Maximum surface resistance considers a square sheet of side L, thickness d, and electrical resistivity p. The resistance measured between opposite edges of the sheet is called the surface resistance: R_sq = pL/Ld = p/d, which is independent of the area L² of the sheet. (R_sq is called the resistance per square and is expressed in ohms per square, because p/d has the dimensions of ohms.) If we express p by (44), then R_sq = m/nde²τ. Suppose now that the minimum value of the collision time is determined by scattering from the surfaces of the sheet, so that τ ≈ d/v_F, where v_F is the Fermi velocity. Thus the maximum surface resistivity is R_sq ≈ mvp/nd²e². Show for a monatomic metal sheet one atom in thickness that R_sq ≈ h/e² = 4.1kΩ