Geondzhian Andrey, Sambri Alessia, De Luca Gabriella M, Di Capua Roberto, Di Gennaro Emiliano, Betto Davide, Rossi Matteo, Peng Ying Ying, Fumagalli Roberto, Brookes Nicholas B, Braicovich Lucio, Gilmore Keith, Ghiringhelli Giacomo, Salluzzo Marco
ESRF-The European Synchrotron, 71 Avenue des Martyrs, CS 40220, F-38043 Grenoble, France.
CNR-SPIN Complesso Monte-Santangelo via Cinthia, I-80126 Napoli, Italy.
Phys Rev Lett. 2020 Sep 18;125(12):126401. doi: 10.1103/PhysRevLett.125.126401.
Despite its simple structure and low degree of electronic correlation, SrTiO_{3} (STO) features collective phenomena linked to charge transport and, ultimately, superconductivity, that are not yet fully explained. Thus, a better insight into the nature of the quasiparticles shaping the electronic and conduction properties of STO is needed. We studied the low-energy excitations of bulk STO and of the LaAlO_{3}/SrTiO_{3} two-dimensional electron gas (2DEG) by Ti L_{3} edge resonant inelastic x-ray scattering. In all samples, we find the hallmark of polarons in the form of intense dd+phonon excitations, and a decrease of the LO3-mode electron-phonon coupling when going from insulating to highly conducting STO single crystals and heterostructures. Both results are attributed to the dynamic screening of the large polaron self-induced polarization, showing that the low-temperature physics of STO and STO-based 2DEGs is dominated by large polaron quasiparticles.
尽管钛酸锶（STO）结构简单且电子关联程度低，但其具有与电荷输运以及最终与超导性相关的集体现象，而这些现象尚未得到充分解释。因此，需要更深入地了解塑造STO电子和导电特性的准粒子的本质。我们通过Ti L₃边共振非弹性X射线散射研究了块状STO以及LaAlO₃/SrTiO₃二维电子气（2DEG）的低能激发。在所有样品中，我们发现了以强烈的dd + 声子激发形式存在的极化子特征，并且当从绝缘的STO单晶和异质结构转变为高导电的STO单晶和异质结构时，LO3模式的电子 - 声子耦合减弱。这两个结果都归因于大极化子自诱导极化的动态屏蔽，表明STO和基于STO的2DEG的低温物理由大极化子准粒子主导。
