Development of a vacuum ultraviolet laser-based angle-resolved photoemission system with a superhigh energy resolution better than 1meV

Liu, Guodong; Wang, Guiling; Zhu, Yong; Zhang, Hongbo; Zhang, Guochun; Wang, Xiaoyang; Zhou, Yong; Zhang, Wentao; Liu, Haiyun; Zhao, Lin; Meng, Jian-Qiao; Dong, Xianlin; Chen, Chuangtian; Xu, Zuyan; Zhou, Xianju

doi:10.1063/1.2835901

Cited by 218 publications

(165 citation statements)

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“…To observe the note-shaped pattern that signals the chiral anomaly it is essential that the induced chemical potential difference δμ is larger than the energy resolution of the experiments, which is of the order of ∼meV [72] Table I as measured by ARPES for Na 3 Bi and Cd 3 As 2 . From Eq.…”

Section: Estimates Of the Chiral Chemical Potential Differencementioning

confidence: 99%

Visualizing the chiral anomaly in Dirac and Weyl semimetals with photoemission spectroscopy

et al. 2016

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Quantum anomalies are the breaking of a classical symmetry by quantum fluctuations. They dictate how physical systems of diverse nature, ranging from fundamental particles to crystalline materials, respond topologically to external perturbations, insensitive to local details. The anomaly paradigm was triggered by the discovery of the chiral anomaly that contributes to the decay of pions into photons and influences the motion of superfluid vortices in 3 He-A. In the solid state, it also fundamentally affects the properties of topological Weyl and Dirac semimetals, recently realized experimentally. In this work we propose that the most identifying consequence of the chiral anomaly, the charge density imbalance between fermions of different chirality induced by nonorthogonal electric and magnetic fields, can be directly observed in these materials with the existing technology of photoemission spectroscopy. With angle resolution, the chiral anomaly is identified by a characteristic note-shaped pattern of the emission spectra, originating from the imbalanced occupation of the bulk states and a previously unreported momentum dependent energy shift of the surface state Fermi arcs. We further demonstrate that the chiral anomaly likewise leaves an imprint in angle averaged emission spectra, facilitating its experimental detection. Thereby, our work provides essential theoretical input to foster the direct visualization of the chiral anomaly in condensed matter, in contrast to transport properties, such as negative magnetoresistance, which can also be obtained in the absence of a chiral anomaly.

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Section: Estimates Of the Chiral Chemical Potential Differencementioning

confidence: 99%

Visualizing the chiral anomaly in Dirac and Weyl semimetals with photoemission spectroscopy

et al. 2016

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“…These finite widths represent the small chance that electrons interacting with the medium, primarily through electron-hole pair creation and plasmonic interaction, will have energy within the final-state gap. Typically, this final-state effect in ARPES is not used to measure unoccupied states, which are instead mapped by inverse photoemission[8] or very-low-energy electron diffraction [5,[9][10][11][12].Here we show that laser-based ARPES [13][14][15], under certain conditions, can be used to map final-state gaps in the electronic states of a material. This method provides the following advantages with respect to standard synchrotron-based ARPES: (a) improved momentum resolution and greater bulk sensitivity, due to the lower photon energy range available in laser-ARPES (6-7 eV)[13], * alanzara@lbl.gov and (b) access to unoccupied electron states closer to the Fermi level.…”

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confidence: 99%

Resolving unoccupied electronic states with laser ARPES in bismuth-based cuprate superconductors

et al. 2015

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Angle-resolved photoemission spectroscopy (ARPES) is typically used to study only the occupied electronic band structure of a material. Here we use laser-based ARPES to observe a feature in bismuth-based superconductors that, in contrast, is related to the unoccupied states. Specifically, we observe a dispersive suppression of intensity cutting across the valence band, which, when compared with relativistic one-step calculations, can be traced to two final-state gaps in the bands 6 eV above the Fermi level. This finding opens up possibilities to bring the ultra-high momentum resolution of existing laser-ARPES instruments to the unoccupied electron states. For cases where the finalstate gap is not the object of study, we find that its effects can be made to vanish under certain experimental conditions.Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental probe that has been used extensively to image the occupied electronic states of materials in an energy-and momentum-resolved manner [1,2]. Since it is based on Einstein's photoelectric effect, it cannot directly probe a material's unoccupied electronic states, but it has nevertheless provided signatures of gaps in the unoccupied states [3][4][5][6]. According to the one-step model [7], some electrons, after absorbing photons, may have energies which lie between two unoccupied bands. We call the space between the unoccupied bands a finalstate gap, although this gap may be confined to a limited momentum range, and disperse within that range. The photoemission intensity of these electrons is suppressed, but not suppressed completely, due to the finite widths of the final states. These finite widths represent the small chance that electrons interacting with the medium, primarily through electron-hole pair creation and plasmonic interaction, will have energy within the final-state gap. Typically, this final-state effect in ARPES is not used to measure unoccupied states, which are instead mapped by inverse photoemission[8] or very-low-energy electron diffraction [5,[9][10][11][12].Here we show that laser-based ARPES [13][14][15], under certain conditions, can be used to map final-state gaps in the electronic states of a material. This method provides the following advantages with respect to standard synchrotron-based ARPES: (a) improved momentum resolution and greater bulk sensitivity, due to the lower photon energy range available in laser-ARPES (6-7 eV)[13], * alanzara@lbl.gov and (b) access to unoccupied electron states closer to the Fermi level.Data are shown for cuprate superconductors Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) and Bi 2 Sr 2−x La x CuO 6 (La-Bi2201) along the Γ-Y direction of the Brillouin zone, using ∼6 eV laser ARPES. In these measurements, a final-state gap can be seen as a line of suppressed intensity that disperses in momentum.When the final-state gap crosses the photoemitted valence band, it creates a distortion 100-140 meV below the Fermi level, depending on the photon energy. A second distortion is seen at 20-50 meV, indicating...

