I05-ARPES
|
Steef
Smit
,
Kourosh L.
Shirkoohi
,
Saumya
Mukherjee
,
Sergio Barquero
Pierantoni
,
Lewis
Bawden
,
Erik
Van Heumen
,
Arnaud Pastel Nono
Tchiomo
,
Jans
Henke
,
Jasper
Van Wezel
,
Yingkai
Huang
,
Takeshi
Kondo
,
Tsunehiro
Takeuchi
,
Timur K.
Kim
,
Cephise
Cacho
,
Marta
Zonno
,
Sergey
Gorovikov
,
Stephen B.
Dugdale
,
Jorge I.
Facio
,
Mariia
Roslova
,
Laura
Folkers
,
Anna
Isaeva
,
Nigel
Hussey
,
Mark
Golden
Diamond Proposal Number(s):
[19403, 22464]
Open Access
Abstract: High-resolution angle-resolved photoemission spectroscopy (ARPES) performed on the single-layered cuprate (Pb
1
−
y
,Bi
y
)
2
Sr
2
−
x
La
x
CuO
6
+
δ
(Bi2201) reveals a 6-10% difference in the nodal
k
F
vectors along the
Γ
Y and
Γ
X directions. This asymmetry is notably larger than the 2% orthorhombic distortion in the CuO
2
plane lattice constants determined using X-ray crystallography from the same samples. First principles calculations indicate that crystal-field splitting of the bands lies at the root of the
k
F
asymmetry. Concomitantly, the nodal Fermi velocities for the
Γ
Y quadrant exceed those for
Γ
X by 4%. Momentum distribution curve widths for the two nodal dispersions are also anisotropic, showing identical energy dependencies, bar a scaling factor of
∼
1.17
±
0.05
between
Γ
Y and
Γ
X. Consequently, the imaginary part of the self-energy is found to be 10-20% greater along
Γ
Y than
Γ
X. These results emphasize the need to account for Fermi surface asymmetry in the analysis of ARPES data on Bi-based cuprate high temperature superconductors such as Bi2201. To illustrate this point, an orthorhombic tight-binding model (with twofold in-plane symmetry) was used to fit ARPES Fermi surface maps spanning all four quadrants of the Brillouin zone, and the ARPES-derived hole-doping (Luttinger count) was extracted. Comparison of the Luttinger count with one assuming four-fold in-plane symmetry strongly suggests the marked spread in previously-reported Fermi surface areas from ARPES on Bi2201 results from the differences in
k
F
along
Γ
Y and
Γ
X. Using this analysis, a new, linear relationship emerges between the hole-doping derived from ARPES (
p
ARPES
) and that derived using the Presland (
p
Presland
) relation such that
p
ARPES
=
p
Presland
+
0.11
. The implications for this difference between the ARPES- and Presland-derived estimates for
p
are discussed and possible future directions to elucidate the origin of this discrepancy are presented.
|
Jun 2025
|
|
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
|
Diamond Proposal Number(s):
[26631]
Open Access
Abstract: Interaction between electrons and phonons in solids is a key effect defining the physical properties of materials, such as electrical and thermal conductivity. In transition metal dichalcogenides (TMDCs), the electron–phonon coupling results in the formation of polarons, quasiparticles that manifest themselves as discrete features in the electronic spectral function. In this study, we report the formation of polarons at the alkali-dosed MoSe2 surface, where Rashba-like spin splitting of the conduction band states is caused by an inversion-symmetry breaking electric field. In addition, we observed a crossover from phonon-like to plasmon-like polaronic spectral features at the MoSe2 surface with increasing doping. Our findings support the concept of electron–phonon coupling-mediated superconductivity in electron-doped layered TMDC materials, as observed using ionic liquid gating technology. Furthermore, the discovered spin-splitting at the Fermi level could offer crucial experimental validation for theoretical models of Ising-type superconductivity in these materials.
|
Nov 2024
|
|
I05-ARPES
|
Christopher W.
Nicholson
,
Maxime
Rumo
,
Aki
Pulkkinen
,
Geoffroy
Kremer
,
Björn
Salzmann
,
Marie-Laure
Mottas
,
Baptiste
Hildebrand
,
Thomas
Jaouen
,
Timur K.
