Improper ferroelectric phase due to condensation of two order parameters in crystals of high-temperature superconductors

Abstract

Using group-theoretical methods it is shown that improper ferroelectric phase may arise in high-temperature superconductors (HTSC) where high-symmetry phases have space groups D _4h ¹ or D _4h ¹⁷. Their appearance is caused by condensation of order parameters (OP's) transforming two irreducible representations (IR's). The most typical phase diagrams are considered, as well as temperature dependence of OP's and the basic structural mechanism of the ferroelectricity arising in the HTSC.

Key Words:

• high-temperature superconductors
• structure phase transitions
• order parameters
• irreducible representation
• improper ferroelectricity.