复合准粒子与晶格上杂质的散射
Scattering of a composite quasiparticle by an impurity on a lattice
摘要：
本文研究了一维离散晶格上的复合准粒子与类δ杂质势的散射。复合准粒子的自由度对应于两个束缚激发之间的相对距离。首先，我们表明，由于其分散体的特定属性，晶格激发绑定到负和正电位的杂质。我们证明了复合激发的有限尺寸导致多个激发杂质束缚态的形成。这些束缚态的数目和局域化程度取决于杂质势的符号和相对大小以及两个准粒子的束缚强度。我们还报道了激发杂质束缚态的存在，其能量位于连续带。其次，我们研究了双激子波包在单杂质散射过程中质心与相对坐标自由度之间的纠缠变化及其引起的退相干，对于晶格上的复合准粒子，由于两粒子哈密顿量的不可分性，其相对坐标自由度与质心之间的纠缠自然产生。我们的研究重点之一是研究这种不可分离性如何影响双激子-杂质束缚态的产生和纠缠动力学。
英文摘要：
We study scattering of a composite quasiparticle, which possesses a degree of freedom corresponding to relative separation between two bound excitations, by a delta-like impurity potential on a one-dimensional discrete lattice. Firstly, we show that, due to specific properties of their dispersion, lattice excitations bind to impurities with both negative and positive potentials. We demonstrate that the finite size of the composite excitation leads to formation of multiple excitation-impurity bound states. The number and the degree of localization of these bound states depend on the signs and relative magnitudes of the impurity potential and the binding strength of two quasiparticles. We also report the existence of excitation-impurity bound states whose energies are located in the continuum band. Secondly, we study a change in the entanglement between the centre of mass and relative coordinate degrees of freedom of a biexciton wave packet during single impurity scattering and decoherence caused by it. For a composite quasiparticle on a lattice, the entanglement between its relative and centre of mass coordinate degrees of freedom arises naturally due to inseparability of the two-particle Hamiltonian. One of the main focuses of our study is to investigate how this inseparability affects the creation of the biexciton-impurity bound states and the entanglement dynamics.
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