I05-ARPES
|
A. Garrison
Linn
,
Peipei
Hao
,
Kyle N.
Gordon
,
Dushyant
Narayan
,
Bryan S.
Berggren
,
Nathaniel
Speiser
,
Sonka
Reimers
,
Richard P.
Campion
,
Vít
Novák
,
Sarnjeet S.
Dhesi
,
Timur K.
Kim
,
Cephise
Cacho
,
Libor
Šmejkal
,
Tomáš
Jungwirth
,
Jonathan D.
Denlinger
,
Peter
Wadley
,
Daniel S.
Dessau
Diamond Proposal Number(s):
[24224]
Open Access
Abstract: Tetragonal CuMnAs is a room temperature antiferromagnet with an electrically reorientable Néel vector and a Dirac semimetal candidate. Direct measurements of the electronic structure of single-crystalline thin films of tetragonal CuMnAs using angle-resolved photoemission spectroscopy (ARPES) are reported, including Fermi surfaces (FS) and energy-wavevector dispersions. After correcting for a chemical potential shift of ≈− 390 meV (hole doping), there is excellent agreement of FS, orbital character of bands, and Fermi velocities between the experiment and density functional theory calculations. In addition, 2×1 surface reconstructions are found in the low energy electron diffraction (LEED) and ARPES. This work underscores the need to control the chemical potential in tetragonal CuMnAs to enable the exploration and exploitation of the Dirac fermions with tunable masses, which are predicted to be above the chemical potential in the present samples.
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May 2023
|
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I05-ARPES
|
Abstract: In recent years, chromium sulphur bromide (CrSBr) has emerged as a promising highly- anisotropic semiconducting two-dimensional (2D) magnetic material to explore spintronics and quantum transport due to its strongly correlated quasiparticle interactions [1]. CrSBr is an A-type layered antiferromagnet; in the bulk material, above the Néel temperature (TN = 132K) it transitions to an intermediate ferromagnetic phase before becoming paramagnetic at high temperature. Experimental work on its fascinating optoelectronic properties has been heavily supported by electronic structure calculations using a variety of methods [2,3], but direct band structure measurements to test these predictions are still lacking. Recent angle- resolved photoemission microscopy (ARPES) measurements of bulk CrSBr were unable to measure below TN due to charging effects [4]. Here, we overcome this limitation through exfoliation of CrSBr flakes onto a template-stripped gold surface (Figure 1a) [5]. Using the nanoARPES endstation of the i05 beamline at Diamond Light Source, ARPES was acquired without charging from thin flakes (~10 nm thick) at temperatures down to < 40 K. Photon energy, and polarisation, dependent measurements confirm a strongly 2D dispersion and link the band dispersions to different atomic orbitals. Temperature-dependent measurements highlight electronic structure changes through the magnetic phase transitions, including shifts of the low energy valence bands and band splitting suggestive of spin-ordering (Figure 1b,c). These results also demonstrate a simple approach for the measurement of the low- temperature band structure of insulating layered materials.
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May 2023
|
|
I05-ARPES
|
Seyeong
Cha
,
Giyeok
Lee
,
Sol
Lee
,
Sae Hee
Ryu
,
Yeongsup
Sohn
,
Gijeong
An
,
Changmo
Kang
,
Minsu
Kim
,
Kwanpyo
Kim
,
Aloysius
Soon
,
Keun Su
Kim
Diamond Proposal Number(s):
[19304, 24691]
Open Access
Abstract: A variety of phase transitions have been found in two-dimensional layered materials, but some of their atomic-scale mechanisms are hard to clearly understand. Here, we report the discovery of a phase transition whose mechanism is identified as interlayer sliding in lead iodides, a layered material widely used to synthesize lead halide perovskites. The low-temperature crystal structure of lead iodides is found not 2H polytype as known before, but non-centrosymmetric 4H polytype. This undergoes the order-disorder phase transition characterized by the abrupt spectral broadening of valence bands, taken by angle-resolved photoemission, at the critical temperature of 120 K. It is accompanied by drastic changes in simultaneously taken photocurrent and photoluminescence. The transmission electron microscopy is used to reveal that lead iodide layers stacked in the form of 4H polytype at low temperatures irregularly slide over each other above 120 K, which can be explained by the low energy barrier of only 10.6 meV/atom estimated by first principles calculations. Our findings suggest that interlayer sliding is a key mechanism of the phase transitions in layered materials, which can significantly affect optoelectronic and optical characteristics.
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Apr 2023
|
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I05-ARPES
|
Q. Q.
Zhang
,
Y.
Shi
,
K. Y.
Zhai
,
W. X.
Zhao
,
X.
Du
,
J. S.
Zhou
,
X.
