On July 22nd, the journal “Nature Nanotechnology” published a paper titled “Even-integer quantum Hall effect in an oxide caused by a hidden Rashba effect” by Professor Hailin Peng from Peking University, a user of the Wuhan National High Magnetic Field Center. This achievement was based on the pulsed high magnetic field facility at the center and was the result of a collaboration between Professor Hailin Peng of Peking University, Professor Hongtao Yuan of Nanjing University, and Professor Binghai Yan of the Weizmann Institute of Science in Israel. The experimental measurements using the pulsed high magnetic field were provided by Professor Zengwei Zhu and Engineer Huakun Zuo from the center.

Recently, the emergence of 2D layered materials has provided opportunities to explore unique spin textures and e quantum Hall effect (QHE), when the electron states and spin textures can be tuned by an external modulation of the electric field and by the inversion-symmetry engineering at the atomic level. However, in the previously reported QHE in 2D layered materials, the quantization in a high magnetic field is mainly prevailed by the Zeeman effect, in which the spin–orbit coupling (SOC) is relatively small due to the light atomic weight therein. In this work, we demonstrate the only even-integer states when the magnetic field is up to 50 T in a Bi₂O₂Se quantum Hall system driven by a unique spin-degenerated Rashba bilayer structure, that is, a hidden Rashba effect, in which two sectors form an inversion partner with opposite Rashba spin polarizations and compensate with each other.

Figure 1. The hidden Rashba effect and even-integer quantum Hall effect in Bi₂O₂Se.

The QHE and quantum oscillations in epitaxial Bi₂O₂Se films were measured by the pulsed-high-magnetic-field facility (55 T) at the Wuhan National High Magnetic Center. The figure shows the QHE in the 1-uc-thick Bi₂O₂Se sample at 4.2 K. We studied the thickness-dependent evolutions of SdH oscillations and QHE in epitaxial Bi₂O₂Se films. Only even-integer quantum Hall plateaus, that is, ν = 2, 4, 6, 8, 10, 12…, can be observed for 6- and 2.5-uc-thick Bi₂O₂Se films under pulsed magnetic fields up to 50 and 55 T. As shown in the figure, an odd-integer quantum Hall plateau of ν = 5 appeared at B > 40 T, which is totally different from the even-integer QHE in thicker films. Meanwhile, two valleys (ν = 6 and ν = 7) between the ν = 5 and ν = 8 plateaus in the R_xx–B curves can be clearly observed, indicating the full separation of spin polarizations under high magnetic fields.

In summary, we demonstrated the experimental observation of the even-integer quantum Hall states originating from the unique degenerated Rashba bilayer structure and hidden Rashba effect in few-layer 2D Bi₂O₂Se films. The quantum Hall states in layered 2D Bi₂O₂Se can be selectively controlled via SOC engineering at the atomic level. The high mobility, as well as the strong and tunable SOC, makes Bi₂O₂Se a promising candidate for realizing novel SOC-related phenomena and potential spintronic applications, such as tunable spin Hall effect, spin galvanic effect, nonlinear physics and spin–orbit torque.

Link: https://www.nature.com/articles/s41565-024-01732-z