Holstein polaron: The effect of coupling to multiple-phonon modes
Holstein polaron: The effect of coupling to multiple-phonon modes
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荷斯坦极化子：多声子模式耦合的影响
DOI：
10.1209/0295-5075/80/67001
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
M. Berciu
中科院分区：
文献类型：
--
作者：
L. Covaci;M. Berciu
研究了多声子耦合对荷斯坦极化子性质的影响。为此，我们推广了动量平均近似MA(0)和MA(1)来处理多声子模。对于单声子模式，这些近似在数值上是非常有效的。对于非常弱或非常强的耦合，它们变得精确，并且在中间区域非常准确，例如，谱权正好遵守前六个，分别是八个和规则。我们的结果表明，对基态性质的影响在本质上是累积的。因此，如果对一种模式的有效耦合比对所有其他模式的有效耦合大得多，则该模式有效地决定了基态特性。然而，即使很弱的耦合到第二个声子模也对高能谱有重要的非微扰效应，特别是对极化子带的色散和声子统计。这对真实材料的数据分析和解释有重要影响。
We investigate the effects of coupling to multiple-phonon modes on the properties of a Holstein polaron. To this end, we generalize the Momentum Average approximations MA(0) and MA(1) to deal with multiple-phonon modes. As for a single-phonon mode, these approximations are found to be numerically very efficient. They become exact for very weak or very strong couplings, and are highly accurate in the intermediate regimes, e.g. the spectral weights obey exactly the first six, respectively eight, sum rules. Our results show that the effect on ground-state properties is cumulative in nature. As a result, if the effective coupling to one mode is much larger than to all the others, this mode effectively determines the ground-state properties. However, even very weak coupling to a second phonon mode has important non-perturbational effects on the higher-energy spectrum, in particular on the dispersion and the phonon statistics of the polaron band. This has important consequences on the analysis and interpretation of data for real materials.