease static power dissipation. Energy-efficient FETs operate in enhancement mode with a small and positive threshold voltage (Vth) for n-type devices. However, most state-of-the-art FETs based on monolayer MoS2 channel operate in depletion mode with negative Vth due to doping from the underlying dielectric substrate. In this work, we identify key properties of the semiconductor/dielectric interface (MoS2 on industrially relevant high dielectric constant (k) HfO2, ZrO2 and hBN for reference) responsible for realizing enhancement-mode operation of 2D MoS2 channel FETs. We find that hBN and ZrO2 dielectric substrates provide low defect interfaces with MoS2 that enables effective modulation of the Vth using gate metals of different work functions (WFs). We use photoluminescence (PL) and synchrotron X-ray photoelectron spectroscopy (XPS) measurements to investigate doping levels in monolayer MoS2 on different dielectrics with different WF gate metals. We complement the FET and spectroscopic measurements with capacitance-voltage analysis on dielectrics with varying thicknesses, which confirms that Vth modulation in ZrO2 devices is correlated with WF of the gate metals – in contrast with HfO2 devices that exhibit signatures of Vth pinning induced by oxide/interface defect states. Finally, we demonstrate FETs using a 2D MoS2 channel and a 6 nm of ZrO2 dielectric, achieving a subthreshold swing of 87 mV dec−1 and a threshold voltage of 0.1 V. Our results offer insights into the role of dielectric/semiconductor interface in 2D MoS2 based FETs for realizing enhancement mode FETs and highlight the potential of ZrO2 as a scalable high-k dielectric.
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Mar 2026
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Cheng
Chen
,
William
Holtzmann
,
Xiao-Wei
Zhang
,
Eric
Anderson
,
Shanmei
He
,
Yuzhou
Zhao
,
Weijie
Li
,
Jieyi
Liu
,
Yucheng
Guo
,
Chris
Jozwiak
,
Aaron
Bostwick
,
Eli
Rotenberg
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Ting
Cao
,
Di
Xiao
,
Xiaodong
Xu
,
Yulin
Chen
Open Access
Abstract: The pursuit of emergent quantum phenomena lies at the forefront of modern condensed matter physics. A recent breakthrough in this arena is the discovery of the fractional quantum anomalous Hall effect (FQAHE) in twisted bilayer MoTe₂ (tbMoTe₂), marking a paradigm shift and establishing a versatile platform for exploring the intricate interplay among topology, magnetism, and electron correlations. While significant progress has been made through both optical and electrical transport measurements, direct experimental insights into the electronic structure – crucial for understanding and modeling this system – have remained elusive. Here, using spatially and angle-resolved photoemission spectroscopy (μ-ARPES), we directly map the electronic band structure of tbMoTe₂. We identify the valence band maximum, whose partial filling underlies the FQAHE, at the K points, situated approximately 150 meV above the Γ valley. By fine-tuning the doping level via in-situ alkali metal deposition, we also resolve the conduction band minimum at the K point, providing direct evidence that tbMoTe₂ exhibits a direct band gap – distinct from all previously known moiré bilayer transition metal dichalcogenide systems. These results offer critical insights for theoretical modeling and advance our understanding of fractionalized excitations and correlated topological phases in this emergent quantum material.
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Jan 2026
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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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NONE-No attached Diamond beamline
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Emily
Heppell
,
Ryuji
Fujita
,
Gautam
Gurung
,
Jheng-Cyuan
Lin
,
Andrew
May
,
Michael
Foerster
,
M. Waqas
Khaliq
,
Miguel Angel
Niño
,
Manuel
Valvidares
,
Javier
Herrero-Martin
,
Pierluigi
Gargiani
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Dirk
Backes
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
Open Access
Abstract: The exploration of two-dimensional (2D) van der Waals ferromagnets has revealed intriguing magnetic properties with significant potential for spintronics applications. In this study, we examine the magnetic properties of Co-doped Fe5GeTe2 using X-ray photoemission electron microscopy (XPEEM) and X-ray magnetic circular dichroism (XMCD), complemented by density functional theory (DFT) calculations. Our XPEEM measurements reveal that the Curie temperature (TC) of a bilayer of (CoxFe1-x)5-δGeTe2 (with x = 0.28) reaches ∼300 K — a notable enhancement over most 2D ferromagnets in the ultrathin limit. Interestingly, the TC shows only a small dependence on film thickness (bulk TC ≈ 340 K), in line with the observed in-plane magnetic anisotropy and robust in-plane exchange coupling. XMCD measurements indicate that the spin moments for both Fe and Co are significantly reduced compared to the theoretical values. These insights highlight the potential of Co-doped Fe5GeTe2 for stable, high-temperature ferromagnetic applications in 2D materials.
