Ultrafast observation of critical nematic fluctuations and giant magnetoelastic coupling in iron pnictides

Journal Article · Thu Feb 06 00:00:00 EST 2014 · Nature Communications

DOI:https://doi.org/10.1038/ncomms4229· OSTI ID:1139987

Patz, Aaron ^[1]; Li, Tianqi ^[1]; Ran, Sheng ^[1]; Fernandes, Rafael M. ^[2]; Schmalian, Joerg ^[3]; Budko, Sergey L. ^[1]; Canfield, Paul C. ^[1]; Perakis, Ilias E. ^[4]; Wang, Jigang ^[1]

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1. Iowa State Univ., Ames, IA (United States); Ames Lab., Ames, IA (United States)
2. Univ. of Minnesota, Minneapolis, MN (United States)
3. Karlsruhe Inst. of Technology (KIT) (Germany)
4. Univ. of Crete, Heraklion (Greece); Foundation for Research and Technology, Hellas (Greece)

Many of the iron pnictides have strongly anisotropic normal-state characteristics, important for the exotic magnetic and superconducting behaviour these materials exhibit. Y et, the origin of the observed anisotropy is unclear. Electronically driven nematicity has been suggested, but distinguishing this as an independent degree of freedom from magnetic and structural orders is difficult, as these couple together to break the same tetragonal symmetry. Here we use time-resolved polarimetry to reveal critical nematic fluctuations in unstrained Ba(Fe_1-x Co_x)₂As₂. The femtosecond anisotropic response, which arises from the two-fold in-plane anisotropy of the complex refractive index, displays a characteristic two-step recovery absent in the isotropic response. The fast recovery appears only in the magnetically ordered state, whereas the slow one persists in the paramagnetic phase with a critical divergence approaching the structural transition temperature. The dynamics also reveal a gigantic magnetoelastic coupling that far exceeds electron–spin and electron–phonon couplings, opposite to conventional magnetic metals.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC02-07CH11358
• OSTI ID: 1139987
• Report Number(s): IS-J 8281
• Journal Information: Nature Communications, Vol. 5; ISSN 2041-1723
• Publisher: Nature Publishing Group
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
physical sciences
condensed matter