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arXiv 2209.04094cond-mat.str-el
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双轨道关联链中的激子密度波、双激子和轨道选择配对

Excitonic density-waves, bi-excitons and orbital selective pairing in two-orbital correlated chains

Chun Yang, Adrian E. Feiguin

摘要:

我们对四分之一填充及以下的一维双轨道模型进行了全面研究,该模型实现了许多非常规阶段。特别是,我们发现了激子密度波,其中激子准凝聚与有限的质心动量和一个序参量,改变相位与波矢量$Q$。在这个阶段,激子表现为没有电荷序的硬核玻色子。此外,激子可以在接近电荷密度波不稳定性的状态下配对以形成双激子。当配对超过轨道间排斥时,我们遇到一个机制,其中一个轨道是金属的,而另一个形成自旋能隙超导体,一个真正的轨道选择性配对状态。所有这些结果都得到了解析和数值计算的支持。通过假设一个准经典近似,我们解决了三体空穴-电子-自旋问题,并表明激子是通过与自旋形成束缚态而结合在一起的。为了保持反铁磁背景,激子获得离$k=0$最小的色散。通过广泛的密度矩阵重整化群计算得到了不同相的完整表征。

英文摘要:

We present a comprehensive study of a one-dimensional two-orbital model at and below quarter-filling that realizes a number of unconventional phases. In particular, we find an excitonic density wave in which excitons quasi-condense with finite center of mass momentum and an order parameter that changes phase with wave-vector $Q$. In this phase, excitons behave as hard-core bosons without charge order. In addition, excitons can pair to form bi-excitons in a state that is close to a charge density-wave instability. When pairing dominates over the inter-orbital repulsion, we encounter a regime in which one orbital is metallic, while the other forms a spin gapped superconductor, a genuine orbital selective paired state. All these results are supported by both, analytical and numerical calculations. By assuming a quasi-classical approximation, we solve the three-body hole-electron-spinon problem and show that excitons are held together by forming a bound state with spinons. In order to preserve the antiferromagnetic background, excitons acquire a dispersion that has a minimum away from $k=0$. The full characterization of the different phases is obtained by means of extensive density matrix renormalization group calculations.

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