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Dec 2024
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I06-Nanoscience (XPEEM)
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Ryuji
Fujita
,
Gautam
Gurung
,
Mohamad‐assaad
Mawass
,
Alevtina
Smekhova
,
Florian
Kronast
,
Alexander Kang-Jun
Toh
,
Anjan
Soumyanarayanan
,
Pin
Ho
,
Angadjit
Singh
,
Emily
Heppell
,
Dirk
Backes
,
Francesco
Maccherozzi
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Daniel A.
Mayoh
,
Geetha
Balakrishnan
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
Diamond Proposal Number(s):
[31730]
Open Access
Abstract: The van der Waals interaction enables atomically thin layers of exfoliated 2D materials to be interfaced in heterostructures with relaxed epitaxy conditions, however, the ability to exfoliate and freely stack layers without any strain or structural modification is by no means ubiquitous. In this work, the piezoelectricity of the exfoliated van der Waals piezoelectric α-In2Se3 is utilized to modify the magnetic properties of exfoliated Fe3GeTe2, a van der Waals ferromagnet, resulting in increased domain wall density, reductions in the transition temperature ranging from 5 to 20 K, and an increase in the magnetic coercivity. Structural modifications at the atomic level are corroborated by a comparison to a graphite/α-In2Se3 heterostructure, for which a decrease in the Tuinstra-Koenig ratio is found. Magnetostrictive ferromagnetic domains are also observed, which may contribute to the enhanced magnetic coercivity. Density functional theory calculations and atomistic spin dynamic simulations show that the Fe3GeTe2 layer is compressively strained by 0.4%, reducing the exchange stiffness and magnetic anisotropy. The incorporation of α-In2Se3 may be a general strategy to electrostatically strain interfaces within the paradigm of hexagonal boron nitride-encapsulated heterostructures, for which the atomic flatness is both an intrinsic property and paramount requirement for 2D van der Waals heterojunctions.
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Mar 2024
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I05-ARPES
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Paulina
Majchrzak
,
Ryan
Muzzio
,
Alfred J. H.
Jones
,
Davide
Curcio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Jacob
Gobbo
,
Simranjeet
Singh
,
Jeremy T.
Robinson
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Timur K.
Kim
,
Cephise
Cacho
,
Jill A.
Miwa
,
Philip
Hofmann
,
Jyoti
Katoch
,
Soeren
Ulstrup
Diamond Proposal Number(s):
[24072]
Open Access
Abstract: To pinpoint the electronic and structural mechanisms that affect intrinsic and extrinsic performance limits of two‐dimensional material devices, it is of critical importance to resolve the electronic properties on the mesoscopic length scale of such devices under operating conditions. The present work utilizes angle‐resolved photoemission spectroscopy with nanoscale spatial resolution (nanoARPES) to map the quasiparticle electronic structure of a twisted bilayer graphene device. The dispersion and linewidth of the Dirac cones associated with top and bottom graphene layers are determined as a function of spatial position on the device under both static and operating conditions. The analysis reveals that microscopic rotational domains in the two graphene layers establish a range of twist angles from 9.8∘ to 12.7∘. Application of current and electrostatic gating lead to strong electric fields with peak strengths of 0.75 V/μm at the rotational domain boundaries in the device. These proof‐of‐principle results demonstrate the potential of nanoARPES to link mesoscale structural variations with electronic states in operating device conditions and to disentangle such extrinsic factors from the intrinsic quasiparticle dispersion.
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Mar 2021
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I05-ARPES
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Davide
Curcio
,
Alfred J. H.
