I05-ARPES
|
Cong
Li
,
Yang
Wang
,
Jianfeng
Zhang
,
Hongxiong
Liu
,
Wanyu
Chen
,
Guowei
Liu
,
Hanbin
Deng
,
Timur K.
Kim
,
Craig
Polley
,
Balasubramanian
Thiagarajan
,
Jiaxin
Yin
,
Youguo
Shi
,
Tao
Xiang
,
Oscar
Tjernberg
Diamond Proposal Number(s):
[34265, 39652]
Open Access
Abstract: For several decades, it was widely believed that a noninteracting disordered electronic system could only undergo an Anderson metal–insulator transition due to Anderson localization. However, numerous recent theoretical works have predicted the existence of a disorder-driven non-Anderson phase transition that differs from Anderson localization. The frustration lies in the fact that this non-Anderson disorder-driven transition has not yet been experimentally demonstrated in any system. Here, using angle-resolved photoemission spectroscopy, we present a case study of observing the non-Anderson disorder-driven transition by visualizing the electronic structure of the Weyl semimetal NdAlSi on surfaces with varying amounts of disorder. Our observations reveal that strong disorder can effectively suppress all surface states in the Weyl semimetal NdAlSi, including the topological surface Fermi arcs. This disappearance of surface Fermi arcs is associated with the vanishing of the topological invariant, indicating a quantum phase transition from a Weyl semimetal to a diffusive metal. These observations provide direct experimental evidence of the non-Anderson disorder-driven transition occurring in real quantum systems, a finding long anticipated by theoretical physicists.
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Oct 2025
|
|
I05-ARPES
|
Y.
Alexanian
,
A.
De La Torre
,
S.
Mckeown Walker
,
M.
Straub
,
G.
Gatti
,
A.
Hunter
,
S.
Mandloi
,
E.
Cappelli
,
S.
Riccò
,
F. Y.
Bruno
,
M.
Radovic
,
N. C.
Plumb
,
M.
Shi
,
J.
Osiecki
,
C.
Polley
,
T. K.
Kim
,
P.
Dudin
,
M.
Hoesch
,
R. S.
Perry
,
A.
Tamai
,
F.
Baumberger
Diamond Proposal Number(s):
[10348, 12404, 17381]
Open Access
Abstract: The fate of the Fermi surface in bulk electron-doped Sr2IrO4 remains elusive, as does the origin and extension of its pseudogap phase. Here, we use high-resolution angle-resolved photoelectron spectroscopy (ARPES) to investigate the electronic structure of Sr2−xLaxIrO4 up to x = 0.2, a factor of two higher than in previous work. We find that the antinodal pseudogap persists up to the highest doping level, and thus beyond the sharp increase in Hall carrier density to ≃ 1 + x recently observed above x* ≃ 0.161. This suggests that doped iridates host a unique phase of matter in which a large Hall density coexists with an anisotropic pseudogap, breaking up the Fermi surface into disconnected arcs. The temperature boundary of the pseudogap is T* ≃ 200 K for x = 0.2, comparable to cuprates and to the energy scale of short range antiferromagnetic correlations in cuprates and iridates.
|
Oct 2025
|
|
I05-ARPES
|
Cong
Li
,
Mengli
Hu
,
Zhilin
Li
,
Yang
Wang
,
Wanyu
Chen
,
Balasubramanian
Thiagarajan
,
Mats
Leandersson
,
Craig
Polley
,
Timur
Kim
,
Hui
Liu
,
Cosma
Fulga
,
Maia G.
Vergniory
,
Oleg
Janson
,
Oscar
Tjernberg
,
Jeroen
Van Den Brink
Diamond Proposal Number(s):
[36464]
Open Access
Abstract: Altermagnets constitute a novel, third fundamental class of collinear magnetic ordered materials, alongside with ferro- and antiferromagnets. They share with conventional antiferromagnets the feature of a vanishing net magnetization. At the same time they show a spin-splitting of electronic bands, just as in ferromagnets, caused by the atomic exchange interaction. On the other hand, topology has recently revolutionized our understanding of condensed matter physics, introducing new phases of matter classified by intrinsic topological order. Here we connect the worlds of altermagnetism and topology, showing that the electronic structure of the altermagnet CrSb is topological. Using high-resolution angle-resolved photoemission spectroscopy, we observe the large momentum-dependent spin-splitting in CrSb that induces altermagnetic Weyl nodes. We observe the related topological Fermi-arcs, which in electronic structure calculations are spin polarized. This indicates that in altermagnets the large energy scale intrinsic to their spin-splitting creates its own realm of robust electronic topology.
