title: Probing low-density carriers in a single atomic layer using terahertz parallel-plate waveguides.
abstract: As novel classes of two-dimensional (2D) materials and heterostructures continue to emerge at an increasing pace, methods are being sought for elucidating their electronic properties rapidly, non-destructively, and sensitively. Terahertz (THz) time-domain spectroscopy is a well-established method for characterizing charge carriers in a contactless fashion, but its sensitivity is limited, making it a challenge to study atomically thin materials, which often have low conductivities. Here, we employ THz parallel-plate waveguides to study monolayer graphene with low carrier densities. We demonstrate that a carrier density of ~2 × 10(11) cm(-2), which induces less than 1% absorption in conventional THz transmission spectroscopy, exhibits ~30% absorption in our waveguide geometry. The amount of absorption exponentially increases with both the sheet conductivity and the waveguide length. Therefore, the minimum detectable conductivity of this method sensitively increases by simply increasing the length of the waveguide along which the THz wave propagates. In turn, enabling the detection of low-conductivity carriers in a straightforward, macroscopic configuration that is compatible with any standard time-domain THz spectroscopy setup. These results are promising for further studies of charge carriers in a diverse range of emerging 2D materials.
authors.forename: Manjakavahoaka
authors.initials: M
authors.lastname: Razanoelina
authors.forename: Filchito Renee
authors.initials: FR
authors.lastname: Bagsican
authors.forename: Iwao
authors.initials: I
authors.lastname: Kawayama
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhang
authors.forename: Lulu
authors.initials: L
authors.lastname: Ma
authors.forename: Hironaru
authors.initials: H
authors.lastname: Murakami
authors.forename: Robert
authors.initials: R
authors.lastname: Vajtai
authors.forename: Pulickel M
authors.initials: PM
authors.lastname: Ajayan
authors.forename: Junichiro
authors.initials: J
authors.lastname: Kono
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Tonouchi