Exotic phases and superconductivity at ambient and high pressure

Some decades ago, resistance upturn at low temperature was believed be most likely due to Anderson localization or Kondo effect. However, some of the upturn phenomena could not be explained within these two frameworks. A satisfactory origin of some of these upturns is found be charge order (CO) associated with quarter-filled system in contrast to Mott insulator for a half-filled case.  Superconductivity is sometimes found in the vicinity of CO as well as Mott insulator.  In certain materials, we can realize both CO and Mott insulator states and observe superconductivity by controlling uniaxial pressure (strain).

Depending on time, I would like to mention about the pressure itself. The importance of the quality of hydrostatic pressure for understanding superconductivity is an urgent issue.