Abstract
Graphene in its purest form is expected to exhibit a semiconducting to metallic transition in its temperature dependent conductivity as a result of the interplay between Coulomb disorder and phonon scattering, the transition temperature, T-c, depending sensitively on the disorder induced carrier density (n(c)). Even for good quality graphene, the n(c) can be quite high (similar to 10(12) cm(-2)) and the transition temperature may be placed well above the ambient, practically rendering it to be only semiconducting over a wide range of temperature. Here we report an experimental study on the transport behavior of twisted multilayer graphene (tMLG) exhibiting T-c well below the ambient temperature. The graphene layers in these tMLG are highly decoupled with one another due to the angular rotation among them; as a result, they exhibit very high Raman I-2D/(IG) values (up to 12) with narrow 2D width (16-24 cm(-1)). The observed T-c values seem to go hand in hand with the Raman I-2D/(IG) values; a multilayer with mean I-2D/(IG) value of 4.6 showed a T-c of 180 K, while that with mean I-2D/(IG) of 4.9 showed lower a T-c of 160 K. Further, another multilayer with even higher mean I-2D/(IG) value of 6.9 was metallic down to 5 K, indicating a very low disorder. The photoresponse behavior also corroborates well with the transition in transport behavior.