I05-ARPES
|
Niels B. M.
Schroeter
,
Samuel
Stolz
,
Kaustuv
Manna
,
Fernando
De Juan
,
Maia G.
Vergniory
,
Jonas A.
Krieger
,
Ding
Pei
,
Thorsten
Schmitt
,
Pavel
Dudin
,
Timur K.
Kim
,
Cephise
Cacho
,
Barry
Bradlyn
,
Horst
Borrmann
,
Marcus
Schmidt
,
Roland
Widmer
,
Vladimir N.
Strocov
,
Claudia
Felser
Diamond Proposal Number(s):
[24703, 20617]
Open Access
Abstract: Topological semimetals feature protected nodal band degeneracies characterized by a topological invariant known as the Chern number (C). Nodal band crossings with linear dispersion are expected to have at most |C|=4
|
C
|
=
4
, which sets an upper limit to the magnitude of many topological phenomena in these materials. Here, we show that the chiral crystal palladium gallium (PdGa) displays multifold band crossings, which are connected by exactly four surface Fermi arcs, thus proving that they carry the maximal Chern number magnitude of 4. By comparing two enantiomers, we observe a reversal of their Fermi-arc velocities, which demonstrates that the handedness of chiral crystals can be used to control the sign of their Chern numbers.
|
Jul 2020
|
|
I05-ARPES
|
Paolo
Sessi
,
Feng-ren
Fan
,
Felix
Küster
,
Kaustuv
Manna
,
Niels B. M.
Schroeter
,
Jing-rong
Ji
,
Samuel
Stolz
,
Jonas A.
Krieger
,
Ding
Pei
,
Timur K.
Kim
,
Pavel
Dudin
,
Cephise
Cacho
,
Remo N.
Widmer
,
Horst
Borrmann
,
Wujun
Shi
,
Kai
Chang
,
Yan
Sun
,
Claudia
Felser
,
Stuart S. P.
Parkin
Diamond Proposal Number(s):
[2470, 20617]
Open Access
Abstract: It has recently been proposed that combining chirality with topological band theory results in a totally new class of fermions. Understanding how these unconventional quasiparticles propagate and interact remains largely unexplored so far. Here, we use scanning tunneling microscopy to visualize the electronic properties of the prototypical chiral topological semimetal PdGa. We reveal chiral quantum interference patterns of opposite spiraling directions for the two PdGa enantiomers, a direct manifestation of the change of sign of their Chern number. Additionally, we demonstrate that PdGa remains topologically non-trivial over a large energy range, experimentally detecting Fermi arcs in an energy window of more than 1.6 eV that is symmetrically centered around the Fermi level. These results are a consequence of the deep connection between chirality in real and reciprocal space in this class of materials, and, thereby, establish PdGa as an ideal topological chiral semimetal.
|
Jul 2020
|
|
I05-ARPES
|
H.
Liu
,
Y.
Cao
,
Y.
Xu
,
D. J.
Gawryluk
,
E.
Pomjakushina
,
S.-y.
Gao
,
P.
Dudin
,
M.
Shi
,
L.
Yan
,
Y.-f.
Yang
,
H.
Ding
Diamond Proposal Number(s):
[22059]
Abstract: We report angle-resolved photoemission spectroscopy and first-principles numerical calculations for the band-structure evolution of the
3
d
heavy-fermion compound
CaC
u
3
R
u
4
O
12
. Below
T
∼
200
K, we observed an emergent hybridization gap between the Cu 3d-electron-like band and the Ru 4d-hole-like band and the resulting flat band features near the Fermi level centered around the Brillouin-zone corner. Our results confirm the non-Kondo nature of the
CaC
u
3
R
u
4
O
12
, in which the
Cu
3
d
xy
electrons are less correlated and not in the Kondo limit. Comparison between theory and experiment also suggests that other mechanisms may be needed to give a full quantitative explanation of the peculiar properties in this material.
|
Jul 2020
|
|
I05-ARPES
I06-Nanoscience
|
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
|
X.
