Merten S, Shapoval O, Damaschke B, Samwer K, Moshnyaga V
I. Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077, Göttingen, Germany.
IIEN, Academy of Sciences of Republic Moldova, Strada Academiei 3/3, MD-2028, Chisinau, Republic of Moldova.
Sci Rep. 2019 Feb 20;9(1):2387. doi: 10.1038/s41598-019-39597-1.
A long-standing issue in the physics of the colossal magnetoresistance is the role of electron-phonon coupling, which manifests itself as Jahn-Teller polarons. The origin and architecture of polarons makes it possible to study their behavior by Raman spectroscopy, which allows to analyze the polaronic behavior in an applied magnetic field. We performed magnetic-field-dependent Raman spectroscopy on thin films of (LaPr)CaMnO in a range of H = 0-50 kOe and compared the obtained Raman spectra with the magnetic field behavior of the electrical resistivity. In the vicinity of the Curie temperature, T = 197 K, the intensity of the Jahn-Teller stretching mode at 614 cm and of the bending mode at 443 cm was found to be suppressed and enhanced, respectively. This observed behavior has a remarkable similarity with the field and temperature dependence of the colossal magnetoresistance in (LaPr)CaMnO. Our work provides direct evidence that the reduction of the amount of Jahn-Teller polarons at the phase transition is the main mechanism underlying the colossal magnetoresistance.
巨磁电阻物理学中一个长期存在的问题是电子 - 声子耦合的作用，这种耦合表现为 Jahn - Teller 极化子。极化子的起源和结构使得通过拉曼光谱研究其行为成为可能，拉曼光谱能够分析外加磁场中的极化子行为。我们在 H = 0 - 50 kOe 的范围内对 (LaPr)CaMnO 薄膜进行了磁场依赖的拉曼光谱实验，并将所得拉曼光谱与电阻率的磁场行为进行了比较。在居里温度 T = 197 K 附近，发现 614 cm 处的 Jahn - Teller 伸缩模式强度被抑制，而 443 cm 处的弯曲模式强度增强。这种观察到的行为与 (LaPr)CaMnO 中巨磁电阻的磁场和温度依赖性具有显著的相似性。我们的工作提供了直接证据，表明在相变时 Jahn - Teller 极化子数量的减少是巨磁电阻的主要机制。
