Angle-Dependent Magnetoresistance in the Weakly Incoherent Interlayer Transport Regime in a Layered Organic Conductor

We present comparative studies of the orientation effect of a strong magnetic field on the interlayer resistance of $\alpha \mathrm{\text{−}}(\mathrm{BEDT}\mathrm{\text{−}}\mathrm{TTF}{)}_2\mathrm{KHg}(\mathrm{SCN}{)}_4$ samples characterized by different crystal quality. We find striking differences in their behavior, which is attributed to the breakdown of the coherent charge transport across the layers in the lower quality sample. In the latter case, the nonoscillating magnetoresistance background is essentially a function of only the out-of-plane field component, in contradiction to the existing Fermi-liquid theories.

Figure 1

Interlayer resistance of two crystals of $\alpha \mathrm{\text{−}}(\mathrm{BEDT}\mathrm{\text{−}}\mathrm{TTF}{)}_2\mathrm{KHg}(\mathrm{SCN}{)}_4$ as a function of the polar angle $\theta$ recorded at different azimuthal angles $\phi$, $P=0\mathrm{kbar}$, $B=10\mathrm{T}$. Insets: (upper panel) details of a $\theta$ sweep for the clean sample, showing the small coherence peak; (lower panel) temperature dependence of the zero-field interlayer resistance of the clean (curve 1) and dirty (curve 2) samples; the shoulder at $\approx 8\mathrm{K}$ is due to the CDW transition.

Figure 2

Angle-dependent magnetoresistance of (a) the clean sample and (b) the dirty sample at $P=6.2\mathrm{kbar}$, $B=20\mathrm{T}$. Insets: (upper panel) fragment of the $\phi =9°$ curve for the clean sample with the coherence peak; (lower panel) temperature-dependent zero-field resistance of the clean (curve 1) and dirty (curve 2) samples at the same pressure.

Figure 3

Magnetoresistance of the dirty sample at $P=0$ as a function of the out-of-plane field component. The raw $\theta$ sweeps recorded at different field strengths are shown in the inset.