I05-ARPES
|
Ola Kenji
Forslund
,
Xiaoxiong
Liu
,
Soohyeon
Shin
,
Chun
Lin
,
Masafumi
Horio
,
Qisi
Wang
,
Kevin
Kramer
,
Saumya
Mukherjee
,
Timur
Kim
,
Cephise
Cacho
,
Chennan
Wang
,
Tian
Shang
,
Victor
Ukleev
,
Jonathan S.
White
,
Pascal
Puphal
,
Yasmine
Sassa
,
Ekaterina
Pomjakushina
,
Titus
Neupert
,
Johan
Chang
Diamond Proposal Number(s):
[22091]
Abstract: The anomalous Hall effect (AHE) has emerged as a key indicator of time-reversal symmetry breaking (TRSB) and topological features in electronic band structures. Absent of a magnetic field, the AHE requires spontaneous TRSB but has proven hard to probe due to averaging over domains. The anomalous component of the Hall effect is thus frequently derived from extrapolating the magnetic field dependence of the Hall response. We show that discerning whether the AHE is an intrinsic property of the field-free system becomes intricate in the presence of strong magnetic fluctuations. As a study case, we use the Weyl semimetal PrAlGe, where TRSB can be toggled via a ferromagnetic transition, providing a transparent view of the AHE’s topological origin. Through a combination of thermodynamic, transport, and muon spin relaxation measurements, we contrast the behavior below the ferromagnetic transition temperature to that of strong magnetic fluctuations above. Our results on PrAlGe provide general insights into the interpretation of anomalous Hall signals in systems where TRSB is debated, such as families of kagome metals or certain transition metal dichalcogenides.
|
Mar 2025
|
|
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.
|
Dec 2024
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Jens
Oppliger
,
M. Michael
Denner
,
Julia
Kuespert
,
Ruggero
Frison
,
Qisi
Wang
,
Alexander
Morawietz
,
Oleh
Ivashko
,
Ann-Christin
Dippel
,
Martin
Von Zimmermann
,
Izabela
Bialo
,
Leonardo
Martinelli
,
Benoît
Fauqué
,
Jaewon
Choi
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Niels
Bech Christensen
,
Tohru
Kurosawa
,
Naoki
Momono
,
Migaku
Oda
,
Fabian D.
Natterer
,
Mark H.
Fischer
,
Titus
Neupert
,
Johan
Chang
Diamond Proposal Number(s):
[31819]
Open Access
Abstract: The removal or cancellation of noise has wide-spread applications in imaging and acoustics. In applications in everyday life, such as image restoration, denoising may even include generative aspects, which are unfaithful to the ground truth. For scientific use, however, denoising must reproduce the ground truth accurately. Denoising scientific data is further challenged by unknown noise profiles. In fact, such data will often include noise from multiple distinct sources, which substantially reduces the applicability of simulation-based approaches. Here we show how scientific data can be denoised by using a deep convolutional neural network such that weak signals appear with quantitative accuracy. In particular, we study X-ray diffraction and resonant X-ray scattering data recorded on crystalline materials. We demonstrate that weak signals stemming from charge ordering, insignificant in the noisy data, become visible and accurate in the denoised data. This success is enabled by supervised training of a deep neural network with pairs of measured low- and high-noise data. We additionally show that using artificial noise does not yield such quantitatively accurate results. Our approach thus illustrates a practical strategy for noise filtering that can be applied to challenging acquisition problems.
|
Feb 2024
|
|
I05-ARPES
|
Ilya
Belopolski
,
Tyler A.
Cochran
,
Xiaoxiong
Liu
,
Zi-Jia
Cheng
,
Xian P.
Yang
,
Zurab
Guguchia
,
Stepan S.
Tsirkin
,
Jia-Xin
Yin
,
Praveen
Vir
,
Gohil S.
Thakur
,
Songtian S.
Zhang
,
Junyi
Zhang
,
Konstantine
Kaznatcheev
,
Guangming
Cheng
,
Guoqing
Chang
,
Daniel
Multer
,
Nana
Shumiya
,
Maksim
Litskevich
,
Elio
Vescovo
,
Timur K.
