Systematic study of electronic states of $\mathrm{Ln}(\mathrm{O},\mathrm{F}){\mathrm{BiS}}_{2}$ by spin- and angle-resolved photoemission spectroscopy

Systematic study of electronic states of $Ln (O, F) {BiS}_{2}$ by spin- and angle-resolved photoemission spectroscopy

Shi-Long Wu, Koichiro Yaji, Yuichi Ota, Ayumi Harasawa, Shik Shin, Takehito Imai, Koji Miyamoto, Masanori Nagao, Satoshi Watauchi, Isao Tanaka, Xiaoping Ma, Huaixin Yang, Yongqing Cai, Lin Zhao, Xingjiang Zhou, and Taichi Okuda

Phys. Rev. B 106, 104511 – Published 20 September 2022

Abstract

The evolution of fine electronic structures in superconducting $Ln O_{1 - x} F_{x} Bi S_{2}$ (Ln denotes lanthanoid) is systematically investigated with spin- and angle-resolved photoemission spectroscopy. A shape change of the Fermi surface (FS) at the $X$ point from elliptical to rectangular with increasing the electron doping is commonly observed in different lanthanide systems. Besides that, an emergent large Fermi surface around the Г point is also observed in all the samples with different doping levels deviating from the theoretical prediction, which might be related to the superconductivity. In addition, we found a humped band around $X$ (π,0) in the highly doped samples only, which may be attributed to the ${BiS}_{2}$ surface reconstruction or surface defects relying on the electron concentration. We also demonstrate the spin-selective excitation of photoelectrons, which indicates the presence of spin-orbital-entangled bulk Rashba splitting in this system. This result may enable the optical tuning of electron spin in a ${BiS}_{2}$ -based system.

Received 29 April 2022
Revised 23 August 2022
Accepted 26 August 2022

DOI:https://doi.org/10.1103/PhysRevB.106.104511

Physics Subject Headings (PhySH)

Spin-orbit coupling Spintronics Superconductivity

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Shi-Long Wu¹, Koichiro Yaji², Yuichi Ota³, Ayumi Harasawa³, Shik Shin³, Takehito Imai^4,5, Koji Miyamoto⁴, Masanori Nagao⁶, Satoshi Watauchi⁶, Isao Tanaka⁶, Xiaoping Ma¹, Huaixin Yang¹, Yongqing Cai¹, Lin Zhao¹, Xingjiang Zhou^1,*, and Taichi Okuda^4,†

¹National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
²Research Center for Advanced Measurement and Characterization, National Institute for Materials Science, Ibaraki 305-0003, Japan
³Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
⁴Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
⁵Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
⁶Center for Crystal Science and Technology (CCST), University of Yamanashi, Yamanashi 400-8511, Japan

^*XJZhou@iphy.ac.cn
^†okudat@hiroshima-u.ac.jp

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Vol. 106, Iss. 10 — 1 September 2022

