The Krylov subspace expansion is a workhorse method for sparse numerics that has been increasingly explored as a source of physical insight into many-body dynamics in recent years. In this work we revisit the venerable Anderson model of localization in dimensions $d=1,2,3,4$ to construct local integrals of motion (LIOMs) in Krylov space. These appear as zero eigenvalue edge states of an effective hopping problem in the Krylov superoperator subspace and can be analytically constructed given the Lanczos coefficients. We exploit this idea, focusing on $d=3$, to study the manifestation of the disorder-driven Anderson transition in the anatomy of LIOMs. We find that the increasing complexity of the Krylov operators results in a suppression of the fluctuations of the Lanczos coefficients. As such, one can study the phenomenology of the integrals of motion in the disorder-averaged Krylov chain. We find edge states localized on a vanishing fraction of Krylov space (of dimension $D_K=V^2$ for cubes of volume $V$), both in localized and in extended phases. Importantly, in the localized phase, disorder induces power-law decaying dimerization in the (Krylov) hopping problem, producing stretched exponential decay of the LIOMs in Krylov space with a stretching exponent $1/2d$. Metallic LIOMs are completely delocalized albeit across only $\propto \sqrt{D_K}$ states. Critical LIOMs exhibit power-law decay with an exponent matching the expected value of 0.29.

Close

PrevNext

View figure in article

• Anderson localization
• Many-body localization
• Quantum chaos
• Disordered systems
• Numerical approximation & analysis