Strong magnetoresistance in a graphene Corbino disk at low magnetic\n fields

Abstract

We have measured magnetoresistance of suspended graphene in the Corbino\ngeometry at magnetic fields up to $B=0.15\\,$T, i.e., in a regime uninfluenced\nby Shubnikov-de Haas oscillations. The low-temperature relative\nmagnetotoresistance $[R(B)-R(0)]/R(0)$ amounts to $4000 B^2\\% $ at the Dirac\npoint ($B$ in Tesla), with a quite weak temperature dependence below $30\\,$K. A\ndecrease in the relative magnetoresistance by a factor of two is found when\ncharge carrier density is increased to $|n| \\simeq 3 \\times 10^{-10}$\ncm$^{-2}$. The gate dependence of the magnetoresistance allows us to\ncharacterize the role of scattering on long-range (Coulomb impurities, ripples)\nand short-range potential, as well as to separate the bulk resistance from the\ncontact one. Furthermore, we find a shift in the position of the charge\nneutrality point with increasing magnetic field, which suggests that magnetic\nfield changes the screening of Coulomb impurities around the Dirac point. The\ncurrent noise of our device amounts to $10^{-23}$ A$^2$/$\\sqrt{\\textrm{Hz}}$ at\n$1\\,$kHz at $4\\,$K, which corresponds to a magnetic field sensitivity of $60$\nnT/$\\sqrt{\\textrm{Hz}}$ in a background field of $0.15\\,$T.\n