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):
[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.
|
Aug 2025
|
|
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.
|
Sep 2024
|
|
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.
|
Jul 2024
|
|
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.
|
Apr 2024
|
|
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
|
Edgar
Abarca Morales
,
Gesa-R.
Siemann
,
Andela
Zivanovic
,
Philip A. E.
Murgatroyd
,
Igor
Markovic
,
Brendan
Edwards
,
Chris A.
Hooley
,
Dmitry A.
Sokolov
,
Naoki
Kikugawa
,
Cephise
Cacho
,
Matthew D.
Watson
,
Timur K.
Kim
,
Clifford W.
Hicks
,
Andrew P.
Mackenzie
,
Phil D. C.
King
Diamond Proposal Number(s):
[27471, 28412]
Abstract: We report the evolution of the electronic structure at the surface of the layered perovskite
Sr
2
RuO
4
under large in-plane uniaxial compression, leading to anisotropic
B
1
g
strains of
ϵ
x
x
−
ϵ
y
y
=
−
0.9
±
0.1
%
. From angle-resolved photoemission, we show how this drives a sequence of Lifshitz transitions, reshaping the low-energy electronic structure and the rich spectrum of van Hove singularities that the surface layer of
Sr
2
RuO
4
hosts. From comparison to tight-binding modeling, we find that the strain is accommodated predominantly by bond-length changes rather than modifications of octahedral tilt and rotation angles. Our study sheds new light on the nature of structural distortions at oxide surfaces, and how targeted control of these can be used to tune density of state singularities to the Fermi level, in turn paving the way to the possible realization of rich collective states at the
Sr
2
RuO
4
surface.
|
Feb 2023
|
|
I09-Surface and Interface Structural Analysis
|
Matthew J.
Smiles
,
Jonathan M.
Skelton
,
Huw
Shiel
,
Leanne A. H.
Jones
,
Jack E. N.
Swallow
,
Holly J.
Edwards
,
Thomas
Featherstone
,
Philip A. E.
Murgatroyd
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Vinod R.
Dhanak
,
Tim D.
Veal
Diamond Proposal Number(s):
[21431, 23160]
Open Access
Abstract: Germanium sulfide and germanium selenide bulk crystals were prepared using a melt growth technique. X-ray photoemission spectroscopy (XPS) was used to determine ionisation potentials of 5.74 and 5.48 eV for GeS and GeSe respectively. These values were used with the previously-measured band gaps to establish the natural band alignments with potential window layers for solar cells and to identify CdS and TiO2 as sensible choices. The ionisation potential of GeS is found to be smaller than in comparable materials. Using XPS and hard x-ray photoemission (HAXPES) measurements in conjunction with density-functional theory calculations, we demonstrate that stereochemically active Ge 4s lone pairs are present at the valence-band maxima. Our work thus provides direct evidence for active lone pairs in GeS and GeSe, with important implications for the applications of these and related materials, such as Ge-based perovskites.
|
Sep 2021
|
|
I09-Surface and Interface Structural Analysis
|
Jack E. N.
Swallow
,
Christian
Vorwerk
,
Piero
Mazzolini
,
Patrick
Vogt
,
Oliver
Bierwagen
,
Alexander
Karg
,
Martin
Eickhoff
,
Jörg
Schörmann
,
Markus R.
Wagner
,
Joseph William
Roberts
,
Paul R.
Chalker
,
Matthew J.
Smiles
,
Philip
Murgatroyd
,
Sara
Mohamed
,
Zachary W.
Lebens-Higgins
,
Louis F. J.
Piper
,
Leanne A. H.
Jones
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Joel B.
Varley
,
Juergen
Furthmüller
,
Claudia
Draxl
,
Tim D.
Veal
,
Anna
Regoutz
Diamond Proposal Number(s):
[21430, 24670]
Abstract: The search for new wide band gap materials is intensifying to satisfy the need for more advanced and energy effcient power electronic devices. Ga2O3 has emerged as an alternative to SiC and GaN, sparking a renewed interest in its fundamental properties beyond the main β-phase. Here, three polymorphs of Ga2O3, α, β, and ε, are investigated using X-ray diffraction, X-ray photoelectron and absorption spectroscopy, and ab initio theoretical approaches to gain insights into their structure - electronic structure relationships. Valence and conduction electronic structure as well as semi-core and core states are probed, providing a complete picture of the influence of local coordination environments on the electronic structure. State-of-the-art electronic structure theory, including all-electron density functional theory and many-body perturbation theory, provide detailed understanding of the spectroscopic results. The calculated spectra provide very accurate descriptions of all experimental spectra and additionally illuminate the origin of observed spectral features. This work provides a strong basis for the exploration of the Ga2O3 polymorphs as materials at the heart of future electronic device generations.
|
Sep 2020
|
|
I09-Surface and Interface Structural Analysis
|
Leanne A. H.
Jones
,
Wojciech M.
Linhart
,
Nicole
Fleck
,
Jack E. N.
Swallow
,
Philip A. E.
Murgatroyd
,
Huw
Shiel
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Laurence J.
Hardwick
,
Jonathan
Alaria
,
Frank
Jaeckel
,
Robert
Kudrawiec
,
Lee A.
Burton
,
Aron
Walsh
,
Jonathan M.
Skelton
,
Tim D.
Veal
,
Vin R.
Dhanak
Diamond Proposal Number(s):
[21431]
Open Access
Abstract: The effects of Sn
5
s
lone pairs in the different phases of Sn sulphides are investigated with photoreflectance, hard x-ray photoemission spectroscopy (HAXPES), and density functional theory. Due to the photon energy-dependence of the photoionization cross sections, at high photon energy, the Sn
5
s
orbital photoemission has increased intensity relative to that from other orbitals. This enables the Sn
5
s
state contribution at the top of the valence band in the different Sn-sulphides, SnS,
Sn
2
S
3
, and
SnS
2
, to be clearly identified. SnS and
Sn
2
S
3
contain Sn(II) cations and the corresponding Sn
5
s
lone pairs are at the valence band maximum (VBM), leading to
∼
1.0
–1.3 eV band gaps and relatively high VBM on an absolute energy scale. In contrast,
SnS
2
only contains Sn(IV) cations, no filled lone pairs, and therefore has a
∼
2.3
eV room-temperature band gap and much lower VBM compared with SnS and
Sn
2
S
3
. The direct band gaps of these materials at 20 K are found using photoreflectance to be 1.36, 1.08, and 2.47 eV for SnS,
Sn
2
S
3
, and
SnS
2
, respectively, which further highlights the effect of having the lone-pair states at the VBM. As well as elucidating the role of the Sn
5
s
lone pairs in determining the band gaps and band alignments of the family of Sn-sulphide compounds, this also highlights how HAXPES is an ideal method for probing the lone-pair contribution to the density of states of the emerging class of materials with
n
s
2
configuration.
|
Jul 2020
|
|
