Electronic band structure of (111) ${\mathrm{SrRuO}}_3$ thin films: An angle-resolved photoemission spectroscopy study

We studied the electronic band structure of pulsed laser deposition (PLD) grown (111)-oriented ${\mathrm{SrRuO}}_3$ thin films using in situ angle-resolved photoemission spectroscopy technique. We observed light bands with a renormalized quasiparticle effective mass of about $0.8m_e$. The electron-phonon coupling underlying this mass renormalization yields a characteristic “kink” in the band dispersion. The self-energy analysis using the Einstein model suggests five optical phonon modes covering an energy range of 44–90 meV contribute to the coupling. In addition, we show that the quasiparticle spectral intensity at the Fermi level is considerably suppressed, and two prominent peaks appear in the valance band spectrum at binding energies of 0.8 and 1.4 eV, respectively. We discuss the possible implications of these observations. Overall, our work demonstrates that high-quality thin films of oxides with large spin-orbit coupling can be grown along the polar (111) orientation by the PLD technique, enabling in situ electronic band structure study. This could allow for characterizing the thickness-dependent evolution of band structure of (111) heterostructures—a prerequisite for exploring possible topological quantum states in the bilayer limit.

Figure 1

(a) RHEED image taken along the $\left[1\overline{1}0\right]$ azimuth. (b) LEED image of $15\mathrm{u}.\mathrm{c}.$ SRO film, taken at an electron kinetic energy of 60 eV. (c) AFM image showing the step-terrace structure, and the inset shows the height profile along the black solid line. (d) Temperature-dependent resistivity of 15 u.$\mathrm{c}.$ (111) SRO, and the inset shows the derivative plot highlighting the onset of ferromagnetism around 127 K.

Figure 2

(a) ARPES data over a wide energy window along the $\overline{\mathrm{\Gamma }}\text{−}\overline{K}$ direction. (b) Corresponding angle-dependent EDC curves. Two triangles indicate the $-1.4$ and $-0.8$ eV peaks.

Figure 3

(a) Three-dimensional energy versus momentum dispersion of the 15 u.c. SRO film. The dashed white line indicates the surface projected BZ. (b) Isoenergy surfaces at energies 0 (Fermi level), $-250$, $-500$, and $-750$ meV, respectively. These isoenergy surfaces are obtained by integrating over an energy window of $+10$ to $-10\mathrm{meV}$ around the corresponding energies. The black dots are guides for the eyes, marking the coordinates of highest hotspot intensity that are obtained by profiling the isoenergy surfaces within the azimuthal angular range of $+{30}^{\circ }$ to $-{30}^{\circ }$.

Figure 4

(a) Energy versus momentum dispersion along the solid white line in the inset figure. (b) Two-dimensional curvature data zooming the marked rectangular region in (a). (c) The MDC dispersion (red circles) obtained by the Lorentzian fitting of MDC curves. The quadratic polynominal fit to the MDC is shown by the blue line. The black triangle indicates the “kink” in the dispersion. (d) The orange circles plot the real part, $\mathrm{Re}\mathrm{\Sigma }\left(\omega \right)$ (upper panel), and the imaginary part, $\mathrm{Im}\mathrm{\Sigma }\left(\omega \right)$ (lower panel), of the self-energy. The solid (dashed) black line marks the fit (simulation) of $\mathrm{Re}\mathrm{\Sigma }\left(\omega \right)$ $\left[\mathrm{Im}\mathrm{\Sigma }\right(\omega \left)\right]$ using the Einstein model. The simulation is performed using parameters that are obtained by fitting $\mathrm{Re}\mathrm{\Sigma }\left(\omega \right)$.