Ultrafast transient generation of spin-density-wave order in the normal state of BaFe2As2 driven by coherent lattice vibrations
Ultrafast transient generation of spin-density-wave order in the normal state of BaFe2As2 driven by coherent lattice vibrations
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DOI：
10.1038/nmat3294
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发表时间：
2012-06-01
期刊：
影响因子：
41.2
通讯作者：
Leitenstorfer, A.
中科院分区：
文献类型：
--
作者：
Kim, K. W.;Pashkin, A.;Leitenstorfer, A.
固体中电荷、自旋和晶格自由度之间的相互作用引起了有趣的宏观量子现象，如巨磁阻、多铁性和高温超导性（1-3）。在这些系统中，不同阶之间的强耦合或竞争是通过外部扰动（如电场和磁场（2）或压力（3））来操纵其功能特性的关键。超短和强光脉冲已经成为研究基本动力学和通过熔化现有秩序控制材料性质的有趣工具（4-6）。在这里，我们采用几个周期的多太赫兹脉冲共振探测的自旋密度波（SDW）的差距的pnictide化合物BaFe 2As 2的飞秒光脉冲激发后的演变。当在低温基态开始时，光激发导致SDW顺序的熔化，然后是超快恢复。与此相反，SDW间隙诱导时，我们激发正常状态以上的转变温度。非常令人惊讶的是，瞬态排序准周期性地遵循相干晶格振荡的频率高达5.5太赫兹。我们的研究结果证明了一个显着的自旋-声子耦合pnictides，支持快速发展的宏观秩序上的小振动位移，即使没有打破晶体的对称性。
The interplay among charge, spin and lattice degrees of freedom in solids gives rise to intriguing macroscopic quantum phenomena such as colossal magnetoresistance, multiferroicity and high-temperature superconductivity(1-3). Strong coupling or competition between various orders in these systems presents the key to manipulate their functional properties by means of external perturbations such as electric and magnetic fields(2) or pressure(3). Ultrashort and intense optical pulses have emerged as an interesting tool to investigate elementary dynamics and control material properties by melting an existing order(4-6). Here, we employ few-cycle multi-terahertz pulses to resonantly probe the evolution of the spin-density-wave (SDW) gap of the pnictide compound BaFe2As2 following excitation with a femtosecond optical pulse. When starting in the low-temperature ground state, optical excitation results in a melting of the SDW order, followed by ultrafast recovery. In contrast, the SDW gap is induced when we excite the normal state above the transition temperature. Very surprisingly, the transient ordering quasi-adiabatically follows a coherent lattice oscillation at a frequency as high as 5.5 THz. Our results attest to a pronounced spin-phonon coupling in pnictides that supports rapid development of a macroscopic order on small vibrational displacement even without breaking the symmetry of the crystal.