Conductance of the edge modes as well as conductance across the co-propagating edge modes around the ν = 4/3, 5/3 and 2 quantum Hall states are measured by individually exciting the modes. Temperature dependent equilibration rates of the outer unity conductance edge mode are presented for different filling fractions. We find that the equilibration rate of the outer unity conductance mode at ν = 2 is higher and more temperature sensitive compared to the mode at fractional filling 5/3 and 4/3. At lowest temperature, equilibration length of the outer unity conductance mode tends to saturate with lowering filling fraction ν by increasing magnetic field B. We speculate this saturating nature of equilibration length is arising from an interplay of Coulomb correlation and spin orthogonality.

Surface potential is an important parameter for the development and optimization of high-performance charge/potential sensitive chemosensors. In this work, we demonstrate a technique of measuring surface potential modulation (SPM) due to chemoselective absorption in functional material (FM), at FM|dielectric (D) interface using graphene-heterostructure-field-effect-transistor (GHFET) made of FM|D|graphene (G). In the GHFET, chemoselective FM acts as a floating gate, where gate voltage is modulated chemically and causes resistive response in graphene. We have developed an analytical model of the GHFET and find that the SPM can be measured as the sum of potential modulation across the dielectric and the Fermi energy modulation of graphene. We experimentally demonstrate the methodology of measuring SPM in GHFET made of Pd|Al2O3|G layers for H2 gas absorption in Pd layer. We find that the SPM shows saturating nature with increasing H2 concentration under N2 gas environment and estimate the value of saturated SPM as 308 ± 21 meV. In air environment, no such saturation of the SPM with H2 gas concentration is observed. Notably, the GHFET of Pd|Al2O3|G layers shows better H2 gas sensitivity response (28 ± 1% at 0.4% H2) under air environment compared to other reported graphene based H2 sensors. Our methodology has an implication for enhancing H2 gas sensing.

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Transition metal dichalcogenides (TMDCs) are potential two-dimentional materials as natural partners of graphene for highly responsive van der Waals (vdW) heterostructure photodetectors. However, the spectral detection range of the detectors is limited by the optical bandgap of the TMDC, which acts as a light-absorbing medium. Bandgap engineering by making alloy TMDC has evolved as a suitable approach for the development of wide-band photodetectors. Here, broadband (visible to near-infrared) photodetection with high sensitivity in the near-infrared region is demonstrated in a MoSSe/graphene heterostructure. In the ambient environment, the photodetector exhibits high responsivity of 0.6 × 10 2 A/W and detectivity of 7.9 × 10 11 Jones at 800 nm excitation with a power density of 17 fW/μm 2 and 10 mV source−drain bias. The photodetector shows appreciable responsivity in self-bias mode due to nonuniform distribution of MoSSe flakes on the graphene layer between the source and drain end and the asymmetry between the two electrodes. Time-dependent photocurrent measurements show fast rise/decay times of ∼38 ms/∼48 ms. A significant gate tunability on the efficiency of the detector has been demonstrated. The device is capable of low power detection and exhibits high operational frequency, gain, and bandwidth. Thus, the MoSSe/graphene heterostructure can be a promising candidate as a high-speed and highly sensitive near-infrared photodetector capable of operating at ambient conditions with low energy consumption.