Linear ac transport in square-shaped graphene nanoconstriction devices En-Jia Ye, Jin Lan, Yi-Jian Shi, Chengliang Zhang, Haifeng Shi and Xuean Zhao Eur. Phys. J. B, 88 3 (2015) 72 Published online: 23 March 2015 DOI: 10.1140/epjb/e2015-50549-0