The search for methods and material systems to achieve high-mobility two-dimensional (2D) semiconductors is a crucial research direction in condensed matter physics and nanoelectronics. Since the first discovery of the quantum Hall effect (QHE) in high-mobility 2D electron gases within quantum wells over 40 years ago, the number of known 2D electronic systems capable of exhibiting either QHE or fractional quantum Hall effect (FQHE) remains very limited. Among them, achieving a well-defined low-temperature ground state in high-mobility intrinsic 2D semiconductors has been particularly challenging, primarily due to the difficulty in realizing reliable Ohmic contacts.

Recently, researchers at the Liaoning Academy of Materials have made a breakthrough in the stable and reliable fabrication of low-temperature Ohmic contacts for n-type molybdenum disulfide (MoS₂) semiconductor field-effect transistors (FETs). Their findings, titled "Fractional quantum Hall phases in high-mobility n-type molybdenum disulfide transistors," were published online in Nature Electronics on October 30, 2024.

In this study, MoS₂ few-layer crystals were encapsulated in hexagonal boron nitride (hBN) within a glovebox, with a pre-patterned hBN top layer featuring micrometer-scale windows for the thermal evaporation of bismuth (Bi) electrodes. This approach enabled the fabrication of Ohmic contacts and high mobility across the entire temperature range (from millikelvin to room temperature) at relatively low carrier densities (Figure 1).

Under millikelvin temperatures and strong magnetic fields, researchers observed the quantum limit at filling factor ν=1 and fractionally quantized Hall conductance plateaus at $\nu =2/5$ and $\nu =4/5$. This marks the first-ever observation of the fractional quantum Hall effect in an intrinsic bandgap n-type 2D semiconductor through electrical transport measurements (in a non-topological system). These experimental results open new possibilities for high-mobility electronic transistors (HEMTs), low-temperature amplifiers, and other nanoelectronic devices based on 2D semiconductors.

Fig. 1. High mobility MoS2 transistor and the FQHE found in them at 34 T、0.3 K.

Read the research paper：https://www.nature.com/articles/s41928-024-01274-1