I05-ARPES
|
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
|
Diamond Proposal Number(s):
[28445]
Open Access
Abstract: The metallic delafossites host ultrahigh-mobility carriers in the bulk, while at their polar surfaces, intrinsic electronic reconstructions stabilize markedly distinct electronic phases, from charge-disproportionated insulators to Rashba-split heavy-hole gases and ferromagnetic metals. The understanding of these phases has been strongly informed by surface spectroscopic measurements, but previous studies have been complicated by the presence of spatially varying terminations of the material surface. Here, we demonstrate the potential of microscopic-area angle-resolved photoemission to overcome these challenges. Our measurements of the model compound PdCoO2 yield extremely high quality spectra of the electronic structure, which allows us to place stringent experimental constraints on the weak electron-phonon coupling in the bulk of PdCoO2, while revealing much stronger interactions at its surfaces. While the CoO2-terminated surface exhibits a conventional weak-coupling behavior, our measurements reveal surprising spectroscopic signatures of polaron formation at the Pd-terminated surface, despite its pronounced metallicity. Together, our findings reveal how mode- and symmetry-selective couplings can markedly tune the electron-phonon interactions in a single host material, here opening routes to stabilize surprisingly persistent polaronic quasiparticles.
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Aug 2025
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I09-Surface and Interface Structural Analysis
I10-Beamline for Advanced Dichroism - scattering
|
Naina
Kushwaha
,
Olivia
Armitage
,
Brendan
Edwards
,
Liam
Trzaska
,
Jennifer
Rigden
,
Peter
Bencok
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Charlotte
Sanders
,
Gerrit
Van Der Laan
,
Peter
Wahl
,
Phil D. C.
King
,
Akhil
Rajan
Diamond Proposal Number(s):
[33239, 38049]
Open Access
Abstract: Chromium ditelluride, CrTe2, is an attractive candidate van der Waals material for hosting 2D magnetism. However, how the room-temperature ferromagnetism of the bulk evolves as the sample is thinned to the single-layer limit has proved controversial. This, in part, reflects its metastable nature, vs. a series of more stable self-intercalation compounds with higher relative Cr:Te stoichiometry. Here, exploiting a recently developed method for enhancing nucleation in molecular-beam epitaxy growth of transition-metal chalcogenides, we demonstrate the selective stabilisation of high-coverage CrTe2 and Cr2+εTe3 epitaxial monolayers. Combining X-ray magnetic circular dichroism, scanning tunnelling microscopy, and temperature-dependent angle-resolved photoemission, we demonstrate that both compounds order magnetically with a similar TC. We find, however, that monolayer CrTe2 forms as an antiferromagnetic metal, while monolayer Cr2+εTe3 hosts an intrinsic ferromagnetic semiconducting state. This work thus demonstrates that control over the self-intercalation of metastable Cr-based chalcogenides provides a powerful route for tuning both their metallicity and magnetic structure, establishing the CrxTey system as a flexible materials class for future 2D spintronics.
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May 2025
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I05-ARPES
I10-Beamline for Advanced Dichroism - scattering
|
E. L.
Arnold
,
J. M.
Riley
,
L. B.
Duffy
,
A. I.
Figueroa
,
R.
Held
,
K. M.
Shen
,
D. G.
Schlom
,
P. D. C.
King
,
M.
Hoesch
,
G.
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[16162, 15481]
Open Access
Abstract: We present a detailed x-ray magnetic circular dichroism (XMCD) study of the magnetic properties of Gd-doped EuO thin films, synthesized via molecular-beam epitaxy with Gd doping levels up to over 12%. The impact of Gd doping on the electronic and magnetic behavior of EuO is studied using XMCD and magnetometry. Gd doping significantly enhances the Curie temperature (𝑇C) from 69 K in undoped EuO to over 120 K, driven by increased carrier density, while preserving the high quality of the single-crystalline films. At higher doping levels, a plateau in 𝑇C is observed, which is attributed to the formation of Eu-Gd nearest-neighbor pairs that limit dopant activation. We also observe a distinctive “double-dome” structure in the temperature-dependent magnetization, which we attribute to both the ferromagnetic ordering of Eu 4𝑓 moments at lower temperatures and the influence of conduction electrons via 4𝑓−5𝑑 exchange interactions at higher temperatures. These findings provide key insights into the mechanisms of carrier-induced magnetic transitions.
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Feb 2025
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I05-ARPES
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Liam
Trzaska
,
Lei
Qiao
,
Matthew D.
Watson
,
Monica
Ciomaga Hatnean
,
Igor
Markovic
,
Edgar
Abarca Morales
,
Tommaso
Antonelli
,
Cephise
Cacho
,
Geetha
Balakrishnan
,
Wei
Ren
,
Silvia
Picozzi
,
Phil D. C.
