Band Gap and Residual Entropy in the Spin Ice Material Dy2Ti2O7

We investigate the origin of the band gap in the spin ice material Dy2Ti2O7. The band gap is caused by Bardeen-Cooper-Schrieffer (BCS)-type electron-electron interactions that are transformed from electron-ion interactions. Additionally, the residual finite entropy at absolute zero temperature results from band gap effects rather than the nature of the Pauling-type spin ice.