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Jul 2025
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I05-ARPES
|
Cong
Li
,
Yang
Wang
,
Jianfeng
Zhang
,
Guowei
Liu
,
Hongxiong
Liu
,
Wanyu
Chen
,
Hanbin
Deng
,
Wenbo
Ma
,
Craig
Polley
,
Balasubramanian
Thiagarajan
,
Timur K.
Kim
,
Jiaxin
Yin
,
Youguo
Shi
,
Tao
Xiang
,
Oscar
Tjernberg
Diamond Proposal Number(s):
[34265]
Open Access
Abstract: Non-Hermitian physics, studying systems described by non-Hermitian Hamiltonians, reveals unique phenomena not present in Hermitian systems. Unlike Hermitian systems, non-Hermitian systems have complex eigenvalues, making their effects less directly observable. Recently, significant efforts have been devoted to incorporating the non-Hermitian effects into condensed matter physics. However, progress is hindered by the absence of a viable experimental approach. Here, the discovery of the surface-selectively spontaneous reconstructed Weyl semimetal NdAlSi provides a feasible experimental platform for studying non-Hermitian physics. Utilizing angle-resolved photoemission spectroscopy (ARPES) measurements, surface-projected density functional theory (DFT) calculations, and scanning tunneling microscopy (STM) measurements, it is demonstrated that surface reconstruction in NdAlSi alters surface Fermi arc (SFA) connectivity and generates new isolated non-topological SFAs (NTSFAs) by introducing non-Hermitian terms. The surface-selective spontaneous reconstructed Weyl semimetal NdAlSi can be viewed as a Hermitian bulk – non-Hermitian boundary system. The isolated non-topological SFAs on the reconstructed surface act as a loss mechanism and open boundary condition (OBC) for the topological electrons and bulk states, serving as non-Hermitian boundary states. This discovery provides a good experimental platform for exploring new physical phenomena and potential applications based on boundary non-Hermitian effects, extending beyond purely mathematical concepts. Furthermore, it provides important enlightenment for constructing topological photonic crystals with surface reconstruction and studying their topological properties.
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Feb 2025
|
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I05-ARPES
|
Chun
Lin
,
Armando
Consiglio
,
Ola Kenji
Forslund
,
Julia
Kuespert
,
M. Michael
Denner
,
Hechang
Lei
,
Alex
Louat
,
Matthew D.
Watson
,
Timur K.
Kim
,
Cephise
Cacho
,
Dina
Carbone
,
Mats
Leandersson
,
Craig
Polley
,
Thiagarajan
Balasubramanian
,
Domenico
Di Sante
,
Ronny
Thomale
,
Zurab
Guguchia
,
Giorgio
Sangiovanni
,
Titus
Neupert
,
Johan
Chang
Diamond Proposal Number(s):
[30650, 33528]
Open Access
Abstract: Tunable quantum materials hold great potential for applications. Of special interest are materials in which small lattice strain induces giant electronic responses. The kagome compounds AV3Sb5 (A = K, Rb, Cs) provide a testbed for electronic tunable states. In this study, through angle-resolved photoemission spectroscopy, we provide comprehensive spectroscopic measurements of the electronic responses induced by compressive and tensile strains on the charge-density-wave (CDW) and van Hove singularity (VHS) in CsV3Sb5. We observe a tripling of the CDW gap magnitudes with ~ 1% strain. Simultaneously, changes of both energy and mass of the VHS are observed. Combined, this reveals an anticorrelation between the unconventional CDW order parameter and the mass of the VHS, and highlight the role of the latter in the superconducting pairing. The substantial electronic responses uncover a rich strain tunability of the versatile kagome system in studying quantum interplays under lattice variations.
