论文标题

多轨Mott系统通过变异离散作用理论的精确基态

Precise ground state of multi-orbital Mott systems via the variational discrete action theory

论文作者

Cheng, Zhengqian, Marianetti, Chris A.

论文摘要

确定多轨道哈伯德模型的基态对于理解强相关的电子材料至关重要,但是现有的方法难以同时达到零温度和无限的系统大小。 \ textIt {de facto}标准是近似具有$ d = \ infty $版本的有限维度多轨式哈伯德模型,然后可以通过动态均值场理论(DMFT)正式解决该模型,尽管DMFT解决方案受到无偏置的Impurity solienty Impurity soligity Impurity solienty Impurity soerity Impurity soerity Impurity sero sero sero温度和多个偏差的限制。最近开发的变分离散动作理论(VDAT)提供了一种新方法来解决$ d = \ infty $ hubbard模型,该模型的变量ANSATZ由整数$ \ MATHCAL {N} $控制,并且单调以越来越多的计算成本以精确的解决方案来处理精确解决方案。在这里,我们提出了一种脱钩的最小化算法,以在$ d = \ indty $中实现多轨哈伯德模型的VDAT,并研究$ \ Mathcal {n} = 2-4 $。在$ \ Mathcal {n} = 2 $时,VDAT严格恢复了多轨gutzwiller近似,重现已知结果。在$ \ Mathcal {n} = 3 $中,VDAT精确地捕获了两个轨道哈伯德模型中的Hubbard $ U $,Hund $ J $和Crystal Field $δ$,并具有可忽略不计的计算成本。对于足够大的$ u/t $和$ j/u $,我们表明$δ$在莫特绝缘制度内驱动了一阶过渡。在有限的$ J/U $的大轨道极化极限中,我们发现相互作用即使对于小$ u/t $,也具有非平凡的效果。 VDAT将对理解多轨模型汉密尔顿人和强烈相关的电子材料具有很大的影响。

Determining the ground state of multi-orbital Hubbard models is critical for understanding strongly correlated electron materials, yet existing methods struggle to simultaneously reach zero temperature and infinite system size. The \textit{de facto} standard is to approximate a finite dimension multi-orbital Hubbard model with a $d=\infty$ version, which can then be formally solved via the dynamical mean-field theory (DMFT), though the DMFT solution is limited by the state of unbiased impurity solvers for zero temperature and multiple orbitals. The recently developed variational discrete action theory (VDAT) offers a new approach to solve the $d=\infty$ Hubbard model, with a variational ansatz that is controlled by an integer $\mathcal{N}$, and monotonically approaches the exact solution at an increasing computational cost. Here we propose a decoupled minimization algorithm to implement VDAT for the multi-orbital Hubbard model in $d=\infty$ and study $\mathcal{N}=2-4$ . At $\mathcal{N}=2$, VDAT rigorously recovers the multi-orbital Gutzwiller approximation, reproducing known results. At $\mathcal{N}=3$, VDAT precisely captures the competition between the Hubbard $U$, Hund $J$, and crystal field $Δ$ in the two orbital Hubbard model over all parameter space, with a negligible computational cost. For sufficiently large $U/t$ and $J/U$, we show that $Δ$ drives a first-order transition within the Mott insulating regime. In the large orbital polarization limit with finite $J/U$, we find that interactions have a nontrivial effect even for small $U/t$. VDAT will have far ranging implications for understanding multi-orbital model Hamiltonians and strongly correlated electron materials.

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