# Sample Size Effects on the Transport Characteristics of Mesoscopic Graphite Samples - Condensed Matter > Materials Science

Abstract: In this work we investigated correlations between the internal microstructureand sample size lateral as well as thickness of mesoscopic, tens of nanometerthick graphite multigraphene samples and the temperature $T$ and field$B$ dependence of their electrical resistivity $hoT,B$. Low energytransmission electron microscopy reveals that the original highly orientedpyrolytic graphite material - from which the multigraphene samples wereobtained by exfoliation - is composed of a stack of $\sim 50$nm thick andmicrometer long crystalline regions separated by interfaces running parallel tothe graphene planes. We found a qualitative and quantitative change in thebehavior of $hoT,B$ upon thickness of the multigraphene samples, indicatingthat their internal microstructure is important.} {The overall results indicatethat the metallic-like behavior of $hoT$ at zero field measured for bulkgraphite samples is not intrinsic of ideal graphite. The results suggest thatthe interfaces between crystalline regions may be responsible for thesuperconducting-like properties observed in graphite. Our transportmeasurements also show that reducing the sample lateral size as well as thelength between voltage electrodes decreases the magnetoresistance, in agreementwith recently published results. The magnetoresistance of the multigraphenesamples shows a scaling of the form $RB - R0-R0-T^\alpha = fB-T$with a sample dependent exponent $\alpha \sim 1$, which applies in the wholetemperature 2 K $\le T \le 270$K and magnetic field range $B \le 8$T.

Author: J. Barzola-Quiquia, J.-L. Yao, P. Rödiger, K. Schindler, P. Esquinazi

Source: https://arxiv.org/