Gu
,
R. Z.
Xu
,
Y. D.
Li
,
Y. F.
Guo
,
Z. K.
Liu
,
C.
Chen
,
S.-K.
Mo
,
T. K.
Kim
,
C.
Cacho
,
J. W.
Yu
,
W.
Li
,
Y. L.
Chen
,
J.-H.
Chu
,
L. X.
Yang
Diamond Proposal Number(s):
[22375]
Abstract: EuTe
4
is a van der Waals material exhibiting a charge density wave (CDW) with a large thermal hysteresis in the resistivity and CDW gap. In this paper, we systematically study the electronic structure and transport properties of
EuTe
4
using high-resolution angle-resolved photoemission spectroscopy (ARPES), magnetoresistance (MR) measurements, and scanning tunneling microscopy (STM). We observe a CDW gap of
∼
200
meV
at low temperatures that persists up to 400 K, suggesting that the CDW transition occurs at a much higher temperature. The ARPES intensity near the Fermi level shows large thermal hysteretic behavior, consistent with the resistivity measurement. The hysteresis in the resistivity measurement does not change under a magnetic field up to 7 T, excluding the thermal magnetic hysteretic effect. Instead, the surface topography measured with STM shows surface domains with different CDW trimerization directions, which may be important for the thermal hysteretic behavior. Interestingly, we reveal a large negative MR at low temperatures that can be associated with the canting of magnetically ordered Eu spins. Our results shed light on the understanding of magnetic, transport, and electronic properties of
EuTe
4
.
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Mar 2023
|
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I05-ARPES
|
Peipei
Hao
,
Haoxiang
Li
,
Dushyant M.
Narayan
,
Rafal
Kurleto
,
Bryan S.
Berggren
,
Andrew G.
Linn
,
Amanda
Shackelford
,
Yu
Zhang
,
Hope
Whitelock
,
Gang
Cao
,
Daniel S.
Dessau
Abstract: High-Tc cuprate superconductors in their normal state are known to have the mysterious strange-metal behavior near optimal doping with strong deviations from the conventional Fermi Liquid form of electronic scattering rates. In particular, these have been described by the marginal-fermi-liquid (MFL) form at optimal doping [1], or more generally the power-law-liquid (PLL) form over all doping levels [2]. Here with careful analysis of the intrinsic line shape of Angle-resolved photoemission (ARPES) dispersion cuts, we report a comparative study of the both ω- and T- dependent scattering rate of (Pb)Bi2Sr2CaCu2O8+δ, La2-xSrxCuO4, as well as the copper-free perovskite superconductor Sr2RuO4. With a unified power-law-liquid form of the imaginary self-energy proposed by Reber et al [2], our fitted parameters reproduce the strange-metal and fermi-liquid-like behavior of the cuprate superconductors and Sr2RuO4, respectively. Surprisingly, we show a much stronger electronic coupling parameter for the scattering in the ruthenates compared to the cuprates, indicating another key difference between these different superconductors.
|
Mar 2023
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[29021]
Abstract: Recent transport experiments revealed a correlated insulating phase and quantum criticality points in twisted transition metal dichalcogenides (TMDs) that were predicted to host flat moire´ mini-bands. Despite these exciting experimental observations and theoretical predictions, no direct measurements of the band structure of twisted TMD are available to date. We report here for the first time on the direct observation of flat band in twisted TMDs investigating 57° twisted bilayer WSe2 by micro-focused angle-resolved photoemission spectroscopy. We resolve multiple moire´ mini-bands with strongly reduced dispersion and significant mini-gaps. By comparison with effective continuum band structure models, we attribute the origin of the flat states to a moderate moire´ potential of ≈ 50 meV emerging from the stacking of the two semiconducting layers. Our results establish a reference for future theoretical and experimental studies of the moire´ physics in twisted TMDs.
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Mar 2023
|
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I05-ARPES
|
Edgar
Abarca Morales
,
Gesa-R.
Siemann
,
Andela
Zivanovic
,
Philip A. E.
Murgatroyd
,
Igor
Markovic
,
Brendan
Edwards
,
Chris A.
Hooley
,
Dmitry A.
Sokolov
,
Naoki
Kikugawa
,
Cephise
Cacho
,
Matthew D.
Watson
,
Timur K.
Kim
,
Clifford W.
Hicks
,
Andrew P.
Mackenzie
,
Phil D. C.