Lou
,
H. C.
Xu
,
C. H. P.
Wen
,
T. L.
Yu
,
W. Z.
Wei
,
Q.
Yao
,
Y. H.
Song
,
E.
Emmanouilidou
,
B.
Shen
,
N.
Ni
,
P.
Dudin
,
Y. B.
Huang
,
J.
Denlinger
,
R.
Sutarto
,
W.
Li
,
R.
Peng
,
D. L.
Feng
Diamond Proposal Number(s):
[20697]
Abstract: BaAg
2
As
2
, a sibling compound of
BaFe
2
As
2
with a nonmagnetic phase transition around 150 K, is studied by the comprehensive measurements of angle-resolved photoemission spectroscopy, synchrotron x-ray diffraction, and resonant soft x-ray scattering. The Fermi surfaces and electronic structure of
BaAg
2
As
2
are revealed, with strong
k
z
dispersion, consistent with the strongly contracted
c
/
a
ratio in
BaAg
2
As
2
. Across the phase transition, splitting of [101] Bragg peak is observed, showing a structural distortion with the in-plane distortion magnitude
δ
=
|
a
−
b
|
/
(
a
+
b
)
=
0.0052
. Although the nesting condition is satisfied in some parallel Fermi-surface sectors, there is no signature of charge density wave order at the nesting wave vector. Moreover, neither a charge density wave gap opening nor band reconstruction are observed across the phase transition. Instead, an enhancement on the spectral weight of dispersive bands is observed across the structural phase transition, which can explain the sharp drop of resistivity below the phase transition temperature. These studies could enrich the understanding of the variable and common features of the structural transition in transition metal pnictide layered materials.
|
Feb 2020
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[1914]
Abstract: The energy scales in rare-earth-based heavy-fermion compounds are relatively small, which can be easily tuned by applying pressure, magnetic field, or chemical doping. By substituting Yb for Ce on the rare-earth site, the ground state of superconductivity can be smoothly suppressed without the appearance of an apparent quantum critical point, and a number of remarkable phenomena have been observed. The slight changes in the electronic structure are supposed to dominate the underlying physics in these compounds. In the present study, we provide an electronic structure study of
Ce
0.85
Yb
0.15
CoIn
5
with a superconducting state but suppressed transition temperature by angle-resolved photoemission spectroscopy, and the results are compared with
CeCoIn
5
. We find that the
f
electrons in
Ce
0.85
Yb
0.15
CoIn
5
are itinerant, forming the weakly dispersive hybridized band at low temperature. More interestingly, the hybridization strength between the
f
electrons and conduction electrons in
Ce
0.85
Yb
0.15
CoIn
5
is comparable with
CeCoIn
5
. Further temperature-dependent measurements provide direct evidence of the localized-to-itinerant crossover behavior of the
4
f
electrons in this compound.
|
Jan 2020
|
|
I05-ARPES
|
Veronika
Sunko
,
Edgar
Abarca Morales
,
Igor
Markovic
,
Mark E.
Barber
,
Dijana
Milosavljević
,
Federico
Mazzola
,
Dmitry A.
Sokolov
,
Naoki
Kikugawa
,
Cephise
Cacho
,
Pavel
Dudin
,
Helge
Rosner
,
Clifford
Hicks
,
Philip D. C.
King
,
Andrew P.
Mackenzie
Diamond Proposal Number(s):
[20427]
Open Access
Abstract: Pressure represents a clean tuning parameter for traversing the complex phase diagrams of interacting electron systems, and as such has proved of key importance in the study of quantum materials. Application of controlled uniaxial pressure has recently been shown to more than double the transition temperature of the unconventional superconductor Sr2RuO4, leading to a pronounced peak in Tc versus strain whose origin is still under active debate. Here we develop a simple and compact method to passively apply large uniaxial pressures in restricted sample environments, and utilise this to study the evolution of the electronic structure of Sr2RuO4 using angle-resolved photoemission. We directly visualise how uniaxial stress drives a Lifshitz transition of the γ-band Fermi surface, pointing to the key role of strain-tuning its associated van Hove singularity to the Fermi level in mediating the peak in Tc. Our measurements provide stringent constraints for theoretical models of the strain-tuned electronic structure evolution of Sr2RuO4. More generally, our experimental approach opens the door to future studies of strain-tuned phase transitions not only using photoemission but also other experimental techniques where large pressure cells or piezoelectric-based devices may be difficult to implement.
|
Dec 2019
|
|
I05-ARPES
|
D. F.
Liu
,
A. J.
Liang
,
E. K.
Liu
,
Q. N.
Xu
,
Y. W.
Li
,
C.
