I05-ARPES
|
Kifu
Kurokawa
,
Shunsuke
Isono
,
Yoshimitsu
Kohama
,
So
Kunisada
,
Shiro
Sakai
,
Ryotaro
Sekine
,
Makoto
Okubo
,
Matthew D.
Watson
,
Timur K.
Kim
,
Cephise
Cacho
,
Shik
Shin
,
Takami
Tohyama
,
Kazuyasu
Tokiwa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[30646, 28930]
Open Access
Abstract: he currently established electronic phase diagram of cuprates is based on a study of single- and double-layered compounds. These CuO2 planes, however, are directly contacted with dopant layers, thus inevitably disordered with an inhomogeneous electronic state. Here, we solve this issue by investigating a 6-layered Ba2Ca5Cu6O12(F,O)2 with inner CuO2 layers, which are clean with the extremely low disorder, by angle-resolved photoemission spectroscopy (ARPES) and quantum oscillation measurements. We find a tiny Fermi pocket with a doping level less than 1% to exhibit well-defined quasiparticle peaks which surprisingly lack the polaronic feature. This provides the first evidence that the slightest amount of carriers is enough to turn a Mott insulating state into a metallic state with long-lived quasiparticles. By tuning hole carriers, we also find an unexpected phase transition from the superconducting to metallic states at 4%. Our results are distinct from the nodal liquid state with polaronic features proposed as an anomaly of the heavily underdoped cuprates.
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Jul 2023
|
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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.
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Jan 2021
|
|
I05-ARPES
|
So
Kunisada
,
Shunsuke
Isono
,
Yoshimitsu
Kohama
,
Shiro
Sakai
,
Cédric
Bareille
,
Shunsuke
Sakuragi
,
Ryo
Noguchi
,
Kifu
Kurokawa
,
Kenta
Kuroda
,
Yukiaki
Ishida
,
Shintaro
Adachi
,
Ryotaro
Sekine
,
Timur K.
Kim
,
Cephise
Cacho
,
Shik
Shin
,
Takami
Tohyama
,
Kazuyasu
Tokiwa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[20445, 20446]
Abstract: In cuprate superconductors with high critical transition temperature (Tc), light hole-doping to the parent compound, which is an antiferromagnetic Mott insulator, has been predicted to lead to the formation of small Fermi pockets. These pockets, however, have not been observed. Here, we investigate the electronic structure of the five-layered Ba2Ca4Cu5O10(F,O)2, which has inner copper oxide (CuO2) planes with extremely low disorder, and find small Fermi pockets centered at (π/2, π/2) of the Brillouin zone by angle-resolved photoemission spectroscopy and quantum oscillation measurements. The d-wave superconducting gap opens along the pocket, revealing the coexistence between superconductivity and antiferromagnetic ordering in the same CuO2 sheet. These data further indicate that superconductivity can occur without contribution from the antinodal region around (π, 0), which is shared by other competing excitations.
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Aug 2020
|
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I05-ARPES
|
Hiroaki
Tanaka
,
Yuita
Fujisawa
,
Kenta
Kuroda
,
Ryo
Noguchi
,
Shunsuke
Sakuragi
,
Cedric
Bareille
,
Barnaby
Smith
,
Cephise
Cacho
,
Sung Won
Jung
,
Takayuki
Muro
,
Yoshinori
Okada
,
Takeshi
Kondo
Diamond Proposal Number(s):
[24488]
Abstract: A large anomalous Hall effect (AHE) has been observed in ferromagnetic
Fe
3
Sn
2
with breathing kagome bilayers. To understand the underlying mechanism for this, we investigate the electronic structure of
Fe
3
Sn
2
by angle-resolved photoemission spectroscopy (ARPES). In particular, we use both vacuum ultraviolet light (VUV) and soft x ray (SX), which allow surface-sensitive and relatively bulk-sensitive measurements, respectively, and distinguish bulk states from surface states, which should be unlikely related to the AHE. While VUV-ARPES observes two-dimensional bands mostly due to surface states, SX-ARPES reveals three-dimensional band dispersions with a periodicity of the rhombohedral unit cell in the bulk. Our data show a good consistency with a theoretical calculation based on density functional theory, suggesting a possibility that
Fe
3
Sn
2
is a magnetic Weyl semimetal.
|
Apr 2020
|
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I05-ARPES
|
Ryo
Noguchi
,
T.
Takahashi
,
K.
Kuroda
,
M.
Ochi
,
T.
Shirasawa
,
M.
Sakano
,
C.
Bareille
,
M.
Nakayama
,
M. D.
Watson
,
K.
Yaji
,
A.
Harasawa
,
H.
Iwasawa
,
P.
Dudin
,
T. K.
Kim
,
M.
Hoesch
,
V.
Kandyba
,
A.
Giampietri
,
A.
Barinov
,
S.
Shin
,
R.
Arita
,
T.
