I05-ARPES
|
Simone M.
Kevy
,
Henriette E.
Lund
,
Laura
Wollesen
,
Kirstine J.
Dalgaard
,
Yu-te
Hsu
,
Steffen
Wiedmann
,
Marco
Bianchi
,
Ann Julie Utne
Holt
,
Davide
Curcio
,
Deepnarayan
Biswas
,
Alfred J. H.
Jones
,
Klara
Volckaert
,
Cephise
Cacho
,
Pavel
Dudin
,
Philip
Hofmann
,
Martin
Bremholm
Diamond Proposal Number(s):
[20218]
Abstract: The crystal structure, electronic structure, and transport properties of crystals with the nominal composition
Nb
0.25
Bi
2
Se
3
are investigated. X-ray diffraction reveals that the as-grown crystals display phase segregation and contain major contributions of BiSe and the superconducting misfit layer compound
(
Bi
Se
)
1.1
Nb
Se
2
. The inhomogeneous character of the samples is also reflected in the electronic structure and transport properties of different single crystals. Angle-resolved photoemission spectroscopy (ARPES) reveals an electronic structure that resembles poor-quality
Bi
2
Se
3
with an ill-defined topological surface state. High-quality topological surface states are instead observed when using a highly focused beam size, i.e., nanoARPES. While the superconducting transition temperature is found to vary between 2.5 and 3.5 K, the majority of the bulk single crystals does not exhibit a zero-resistance state suggesting filamentary superconductivity in the materials. Susceptibility measurements of the system together with the temperature dependence of the coherence length extracted from the upper critical field are consistent with conventional BCS superconductivity of a type II superconductor.
|
Feb 2021
|
|
I05-ARPES
|
Niels B. M.
Schroeter
,
Iñigo
Robredo
,
Sebastian
Klemenz
,
Robert J.
Kirby
,
Jonas A.
Krieger
,
Ding
Pei
,
Tianlun
Yu
,
Samuel
Stolz
,
Thorsten
Schmitt
,
Pavel
Dudin
,
Timur K.
Kim
,
Cephise
Cacho
,
Andreas
Schnyder
,
Aitor
Bergara
,
Vladimir N.
Strocov
,
Fernando
De Juan
,
Maia G.
Vergniory
,
Leslie M.
Schoop
Diamond Proposal Number(s):
[26098, 20617]
Open Access
Abstract: Magnetic Weyl semimetals are a newly discovered class of topological materials that may serve as a platform for exotic phenomena, such as axion insulators or the quantum anomalous Hall effect. Here, we use angle-resolved photoelectron spectroscopy and ab initio calculations to discover Weyl cones in CoS2, a ferromagnet with pyrite structure that has been long studied as a candidate for half-metallicity, which makes it an attractive material for spintronic devices. We directly observe the topological Fermi arc surface states that link the Weyl nodes, which will influence the performance of CoS2 as a spin injector by modifying its spin polarization at interfaces. In addition, we directly observe a minority-spin bulk electron pocket in the corner of the Brillouin zone, which proves that CoS2 cannot be a true half-metal.
|
Dec 2020
|
|
I05-ARPES
|
Davide
Curcio
,
Alfred J. H.
Jones
,
Ryan
Muzzio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Charlotte E.
Sanders
,
Pavel
Dudin
,
Cephise
Cacho
,
Simranjeet
Singh
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Jill A.
Miwa
,
Jyoti
Katoch
,
Soeren
Ulstrup
,
Philip
Hofmann
Diamond Proposal Number(s):
[20218]
Abstract: The presence of an electrical transport current in a material is one of the simplest and most important realizations of nonequilibrium physics. The current density breaks the crystalline symmetry and can give rise to dramatic phenomena, such as sliding charge density waves, insulator-to-metal transitions, or gap openings in topologically protected states. Almost nothing is known about how a current influences the electron spectral function, which characterizes most of the solid’s electronic, optical, and chemical properties. Here we show that angle-resolved photoemission spectroscopy with a nanoscale light spot provides not only a wealth of information on local equilibrium properties, but also opens the possibility to access the local nonequilibrium spectral function in the presence of a transport current. Unifying spectroscopic and transport measurements in this way allows simultaneous noninvasive local measurements of the composition, structure, many-body effects, and carrier mobility in the presence of high current densities. In the particular case of our graphene-based device, we are able to correlate the presence of structural defects with locally reduced carrier lifetimes in the spectral function and a locally reduced mobility with a spatial resolution of 500 nm.
|
Dec 2020
|
|
I05-ARPES
|
Georg
Poelchen
,
Susanne
Schulz
,
Max
Mende
,
Monika
Guttler
,
Alexander
Generalov
,
Alexander V.
Fedorov
,
Nubia
Caroca-canales
,
Christoph
Geibel
,
Kristin
Kliemt
,
Cornelius
Krellner
,
Steffen
Danzenbacher
,
Dmitry Y.
Usachov
,
Pavel
Dudin
,
Victor N.
Antonov
,
James W.
Allen
,
Clemens
Laubschat
,
Kurt
Kummer
,
Yuri
Kucherenko
,
Denis V.
Vyalikh
Diamond Proposal Number(s):
[17761, 24339]
Open Access
Abstract: Ultra-violet angle-resolved photoemission spectroscopy (UV-ARPES) was used to explore the temperature dependence of the Ce-4f spectral responses for surface and bulk in the antiferromagnetic Kondo lattice CeRh2Si2. Spectra were taken from Ce- and Si-terminated surfaces in a wide temperature range, and reveal characteristic 4f patterns for weakly (surface) and strongly (bulk) hybridized Ce, respectively. The temperature dependence of the Fermi level peak differs strongly for both cases implying that the effective Kondo temperature at the surface and bulk can be rather distinct. The greatly reduced crystal–electric-field (CEF) splitting at the surface gives reason to believe that the surface may exhibit a larger effective Kondo temperature because of a higher local-moment effective degeneracy. Further, the hybridization processes could strongly affect the 4f peak intensity at the Fermi level. We derived the k-resolved dispersion of the Kondo peak which is also found to be distinct due to different sets of itinerant bands to which the 4f states of surface and bulk Ce are coupled. Overall our study brings into reach the ultimate goal of quantitatively testing many-body theories that link spectroscopy and transport properties, for both the bulk and the surface, separately. It also allows for a direct insight into the broader problem of Kondo lattices with two different local-moment sublattices, providing some understanding of why the cross-talking between the two Kondo effects is weak.
|
Oct 2020
|
|
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
|
|
