Atomic simulation studies of hole formation and Ca doping in YBa2Cu4O8

Hole formation and Ca doping in YBa 2 Cu 4 O 8 have been studied using atomistic simulation techniques. The results predict that it is energetically favourable for Ca ions to enter the Ba sites suggesting that the increase in T c upon Ca doping cannot be explained by an increase in hole concentration. The authors also show that the structural changes in YBa 2 Cu 4 O 8 upon Ca doping are similar to those induced by high pressure, which implies that the enhancement of T c in YBa 2 Cu 4 O 8 upon either Ca doping or due to pressure may have the same root cause.