Direct evidence of real-space pairing in $\mathrm{Ba}{\mathrm{BiO}}_{3}$

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Direct evidence of real-space pairing in $Ba {BiO}_{3}$

A. P. Menushenkov, A. Ivanov, V. Neverov, A. Lukyanov, A. Krasavin, A. A. Yastrebtsev, I. A. Kovalev, Y. Zhumagulov, A. V. Kuznetsov, V. Popov, G. Tselikov, I. Shchetinin, O. Krymskaya, A. Yaroslavtsev, R. Carley, L. Mercadier, Z. Yin, S. Parchenko, L. P. Hoang, N. Ghodrati, Y. Y. Kim, J. Schlappa, M. Izquierdo, S. Molodtsov, and A. Scherz

Phys. Rev. Research 6, 023307 – Published 21 June 2024

Abstract

The parent compound ${BaBiO}_{3}$ of bismuthate high-temperature superconductors (HTSCs) $BaBi (Pb) O_{3}$ and $Ba (K) {BiO}_{3}$ with perovskitelike structure exhibits unusual electronic and structural properties, which can be satisfactorily explained if we assume that all charge carriers are in the paired state. However, the prior experiments and the first-principle calculations only indirectly indicate the existence of paired charge carriers in ${BaBiO}_{3}$ . In this work, we report the direct evidence of initially paired electrons and holes in the upper antibonding Bi $6 s - O 2 p_{σ^{*}}$ orbital of the neighboring octahedral complexes in the ground state of ${BaBiO}_{3}$ using the time-resolved x-ray absorption spectroscopy (XAS) to monitor the electron dynamics after the femtosecond resonant 633 nm laser excitation. We observe strong changes in the oxygen $K$ -edge XAS preedge region, defined by the $Bi 6 s - O 2 p_{σ^{*}}$ orbitals. We interpret them as a fast ( $\leq 0.3$ ps) breaking of charge carrier pairs and slower (0.3–0.8 ps) lattice rearrangement from the distorted monoclinic structure into the new metastable state with a cubic lattice, which persists at least up to 60 ps after the excitation. Analysis of the intermediate state at the fast excitation shows that the bond disproportionation and monoclinic distortion of ${BaBiO}_{3}$ structure are energetically favorable due to the charge carrier pairing. Thus the compound ${BaBiO}_{3}$ forms a new quantum state that we define as a local pair density wave. Taking into account a large number of similarities between bismuthate and cuprate high-temperature superconductors, we believe that our work will give a new impetus to understanding the nature of superconductivity in perovskite HTSCs.

Received 13 December 2023
Revised 29 March 2024
Accepted 17 May 2024

DOI:https://doi.org/10.1103/PhysRevResearch.6.023307

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Charge density waves Electronic structure Pairing mechanisms Superconductivity

Charge-transfer insulators High-temperature superconductors Superconductors

Density functional calculations Density functional theory Laser ablation X-ray absorption near-edge spectroscopy X-ray absorption spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

A. P. Menushenkov ^1,*, A. Ivanov ¹, V. Neverov¹, A. Lukyanov¹, A. Krasavin¹, A. A. Yastrebtsev¹, I. A. Kovalev ¹, Y. Zhumagulov², A. V. Kuznetsov¹, V. Popov¹, G. Tselikov ³, I. Shchetinin⁴, O. Krymskaya¹, A. Yaroslavtsev ⁵, R. Carley⁶, L. Mercadier⁶, Z. Yin ⁶, S. Parchenko⁶, L. P. Hoang⁶, N. Ghodrati ⁶, Y. Y. Kim⁶, J. Schlappa⁶, M. Izquierdo⁶, S. Molodtsov^6,7,8, and A. Scherz⁶

¹National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow 115409, Russia
²University of Regensburg, Regensburg 93040, Germany
³Emerging Technologies Research Center, XPANCEO, Internet City, Emmay Tower, Dubai 00000, United Arab Emirates
⁴National University of Science and Technology MISiS, Moscow 119049, Russia
⁵Department of Physics and Astronomy, Uppsala University, Uppsala 75120, Sweden
⁶European XFEL GmbH, Schenefeld 22869, Germany
⁷Institute of Experimental Physics, TU Bergakademie Freiberg, Leipziger Strasse 23, 09599 Freiberg, Germany
⁸Center for Efficient High Temperature Processes and Materials Conversion (ZeHS), TU Bergakademie Freiberg, Winklerstrasse 5, 09599 Freiberg, Germany

^*Corresponding author: menushen@gmail.com

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Vol. 6, Iss. 2 — June - August 2024

