Electronic Structure and Resonant Circular Dichroism of La$_{0.7}$Sr$_{0.3}$MnO$_3$ from Soft X-ray Angle-Resolved Photoemission

Abstract

Coupling between spin, orbital, charge, and lattice degrees of freedom in transition-metal oxides produces a variety of electronic and magnetic phenomena of importance for future technologies. Here, we explore the electronic band structure of a (111)-oriented La0.7Sr0.3MnO3 thin film through soft X-ray angle-resolved photoemission spectroscopy (ARPES). The measurements agree with the electronic band structure calculated with density functional theory using Hubbard U correction. Furthermore, we probe the circular dichroism in ARPES, and observe a pronounced momentum- resolved magnetic circular dichroism in resonant photoemission from the Mn L-edge. The approach combines the momentum- and spin-selectivity of ARPES and X-ray magnetic circular dichroism, respectively, which could provide a useful approach for the study of unconventional magnetism.

Figures (5)

• Figure 1: (a) Supercell used in the DFT+$U$ calculations. (b) Diagram of the cubic Brillouin zone with high symmetry points indicated. (c) Density of states calculation for spin-up (left) and spin-down (right) electrons. All contributions besides O 2p and Mn 3d are negligible in the plotted range. (d) Unfolded spin-up band structure diagram calculated by DFT+$U$.
• Figure 2: (a) ARPES momentum map at the Fermi level along the [111] (out-of-plane) direction $k_z$ and the in-plane direction $k_x$ along [$11\bar{2}$] as indicated in Fig. \ref{['fig:scfig']}(b). The data was obtained by varying the photon energy from $h\nu =$300 to 530. Two main features are observed: a large pocket around the R point, and a smaller pocket around the $\Gamma$ point. Traces of these features are added as guides to the eye. (b) DFT+$U$ calculated Fermi surface along the same cut through the Brillouin zone as in (a).
• Figure 3: Fermi surface cuts calculated by DFT+$U$for the (a) R-X and (b) $\Gamma$-M high symmetry planes [cf. Fig. \ref{['fig:scfig']}(b)]. The labels (1-4) denote the most prominent features in each of the Fermi surface cuts. Calculated valence band dispersions along the (c) R-X and (d) $\Gamma$-M directions. Bands crossing the Fermi level are marked according to the labels in (a) and (b). ARPES momentum maps at the Fermi level taken in the (e) R-X high symmetry plane, obtained with a photon energy of $h\nu =$369, and in the (f) $\Gamma$-M high symmetry plane, obtained with a photon energy of $h\nu =$475. Measured band dispersions along the R-X and $\Gamma$-M directions are shown in (g) and (h), respectively. The features identified in the DFT+$U$calculations are indicated by the corresponding labels in (e)-(h). In (f), a trace of feature 4 from the DFT+$U$ calculation is overlaid as a guide to the eye.
• Figure 4: (a) Experimental geometry of the measurements probing the circular dichroism in ARPES. The photons, either left or right circularly polarized, impinge on the sample along the black arrow at an incidence angle of 20$^{\circ}$. The plane of light incidence is in the xz plane, shown in gray, which coincides with the mirror plane along the $[11\bar{2}]$ crystallographic axis. In this geometry, a magnetization $M_x$ is expected to induce magnetic circular dichroism. (b) Angle-integrated CD ($I_{CD}=I_L-I_R$) in photoemission measured at photon energies before, on, and after the Mn $L_3$ and $L_2$ resonances. (c) Angle-integrated photoemission intensity ($I=I_L + I_R$) as a function of photon energy at $E-E_F =$-2.18 integrated over a range of 0.1, as indicated by the vertical dashed line and shaded area in (b). (d) Angle-integrated CD as a function of photon energy at $E-E_F =$-2.18 integrated over a range of 0.1. The photon energies depicted in (b) are highlighted by their respective colors in (c) and (d).
• Figure 5: ARPES data measured at the Fermi level ($E-E_F = 0$) with a photon energy $h\nu =$645 tuned to the Mn $L_3$ resonance (cf. Fig. 4). (a) Total intensity obtained by taking the sum of left and right circularly polarized light, $I=I_L+I_R$. (b) Circular dichroism obtained by taking the difference between left and right circularly polarized light, $I_{CD}=I_L-I_R$. (c) Anti-symmetric contribution to $I_{CD}$ extracted from (b), representing the geometrically induced circular dichroism. (d) Symmetric contribution to $I_{CD}$ extracted from (b), representing the magnetically induced circular dichroism.