Trivial topological phase of CaAgP and the topological nodal-line transition in $\mathrm{CaAg}({\mathrm{P}}_{1\text{\ensuremath{-}}x}\mathrm{A}{\mathrm{s}}_{x})$

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Trivial topological phase of CaAgP and the topological nodal-line transition in $CaAg (P_{1 − x} A s_{x})$

N. Xu, Y. T. Qian, Q. S. Wu, G. Autès, C. E. Matt, B. Q. Lv, M. Y. Yao, V. N. Strocov, E. Pomjakushina, K. Conder, N. C. Plumb, M. Radovic, O. V. Yazyev, T. Qian, H. Ding, J. Mesot, and M. Shi

Phys. Rev. B 97, 161111(R) – Published 23 April 2018

Abstract

By performing angle-resolved photoemission spectroscopy and first-principles calculations, we address the topological phase of CaAgP and investigate the topological phase transition in $CaAg (P_{1 − x} A s_{x})$ . We reveal that in CaAgP, the bulk band gap and surface states with a large bandwidth are topologically trivial, in agreement with hybrid density functional theory calculations. The calculations also indicate that application of “negative” hydrostatic pressure can transform trivial semiconducting CaAgP into an ideal topological nodal-line semimetal phase. The topological transition can be realized by partial isovalent P/As substitution at $x = 0.38$ .

Received 23 January 2018

DOI:https://doi.org/10.1103/PhysRevB.97.161111

Physics Subject Headings (PhySH)

Electronic structure First-principles calculations Topological materials

Angle-resolved photoemission spectroscopy X-ray photoelectron spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

N. Xu^1,*, Y. T. Qian^2,3,4,5, Q. S. Wu^2,3, G. Autès^2,3, C. E. Matt⁶, B. Q. Lv^4,5,6, M. Y. Yao⁶, V. N. Strocov⁶, E. Pomjakushina⁷, K. Conder⁷, N. C. Plumb⁶, M. Radovic⁶, O. V. Yazyev^2,3, T. Qian⁴, H. Ding^4,5,8, J. Mesot^2,6,9, and M. Shi^6,†

¹The Institute of Advanced Studies, Wuhan University, Wuhan 430072, China
²Institute of Physics, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
³National Centre for Computational Design and Discovery of Novel Materials MARVEL, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
⁴Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
⁵University of Chinese Academy of Sciences, Beijing 100049, China
⁶Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
⁷Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
⁸Collaborative Innovation Center of Quantum Matter, Beijing, China
⁹Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland

^*nxu@whu.edu.cn
^†ming.shi@psi.ch

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Vol. 97, Iss. 16 — 15 April 2018

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Figure 1
Topological nodel-line semimetal phase in CaAgP/CaAgAs. (a), (b) Side and top views of the crystal structure of CaAgP/CaAgAs. (c) The picture of a typical piece of CaAgP single crystal used in ARPES experiments, taken under the microscope on a millimeter scale. (d) Bulk and surface BZs with high-symmetry points labelled. (e), (f) Illustration of the band dispersions near the nodal line in the $k_{x} − k_{y}$ plane. (g) The bulk electronic structure of CaAgP and CaAgAs from PBE calculations.
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Figure 2
Surface states at the $(\bar{1} 100)$ surface of CaAgP. (a) The FS acquired with VUV ARPES in the photon energy range from 30 to 120 eV. $k_{x} (k_{y})$ is the in-plane (out-of-plane) component of the crystal momentum. Red arrows indicate the FS of 2D surface states. (b) The FS in the surface BZ, obtained from the ARPES experiment (left) and calculation (right). (c), (d) Band structure along the $\bar{Γ} − \bar{X}$ and $\bar{Γ} − \bar{A}$ directions, obtained from the ARPES experiment (left) and HSE calculations (right).
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Figure 3
The bulk band structure of CaAgP. (a) The FS in the $k_{x} − k_{y}$ plane of the bulk BZ, acquired with SX-ARPES in the photon energy range from 350 to 650 eV. (b) The FS recorded with $h = 580 eV$ . (c) ARPES spectra along the high-symmetry line $Γ − K − M$ [cut 1 in (a)]; the band structures obtained from PBE and HSE calculations are overlaid on the spectra. (d) ARPES spectra along $Γ − M$ and the electronic structure from PBE calculations. (e) The curvature plots of ARPES spectra in (d), overlaid with the band structure from HSE calculations. (f), (g) Same as (d) and (e), but along the $Γ − A$ direction. (h), (i) Energy distribution curves along the $Γ − M$ and $Γ − A$ directions, respectively. (j) Extracted and fitting holelike band dispersion along the $Γ − M$ and $Γ − A$ directions.
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Figure 4
Simulations of the hydrostatic pressure effect and isovalent As substitution in CaAgP. (a) The topological phase diagram with hydraulic pressure and isovalent As substitution in CaAgP. The energy difference between conduction and valence bands $(E_{c} - E_{v})$ induced by isovalent As substitution is extracted from the Wannier function interpolations of CaAgP and CaAgAs within the HSE calculations. The hydrostatic pressure effect in CaAgP is simulated by isotropically scaling lattice parameter $ɛ = a / a_{0} = b / b_{0} = c / c_{0}$ . (b) Calculated band structures near $E_{F}$ by using HSE functional for $CaAg (P_{1 − x} A s_{x})$ with $x = 0$ , 0.38, and 1, respectively.
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Physical Review B

covering condensed matter and materials physics

Trivial topological phase of CaAgP and the topological nodal-line transition in $CaAg (P_{1 − x} A s_{x})$

N. Xu, Y. T. Qian, Q. S. Wu, G. Autès, C. E. Matt, B. Q. Lv, M. Y. Yao, V. N. Strocov, E. Pomjakushina, K. Conder, N. C. Plumb, M. Radovic, O. V. Yazyev, T. Qian, H. Ding, J. Mesot, and M. Shi

Phys. Rev. B 97, 161111(R) – Published 23 April 2018

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Physical Review B

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Trivial topological phase of CaAgP and the topological nodal-line transition in CaAg(P1−xAsx)

N. Xu, Y. T. Qian, Q. S. Wu, G. Autès, C. E. Matt, B. Q. Lv, M. Y. Yao, V. N. Strocov, E. Pomjakushina, K. Conder, N. C. Plumb, M. Radovic, O. V. Yazyev, T. Qian, H. Ding, J. Mesot, and M. Shi

Phys. Rev. B 97, 161111(R) – Published 23 April 2018

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Trivial topological phase of CaAgP and the topological nodal-line transition in $CaAg (P_{1 − x} A s_{x})$