Chen
,
D.
Pei
,
W. J.
Shi
,
S. K.
Mo
,
P.
Dudin
,
T.
Kim
,
C.
Cacho
,
G.
Li
,
Y.
Sun
,
L. X.
Yang
,
Z. K.
Liu
,
S. S. P.
Parkin
,
C.
Felser
,
Y. L.
Chen
Diamond Proposal Number(s):
[22367, 20683]
Abstract: Weyl semimetals are crystalline solids that host emergent relativistic Weyl fermions and have characteristic surface Fermi-arcs in their electronic structure. Weyl semimetals with broken time reversal symmetry are difficult to identify unambiguously. In this work, using angle-resolved photoemission spectroscopy, we visualized the electronic structure of the ferromagnetic crystal Co3Sn2S2 and discovered its characteristic surface Fermi-arcs and linear bulk band dispersions across the Weyl points. These results establish Co3Sn2S2 as a magnetic Weyl semimetal that may serve as a platform for realizing phenomena such as chiral magnetic effects, unusually large anomalous Hall effect and quantum anomalous Hall effect.
|
Sep 2019
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[15074, 19041]
Open Access
Abstract: A fundamental part of the puzzle of unconventional superconductivity in the Fe-based superconductors is the understanding of the magnetic and nematic instabilities of the parent compounds. The issues of which of these can be considered the leading instability, and whether weak- or strong-coupling approaches are applicable, are both critical and contentious. Here, we revisit the electronic structure of BaFe2As2 using angle-resolved photoemission spectroscopy (ARPES). Our high-resolution measurements of samples “detwinned” by the application of a mechanical strain reveal a highly anisotropic 3D Fermi surface in the low-temperature antiferromagnetic phase. By comparison of the observed dispersions with ab initio calculations, we argue that overall it is magnetism, rather than orbital/nematic ordering, which is the dominant effect, reconstructing the electronic structure across the Fe 3d bandwidth. Finally, using a state-of-the-art nano-ARPES system, we reveal how the observed electronic dispersions vary in real space as the beam spot crosses domain boundaries in an unstrained sample, enabling the measurement of ARPES data from within single antiferromagnetic domains, and showing consistence with the effective mono-domain samples obtained by detwinning.
|
Jul 2019
|
|
I05-ARPES
|
Soeren
Ulstrup
,
Cristina E.
Giusca
,
Jill A.
Miwa
,
Charlotte
Sanders
,
Alex
Browning
,
Pavel
Dudin
,
Cephise
Cacho
,
Olga
Kazakova
,
D. Kurt
Gaskill
,
Rachael L.
Myers-ward
,
Tianyi
Zhang
,
Mauricio
Terrones
,
Philip
Hofmann
Diamond Proposal Number(s):
[19260]
Open Access
Abstract: Control of atomic-scale interfaces between materials with distinct electronic structures is crucial for the design and fabrication of most electronic devices. In the case of two-dimensional materials, disparate electronic structures can be realized even within a single uniform sheet, merely by locally applying different vertical gate voltages. Here, we utilize the inherently nano-structured single layer and bilayer graphene on silicon carbide to investigate lateral electronic structure variations in an adjacent single layer of tungsten disulfide (WS2). The electronic band alignments are mapped in energy and momentum space using angle-resolved photoemission with a spatial resolution on the order of 500 nm (nanoARPES). We find that the WS2 band offsets track the work function of the underlying single layer and bilayer graphene, and we relate such changes to observed lateral patterns of exciton and trion luminescence from WS2.
|
Jul 2019
|
|
