Some solids with a high N ( E F ) form density waves while others choose a superconducting or magnetic ground state at low temperatures, because of the existence of nesting vectors in the materials' Fermi surfaces. The concept of a nesting vector is illustrated in the Figure for the famous case of chromium, which transitions from a paramagnetic to SDW state at a Néel temperature of 311 K. Cr is a body-centered cubic metal whose Fermi surface features many parallel boundaries between electron pockets centered at Γ Γ and hole pockets at H. These large parallel regions can be spanned by the nesting wavevector q shown in red. The real-space periodicity of the resulting spin-density wave is given by 2 π π / q . The formation of an SDW with a corresponding spatial frequency causes the opening of an energy gap that lowers the system's energy. The existence of the SDW in Cr was first posited in 1960 by Albert Overhauser of Purdue. The theory of CDWs was first put forth by Rudolf Peierls of Oxford University, who was trying to explain superconductivity.