When electrons in a solid are excited by light, they can alter the free energy landscape and access phases of matter that are out of reach in thermal equilibrium. This accessibility becomes important in the presence of phase competition, when one state of matter is preferred over another by only a small energy scale that, in principle, is surmountable by the excitation. Here, we study a layered compound, LaTe3, where a small lattice anisotropy in the a–c plane results in a unidirectional charge density wave (CDW) along the c axis1,2. Using ultrafast electron diffraction, we find that, after photoexcitation, the CDW along the c axis is weakened and a different competing CDW along the a axis subsequently emerges. The timescales characterizing the relaxation of this new CDW and the reestablishment of the original CDW are nearly identical, which points towards a strong competition between the two orders. The new density wave represents a transient non-equilibrium phase of matter with no equilibrium counterpart, and this study thus provides a framework for discovering similar states of matter that are ‘trapped’ under equilibrium conditions.
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We thank P.A. Lee, E. Demler, B.V. Fine and A. Aristova for illuminating discussions regarding this work. We thank B. Freelon for pioneering the instrumentation work of the keV UED set-up at MIT. We acknowledge support from the US Department of Energy, BES DMSE (keV UED), from the Gordon and Betty Moore Foundation’s EPiQS Initiative grant GBMF4540 (data analysis, manuscript writing) and the Skoltech NGP Program (Skoltech-MIT joint project) (theory). We acknowledge support from the US Department of Energy BES SUF Division Accelerator & Detector R&D program, the LCLS Facility and SLAC under contracts DE-AC02-05-CH11231 and DE-AC02-76SF00515 (MeV UED at SLAC). Sample growth and characterization work at Stanford was supported by the US Department of Energy, Office of Basic Energy Sciences, under contract DE-AC02-76SF00515. I.-C.T. and H.W. acknowledge support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract DE-SC0012509. Y.-Q.B., Xirui Wang, Y.Y. and P.J.-H. acknowledge support from the Center for Excitonics, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under award no. DE-SC0001088, as well as the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant no. GBMF4541 (sample preparation and characterization).
The authors declare no competing interests.
Peer review statement Nature Physics thanks Peter Baum, Sheng Meng and Claus Ropers and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Kogar, A., Zong, A., Dolgirev, P.E. et al. Light-induced charge density wave in LaTe3. Nat. Phys. (2019) doi:10.1038/s41567-019-0705-3