Magnetoconductance Oscillations and Evidence for Fractional Quantum Hall States in Suspended Bilayer and Trilayer Graphene

We report pronounced magnetoconductance oscillations observed on suspended bilayer and trilayer graphene devices with mobilities up to $270000{\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$. For bilayer devices, we observe conductance minima at all integer filling factors $\nu$ between 0 and $-8$, as well as a small plateau at $\nu =1/3$. For trilayer devices, we observe features at $\nu =-1$, $-2$, $-3$, and $-4$, and at $\nu \sim 0.5$ that persist to 4.5 K at $B=8\mathrm{T}$. All of these features persist for all accessible values of $V_g$ and $B$, and could suggest the onset of symmetry breaking of the first few Landau levels and fractional quantum Hall states.

Figure 1

$G(V_g)$ for (a) BLG and (b) TLG devices at $T=4.2\mathrm{K}$. Upper and lower curves are taken before and after current annealing, respectively. Inset: SEM image of a suspended graphene device.

Figure 2

Data from a bilayer device BL1 at 300 mK. (a) $G$ vs $1/B$ at $V_g=3$, 4, 5, 6,7, 7.5, 8, 8.5, 9, and 9.8 V (bottom to top). The traces are offset for clarity. (b) $B_F(V_g)$ and a linear fit to the data points. (c) $G(V_g)$ at $B=3$, 2, and 1.5 T (bottom to top). The traces are offset for clarity. The numbers indicate the $|\nu |$ values that correspond to the local conductance minima. (d) $G$ in $e^2/h$ (upper) and $dG/d{V}_g$ (lower panel) vs $B$ and $V_g$. The dotted lines correspond to features with integer $\nu$ between $\nu =0$ and $-8$.

Figure 3

High field data for BL1. (a) $G(V_g,B)$ at 300 mK. (b),(c) Line traces from (a) at $B=15$, 17.5, 20, 23, and 28.5 T [right to left in (b)], plotting against $V_g$ and $\nu$, respectively. (d) $G(V_g)$ at $B=20\mathrm{T}$ and different $T$. The traces are not offset.

Figure 4

Data from a trilayer device TL1. (a) $G(V_g,B)$ at 260 mK. (b),(c) $G(V_g)$ and $G(\nu )$ at $B=2.2$, 2.5, 3.0, 3.5, 3.8 T. (d),(e) $G(V_g)$ and $G(\nu )$ at $B=4$, 5, 6,7, and 8 T. (f) $G(V_g)$ at and $T=4.5$, 2.7, 1.9, 1.6, 1.3, 1.0, 0.7, 0.4, and 0.26 K (top to bottom). The traces are offset for clarity.