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Collapse of long-range charge order tracked by time-resolved photoemission at high momenta


Intense femtosecond (10−15 s) light pulses can be used to transform electronic, magnetic and structural order in condensed-matter systems on timescales of electronic and atomic motion1,2,3. This technique is particularly useful in the study4,5 and in the control6 of materials whose physical properties are governed by the interactions between multiple degrees of freedom. Time- and angle-resolved photoemission spectroscopy is in this context a direct and comprehensive, energy- and momentum-selective probe of the ultrafast processes that couple to the electronic degrees of freedom7,8,9,10. Previously, the capability of such studies to access electron momentum space away from zero momentum was, however, restricted owing to limitations of the available probing photon energy10,11. Here, using femtosecond extreme-ultraviolet pulses delivered by a high-harmonic-generation source, we use time- and angle-resolved photoemission spectroscopy to measure the photoinduced vaporization of a charge-ordered state in the potential excitonic insulator 1T-TiSe2 (refs 12, 13). By way of stroboscopic imaging of electronic band dispersions at large momentum, in the vicinity of the edge of the first Brillouin zone, we reveal that the collapse of atomic-scale periodic long-range order happens on a timescale as short as 20 femtoseconds. The surprisingly fast response of the system is assigned to screening by the transient generation of free charge carriers. Similar screening scenarios are likely to be relevant in other photoinduced solid-state transitions and may generally determine the response times. Moreover, as electron states with large momenta govern fundamental electronic properties in condensed matter systems14, we anticipate that the experimental advance represented by the present study will be useful to study the ultrafast dynamics and microscopic mechanisms of electronic phenomena in a wide range of materials.

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Figure 1: CDW phase transition of 1T-TiSe2.
Figure 2: Tracking the photoinduced transition by femtosecond time-resolved ARPES.
Figure 3: Fluence dependence of the photoinduced transition.

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M.B. and S.M. thank M. Aeschlimann for support and discussion. M.B. and S.M. also thank M. Murnane and H. Kapteyn for their support through the NSF EUV ERC. A.C. acknowledges support from the JILA Physics Frontier Center. This work was supported by the German Science Foundation (DFG) within the SFB 855 (C.S., M.B., L.K., K.R.) and by the European Community's FP7 under Marie Curie International Outgoing Fellowship GA 253316 (S.M.). Operation of the Advanced Light Source is supported by the US Department of Energy, Office of Basic Energy Sciences.

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Authors and Affiliations



M.B. and K.R. conceived the experiment and wrote the paper. T.R., S.H., M.W., B.S., S.M., L.K., M.B. and K.R. realized the experimental time-resolved ARPES setup. A.C., L.M.A. and Y.L. designed and fabricated the EUV multilayer mirrors. T.R., S.H., M.W., C.S. and A.S. collected the time-resolved photoemission data and performed the data analysis. M.K. and K.R. collected and analysed the static photoemission data at the Advanced Light Source. All authors discussed the results and commented on the manuscript.

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Correspondence to Kai Rossnagel or Michael Bauer.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

The file contains Supplementary Text, Supplementary Figures 1-5 with legends and additional references. (PDF 911 kb)

Supplementary Movie 1

The movie shows photo-induced phase transition (see Supplementary Information S1 for full legend). (MOV 5118 kb)

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Rohwer, T., Hellmann, S., Wiesenmayer, M. et al. Collapse of long-range charge order tracked by time-resolved photoemission at high momenta. Nature 471, 490–493 (2011).

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