Photogeneration of superparaelectric large polarons in dielectrics with soft anharmonic T 1 u phonons
Photogeneration of superparaelectric large polarons in dielectrics with soft anharmonic T 1 u phonons
复制标题
具有软非简声 T 1 u 声子的电介质中超顺电大极化子的光生
DOI：
--
复制
发表时间：
2003
期刊：
影响因子：
--
通讯作者：
K. Nasu
中科院分区：
文献类型：
--
作者：
K. Nasu
结合最近关于光增强SrTiO3光电导和准静态电极化率的实验，我们从理论上研究了光生电子在这种介质中的全局宇称破坏和局域宇称破坏。假定光生电子在钛的3d能带中相当巡游，与该介质中的软非谐T1 u声子弱而二次耦合。还假定电子与呼吸(A1g)型高能声子强烈而线性地耦合。我们将证明这两种类型的电子-声子(e-p)耦合导致两种类型的极化子，一个是具有准全局宇称破坏的“超顺电大极化子”，另一个是只具有局部宇称破坏的“偏心型自陷极化子”。如果这些e-p耦合的作用力范围很小，则这两个态被绝热势垒分开。如果没有T1 u声子，这两个态将退化为众所周知的大极化子和自陷极化子，这两个态的奇偶数都是偶数。我们还将证明这种超顺电大极化子提高了电子电导率和准静态电极化率，这与实验定性地一致。
In connection with the recent experiments on photoenhancements of the electronic conductivity and the quasistatic electric susceptibility of SrTiO 3 , we theoretically study global versus local parity violation of a photogenerated electron in this dielectric. The photogenerated electron, being quite itinerant in the 3d band of Ti, is assumed to couple weakly but quadratically with soft-anharmonic T 1 u phonons in this dielectric. The electron is also assumed to couple strongly but linearly to the breathing (A 1 g ) type high energy phonons. We will show that these two types of electron-phonon (e-p) couplings result in two types of polarons, a "superparaelectric large polaron" with a quasiglobal parity violation, and an "off-center type self-trapped polaron" with only a local parity violation. These two states are shown to be separated by an adiabatic potential barrier, if these e-p couplings are short in their force ranges. Without the T 1 u phonon, these two states reduce to the well-known large polaron and the self-trapped one, both of which have even parities. We will also show that this superparaelectric large polaron enhances both the electronic conductivity and the quasistatic electric susceptibility, in qualitative agreements with the experiments.