King
Diamond Proposal Number(s):
[21986, 25564]
Open Access
Abstract: The recent discovery of the persistence of long-range magnetic order when van der Waals magnets are thinned towards monolayers provides a tunable platform for engineering of novel magnetic structures and devices. Here, we study the evolution of the electronic structure of CrGeTe3 as a function of surface electron doping. From angle-resolved photoemission, we observe spectroscopic fingerprints that this electron doping drives a marked increase in TC, reaching values more than double that of the undoped material, in agreement with recent studies using electrostatic gating. Together with density functional theory calculations and Monte Carlo simulations, we show that, surprisingly, the increased TC is mediated by the population of spin-minority Cr t2g states, forming a half-metallic 2D electron gas. This promotes a novel variant of double exchange, and unlocks a significant influence of Ge – which was previously thought to be electronically inert in this system – in mediating Cr-Cr exchange.
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Jan 2025
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I05-ARPES
|
Chi Ming
Yim
,
Gesa-R.
Siemann
,
Srdjan
Stavrić
,
Seunghyun
Khim
,
Izidor
Benedičič
,
Philip A. E.
Murgatroyd
,
Tommaso
Antonelli
,
Matthew D.
Watson
,
Andrew P.
Mackenzie
,
Silvia
Picozzi
,
Phil D. C.
King
,
Peter
Wahl
Diamond Proposal Number(s):
[28445]
Open Access
Abstract: Doping of a Mott insulator gives rise to a wide variety of exotic emergent states, from high-temperature superconductivity to charge, spin, and orbital orders. The physics underpinning their evolution is, however, poorly understood. A major challenge is the chemical complexity associated with traditional routes to doping. Here, we study the Mott insulating CrO2 layer of the delafossite PdCrO2, where an intrinsic polar catastrophe provides a clean route to doping of the surface. From scanning tunnelling microscopy and angle-resolved photoemission, we find that the surface stays insulating accompanied by a short-range ordered state. From density functional theory, we demonstrate how the formation of charge disproportionation results in an insulating ground state of the surface that is disparate from the hidden Mott insulator in the bulk. We demonstrate that voltage pulses induce local modifications to this state which relax over tens of minutes, pointing to a glassy nature of the charge order.
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Sep 2024
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I05-ARPES
I09-Surface and Interface Structural Analysis
|
Brendan
Edwards
,
Darius-A.
Deaconu
,
Philip A. E.
Murgatroyd
,
Sebastian
Buchberger
,
Tommaso
Antonelli
,
Daniel
Halliday
,
Gesa-R.
Siemann
,
Andela
Zivanovic
,
Liam
Trzaska
,
Akhil
Rajan
,
Edgar
Abarca Morales
,
Daniel A.
Mayoh
,
Amelia E.
Hall
,
Rodion V.
Belosludov
,
Matthew D.
Watson
,
Timur K.
Kim
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Craig M.
Polley
,
Dina
Carbone
,
Mats
Leandersson
,
Geetha
Balakrishnan
,
Mohammad Saeed
Bahramy
,
Phil D. C.
King
Diamond Proposal Number(s):
[32937, 30125, 31465]
Open Access
Abstract: The addition of metal intercalants into the van der Waals gaps of transition metal dichalcogenides has shown great promise as a method for controlling their functional properties. For example, chiral helimagnetic states, current-induced magnetization switching, and a giant valley-Zeeman effect have all been demonstrated, generating significant renewed interest in this materials family. Here, we present a combined photoemission and density-functional theory study of three such compounds:
V1/3NbS2
,
Cr1/3NbS2
, and
Fe1/3NbS2
, to investigate chemical trends of the intercalant species on their bulk and surface electronic structure. Our resonant photoemission measurements indicate increased hybridization with the itinerant NbS2-derived conduction states with increasing atomic number of the intercalant, leading to pronounced mixing of the nominally localized intercalant states at the Fermi level. Using spatially and angle-resolved photoemission spectroscopy, we show how this impacts surface-termination-dependent charge transfers and leads to the formation of new dispersive states of mixed intercalant-Nb character at the Fermi level for the intercalant-terminated surfaces. This provides an explanation for the origin of anomalous states previously reported in this family of compounds and paves the way for tuning the nature of the magnetic interactions in these systems via control of the hybridization of the magnetic ions with the itinerant states.
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Jul 2024
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I05-ARPES
|
Carolina A.
Marques
,
Philip A. E.
Murgatroyd
,
Rosalba
Fittipaldi
,
Weronika
Osmolska
,
Brendan
Edwards
,
Izidor
Benedičič
,
Gesa-R.
Siemann
,
Luke C.