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Dec 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
|
|
I05-ARPES
|
Jonas A.
Krieger
,
Samuel
Stolz
,
Iñigo
Robredo
,
Kaustuv
Manna
,
Emily C.
Mcfarlane
,
Mihir
Date
,
Banabir
Pal
,
Jiabao
Yang
,
Eduardo
B. Guedes
,
J. Hugo
Dil
,
Craig M.
Polley
,
Mats
Leandersson
,
Chandra
Shekhar
,
Horst
Borrmann
,
Qun
Yang
,
Mao
Lin
,
Vladimir N.
Strocov
,
Marco
Caputo
,
Matthew D.
Watson
,
Timur K.
Kim
,
Cephise
Cacho
,
Federico
Mazzola
,
Jun
Fujii
,
Ivana
Vobornik
,
Stuart S. P.
Parkin
,
Barry
Bradlyn
,
Claudia
Felser
,
Maia G.
Vergniory
,
Niels B. M.
Schröter
Diamond Proposal Number(s):
[20617, 26098, 24703]
Open Access
Abstract: Spin-orbit coupling in noncentrosymmetric crystals leads to spin-momentum locking – a directional relationship between an electron’s spin angular momentum and its linear momentum. Isotropic orthogonal Rashba spin-momentum locking has been studied for decades, while its counterpart, isotropic parallel Weyl spin-momentum locking has remained elusive in experiments. Theory predicts that Weyl spin-momentum locking can only be realized in structurally chiral cubic crystals in the vicinity of Kramers-Weyl or multifold fermions. Here, we use spin- and angle-resolved photoemission spectroscopy to evidence Weyl spin-momentum locking of multifold fermions in the chiral topological semimetal PtGa. We find that the electron spin of the Fermi arc surface states is orthogonal to their Fermi surface contour for momenta close to the projection of the bulk multifold fermion at the Γ point, which is consistent with Weyl spin-momentum locking of the latter. The direct measurement of the bulk spin texture of the multifold fermion at the R point also displays Weyl spin-momentum locking. The discovery of Weyl spin-momentum locking may lead to energy-efficient memory devices and Josephson diodes based on chiral topological semimetals.
|
May 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
|
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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
|
|
I09-Surface and Interface Structural Analysis
|
Philip
Schädlich
,
Chitran
Ghosal
,
Monja
Stettner
,
Bharti
Matta
,
Susanne
Wolff
,
Franziska
Schölzel
,
Peter
Richter
,
Mark
Hutter
,
Anja
Haags
,
Sabine
Wenzel
,
Zamin
Mamiyev
,
Julian
Koch
,
Serguei
Soubatch
,
Philipp
Rosenzweig
,
Craig
Polley
,
Frank Stefan
Tautz
,
Christian
Kumpf
,
Kathrin
Küster
,
Ulrich
Starke
,
Thomas
Seyller
,
Francois C.
Bocquet
,
Christoph
Tegenkamp
Diamond Proposal Number(s):
[26188, 33755]
Open Access
Abstract: The synthesis of new graphene-based quantum materials by intercalation is an auspicious approach. However, an accompanying proximity coupling depends crucially on the structural details of the new heterostructure. It is studied in detail the Pb monolayer structure after intercalation into the graphene buffer layer on the SiC(0001) interface by means of photoelectron spectroscopy, x-ray standing waves, and scanning tunneling microscopy. A coherent fraction close to unity proves the formation of a flat Pb monolayer on the SiC surface. An interlayer distance of 3.67 Å to the suspended graphene underlines the formation of a truly van der Waals heterostructure. The 2D Pb layer reveals a quasi ten-fold periodicity due to the formation of a grain boundary network, ensuring the saturation of the Si surface bonds. Moreover, the densely-packed Pb layer also efficiently minimizes the doping influence by the SiC substrate, both from the surface dangling bonds and the SiC surface polarization, giving rise to charge-neutral monolayer graphene. The observation of a long-ranged (
) reconstruction on the graphene lattice at tunneling conditions close to Fermi energy is most likely a result of a nesting condition to be perfectly fulfilled.
|
Jul 2023
|
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