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Figure 1
(a) Crystal structure of $LnOBiS {(Se)}_{2}$ . A black-dashed line denotes the position of the cleavage surface. (b) The top view of the ${BiS}_{2}$ surface. Two perpendicular nano-zigzag Bi-S chains, shown in a black-dashed box, reconstruct the ${BiS}_{2}$ surface and electronic structures. LDOS is defined as low density of states of Bi $6 p$ electrons, and HDOS is defined as high density of states of Bi $6 p$ electrons [27]. (c) Schematic diagrams of experimental geometries with reference to the spin-orbital-entangled Fermi surface of $Ln O_{1 - x} F_{x} BiS {(Se)}_{2}$ .
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Figure 2
(a) ARPES intensity mapping of the first Brillouin zone of ${LaO}_{0.5} F_{0.5} {BiSe}_{2}$ [number 7 in Fig. 1], α branch electron pocket, and its spectra cutting line β. Coordinate axes ( $P_{X}, P_{Y}, P_{Z}$ ) denote positive directions of spin vectors. (b) Comparative ARPES mapping of α branch electron-pocket in ${PrO}_{1 - x} F_{x} {BiS}_{2}$ (numbers 1–3) and their energy dispersion curves (EDCs). “Λ” represents an opened band gap near FS. (c) $T_{C}$ (left axis) vs electron-doping levels (bottom axis) of samples ( $①$ – $⑦$ ) (error-bar marks). Electron-doping levels are denoted with black marks corresponding to the energy-dispersive X-ray spectroscopy (EDX); the red marks represent the doping levels extracted from ARPES mappings of two-dimensional FS enclosures according to Luttinger' s theorem.
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Figure 3
(a) The bulk lowest conduction band (LCB) of sample $⑦$ measured by ARPES $(h ν = 21.2 eV)$ along the cutting line β in Fig. 2; the arrows “1” and “2” denote two branches of a double-split band. (b) The bulk LCB branches along the cut β marked with numbers “1” and “2” as well as the undispersive states (“3”) of samples $①$ − $③$ ( $x = 0.13$ , 0.23, and 0.26, respectively). A double arrow line denotes a band gap between the LCB and HVB. The flat in-gap band “4” is denoted with a dashed blue line.
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Figure 4
Schematic diagrams of spin textures of FS and spin-resolved EDCs of ${PrO}_{0.87} F_{0.13} {BiS}_{2}$ (sample $①$ ) and ${PrO}_{0.77} F_{0.23} {BiS}_{2}$ (sample $②$ ) and ${CeO}_{0.73} F_{0.27} {BiS}_{2}$ (sample $④$ ) by synchrotron radiation based (SR)-SARPES. (a), (c), and (e) SR-ARPES intensity mapping and schematic plotting of spin textures of FS of ${PrO}_{0.87} F_{0.13} {BiS}_{2}$ and ${PrO}_{0.77} F_{0.23} {BiS}_{2}$ and ${CeO}_{0.73} F_{0.27} {BiS}_{2}$ . (b), (d), and (f) Spin-resolved EDCs around $X$ at momentum points from “1” to “4” with $p$ -polarized SR light of 18 eV photon energy, which is corresponding to ${PrO}_{0.87} F_{0.13} {BiS}_{2}$ and ${PrO}_{0.77} F_{0.23} {BiS}_{2}$ and ${CeO}_{0.73} F_{0.27} {BiS}_{2}$ , respectively.
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Figure 5
(a) LCB of sample ( $x = 0.29$ , 5) along the cutting line β measured by ARPES with a $p$ -polarized ultraviolet (UV) laser source of 6.994 eV photon energy [43]. (b) The concatenation of experimental spin-resolved LCB dispersion (left side) and theoretical simulation of LCB dispersion (bands “1” and “2” only; see the supplemental material) (right side). (c) Spin-resolved energy distribution curves (EDCs) at EDC cut χ taken with $p$ - and $s$ -polarized UV lasers, respectively.
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Physical Review B

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Systematic study of electronic states of $Ln (O, F) {BiS}_{2}$ by spin- and angle-resolved photoemission spectroscopy

Shi-Long Wu, Koichiro Yaji, Yuichi Ota, Ayumi Harasawa, Shik Shin, Takehito Imai, Koji Miyamoto, Masanori Nagao, Satoshi Watauchi, Isao Tanaka, Xiaoping Ma, Huaixin Yang, Yongqing Cai, Lin Zhao, Xingjiang Zhou, and Taichi Okuda

Phys. Rev. B 106, 104511 – Published 20 September 2022

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Physical Review B

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Systematic study of electronic states of Ln(O,F)BiS2 by spin- and angle-resolved photoemission spectroscopy

Shi-Long Wu, Koichiro Yaji, Yuichi Ota, Ayumi Harasawa, Shik Shin, Takehito Imai, Koji Miyamoto, Masanori Nagao, Satoshi Watauchi, Isao Tanaka, Xiaoping Ma, Huaixin Yang, Yongqing Cai, Lin Zhao, Xingjiang Zhou, and Taichi Okuda

Phys. Rev. B 106, 104511 – Published 20 September 2022

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Systematic study of electronic states of $Ln (O, F) {BiS}_{2}$ by spin- and angle-resolved photoemission spectroscopy