Sasagawa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[15095, 16161]
Abstract: The major breakthroughs in understanding of topological materials over the past decade were all triggered by the discovery of the Z2-type topological insulator—a type of material that is insulating in its interior but allows electron flow on its surface. In three dimensions, a topological insulator is classified as either ‘strong’ or ‘weak’ and experimental confirmations of the strong topological insulator rapidly followed theoretical predictions. By contrast, the weak topological insulator (WTI) has so far eluded experimental verification, because the topological surface states emerge only on particular side surfaces, which are typically undetectable in real three-dimensional crystals. Here we provide experimental evidence for the WTI state in a bismuth iodide, β-Bi4I4. Notably, the crystal has naturally cleavable top and side planes—stacked via van der Waals forces—which have long been desirable for the experimental realization of the WTI state. As a definitive signature of this state, we find a quasi-one-dimensional Dirac topological surface state at the side surface (the (100) plane), while the top surface (the (001) plane) is topologically dark with an absence of topological surface states. We also find that a crystal transition from the β-phase to the α-phase drives a topological phase transition from a nontrivial WTI to a normal insulator at roughly room temperature. The weak topological phase—viewed as quantum spin Hall insulators stacked three-dimensionally—will lay a foundation for technology that benefits from highly directional, dense spin currents that are protected against backscattering.
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Feb 2019
|
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I05-ARPES
|
M.
Nakayama
,
T.
Kondo
,
K.
Kuroda
,
C.
Bareille
,
M. D.
Watson
,
S.
Kunisada
,
R.
Noguchi
,
T. K.
Kim
,
M.
Hoesch
,
Y.
Yoshida
,
S.
Shin
Diamond Proposal Number(s):
[15095, 16161, 17816, 20445]
Abstract: We reveal the orbital-selective metal-insulator transition in a 4d multiorbital system, Sr3(Ru1−xMnx)2O7(x=0−0.2), by means of angle-resolved photoemission spectroscopy. With a small substitution (x=0.05) of Mn with localized 3d orbitals, the spectra for the 4dxy band become incoherent with a large gap, while the 4dxz/yz bands stay metallic with sharp quasiparticle peaks. Intriguingly, this lifts band hybridization among 4d orbitals, and causes a two- to one-dimensional crossover in the remaining Fermi surface. Significant nesting in the remaining Fermi surface is implied to induce the reported magnetic ordering, and yields the insulating bulk state at higher Mn substitution, where all bands are gapped and totally incoherent. The availability of orbital-selective tuning of the pseudogap by a small impurity will prompt further theoretical studies of Hund's metals, which were recognized only recently in condensed matter physics.
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Oct 2018
|
|
I05-ARPES
|
K.
Kuroda
,
M.
Ochi
,
H. s.
Suzuki
,
M.
Hirayama
,
M.
Nakayama
,
R.
Noguchi
,
C.
Bareille
,
S.
Akebi
,
S.
Kunisada
,
T.
Muro
,
M. D.
Watson
,
H.
Kitazawa
,
Y.
Haga
,
T. K.
Kim
,
M.
Hoesch
,
S.
Shin
,
R.
Arita
,
T.
Kondo
Diamond Proposal Number(s):
[16161]
Abstract: Experimental determinations of bulk band topology in the solid states have been so far restricted to only indirect investigation through the probing of surface states predicted by electronic structure calculations. We here present an alternative approach to determine the band topology by means of bulk-sensitive soft x-ray angle-resolved photoemission spectroscopy. We investigate the bulk electronic structures of the series materials, Ce monopnictides (CeP, CeAs, CeSb, and CeBi). By performing a paradigmatic study of the band structures as a function of their spin-orbit coupling, we draw the topological phase diagram and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion. The underlying mechanism of the phase transition is elucidated in terms of spin-orbit coupling in concert with their semimetallic band structures. Our comprehensive observations provide a new insight into the band topology hidden in the bulk states.
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Feb 2018
|
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I05-ARPES
|
Ilya
Belopolski
,
Su-Yang
Xu
,
Yukiaki
Ishida
,
Xingchen
Pan
,
Peng
Yu
,
Daniel S.
Sanchez
,
Hao
Zheng
,
Madhab
Neupane
,
Nasser
Alidoust
,
Guoqing
Chang
,
Tay-Rong
Chang
,
Yun
Wu
,
Guang
Bian
,
Shin-Ming
Huang
,
Chi-Cheng
Lee
,
Daixiang
Mou
,
Lunan
Huang
,
You
Song
,
Baigeng
Wang
,
Guanghou
Wang
,
Yao-Wen
Yeh
,
Nan
Yao
,
Julien E.
Rault
,
Patrick
Le Fèvre
,
François
Bertran
,
Horng-Tay
Jeng
,
Takeshi
Kondo
,
Adam
Kaminski
,
Hsin
Lin
,
Zheng
Liu
,
Fengqi
Song
,
Shik
Shin
,
M. Zahid
Hasan
Diamond Proposal Number(s):
[13653]
Abstract: It has recently been proposed that electronic band structures in crystals can give rise to a previously overlooked type of Weyl fermion, which violates Lorentz invariance and, consequently, is forbidden in particle physics. It was further predicted that MoxW1−xTe2 may realize such a type-II Weyl fermion. Here, we first show theoretically that it is crucial to access the band structure above the Fermi level ɛF to show a Weyl semimetal in MoxW1−xTe2. Then, we study MoxW1−xTe2 by pump-probe ARPES and we directly access the band structure >0.2 eV above ɛF in experiment. By comparing our results with ab initio calculations, we conclude that we directly observe the surface state containing the topological Fermi arc. We propose that a future study of MoxW1−xTe2 by pump-probe ARPES may directly pinpoint the Fermi arc. Our work sets the stage for the experimental discovery of the first type-II Weyl semimetal in MoxW1−xTe2.
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Aug 2016
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