Abnormal Hall Effect of Trigonal Phase Single-Crystal RhO₂

The two-dimensional (2D) metastable phase van der Waals oxide is regarded as a novel subset of the 2D material family, demonstrating fascinating physical and chemical properties. In this work, we report a notable Hall effect in the trigonal phase RhO2 single crystal: the Hall coefficient shifts from negative at temperatures below 100 K to positive above 150 K. This transition suggests that the trigonal phase RhO2 crystal is n-type at low temperature and transitions to p-type at high temperature, indicating a phase transition around 130–140 K. This discovery adds a new dimension to the 2D material family, paving up the way for their potential integration into advanced next-generation devices.