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arXiv · 1002.1466

Strong energy-momentum dispersion of phonon-dressed carriers in the lightly doped band insulator SrTiO$_3$

W. Meevasana·X. J. Zhou·B. Moritz·C-C. Chen·R. H. He·S. -I. Fujimori·D. H. Lu·S. -K. Mo·R. G. Moore·F. Baumberger·T. P. Devereaux·D. van der Marel·N. Nagaosa·J. Zaanen·Z. -X. Shen
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Abstract

Much progress has been made recently in the study of the effects of electron-phonon (el-ph) coupling in doped insulators using angle resolved photoemission (ARPES), yielding evidence for the dominant role of el-ph interactions in underdoped cuprates. As these studies have been limited to doped Mott insulators, the important question arises how this compares with doped band insulators where similar el-ph couplings should be at work. The archetypical case is the perovskite SrTiO$_3$ (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La$_2$CuO$_4$ by a factor of 500. Based on this fact, it has been suggested that doped STO should be the archetypical bipolaron superconductor. Here we report an ARPES study from high-quality surfaces of lightly doped SrTiO$_3$. Comparing to lightly doped Mott insulators, we find the signatures of only moderate electron-phonon coupling: a dispersion anomaly associated with the low frequency optical phonon with a $λ'\sim0.3$ and an overall bandwidth renormalization suggesting an overall $λ'\sim0.7$ coming from the higher frequency phonons. Further, we find no clear signatures of the large pseudogap or small polaron phenomena. These findings demonstrate that a large dielectric constant itself is not a good indicator of el-ph coupling and highlight the unusually strong effects of the el-ph coupling in doped Mott insulators.

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W. Meevasana, X. J. Zhou, B. Moritz, C-C. Chen, R. H. He, S. -I. Fujimori, D. H. Lu, S. -K. Mo, R. G. Moore, F. Baumberger, T. P. Devereaux, D. van der Marel, N. Nagaosa, J. Zaanen, Z. -X. Shen. 2010-02-07. Strong energy-momentum dispersion of phonon-dressed carriers in the lightly doped band insulator SrTiO$_3$. https://doi.org/10.1088/1367-2630%2F12%2F2%2F023004

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