Kim
,
Saumya
Mukherjee
,
Keyuan
Ma
,
Matthias
Muntwiler
,
Fabian O.
Von Rohr
,
Cephise
Cacho
,
Claude
Monney
Diamond Proposal Number(s):
[24880]
Open Access
Abstract: Strain is ubiquitous in solid-state materials, but despite its fundamental importance and technological relevance, leveraging externally applied strain to gain control over material properties is still in its infancy. In particular, strain control over the diverse phase transitions and topological states in two-dimensional transition metal dichalcogenides remains an open challenge. Here, we exploit uniaxial strain to stabilize the long-debated structural ground state of the 2D topological semimetal IrTe2, which is hidden in unstrained samples. Combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy data reveal the strain-stabilized phase has a 6 × 1 periodicity and undergoes a Lifshitz transition, granting unprecedented spectroscopic access to previously inaccessible type-II topological Dirac states that dominate the modified inter-layer hopping. Supported by density functional theory calculations, we show that strain induces an Ir to Te charge transfer resulting in strongly weakened inter-layer Te bonds and a reshaped energetic landscape favoring the 6×1 phase. Our results highlight the potential to exploit strain-engineered properties in layered materials, particularly in the context of tuning inter-layer behavior.
|
Mar 2021
|
|
I05-ARPES
I06-Nanoscience (XPEEM)
|
Sung Won
Jung
,
Sangyeon
Pak
,
Sanghyo
Lee
,
Sonka
Reimers
,
Saumya
Mukherjee
,
Pavel
Dudin
,
Timur K.
Kim
,
Mattia
Cattelan
,
Neil
Fox
,
Sarnjeet S.
Dhesi
,
Cephise
Cacho
,
Seungnam
Cha
Diamond Proposal Number(s):
[24367, 22901]
Abstract: The recent rise of van der Waals (vdW) crystals has opened new prospects for studying versatile and exotic fundamental physics with future device applications such as twistronics. Even though the recent development on Angle-resolved photoemission spectroscopy (ARPES) with Nano-focusing optics, making clean surfaces and interfaces of chemically transferred crystals have been challenging to obtain high-resolution ARPES spectra. Here, we show that by employing nano-ARPES with submicron sized beam and polystyrene-assisted transfer followed by annealing process in ultra-high vacuum environment, remarkably clear ARPES spectral features such as spin-orbit splitting and band renormalization of CVD-grown, monolayered MoS2 can be measured. Our finding paves a way to exploit chemically transferred crystals for measuring high-resolution ARPES spectra to observe exotic quasi-particles in vdW heterostructures.
|
Jul 2020
|
|
I05-ARPES
|
Saumya
Mukherjee
,
Sung Won
Jung
,
Sophie F.
Weber
,
Chunqiang
Xu
,
Dong
Qian
,
Xiaofeng
Xu
,
Pabitra K.
Biswas
,
Timur K.
Kim
,
Laurent C.
Chapon
,
Matthew D.
Watson
,
Jeffrey B.
Neaton
,
Cephise
Cacho
Diamond Proposal Number(s):
[21591]
Open Access
Abstract: Transition-metal dichalcogenides (TMDs) offer an ideal platform to experimentally realize Dirac fermions. However, typically these exotic quasiparticles are located far away from the Fermi level, limiting the contribution of Dirac-like carriers to the transport properties. Here we show that NiTe2 hosts both bulk Type-II Dirac points and topological surface states. The underlying mechanism is shared with other TMDs and based on the generic topological character of the Te p-orbital manifold. However, unique to NiTe2, a significant contribution of Ni d orbital states shifts the energy of the Type-II Dirac point close to the Fermi level. In addition, one of the topological surface states intersects the Fermi energy and exhibits a remarkably large spin splitting of 120 meV. Our results establish NiTe2 as an exciting candidate for next-generation spintronics devices.
|
Jul 2020
|
|
I05-ARPES
|
Zakariae
El Youbi
,
Sungwon
Jung
,
Saumya
Mukherjee
,
Mauro
Fanciulli
,
Jakub
Schusser
,
Olivier
Heckmann
,
Christine
Richter
,
Jan
Minar
,
Karol
Hricovini
,
Matthew D.
