2015 Fiscal Year Research-status Report
Dynamical screening effects in pump-probe Hard X-ray Photoelectron Spectroscopy
| Project/Area Number |
15K13526
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
Chainani Ashish 国立研究開発法人理化学研究所, 放射光科学総合研究センター, 専任研究員 (80425636)
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| Project Period (FY) |
2015-04-01 – 2017-03-31
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| Keywords | Pump-probe / HAXPES / time-resolved |
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| Outline of Annual Research Achievements |
We have carried out time-resolved HAXPES measurements for quantifying space charge effects and material dynamics at the SACLA XFEL. In the first set of experiments carried out in April 2015, we measured HAXPES of La-doped SrTiO3 using an IR pump (1.55 eV) and 8 KeV SACLA-XFEL as a probe. We carried out HAXPES measurements of the Ti 1s core level as a function of the X-ray probe pulse energy from 2.1 nJ/pulse to 0.49 microJ/pulse. We also carried out Ti 1s core level HAXPES of La-doped SrTiO3 with the SPring-8 synchrotron for comparison.
In the second set of experiments carried out in October 2015, we measured the pump energy dependence of the SACLA XFEL induced HAXPES of La-doped SrTiO3. From systematic studies we have identified the pump and probe pulse energy dependence of vacuum space charge effects using a microfocused XFEL probe. Preliminary results indicate that the pump pulse energy can be used to control and suppress space charge effects. We have obtained data indicating that the space charge effects in high kinetic energy photoelectrons from the Ti 1s core level can be compensated by the low energy laser (1.55 eV) pump-induced photoholes. If we can confirm this result, it will prove that we can use time-resolved HAXPES measurements with SACLA XFEL for addressing the carrier recombination dynamics in a material. The results are being further analyzed using model theoretical calculations.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We have suceeded to obtain data indicating that the space charge effects in high kinetic energy photoelectrons from the Ti 1s core level can be compensated by the low energy laser (1.55 eV) pump-induced photoholes. Based on this experimental result that we have found, namely, the pump pulse energy can be used to compensate space charge effects, as seen in the time-resolved Ti 1s HAXPES core level spectra, we feel confident that we will be able to analyze the data to obtain material-specific electron dynamics
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| Strategy for Future Research Activity |
We hope to measure time-resolved HAXPES of Nb-doped TiO2 using a low energy laser (1.55 eV) pump and the SACLA XFEL as a probe. From systematic studies, we will first try to identify the pump and probe pulse energy dependence of vacuum space charge effects using a microfocused XFEL probe. We will then carry out time-resolved HAXPES studies of the Ti 1s core level spectra of Nb-doped TiO2. We will try to confirm that the pump pulse energy can be used to control and suppress space charge effects for a different material. This is important for establishing that the space charge effects in high kinetic energy Ti 1s core level spectra can be compensated by the low energy laser (1.55 eV) pump-induced photoholes. The results will be analyzed using model theoretical calculations to determine the role of pump and probe induced dynamics. The study will establish a method for separating out space-charge effects and determining carrier recombination dynamics by time-resolved HAXPES measurements using a low energy laser (1.55 eV) pump and the high energy 8 KeV SACLA-XFEL as a probe.
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| Causes of Carryover |
Our original plan was to do room temperature measurements and then compare the results with corresponding low temperature measurements. So we carried out the room temperature measurements and found that due to the low count-rates it took us much longer to complete the room temperature experiments. However, we have succeeded to get data which is now being analyzed, and we hope to write a paper with the room temperature data. Consequently, we could not utilize the money for the projected requirement of liquid Helium in the first year.
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| Expenditure Plan for Carryover Budget |
Since we could not get enough time to do the low temperature measurements in the first year, we needed to postpone them to the second year. Accordingly, we will do additional low temperature experiments in the second year fiscal plan and utilize the available amount.
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Research Products
(3 results)
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[Journal Article] Electronic structure evolution across the Peierls metal-insulator transition in a correlated ferromagnet2015
Author(s)
P. A. Bhobe, A. Kumar, M. Taguchi, R. Eguchi, M. Matsunami, Y. Takata, A. K. Nandy, P. Mahadevan, D. D. Sarma, A. Neroni, E. Sasioglu, M. Lezaic, M. Oura, Y. Senba, H. Ohashi, K. Ishizaka, M. Okawa, S. Shin, K. Tamasaku, Y. Kohmura, M. Yabashi, T. Ishikawa, K. Hasegawa, M. Isobe, Y. Ueda, and A. Chainani
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Journal Title
Physical Review X
Volume: 5
Pages: 041004-1 to 9
DOI
Peer Reviewed / Open Access / Int'l Joint Research / Acknowledgement Compliant
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