Unconventional ballistic transport through bilayer graphene electrostatic barriers

The asymmetric Fano resonances (FRs) are noted for the first time in the coherent ballistic transmission spectrum of bilayer graphene tunneling structures. This characteristic tunneling transmission that occurs particularly at small glancing incidence mainly arises due to the quadratic dispersion of chiral charge carriers. The Fano line shape is found to be highly sensitive with respect to the direction of incidence of the charge carriers, the applied homogeneous electric field, as well as to the barrier height and width. The absence of the FR at normal incidence is in accordance with the conservation of chirality of the Dirac fermions in bilayer graphene. The sharp antiresonance at the center of the tunneling band arising due to destructive interference between the electron and the holelike states might be responsible for high negative differential conductivity (NDC) in bilayer graphene.

Figure 1

Schematic diagram for the potential profile in bilayer graphene double-barrier structure of barrier width “$b$,” well width “$a$,” and barrier height $V_0$; (a) under the field-free condition of the system; (b) under the applied electric field ($E^{\prime }$); (c) field-free planar structure showing the normal to the well barrier interface and the angle of incidence ($\theta$).

Figure 2

Transmission coefficient ($T_c$) as a function of incident electron energy ($E$) under the field-free condition; $b$ = $a$ $=$ 10 nm.

Figure 3

Same as Fig. 2 but for $k_y$ = $1\times {10}^7{\mathrm{m}}^{-1}$ and $a$ = 10 nm; (a) for SBGBL and (b) for DBGBL.

Figure 4

Same as Fig. 2 but under biased condition; (a) for SBGBL and (b) for DBGBL.

Figure 5

Ballistic conductivity (in units of $e^2/h$) is plotted as a function of the applied in plane electric bias $V_a$. Here $a$ = $b$ = 10 nm, $V_0$ = 50 mV, and the Fermi energy $E_F$ = 20 meV.