Kim
,
Cephise
Cacho
,
Nan
Yao
,
Claudia
Felser
,
Titus
Neupert
,
M. Zahid
Hasan
Diamond Proposal Number(s):
[17924, 19313]
Abstract: The manipulation of topological states in quantum matter is an essential pursuit of fundamental physics and next-generation quantum technology. Here we report the magnetic manipulation of Weyl fermions in the kagome spin-orbit semimetal
Co
3
Sn
2
S
2
, observed by high-resolution photoemission spectroscopy. We demonstrate the exchange collapse of spin-orbit-gapped ferromagnetic Weyl loops into paramagnetic Dirac loops under suppression of the magnetic order. We further observe that topological Fermi arcs disappear in the paramagnetic phase, suggesting the annihilation of exchange-split Weyl points. Our findings indicate that magnetic exchange collapse naturally drives Weyl fermion annihilation, opening new opportunities for engineering topology under correlated order parameters.
|
Dec 2021
|
|
I05-ARPES
|
Jia-Xin
Yin
,
Wenlong
Ma
,
Tyler A.
Cochran
,
Xitong
Xu
,
Songtian S.
Zhang
,
Hung-Ju
Tien
,
Nana
Shumiya
,
Guangming
Cheng
,
Kun
Jiang
,
Biao
Lian
,
Zhida
Song
,
Guoqing
Chang
,
Ilya
Belopolski
,
Daniel
Multer
,
Maksim
Litskevich
,
Zi-Jia
Cheng
,
Xian P.
Yang
,
Bianca
Swidler
,
Huibin
Zhou
,
Hsin
Lin
,
Titus
Neupert
,
Ziqiang
Wang
,
Nan
Yao
,
Tay-Rong
Chang
,
Shuang
Jia
,
M.
Zahid Hasan
Diamond Proposal Number(s):
[22332]
Abstract: The quantum-level interplay between geometry, topology and correlation is at the forefront of fundamental physics. Kagome magnets are predicted to support intrinsic Chern quantum phases owing to their unusual lattice geometry and breaking of time-reversal symmetry. However, quantum materials hosting ideal spin–orbit-coupled kagome lattices with strong out-of-plane magnetization are lacking. Here, using scanning tunnelling microscopy, we identify a new topological kagome magnet, TbMn6Sn6, that is close to satisfying these criteria. We visualize its effectively defect-free, purely manganese-based ferromagnetic kagome lattice with atomic resolution. Remarkably, its electronic state shows distinct Landau quantization on application of a magnetic field, and the quantized Landau fan structure features spin-polarized Dirac dispersion with a large Chern gap. We further demonstrate the bulk–boundary correspondence between the Chern gap and the topological edge state, as well as the Berry curvature field correspondence of Chern gapped Dirac fermions. Our results point to the realization of a quantum-limit Chern phase in TbMn6Sn6, and may enable the observation of topological quantum phenomena in the RMn6Sn6 (where R is a rare earth element) family with a variety of magnetic structures. Our visualization of the magnetic bulk–boundary–Berry correspondence covering real space and momentum space demonstrates a proof-of-principle method for revealing topological magnets.
|
Jul 2020
|
|
I05-ARPES
|
D.
Sutter
,
M.
Kim
,
C. E.
Matt
,
M.
Horio
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
K.
Hauser
,
Y.
Sassa
,
G.
Gatti
,
M.
Grioni
,
M.
Hoesch
,
T. K.
Kim
,
E.
Rienks
,
N. C.
Plumb
,
M.
Shi
,
T.
Neupert
,
A.
Georges
,
J.
Chang
Diamond Proposal Number(s):
[15296]
Abstract: We present a comprehensive angle-resolved photoemission spectroscopy study of
Ca
1.8
Sr
0.2
RuO
4
. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis and comparison to dynamical mean-field theory calculations. Bands assigned to
d
x
z
,
d
y
z
orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions—associated with a predominantly
d
x
y
band character—are shown to display non-Fermi-liquid behavior. We thus demonstrate that
Ca
1.8
Sr
0.2
RuO
4
is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.
|
Mar 2019
|
|
I05-ARPES
|
C. E.
Matt
,
D.
Sutter
,
A. M.
Cook
,
Y.
Sassa
,
Martin
Mansson
,
O.
Tjernberg
,
L.
Das
,
M.
Horio
,
D.
Destraz
,
C. G.
Fatuzzo
,
K.
Hauser
,
M.
Shi
,
M.
Kobayashi
,
V. N.
Strocov
,
T.
Schmitt
,
P.
Dudin
,
M.
Hoesch
,
S.
Pyon
,
T.
Takayama
,
H.
Takagi
,
O. J.
Lipscombe
,
S. M.
Hayden
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
T.
Neupert
,
J.
