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arXiv 1702.04210cond-mat.stat-mechcond-mat.str-elquant-ph
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可积系统中非均匀猝灭的自旋扩散

Spin diffusion from an inhomogeneous quench in an integrable system

Marko Ljubotina, Marko Znidaric, Tomaz Prosen

摘要:

广义流体力学预测普遍弹道输运在可积晶格系统时,准备在一般的非均匀初始状态。然而,在具有额外离散对称性的系统中,弹道对输运的贡献可能消失。在这里,我们进行大规模的数值模拟自旋动力学的各向异性海森堡$XXZ$自旋$1/2$链从一个非均匀的混合初始状态,这是对称的自旋反转和空间反射的组合。在各向同性和易轴制度,我们发现非弹道自旋输运,我们详细分析的标度指数的运输磁化强度和标度的自旋密度。虽然在易轴制度,我们发现正常扩散的准确证据,自旋输运在各向同性的情况下,显然是超扩散,标度指数非常接近$2/3$,但与普遍的标度动力学服从扩散方程在非线性标度时间。

英文摘要:

Generalised hydrodynamics predicts universal ballistic transport in integrable lattice systems when prepared in generic inhomogeneous initial states. However, the ballistic contribution to transport can vanish in systems with additional discrete symmetries. Here we perform large scale numerical simulations of spin dynamics in the anisotropic Heisenberg $XXZ$ spin $1/2$ chain starting from an inhomogeneous mixed initial state which is symmetric with respect to a combination of spin-reversal and spatial reflection. In the isotropic and easy-axis regimes we find non-ballistic spin transport which we analyse in detail in terms of scaling exponents of the transported magnetisation and scaling profiles of the spin density. While in the easy-axis regime we find accurate evidence of normal diffusion, the spin transport in the isotropic case is clearly super-diffusive, with the scaling exponent very close to $2/3$, but with universal scaling dynamics which obeys the diffusion equation in nonlinearly scaled time.

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