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Figure 1
Local crystal and electronic structure of ${BaBiO}_{3}$ . Left: ground state with larger $Bi {\underset{̲}{L}}^{0} O_{6}$ and smaller $Bi {\underset{̲}{L}}^{2} O_{6}$ octahedra carrying the electron and hole pairs on the upper antibonding $Bi 6 s - O 2 p_{σ^{*}}$ orbital, respectively. Right: excited state after resonant laser excitation $ℏ ω_{G}$ through the optical gap with broken pairs and equal octahedra. Circles denote paired states. ${\underset{̲}{L}}^{2}, {\underset{̲}{L}}^{0}$ , and ${\underset{̲}{L}}^{1}$ denote a local hole pair, a local electron pair, and a single electron (hole), respectively.
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Figure 2
Pump-induced excitation of ${BaBiO}_{3}$ ground state in the O $K$ -edge XAS experiment at XFEL. (a) Schematics of the tr-XAS experiment at the SCS instrument. (b) Top panel: the experimental ground state (black line) and the excited state (red line) O $K$ XAS of ${BaBiO}_{3}$ measured at the delay time 0.3 ps and optical pump fluence $8 mJ / {cm}^{2}$ . Three characteristic spectral ranges are marked with colors: (red) the pre-edge O $K$ XAS peak corresponding to the Bi $6 s - O 2 p_{σ^{*}}$ antibonding orbital; (green) the rising edge of the main O $K$ XAS peak corresponding to the hybridized $O 2 p - Bi 6 p$ states; (blue) the main O $K$ XAS peak corresponding to the hybridized $O 2 p - Ba 5 d$ states (the “lattice” states). Bottom panel: the difference between the excited and ground state spectra $Δ XAS$ of ${BaBiO}_{3}$ measured at the different delay times from $- 0.1$ to 59.8 ps. The positive peak A and negative peak B in $Δ XAS$ are marked with the vertical dashed lines. (c) The evolution of peak A in $Δ XAS$ with the delay time changing from 0.1 to 1.8 ps. (d) The energy position of peak A $vs$ the delay time.
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Figure 3
Dynamics of ${BaBiO}_{3} K$ O XAS preedge peak. Top panel: the preedge peak of ${BaBiO}_{3}$ O $K$ XAS measured at the ground (unpumped) state and different delay times after the excitation (0.2, 0.8, and 4.8 ps) at three optical pump fluences. Bottom panel: the experimental preedge XAS peak at the delay time 4.8 ps (blue circles) and its fitting (solid red line) with the sum of calculated ground (green) and excited (purple) state DOS. Inset in the bottom panel: the fraction of the excited state $α$ in the resulting XAS spectrum $vs$ the optical pump fluence.
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Figure 4
Three-exponential fitting of time-dependent $Δ XAS$ at the photon energy 528.2 eV (peak A). (Red circles) The delay time scan measured at the fixed photon energy 528.2 eV corresponding to the peak A in the difference spectrum $Δ XAS$ and the pump fluence $8 mJ / {cm}^{2}$ . (Solid red line) Three-exponential fitting of the time scan. The time ranges where three characteristic processes give the biggest impact are marked with colors: (orange) electronic structure excitation, (green) electronic structure relaxation, and (blue) lattice rearrangement. Inset: three characteristic times obtained from the exponential fit.
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Figure 5
Scheme of ${BaBiO}_{3}$ ground state excitation by a resonant optical photon. The main changes occur in ${BaBiO}_{3}$ upon the fast resonant excitation over the optical gap. The simultaneous rearrangement of local electronic (bottom panel) and local crystal (top panel) structures is reflected in the shape of the O $K$ -edge XAS and the difference spectrum $Δ XAS$ of ${BaBiO}_{3}$ at the delay time 0.8 ps (right panel).
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Figure 6
Scheme of fast transients occurring in ${BaBiO}_{3}$ at short delay times after excitation. The detailed scheme of ${BaBiO}_{3}$ local electronic structure (top) and local crystal structure (bottom) rearrangement observed at the delay times $0 - 0.8$ ps after femtosecond resonant excitation over the optical gap $ℏ ω_{G} = E_{G}$ . Left panel: the two-particle paired ground state $E_{0} ({\underset{̲}{L}}^{0}) + E_{0} ({\underset{̲}{L}}^{2})$ ; middle panel: the single-particle unpaired intermediate excited state $E_{2}^{*} ({\underset{̲}{L}}^{0}) + E_{2}^{*} ({\underset{̲}{L}}^{2})$ ; right panel: the single-particle metastable final excited state $2 E_{1}^{*} ({\underset{̲}{L}}^{1}$ ).
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Direct evidence of real-space pairing in BaBiO3

Phys. Rev. Research 6, 023307 – Published 21 June 2024

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Direct evidence of real-space pairing in $Ba {BiO}_{3}$