Research Highlights

For two-dimensional (2D) materials—such as bilayer graphene—the path toward practical device applications that promise to revolutionize electronics must first go through the precise characterization of their exotic electronic properties.

Because the properties of these 2D materials often involve changes in electronic states on very short timescales, their characterization requires high-frequency measurement methods, such as radio-frequency (RF) reflectometry.

However, conventional quantum-device setups used for this kind of measurement typically use SiO₂ as an insulator and highly doped Si as back-gates; these materials increase the stray capacitances that lead to substantial RF signal leakage.

In a 2023 article, Otsuka and co-workers from AIMR addressed this problem with a new quantum-device design that excludes SiO₂ and doped Si¹.

“Our design integrated a microscale graphite back-gate using undoped Si as the substrate and hexagonal BN as the insulator,” explains Otsuka. “This approach produced a bilayer-graphene device that not only improved the matching condition of the tank circuit but also enhanced the sensitivity of the RF reflectometry measurements.”

The research team probed the quantum dots formed within the bilayer graphene of the device and observed the Coulomb blockade using both direct-current and RF reflectometry measurements. The detection of Coulomb diamonds by the latter method further suggested that real-time characterization of 2D material properties can be achieved with the new quantum-device design.

“By demonstrating high-speed, precise measurements in bilayer graphene-based quantum devices, our work has opened new avenues for interrogating the quantum dynamics of 2D materials,” says Otsuka. “We look forward to exploring new 2D quantum systems with this approach.”

(Author: Patrick Han)