A research team from Nanjing University has developed an in-situ on-device electrochemical intercalation method to manipulate the structural and electronic properties of MoS2 thin flakes, resulting in a robust nonlinear Hall effect (NLHE) observable at room temperature. By intercalating cetyltrimethylammonium ions (CTA+) into the van der Waals (vdW) gap of MoS2, the inversion symmetry is broken and NLHE can be observed up to 300 K. This work provides a new approach for regulating NLHE and symmetry in 2D materials and opens new avenues for designing new electronic and spintronic devices.
As an important member of the Hall effect family, NLHE has attracted considerable research attention in recent years due to its advantage of generating high-harmonic Hall voltage without breaking time-reversal symmetry, which exhibits great potential in energy harvesting, wireless communications and infrared detection. In this context, two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2, are particularly attractive platform due to their tunable electronic properties and potential applications in electronics, optoelectronics, and quantum technologies. Nevertheless, the realization of nonlinear transport phenomena such as the NLHE in TMDs remains nontrivial. The NLHE requires specific symmetry conditions (broken inversion symmetry) that are difficult to achieve or maintain in pristine or device-scale TMD systems. Consequently, the experimental observation of stable, large-magnitude NLHE at room temperature has largely relied on approaches such as strain engineering, precise twist-angle control, or the application of external fields, which often suffer from limited scalability, reproducibility, and long-term stability.
As a promising alternative, intercalation has emerged as a versatile strategy to tailor the physical properties of two-dimensional materials by introducing guest species into the host lattice, thereby modulating their intrinsic electronic and symmetry-related characteristics. Despite its demonstrated effectiveness in tuning electronic, magnetic, and structural properties, the use of intercalation to regulate the NLHE has received little attention to date.
The Solution: The researchers fabricated CTA+-intercalated MoS2 thin flake devices via an in-situ on-device electrochemical intercalation method. Structural characterization demonstrates that the atomic structure within the layers remains unchanged, but the layer distance expands from 0.61 nm to 1.06 nm distinguish with the previous research, thus achieving atomic-layer manipulation. Due to the substantial injection of electrons by the intercalation process, the transport behavior of MoS2 transforms from semi-metallic to metallic and the carrier concentration is estimated to be approximately -6.94 × 1020 cm-3. With the incorporation of CTA into the van der Waals gap of MoS2, the inversion symmetry of the MoS2 is broken, which in turn successfully triggers the emergence of NLHE. At a temperature of 10 K, the maximum V⊥2ω exceeds 7 μV, and the corresponding current is 100 μA. In the measurement of temperature-dependent NLHE, not only the main mechanism of skew scattering is confirmed by the nonlinear susceptibility analysis, but also a significant NLHE can be still observed under room temperature of 300 K. This work provides a new class of materials exhibiting NLHE at room temperature. Compared with other systems, intercalated MoS2 exhibits a non-negligible nonlinear Hall susceptibility. Owing to its well-established growth process and excellent chemical stability, this material holds considerable potential for practical applications.
The Future: NLHE, benefiting from its rectification characteristics, holds great potential for applications in photodetection, energy storage, and other related fields. Based on the practical scenarios of these applications, future research will focus on improving the nonlinear susceptibility at room temperature. On the one hand, different host materials and guest materials can be selected to observe their influence on NLHE. On the other hand, specific parameters of electrochemical intercalation also play a significant role in the regulation of NLHE. As the film growth technology of TMDs well-developed, it is expected to achieve large-scale, industrialized, and integrated production and application of room-temperature NLHE in TMDs.
The Impact: This work expands the candidates of room-temperature NLHE materials and provides a new perspective for investigating the NLHE and symmetry engineering in two-dimensional materials.
The research has been recently published in the online edition of Materials Futures, a prominent international journal in the field of interdisciplinary materials science research.
Reference: Fuwei Zhou, Yu Du, Tianqi Wang, Heng Zhang, Jiajun Li, Wuyi Qi, Yefan Yu, Fucong Fei, Fengqi Song. The nonlinear Hall effect induced by electrochemical intercalation in MoS2 thin flake devices[J]. Materials Futures, 2026, 5(2): 025302. DOI: 10.1088/2752-5724/ae31fa
