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
|
Wujun
Shi
,
Benjamin J.
Wieder
,
Holger L.
Meyerheim
,
Yan
Sun
,
Yang
Zhang
,
Yiwei
Li
,
Lei
Shen
,
Yanpeng
Qi
,
Lexian
Yang
,
Jagannath
Jena
,
Peter
Werner
,
Klaus
Koepernik
,
Stuart
Parkin
,
Yulin
Chen
,
Claudia
Felser
,
B. Andrei
Bernevig
,
Zhijun
Wang
Abstract: Topological physics and strong electron–electron correlations in quantum materials are typically studied independently. However, there have been rapid recent developments in quantum materials in which topological phase transitions emerge when the single-particle band structure is modified by strong interactions. Here we demonstrate that the room-temperature phase of (TaSe4)2I is a Weyl semimetal with 24 pairs of Weyl nodes. Owing to its quasi-one-dimensional structure, (TaSe4)2I also hosts an established charge-density wave instability just below room temperature. We show that the charge-density wave in (TaSe4)2I couples the bulk Weyl points and opens a bandgap. The correlation-driven topological phase transition in (TaSe4)2I provides a route towards observing condensed-matter realizations of axion electrodynamics in the gapped regime, topological chiral response effects in the semimetallic phase, and represents an avenue for exploring the interplay of correlations and topology in a solid-state material.
|
Jan 2021
|
|
I05-ARPES
|
Ryo
Noguchi
,
Masaru
Kobayashi
,
Zhanzhi
Jiang
,
Kenta
Kuroda
,
Takanari
Takahashi
,
Zifan
Xu
,
Daehun
Lee
,
Motoaki
Hirayama
,
Masayuki
Ochi
,
Tetsuroh
Shirasawa
,
Peng
Zhang
,
Chun
Lin
,
Cédric
Bareille
,
Shunsuke
Sakuragi
,
Hiroaki
Tanaka
,
So
Kunisada
,
Kifu
Kurokawa
,
Koichiro
Yaji
,
Ayumi
Harasawa
,
Viktor
Kandyba
,
Alessio
Giampietri
,
Alexei
Barinov
,
Timur K.
Kim
,
Cephise
Cacho
,
Makoto
Hashimoto
,
Donghui
Lu
,
Shik
Shin
,
Ryotaro
Arita
,
Keji
Lai
,
Takao
Sasagawa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[20445]
Abstract: Low-dimensional van der Waals materials have been extensively studied as a platform with which to generate quantum effects. Advancing this research, topological quantum materials with van der Waals structures are currently receiving a great deal of attention. Here, we use the concept of designing topological materials by the van der Waals stacking of quantum spin Hall insulators. Most interestingly, we find that a slight shift of inversion centre in the unit cell caused by a modification of stacking induces a transition from a trivial insulator to a higher-order topological insulator. Based on this, we present angle-resolved photoemission spectroscopy results showing that the real three-dimensional material Bi4Br4 is a higher-order topological insulator. Our demonstration that various topological states can be selected by stacking chains differently, combined with the advantages of van der Waals materials, offers a playground for engineering topologically non-trivial edge states towards future spintronics applications.
|
Jan 2021
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[13398, 5282]
Open Access
Abstract: Discrepancies in the low-energy quasiparticle dispersion extracted from angle-resolved photoemission, scanning tunneling spectroscopy, and quantum oscillation data are common and have long haunted the field of quantum matter physics. Here, we directly test the consistency of results from these three techniques by comparing data from the correlated metal Sr2RhO4. Using established schemes for the interpretation of the experimental data, we find good agreement for the Fermi surface topography and carrier effective masses. Hence, the apparent absence of such an agreement in other quantum materials, including the cuprates, suggests that the electronic states in these materials are of different, non-Fermi liquid-like nature. Finally, we discuss the potential and challenges in extracting carrier lifetimes from photoemission and quasiparticle interference data.
|
Dec 2020
|
|
I05-ARPES
|
L.
Kang
,
L.
Shen
,
Y. J.
Chen
,
S. C.
Sun
,
X.
Gu
,
H. J.
Zheng
,
Z. K.
Liu
,
J. X.
Wu
,
H. L.
Peng
,
F. W.
Zheng
,
P.
Zhang
,
L. X.
Yang
,
Y. L.
Chen
Diamond Proposal Number(s):
[23648, 24827]
Abstract: Using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structure of β-InSe, a van der Waals semiconductor with a direct band gap. Our measurements show a good agreement with ab initio calculations, which helps reveal the important impact of spin-orbit coupling on the electronic structure of β-InSe. Using surface potassium doping, we tune the chemical potential of the system and observe the unoccupied conduction band. The direct band gap is determined to be about 1.3 eV. Interestingly, we observe a global band shift when the sample is illuminated by a continuous-wave laser at 632.8 nm, which can be understood by an efficient surface photovoltaic effect. The surface photovoltaic can be tuned by in situ surface potassium doping. Our results not only provide important insights into the semiconducting properties of InSe, but also suggest a feasible method to study and engineer the surface photovoltaic effect in InSe-based devices.
|
Dec 2020
|
|
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
|
Diamond Proposal Number(s):
[5008, 9689]
Abstract: The role of nematic order for the mechanism of high-temperature superconductivity is highly debated. In most iron-based superconductors (IBSs) the tetragonal symmetry is broken already in the normal state, resulting in orthorhombic lattice distortions, static stripe magnetic order, or both. Superconductivity then emerges, at least at weak doping, already from the state with broken
C
4
rotational symmetry. One of the few stoichiometric IBSs, lithium iron arsenide superconducts below 18 K and does not display either structural or magnetic transition in the normal state. Here we demonstrate, using angle-resolved photoemission spectroscopy, that even the superconducting state in LiFeAs is also a nematic one. We observe spontaneous breaking of the rotational symmetry in the gap amplitude on all Fermi surfaces, as well as unidirectional distortion of the Fermi pockets. Remarkably, these deformations are hardly visible above superconducting
T
c
. Our results demonstrate the realization of the phenomenon of superconductivity-induced nematicity in IBSs, emphasizing the intimate relation between them. We suggest a theoretical explanation based on the emergence of a secondary instability inside the superconducting state, which leads to the nematic order and
s
−
d
mixing in the gap function.
|
Nov 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
|
Takafumi
Sato
,
Zhiwei
Wang
,
Daichi
Takane
,
Seigo
Souma
,
Chaoxi
Cui
,
Yongkai
Li
,
Kosuke
Nakayama
,
Tappei
Kawakami
,
Yuya
Kubota
,
Cephise
Cacho
,
Timur
Kim
,
Arian
Arab
,
Vladimir N.
Strocov
,
Yugui
Yao
,
Takashi
Takahashi
Diamond Proposal Number(s):
[23799]
Open Access
Abstract: We have performed angle-resolved photoemission spectroscopy on
EuIn
2
As
2
which is predicted to be an axion insulator in the antiferromagnetic state. By utilizing soft-x-ray and vacuum-ultraviolet photons, we revealed a three-dimensional hole pocket centered at the
Γ
point of the bulk Brillouin zone together with a heavily hole-doped surface state in the paramagnetic phase. Upon entering the antiferromagnetic phase, the band structure exhibits a marked reconstruction characterized by the emergence of an “M”-shaped bulk band near the Fermi level. The qualitative agreement with first-principles band-structure calculations suggests the occurrence of bulk-band inversion at the
Γ
point in the antiferromagnetic phase. We suggest that
EuIn
2
As
2
provides a good opportunity to study the exotic quantum phases associated with a possible axion-insulator phase.
|
Sep 2020
|
|