Watson
,
Cephise
Cacho
Diamond Proposal Number(s):
[24921]
Open Access
Abstract: The dosing of layered materials with alkali metals has become a commonly used strategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we perform a systematic study of 1T-
HfTe
2
, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of potassium (K) deposition. From the
k
z
maps, we observe the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wave-function confinement at the topmost layer. In our highest-dosing cases, a monolayerlike electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below
E
F
, we can directly measure a band overlap of
∼
0.2
eV. However, 3D bulklike states still contribute to the spectra even after considerable dosing. Our work provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES.
|
Jun 2020
|
|
I05-ARPES
|
Igor
Markovic
,
Matthew D.
Watson
,
Oliver J.
Clark
,
Federico
Mazzola
,
Edgar
Abarca Morales
,
Chris A.
Hooley
,
Helge
Rosner
,
Craig M.
Polley
,
Thiagarajan
Balasubramanian
,
Saumya
Mukherjee
,
Naoki
Kikugawa
,
Dmitry A.
Sokolov
,
Andrew P.
Mackenzie
,
Phil D. C.
King
Diamond Proposal Number(s):
[21986, 25040]
Abstract: The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure of Ca3Ru2O7
, a 4d
oxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spin-reorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin–orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.
|
Jun 2020
|
|
I05-ARPES
I10-Beamline for Advanced Dichroism - scattering
|
Matthew D.
Watson
,
Igor
Markovic
,
Federico
Mazzola
,
Akhil
Rajan
,
Edgar A.
Morales
,
David
Burn
,
Thorsten
Hesjedal
,
Gerrit
Van Der Laan
,
Saumya
Mukherjee
,
Timur K.
Kim
,
Chiara
Bigi
,
Ivana
Vobornik
,
Monica
Ciomaga Hatnean
,
Geetha
Balakrishnan
,
Philip D. C.
King
Diamond Proposal Number(s):
[21986, 22794, 23785]
Abstract: We investigate the temperature-dependent electronic structure of the van der Waals ferromagnet, CrGeTe3. Using angle-resolved photoemission spectroscopy, we identify atomic- and orbital-specific band shifts upon cooling through TC. From these, together with x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we identify the states created by a covalent bond between the Te 5p and the Cr eg orbitals as the primary driver of the ferromagnetic ordering in this system, while it is the Cr t2g states that carry the majority of the spin moment. The t2g states furthermore exhibit a marked bandwidth increase and a remarkable lifetime enhancement upon entering the ordered phase, pointing to a delicate interplay between localized and itinerant states in this family of layered ferromagnets.
|
May 2020
|
|
|
|
Saumya
Mukherjee
,
Kenta
Shimamoto
,
Yoav William
Windsor
,
Mahesh
Ramakrishnan
,
Sergii
Parchenko
,
Urs
Staub
,
Laurent
Chapon
,
Bachir
Ouladdiaf
,
Marisa
Medarde
,
Tian
Shang
,
Elisabeth A.
Müller
,
Michel
Kenzelmann
,
Thomas
Lippert
,
Christof W.
Schneider
,
Christof
Niedermayer
Abstract: We present a generalized multiferroic phase diagram for orthorhombic RMnO3(R=Gd–Lu) based on coherently grown thin films. The magnetic order was identified by neutron-diffraction and resonant soft x-ray scattering experiments. For large R-ions (R=Gd–Dy), the transition temperature to a long-range ordered antiferromagnetic phase is only weakly dependent on the R-ion radius, but decreases monotonically with decreasing R-ion radius for films with R=Ho–Lu. The antiferromagnetic phase is characterized by an incommensurate order of the Mn3+ spins, which successively locks into a commensurate E-type state. These findings confirm a uniform multiferroic ground state independent of the R ion and are in excellent agreement with predicted properties of strain-induced multiferroicity in these materials. In particular, strong variation of multiferroic properties in these epitaxial films compared to bulk highlights the tuning ability of strain.
|
Nov 2018
|
|
