Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy

被引：33

作者：

Yamakawa, H. ^{[1
]}

Miyamoto, T. ^{[1
]}

Morimoto, T. ^{[1
]}

Yada, H. ^{[1
]}

Kinoshita, Y. ^{[1
]}

Sotome, M. ^{[1
]}

Kida, N. ^{[1
]}

Yamamoto, K. ^{[2
]}

Iwano, K. ^{[3
]}

Matsumoto, Y. ^{[4
]}

Watanabe, S. ^{[4
]}

Shimoi, Y. ^{[4
]}

Suda, M. ^{[5
]}

Yamamoto, H. M. ^{[5
,6
]}

Mori, H. ^{[7
]}

Okamoto, H. ^{[1
]}

机构：

[1] Univ Tokyo, Dept Adv Mat Sci, Chiba 2778561, Japan

[2] Okayama Univ Sci, Dept Appl Phys, Okayama 7000005, Japan

[3] High Energy Accelerator Res Org KEK, Grad Univ Adv Studies, Inst Mat Struct Sci, Tsukuba, Ibaraki 3050801, Japan

[4] Natl Inst Adv Ind Sci & Technol, Tsukuba, Ibaraki 3058568, Japan

[5] Natl Inst Nat Sci, Inst Mol Sci, Res Ctr Integrat Mol Syst CIMoS, Div Funct Mol Syst, 38 Nishigonaka, Okazaki, Aichi 4448585, Japan

[6] RIKEN, 2-1 Hirosawa, Wako, Saitama 3510198, Japan

[7] Univ Tokyo, Inst Solid State Phys, Chiba 2778581, Japan

来源：

SCIENTIFIC REPORTS | 2016年 / 6卷

基金：

日本学术振兴会;

关键词：

THZ-PULSE; POLARIZATION; AMPLITUDE; DYNAMICS; PHASE; METAL;

D O I：

10.1038/srep20571

中图分类号：

O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];

学科分类号：

07 ; 0710 ; 09 ;

摘要：

In electronic-type ferroelectrics, where dipole moments produced by the variations of electron configurations are aligned, the polarization is expected to be rapidly controlled by electric fields. Such a feature can be used for high-speed electric-switching and memory devices. Electronic-type ferroelectrics include charge degrees of freedom, so that they are sometimes conductive, complicating dielectric measurements. This makes difficult the exploration of electronic-type ferroelectrics and the understanding of their ferroelectric nature. Here, we show unambiguous evidence for electronic ferroelectricity in the charge-order (CO) phase of a prototypical ET-based molecular compound, a( ET)(2)I-3 (ET:bis(ethylenedithio) tetrathiafulvalene), using a terahertz pulse as an external electric field. Terahertz-pump second-harmonic-generation(SHG)-probe and optical-reflectivity-probe spectroscopy reveal that the ferroelectric polarization originates from intermolecular charge transfers and is inclined 27 degrees from the horizontal CO stripe. These features are qualitatively reproduced by the density-functional-theory calculation. After sub-picosecond polarization modulation by terahertz fields, prominent oscillations appear in the reflectivity but not in the SHG-probe results, suggesting that the CO is coupled with molecular displacements, while the ferroelectricity is electronic in nature. The results presented here demonstrate that terahertz-pump optical-probe spectroscopy is a powerful tool not only for rapidly controlling polarizations, but also for clarifying the mechanisms of ferroelectricity.

引用

页数：10

共 40 条

[1] Essential role of anions in the charge ordering transition of α-(BEDT-TTF)2I3 [J].