Effect of the Zero-Mode Landau Level on Interlayer Magnetoresistance in Multilayer Massless Dirac Fermion Systems

We report on the experimental results of interlayer magnetoresistance in the multilayer massless Dirac fermion system $\alpha \mathrm{\text{−}}(\mathrm{BEDT}\mathrm{\text{−}}\mathrm{TTF}{)}_2{\mathrm{I}}_3$ under hydrostatic pressure and its interpretation. We succeeded in detecting the zero-mode Landau level ($n=0$ Landau level) that is expected to appear at the contact points of Dirac cones in the magnetic field normal to the two-dimensional plane. The characteristic feature of zero-mode Landau carriers including the Zeeman effect is clearly seen in the interlayer magnetoresistance.

Figure 1

(a) Magnetic field dependence of interlayer resistance under the pressure about 1.7 GPa at 4 K. When $B>0.2\mathrm{T}$, remarkable negative magnetoresistance is observed. As for negative magnetoresistance, fitting is done with Eq. (1), $R_{zz}\propto 1/(|B|+B_0)$ (red line). The inset shows the Landau levels of this system. (b) Angle dependence of magnetoresistance. When $\theta =0$ and $\theta =180°$, the direction of the magnetic field is parallel to the 2D plane. $\theta =90°$ is the direction normal to the 2D plane. Fitting of the data measured at 1, 2, and 3 T was done using Eq. (1).

Figure 2

(a) Magnetic field dependence of interlayer resistance for the magnetic field normal to the 2D plane at several temperatures from 0.06 to 9.6 K. (b) Temperature dependence of $B_1$ when resistance is assumed to be $R_{zz}\propto \exp (B/B_1)$. (c) Temperature dependence of the width of Landau levels ($2\hslash /\tau$).