论文标题
2D Holstein模型中的超导性和电荷密度波顺序
Superconductivity and charge density wave order in the 2D Holstein model
论文作者
论文摘要
荷斯坦汉密尔顿人描述了在晶格上跳跃的费米子，并与无散的声子自由程度在本地互动。在低密度极限中，穿着的准颗粒，极化物和双圆龙以有效的质量传播。在较高的密度下，对可以凝结成低温超导相，并在双方晶格上或附近相应地填充，以充电密度波（CDW）顺序。 CDW的形成破坏了离散的对称性，因此通过二阶（ISING）过渡发生，因此在有限的$ t _ {\ rm cdw} $中以二维为单位。量子蒙特卡洛计算已确定$ t _ {\ rm cdw} $用于各种几何形状，包括方形，蜂窝和lieb lattices。另一方面，$ d = 2 $的超导过渡是在kosterlitz- thouless-thouless（kt）通用类中，并且特征的特征差得多。在本文中，我们确定了平方晶格的$ t _ {\ rm sc} $，对于密度$ρ$和Phonon频率$ω_0$的几个值。我们发现，准长范围顺序设置为$ t _ {\ rm sc} \ Lessim t/20 $，其中$ t $是近邻居跳跃的幅度，这与以前的粗略估计相一致，这些模拟只有外推到温度，我们从高度更高的$ t $到达了温度。我们还展示了随着CDW过渡的半填充，密度不连续演变的证据。
The Holstein Hamiltonian describes fermions hopping on a lattice and interacting locally with dispersionless phonon degrees of freedom. In the low density limit, dressed quasiparticles, polarons and bipolarons, propagate with an effective mass. At higher densities, pairs can condense into a low temperature superconducting phase and, at or near commensurate filling on a bipartite lattice, to charge density wave (CDW) order. CDW formation breaks a discrete symmetry and hence occurs via a second order (Ising) transition, and therefore at a finite $T_{\rm cdw}$ in two dimensions. Quantum Monte Carlo calculations have determined $T_{\rm cdw}$ for a variety of geometries, including square, honeycomb, and Lieb lattices. The superconducting transition, on the other hand, in $d=2$ is in the Kosterlitz-Thouless (KT) universality class, and is much less well characterized. In this paper we determine $T_{\rm sc}$ for the square lattice, for several values of the density $ρ$ and phonon frequency $ω_0$. We find that quasi-long range order sets in at $T_{\rm sc} \lesssim t/20$, where $t$ is the near neighbor hopping amplitude, consistent with previous rough estimates from simulations which only extrapolated to the temperatures we reach from considerably higher $T$. We also show evidence for a discontinuous evolution of the density as the CDW transition is approached at half-filling.