Rhodes
,
Sebastian
Buchberger
,
Masahiro
Naritsuka
,
Edgar
Abarca-Morales
,
Daniel
Halliday
,
Craig
Polley
,
Mats
Leandersson
,
Masafumi
Horio
,
Johan
Chang
,
Raja
Arumugam
,
Mariateresa
Lettieri
,
Veronica
Granata
,
Antonio
Vecchione
,
Phil D. C.
King
,
Peter
Wahl
Diamond Proposal Number(s):
[28412]
Open Access
Abstract: Van Hove singularities (VHss) in the vicinity of the Fermi energy often play a dramatic role in the physics of strongly correlated electron materials. The divergence of the density of states generated by VHss can trigger the emergence of phases such as superconductivity, ferromagnetism, metamagnetism, and density wave orders. A detailed understanding of the electronic structure of these VHss is therefore essential for an accurate description of such instabilities. Here, we study the low-energy electronic structure of the trilayer strontium ruthenate Sr4Ru3O10, identifying a rich hierarchy of VHss using angle-resolved photoemission spectroscopy and millikelvin scanning tunneling microscopy. Comparison of k-resolved electron spectroscopy and quasiparticle interference allows us to determine the structure of the VHss and demonstrate the crucial role of spin-orbit coupling in shaping them. We use this to develop a minimal model from which we identify a mechanism for driving a field-induced Lifshitz transition in ferromagnetic metals.
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Apr 2024
|
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I05-ARPES
I10-Beamline for Advanced Dichroism - scattering
|
Gesa-R.
Siemann
,
Seo-Jin
Kim
,
Edgar
Abarca Morales
,
Philip A. E.
Murgatroyd
,
Andela
Zivanovic
,
Brendan
Edwards
,
Igor
Markovic
,
Federico
Mazzola
,
Liam
Trzaska
,
Oliver J.
Clark
,
Chiara
Bigi
,
Haijing
Zhang
,
Barat
Achinuq
,
Thorsten
Hesjedal
,
Matthew D.
Watson
,
Timur K.
Kim
,
Peter
Bencok
,
Gerrit
Van Der Laan
,
Craig M.
Polley
,
Mats
Leandersson
,
Hanna
Fedderwitz
,
Khadiza
Ali
,
Thiagarajan
Balasubramanian
,
Marcus
Schmidt
,
Michael
Baenitz
,
Helge
Rosner
,
Phil D. C.
King
Diamond Proposal Number(s):
[28412, 31035]
Open Access
Abstract: In half-metallic systems, electronic conduction is mediated by a single spin species, offering enormous potential for spintronic devices. Here, using microscopic-area angle-resolved photoemission, we show that a spin-polarised two-dimensional hole gas is naturally realised in the polar magnetic semiconductor AgCrSe2 by an intrinsic self-doping at its CrSe2-terminated surface. Through comparison with first-principles calculations, we unveil a striking role of spin-orbit coupling for the surface hole gas, unlocked by both bulk and surface inversion symmetry breaking, suggesting routes for stabilising complex magnetic textures in the surface layer of AgCrSe2.
|
Oct 2023
|
|
I05-ARPES
|
Federico
Mazzola
,
Stefan
Enzner
,
Philipp
Eck
,
Chiara
Bigi
,
Matteo
Jugovac
,
Iulia
Cojocariu
,
Vitaliy
Feyer
,
Zhixue
Shu
,
Gian Marco
Pierantozzi
,
Alessandro
De Vita
,
Pietro
Carrara
,
Jun
Fujii
,
Phil D. C.
King
,
Giovanni
Vinai
,
Pasquale
Orgiani
,
Cephise
Cacho
,
Matthew D.
Watson
,
Giorgio
Rossi
,
Ivana
Vobornik
,
Tai
Kong
,
Domenico
Di Sante
,
Giorgio
Sangiovanni
,
Giancarlo
Panaccione
Diamond Proposal Number(s):
[30171]
Open Access
Abstract: Engineering surfaces and interfaces of materials promises great potential in the field of heterostructures and quantum matter designers, with the opportunity to drive new many-body phases that are absent in the bulk compounds. Here, we focus on the magnetic Weyl kagome system Co3Sn2S2 and show how for the terminations of different samples the Weyl points connect differently, still preserving the bulk-boundary correspondence. Scanning tunneling microscopy has suggested such a scenario indirectly, and here, we probe the Fermiology of Co3Sn2S2 directly, by linking it to its real space surface distribution. By combining micro-ARPES and first-principles calculations, we measure the energy-momentum spectra and the Fermi surfaces of Co3Sn2S2 for different surface terminations and show the existence of topological features depending on the top-layer electronic environment. Our work helps to define a route for controlling bulk-derived topological properties by means of surface electrostatic potentials, offering a methodology for using Weyl kagome metals in responsive magnetic spintronics.
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Aug 2023
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