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“…It has established a universality of the nodal kink in both electron-and hole-doped cuprate superconductors. It also suggests that the different behaviors between electronand hole-doped cuprates may not be dictated by the nodal electron coupling, but by their distinct doping-dependent electronic structure.The angle-resolved photoemission measurements were performed on our recently developed vacuum ultra-violet (VUV) laser-based ARPES system at the Institute of Physics, Chinese Academy of Sciences, which has some unique advantages such as super-high energy resolution (better than 1 meV), high momentum resolution, super-high photon flux and enhanced bulk sensitivity [15]. The photon energy of the VUV laser is 6.994 eV with a bandwidth of 0.26 meV.…”

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confidence: 99%

“…The angle-resolved photoemission measurements were performed on our recently developed vacuum ultra-violet (VUV) laser-based ARPES system at the Institute of Physics, Chinese Academy of Sciences, which has some unique advantages such as super-high energy resolution (better than 1 meV), high momentum resolution, super-high photon flux and enhanced bulk sensitivity [15]. The photon energy of the VUV laser is 6.994 eV with a bandwidth of 0.26 meV.…”

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confidence: 99%

Identification of Nodal Kink in Electron-Doped (Nd_1.85Ce_0.15)CuO₄Superconductor from Laser-Based Angle-Resolved Photoemission Spectroscopy

Liu

Zhang

et al. 2012

EPJ Web of Conferences

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Abstract. High-resolution laser-based angle-resolved photoemission measurements have been carried out on the electron-doped (Nd 1.85 Ce 0.15 )CuO 4 high temperature superconductor. We have revealed a clear kink at ∼60 meV in the dispersion along the (0,0)-(π,π) nodal direction, accompanied by a peak-dip-hump feature in the photoemission spectra. This indicates that the nodal electrons are coupled to collective excitations (bosons) in electron-doped superconductors, with the phonons as the most likely candidate of the boson. This finding has established a universality of nodal electron coupling in both hole-and electron-doped high temperature cuprate superconductors.High temperature superconductivity in cuprates is achieved by doping an appropriate amount of charge carriers (electrons or holes) into the parent antiferromagnetic Mott insulators [1]. It is known that the unusual physical properties of high-T c cuprate superconductors stem from the complex interplay between electron charge, spin and lattice vibrations. Investigation of these many-body effects is essential to understand the macroscopic physical properties and the mechanism of high temperature superconductivity. High resolution angle-resolved photoemission spectroscopy (ARPES) has become a powerful tool to probe many-body effects because the interaction of electrons with a collective excitation gives rise to a change in the electron self-energy which can be measured directly from ARPES [2]. In hole-doped cuprates, ARPES measurements have revealed a ubiquitous existence of a kink in the dispersion at ∼70meV along the (0,0)-(π,π) nodal direction signaling an electron coupling with low energy collective excitations (phonons or magnetic resonance mode) [3][4][5][6][7][8]. In the electron-doped cuprates, indication of the nodal kink was found recently[9] which was not identified before [10][11][12]. It is well-known that the electron-doped superconductors exhibit different behaviors from its hole-doped counterparts, such as the narrower superconducting doping range and lower superconducting transition temperature (T c ) [13]. This raises interesting questions on whether the nodal electron dynamics in the electron-doped cuprates is inherently different from the hole-doped ones and whether such a difa Corresponding author: XJZhou@aphy.iphy.ac.cn ference may be responsible for the distinct behaviors between the electron-and hole-doped cuprates [14].In this paper we report an identification of a kink in the nodal dispersion of the electron-doped (Nd 1.85 Ce 0.15 )CuO 4 superconductor by taking advantage of the high performance laser-based ARPES system. In both optimally-doped and underdoped (Nd 1.85 Ce 0.15 )CuO 4 superconductors, we have clearly identified a kink in the nodal dispersion near 60 meV, accompanied by peak-dip-hump structure in the photoemission spectra and a drop in the quasiparticle scattering rate. These observations indicate that, in the electrondoped cuprates, the nodal electrons couple with some collective excitations with phonons as the mo...

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Development of a vacuum ultraviolet laser-based angle-resolved photoemission system with a superhigh energy resolution better than 1meV

Cited by 218 publications

References 42 publications

Visualizing the chiral anomaly in Dirac and Weyl semimetals with photoemission spectroscopy

Visualizing the chiral anomaly in Dirac and Weyl semimetals with photoemission spectroscopy

Resolving unoccupied electronic states with laser ARPES in bismuth-based cuprate superconductors

Identification of Nodal Kink in Electron-Doped (Nd_1.85Ce_0.15)CuO₄Superconductor from Laser-Based Angle-Resolved Photoemission Spectroscopy

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Development of a vacuum ultraviolet laser-based angle-resolved photoemission system with a superhigh energy resolution better than 1meV

Cited by 218 publications

References 42 publications

Visualizing the chiral anomaly in Dirac and Weyl semimetals with photoemission spectroscopy

Visualizing the chiral anomaly in Dirac and Weyl semimetals with photoemission spectroscopy

Resolving unoccupied electronic states with laser ARPES in bismuth-based cuprate superconductors

Identification of Nodal Kink in Electron-Doped (Nd1.85Ce0.15)CuO4Superconductor from Laser-Based Angle-Resolved Photoemission Spectroscopy

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Identification of Nodal Kink in Electron-Doped (Nd_1.85Ce_0.15)CuO₄Superconductor from Laser-Based Angle-Resolved Photoemission Spectroscopy