Spin-selective evolution of the Zhang-Rice state in binary transition metal oxide MnO(001) film

Asish K. Kundu, Polina M. Sheverdyaeva, Paolo Moras, Krishnakumar S. R. Menon, Subhasish Mandal, and Carlo Carbone

Phys. Rev. B 109, 195111 – Published 3 May 2024

Abstract

The Zhang-Rice (ZR) state is a strongly hybridized bound state formed by transition-metal and oxygen atoms. The spin fluctuations within the ZR state are known to play an important role in high- $T_{c}$ superconductivity in cuprates. Here, we employ a combination of angle-resolved photoemission spectroscopy (ARPES), x-ray photoemission spectroscopy (XPS), and ab initio embedded dynamical mean-field theory (eDMFT) to investigate the influence of magnetic ordering on the spectral characteristics of the valence band and Mn $2 p$ core-level in MnO (001) ultrathin films. Our results demonstrate that a complex spin-selective evolution of Mn $3 d - O 2 p$ hybridization develops due to the long-range antiferromagnetic (AFM) ordering. This hybridization significantly alters the spectral shape and weight of the ZR state. Specifically, in the AFM phase, we observed the sharpening of the ZR state and band folding with the periodicity of the AFM unit cell of MnO(001). We also demonstrated a strong connection between the spectral evolution of the ZR state and the non-local screening channels of the photoexcited core holes. Further, our detailed temperature-dependent study reveals the presence of short-range antiferromagnetic correlations that exist at much higher temperatures than Neel temperature $(T_{N})$ and shows the evolution of the ZR state across the magnetic transitions and its implication to the core-hole screening in $3 d$ binary transition metal oxides.

Received 31 October 2023
Revised 2 April 2024
Accepted 17 April 2024

DOI:https://doi.org/10.1103/PhysRevB.109.195111

Physics Subject Headings (PhySH)

Density of states Electronic structure Fermi surface First-principles calculations Magnetic phase transitions Magnetism

Antiferromagnets Mott insulators Strongly correlated systems Thin films

Angle-resolved photoemission spectroscopy Density functional theory Dynamical mean field theory Epitaxy Evaporation Photoemission spectroscopy X-ray photoelectron spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Asish K. Kundu ^1,2,3,4,*, Polina M. Sheverdyaeva ², Paolo Moras ², Krishnakumar S. R. Menon ⁵, Subhasish Mandal ^6,†, and Carlo Carbone²

¹International Center for Theoretical Physics (ICTP), Trieste 34151, Italy
²Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), Trieste 34149, Italy
³Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
⁴National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA
⁵Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata 700064, India
⁶Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, USA

^*asishkumar2008@gmail.com
^†subhasish.mandal@mail.wvu.edu

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Vol. 109, Iss. 19 — 15 May 2024

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Images

Figure 1
Crystal structure and electronic band dispersion of MnO films on Ag(001) showing magnetism-induced band folding. (a) Schematic diagram of the MnO lattice, including spin arrangements of ${Mn}^{2 +}$ . The $O^{2 -}$ ions are not shown in the figure. The red and black arrows represent the antiparallel arrangement of spins between two consecutive (111) planes. (b) The spin arrangements of ${Mn}^{2 +}$ ions on the MnO(100) surface. The dashed ( $1 \times 1$ ) square and ( $2 \times 1$ ) rectangle represent the chemical and magnetic unit cells of MnO(001), respectively. (c) Bulk Brillouin zone (BZ) of MnO and its [001] surface projection. (d) The schematic of the ( $1 \times 1$ ) SBZ (green) and two orthogonal ( $2 \times 1$ ) antiferromagnetic domains (red and black). (e), (f) Energy-momentum dispersions along $\bar{X} − \bar{Γ} − \bar{X}$ path of the MnO(001) SBZ using a photon energy of $125 eV (k_{z} = 0)$ at 300 K and 20 K, respectively. (g), (h) The second derivatives of (e) and (f), respectively. The inset shows the zoomed view of the top part of the valence band (Zhang-Rice bound state, ZRB) as indicated by dashed rectangles in (e) and (f). Dashed curves (red) are used to guide the eye showing the band folding. (i), (j) Constant-energy contours through the ZRB state in the PM and AFM phase, respectively, using a photon energy of 40 eV. The square (green) denotes the SBZ. Solid (red) and dashed (yellow) squares with circles at the corners denote the spectral features in the Fermi surface and their folding, respectively.
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Figure 2
ARPES and eDMFT spectra of MnO across $T_{N}$ . (a), (b) ARPES spectra of MnO (001) films along the $\bar{M} − \bar{Γ} − \bar{M}$ path of the SBZ using a photon energy of 40 eV at 300 K and 20 K, respectively. (c), (d) Theoretical band structure using eDMFT along X- $Γ$ -X path of the bulk BZ in the PM and AFM phase. The $k_{z}$ dependency of electronic band structure using ARPES along the $Γ − X − Γ_{1}$ directions of bulk BZ, perpendicular to the (001): (e) PM ( $h ν = 25 - 125 eV$ , 300 K) and (f) AFM ( $h ν = 25 - 140 eV$ , 20 K) phase, respectively. (g) Integrated EDCs within the whole momentum range ( $Γ − X − Γ_{1}$ ) from (e) and (f). (h) Stack of normal emission ARPES spectra ( $\bar{Γ} = 0$ ) for various temperatures showing the ZRBS evolution (the data were collected at $h ν = 40 eV$ ). The vertical dashed line indicates the $T_{N}$ in our MnO(001) film. Filled circles outline the dispersion of the electronic states. (i) EDCs at various temperatures integrated over $\bar{Γ} \pm 0.5 Å^{- 1}$ along $\bar{Γ} - \bar{X}$ .
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Figure 3
Partial density of states (PDOS) and hybridization function computed using eDMFT in the PM and AFM phase. (a) PDOS of Mn $3 d$ and O $2 p$ . (b) Hybridization function. (c) Orbital (Mn $3 d$ and O $2 p$ ) projected band structure for the (c) PM and (d), (e) AFM spin down (minority) and spin up (majority), respectively. Green and red represent the Mn $3 d$ and O $2 p$ contributions, respectively, with some mixed states appearing dark. Red color is enhanced to show O $2 p$ clearly. In (c), we considered the PM unit cell dimension is same to that of the AFM cell.
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Figure 4
Temperature dependence of the Mn $2 p$ core level of MnO films showing the variation of local and nonlocal screening of core hole. (a) Temperature dependence of Mn $2 p$ core- levels using a photon energy of 750 eV, where A and B peaks are the multiplet structure of $2 p_{3 / 2}$ associated with the local and nonlocal screening, respectively, and S is the charge transfer satellite. States are marked with the final state photoemission as obtained from the Ligand field picture. (b) Same spectra as (a) but superimposed on top of one another to understand the overall change of spectral shape. Inset shows zoomed view of Mn $2 p_{3 / 2}$ peak.
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