钛酸锶晶体的光致介电常数激增以及超顺电大极化子理论

Great photo-enhancement of dielectric constant and super-papa-electric large polaron theory in SrTiO_(3)

钙钛矿类化合物钛酸锶具有明显的光致介电增长的性质,这是由于被光激发至Ti^(4+)的3d能带上的电子具有良好的巡游特性,为了进一步揭示光致介电增长的微观机理,这里假设巡游电子同时与两类声子发生耦合作用,一方面,电子与A_(1g)模式的晶格呼吸子发生强相互作用,另一方面,电子还与T_(1u)模式的非简谐声子具有相对较弱的耦合.通过变分法计算可得,这种复杂的电声耦合作用在晶体中形成两种极化子:自陷极化子和超顺电大极化子.正是由于超顺电大极化子的形成,导致了光致介电激增的现象.

The perovskite type compound SrTiO_(3) has an evident property of great enhancement in dielectric constant after photoexcitation.This is partly due to that the photo-generated electron is quite itinerant in the 3d band of Ti^(4+).In order to discover the microscopic mechanism of the photoenhancement of the dielectric constant further here,it is supposed that these electrons are coupled with two types of phonons at the same time.On the one hand,the electrons are strongly coupled with the breathing type A_(1g) mode phonons.On the other hand,the electrons are weakly coupled with the anharmonic T_(1u) mode phonons.By way of a variational methoed,the complicated electron-phonon interactions give rise to two kinds of polarons,self trapped polarons and supar-para-electric large polarons,in the crystal.It is the birth of super-para-electric large polaron that leads to the great photo-enhanecment in dielectric constant in SrTiO_(3).