films grown by gas source MBE*

Research on quantum transport in high electron mobility oxides started from such conventional semiconductors as ZnO and SrTiO₃ (STO). To extend the research further, EuTiO₃ (ETO) is an ideal system by adding a knob of magnetic control (local 4f⁷ moment on Eu²⁺). We employ a metalorganic gas source molecular beam epitaxy (gas source MBE) at very high substrate temperatures that enabled us to observe quantum Hall effect in STO quantum well [1]. In the case of strained films of La doped ETO, we observed additional terms in the anomalous Hall effect during the magnetization process, which is not proportional to the magnetization [2]. The mobility in ETO films for strain-free films on STO substrates has reached to 3,000 cm²V^-1s^-1 at 2 K [3]. Our samples exhibited strong Shubnikov–de Haas (SdH) oscillations in a forced-ferromagnetic state above 4 T at 2 K, making them distinct from the conventional magnetic semiconductors whose lack of high carrier mobility is known to suppress such quantum oscillations. Our band calculation suggests that the high mobility electrons populate in the bands, which are originally derived from Ti 3d orbitals and are fully spin polarized and modified by the f-d coupling between Eu 4f and Ti 3d orbitals. These new findings strongly suggest that the electron-doped ETO film with high mobility is an ideal magnetic semiconductor to explore novel magneto ‘quantum’ transport phenomena.

References:
[1] Y. Matsubara, K. S. Takahashi et al., Nat. Commun. 7, 11631 (2016).
[2] K. S. Takahashi et al., Sci. Adv. 4, eaar7880 (2018).
[3] K. Maruhashi, K. S. Takahashi et al., Adv. Mater. 32, 1908315 (2020).