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Nonequilibrium quasiparticle relaxation dynamics in single crystals of hole- and electron-doped BaFe_2As_2

Torchinsky, D. H. and McIver, James W. and Hsieh, David and Chen, G. F. and Luo, J. L. and Wang, N. L. and Gedik, Nuh (2011) Nonequilibrium quasiparticle relaxation dynamics in single crystals of hole- and electron-doped BaFe_2As_2. Physical Review B, 84 (10). Art. No. 104518. ISSN 1098-0121. doi:10.1103/PhysRevB.84.104518.

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We report on the nonequilibrium quasiparticle dynamics in BaFe_2As_2 on both the hole-doped (Ba_(1−x)K_xFe_2As_2) and electron-doped (BaFe2−yCoyAs2) sides of the phase diagram using ultrafast pump-probe spectroscopy. Below Tc, measurements conducted at low photoinjected quasiparticle densities in the optimally and overdoped Ba1−xKxFe2As2 samples reveal two distinct relaxation processes: a fast component whose decay rate increases linearly with excitation density and a slow component with an excitation density independent decay rate. We argue that these two processes reflect the recombination of quasiparticles in the two hole bands through intraband and interband processes. We also find that the thermal recombination rate of quasiparticles increases quadratically with temperature in these samples. The temperature and excitation density dependence of the decays indicates fully gapped hole bands and nodal or very anisotropic electron bands. At higher excitation densities and lower hole dopings, the dependence of the dynamics on quasiparticle density disappears as the data are more readily understood in terms of a model which accounts for the quasiequilibrium temperature attained by the sample. In the BaFe_(2−y)Co_yAs_2 samples, dependence of the recombination rate on quasiparticle density at low dopings (i.e., y=0.12) is suppressed upon submergence of the inner hole band and quasiparticle relaxation occurs in a slow, density-independent manner.

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Hsieh, David0000-0002-0812-955X
Alternate Title:Nonequilibrium quasiparticle relaxation dynamics in single crystals of hole- and electron-doped BaFe2As2
Additional Information:© 2011 American Physical Society. Received 11 February 2011. Revised 3 June 2011. Published 13 September 2011. The authors thank B. Andrei Bernevig and Alex Frenzel for useful discussions. This work was supported by DOE Grant No. DE-FG02-08ER46521, the MRSEC Program of the National Science Foundation under Award No. DMR - 0819762, the NSFC, CAS, and the 973 Project of the MOST of China.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-08ER46521
National Science Foundation China (NSFC)UNSPECIFIED
973 Project of the MOST of ChinaUNSPECIFIED
Issue or Number:10
Classification Code:PACS number(s): 74 . 25 . Gz, 78 . 47 . jh
Record Number:CaltechAUTHORS:20140815-104401227
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48611
Deposited By: Joy Painter
Deposited On:22 Aug 2014 06:24
Last Modified:10 Nov 2021 18:33

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