King
Diamond Proposal Number(s):
[27471, 28412]
Abstract: We report the evolution of the electronic structure at the surface of the layered perovskite
Sr
2
RuO
4
under large in-plane uniaxial compression, leading to anisotropic
B
1
g
strains of
ϵ
x
x
−
ϵ
y
y
=
−
0.9
±
0.1
%
. From angle-resolved photoemission, we show how this drives a sequence of Lifshitz transitions, reshaping the low-energy electronic structure and the rich spectrum of van Hove singularities that the surface layer of
Sr
2
RuO
4
hosts. From comparison to tight-binding modeling, we find that the strain is accommodated predominantly by bond-length changes rather than modifications of octahedral tilt and rotation angles. Our study sheds new light on the nature of structural distortions at oxide surfaces, and how targeted control of these can be used to tune density of state singularities to the Fermi level, in turn paving the way to the possible realization of rich collective states at the
Sr
2
RuO
4
surface.
|
Feb 2023
|
|
I05-ARPES
|
Haifeng
Yang
,
Jingjing
Gao
,
Yingying
Cao
,
Yuanji
Xu
,
Aiji
Liang
,
Xiang
Xu
,
Yujie
Chen
,
Shuai
Liu
,
Kui
Huang
,
Lixuan
Xu
,
Chengwei
Wang
,
Shengtao
Cui
,
Meixiao
Wang
,
Lexian
Yang
,
Xuan
Luo
,
Yuping
Sun
,
Yi-Feng
Yang
,
Zhongkai
Liu
,
Yulin
Chen
Open Access
Abstract: Mott physics plays a critical role in materials with strong electronic correlations. Mott insulator-to-metal transition can be driven by chemical doping, external pressure, temperature and gate voltage, which is often seen in transition metal oxides with 3d electrons near the Fermi energy (e.g. cuprate superconductor). In 4f-electron system, however, the insulator-to-metal transition is mostly driven by Kondo hybridization and the Mott physics has rarely been explored in experiments. Here, by combining the angle-resolved photoemission spectroscopy and strongly correlated band structure calculations, we show that an unusual Mott instability exists in YbInCu4 accompanying its mysterious first-order valence transition. This contrasts with the prevalent Kondo picture and demonstrates that YbInCu4 is a unique platform to explore the Mott physics in Kondo lattice systems. Our work provides important insight for the understanding and manipulation of correlated quantum phenomena in the f-electron system.
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Feb 2023
|
|
I05-ARPES
|
Hongwei
Fang
,
Meng
Lyu
,
Hao
Su
,
Jian
Yuan
,
Yiwei
Li
,
Lixuan
Xu
,
Shuai
Liu
,
Liyang
Wei
,
Xinqi
Liu
,
Haifeng
Yang
,
Qi
Yao
,
Meixiao
Wang
,
Yanfeng
Guo
,
Wujun
Shi
,
Yulin
Chen
,
Enke
Liu
,
Zhongkai
Liu
Abstract: The kagome-lattice crystal hosts various intriguing properties including the frustrated magnetism, charge order, topological state, superconductivity and correlated phenomena. To achieve high-performance kagome-lattice compounds for electronic and spintronic applications, careful tuning of the band structure would be desired. Here, the electronic structures of kagome-lattice crystal Ni3In2S2 were investigated by transport measurements, angle-resolved photoemission spectroscopy as well as ab initio calculations. The transport measurements reveal Ni3In2S2 as a compensated semimetal with record-high carrier mobility (∼8683 and 7356 cm2 V−1 S−1 for holes and electrons) and extreme magnetoresistance (15,518% at 2 K and 13 T) among kagome-lattice materials. These extraordinary properties are well explained by its band structure with indirect gap, small electron/hole pockets and large bandwidth of the 3d electrons of Ni on the kagome lattice. This work demonstrates that the crystal field and doping serve as the key tuning knobs to optimize the transport properties in kagome-lattice crystals. Our work provides material basis and optimization routes for kagome-lattice semimetals towards electronics and spintronics applications.
|
Feb 2023
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[17595]
Open Access
Abstract: The discovery of superconductivity in planar nickelates raises the question of how the electronic structure and correlations of Ni1+ compounds compare to those of the Cu2+ cuprate superconductors. Here, we present an angle-resolved photoemission spectroscopy (ARPES) study of the trilayer nickelate Pr4Ni3O8, revealing a Fermi surface resembling that of the hole-doped cuprates but with critical differences. Specifically, the main portions of the Fermi surface are extremely similar to that of the bilayer cuprates, with an additional piece that can accommodate additional hole doping. We find that the electronic correlations are about twice as strong in the nickelates and are almost k-independent, indicating that they originate from a local effect, likely the Mott interaction, whereas cuprate interactions are somewhat less local. Nevertheless, the nickelates still demonstrate the strange-metal behavior in the electron scattering rates. Understanding the similarities and differences between these two families of strongly correlated superconductors is an important challenge.
|
Jan 2023
|
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