Jones
,
Ryan
Muzzio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Charlotte E.
Sanders
,
Pavel
Dudin
,
Cephise
Cacho
,
Simranjeet
Singh
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Jill A.
Miwa
,
Jyoti
Katoch
,
Soeren
Ulstrup
,
Philip
Hofmann
Diamond Proposal Number(s):
[20218]
Abstract: The presence of an electrical transport current in a material is one of the simplest and most important realizations of nonequilibrium physics. The current density breaks the crystalline symmetry and can give rise to dramatic phenomena, such as sliding charge density waves, insulator-to-metal transitions, or gap openings in topologically protected states. Almost nothing is known about how a current influences the electron spectral function, which characterizes most of the solid’s electronic, optical, and chemical properties. Here we show that angle-resolved photoemission spectroscopy with a nanoscale light spot provides not only a wealth of information on local equilibrium properties, but also opens the possibility to access the local nonequilibrium spectral function in the presence of a transport current. Unifying spectroscopic and transport measurements in this way allows simultaneous noninvasive local measurements of the composition, structure, many-body effects, and carrier mobility in the presence of high current densities. In the particular case of our graphene-based device, we are able to correlate the presence of structural defects with locally reduced carrier lifetimes in the spectral function and a locally reduced mobility with a spatial resolution of 500 nm.
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Dec 2020
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I05-ARPES
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Alfred J. H.
Jones
,
Ryan
Muzzio
,
Paulina
Majchrzak
,
Sahar
Pakdel
,
Davide
Curcio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Jacob
Gobbo
,
Simranjeet
Singh
,
Jeremy T.
Robinson
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Timur K.
Kim
,
Cephise
Cacho
,
Nicola
Lanata
,
Jill A.
Miwa
,
Philip
Hofmann
,
Jyoti
Katoch
,
Soeren
Ulstrup
Diamond Proposal Number(s):
[24072]
Abstract: The possibility of triggering correlated phenomena by placing a singularity
of the density of states near the Fermi energy remains an intriguing avenue toward engineering the properties of quantum materials. Twisted bilayer gra- phene is a key material in this regard because the superlattice produced by the rotated graphene layers introduces a van Hove singularity and flat bands near the Fermi energy that cause the emergence of numerous correlated phases, including superconductivity. Direct demonstration of electrostatic control of the superlattice bands over a wide energy range has, so far, been critically missing. This work examines the effect of electrical doping on the electronic band structure of twisted bilayer graphene using a back-gated device archi- tecture for angle-resolved photoemission measurements with a nano-focused light spot. A twist angle of 12.2° is selected such that the superlattice Brillouin zone is sufficiently large to enable identification of van Hove singularities and flat band segments in momentum space. The doping dependence of these fea- tures is extracted over an energy range of 0.4 eV, expanding the combinations of twist angle and doping where they can be placed at the Fermi energy and thereby induce new correlated electronic phases in twisted bilayer graphene.
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Jun 2020
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Krios I-Titan Krios I at Diamond
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Diamond Proposal Number(s):
[22985]
Open Access
Abstract: The fundamental unit of chromatin, the nucleosome, is an intricate structure that requires histone chaperones for assembly. ATAD2 AAA+ ATPases are a family of histone chaperones that regulate nucleosome density and chromatin dynamics. Here, we demonstrate that the fission yeast ATAD2 homolog, Abo1, deposits histone H3–H4 onto DNA in an ATP-hydrolysis-dependent manner by in vitro reconstitution and single-tethered DNA curtain assays. We present cryo-EM structures of an ATAD2 family ATPase to atomic resolution in three different nucleotide states, revealing unique structural features required for histone loading on DNA, and directly visualize the transitions of Abo1 from an asymmetric spiral (ATP-state) to a symmetric ring (ADP- and apo-states) using high-speed atomic force microscopy (HS-AFM). Furthermore, we find that the acidic pore of ATP-Abo1 binds a peptide substrate which is suggestive of a histone tail. Based on these results, we propose a model whereby Abo1 facilitates H3–H4 loading by utilizing ATP.
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Dec 2019
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