Chang
Diamond Proposal Number(s):
[10550]
Open Access
Abstract: The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper–oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (d x 2 −y 2
dx2-y2
and d z 2
dz2
) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.
|
Mar 2018
|
|
I05-ARPES
|
Su-Yang
Xu
,
Nasser
Alidoust
,
Guoqing
Chang
,
Hong
Lu
,
Bahadur
Singh
,
Ilya
Belopolski
,
Daniel S.
Sanchez
,
Xiao
Zhang
,
Guang
Bian
,
Hao
Zheng
,
Marious-Adrian
Husanu
,
Yi
Bian
,
Shin-Ming
Huang
,
Chuang-Han
Hsu
,
Tay-Rong
Chang
,
Horng-Tay
Jeng
,
Arun
Bansil
,
Titus
Neupert
,
Vladimir N.
Strocov
,
Hsin
Lin
,
Shuang
Jia
,
M. Zahid
Hasan
Open Access
Abstract: In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey the celebrated Lorentz symmetry. Their low-energy condensed matter analogs are Weyl semimetals, which are conductors whose electronic excitations mimic the Weyl fermion equation of motion. Although the traditional (type I) emergent Weyl fermions observed in TaAs still approximately respect Lorentz symmetry, recently, the so-called type II Weyl semimetal has been proposed, where the emergent Weyl quasiparticles break the Lorentz symmetry so strongly that they cannot be smoothly connected to Lorentz symmetric Weyl particles. Despite some evidence of nontrivial surface states, the direct observation of the type II bulk Weyl fermions remains elusive. We present the direct observation of the type II Weyl fermions in crystalline solid lanthanum aluminum germanide (LaAlGe) based on our photoemission data alone, without reliance on band structure calculations. Moreover, our systematic data agree with the theoretical calculations, providing further support on our experimental results.
|
Jun 2017
|
|
I05-ARPES
|
D.
Sutter
,
C. G.
Fatuzzo
,
S.
Moser
,
M.
Kim
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
Y.
Sassa
,
F.
Cossalter
,
G.
Gatti
,
M.
Grioni
,
H. M.
Rønnow
,
N. C.
Plumb
,
C. E.
Matt
,
M.
Shi
,
M.
Hoesch
,
T. K.
Kim
,
T.-R.
Chang
,
H.-T.
Jeng
,
C.
Jozwiak
,
A.
Bostwick
,
E.
Rotenberg
,
A.
Georges
,
T.
Neupert
,
J.
Chang
Diamond Proposal Number(s):
[14617, 12926]
Open Access
Abstract: A paradigmatic case of multi-band Mott physics including spin-orbit and Hund’s coupling is realized in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide—using angle-resolved photoemission electron spectroscopy—the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund’s coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund’s coupling that together generate the Mott insulating state of Ca2RuO4.
|
May 2017
|
|
I05-ARPES
|
Cheng-Long
Zhang
,
Su-Yang
Xu
,
Ilya
Belopolski
,
Zhujun
Yuan
,
Ziquan
Lin
,
Bingbing
Tong
,
Guang
Bian
,
Nasser
Alidoust
,
Chi-Cheng
Lee
,
Shin-Ming
Huang
,
Tay-Rong
Chang
,
Guoqing
Chang
,
Chuang-Han
Hsu
,
Horng-Tay
Jeng
,
Madhab
Neupane
,
Daniel
Sanchez
,
Hao
Zheng
,
Junfeng
Wang
,
Hsin
Lin
,
Chi
Zhang
,
Hai-Zhou
Lu
,
Shun-Qing
Shen
,
Titus
Neupert
,
M.
Zahid Hasan
,
Shuang
Jia
Open Access
Abstract: Weyl semimetals provide the realization of Weyl fermions in solid-state physics. Among all the physical phenomena that are enabled by Weyl semimetals, the chiral anomaly is the most unusual one. Here, we report signatures of the chiral anomaly in the magneto-transport measurements on the first Weyl semimetal TaAs. We show negative magnetoresistance under parallel electric and magnetic fields, that is, unlike most metals whose resistivity increases under an external magnetic field, we observe that our high mobility TaAs samples become more conductive as a magnetic field is applied along the direction of the current for certain ranges of the field strength. We present systematically detailed data and careful analyses, which allow us to exclude other possible origins of the observed negative magnetoresistance. Our transport data, corroborated by photoemission measurements, first-principles calculations and theoretical analyses, collectively demonstrate signatures of the Weyl fermion chiral anomaly in the magneto-transport of TaAs.
|
Feb 2016
|
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