Approximate Hofstadter- and Kapit-Mueller-like parent Hamiltonians for Laughlin states on fractals

Abstract

Recently, it was shown that fractional quantum Hall states can be defined on fractal lattices. Proposed exact parent Hamiltonians for these states are nonlocal and contain three-site terms. In this work, we look for simpler, approximate parent Hamiltonians for bosonic Laughlin states at half filling, which contain only onsite potentials and two-site hopping with the interaction generated implicitly by hardcore constraints (as in the Hofstadter and Kapit-Mueller models on periodic lattices). We use an "inverse method" to determine such Hamiltonians on finite-generation Sierpiński carpet and triangle lattices. The ground states of some of the resulting models display relatively high overlap with the model states if up to third neighbor hopping terms are considered, and by increasing the maximum hopping distance one can achieve nearly perfect overlaps. When the number of particles is reduced and additional potentials are introduced to trap quasiholes, the overlap with a model quasihole wavefunction is also high in some cases, especially for the nonlocal Hamiltonians. We also study how the small system size affects the braiding properties for the model quasihole wavefunctions and perform analogous computations for Hamiltonian models.

Properties of Laughlin states on fractal lattices

“…Examples of integer quantum Hall models in fractals [11][12][13][14][15][16][17] already show features that are not present for periodic lattices in two dimensions, such as inner edge states. FQH physics has also been investigated on fractal lattices [18][19][20][21], and one of the interesting observations here is that the entropy can scale differently with subsystem size than it does in two dimensions.…”

“…This point turns out to be important to obtain the desired physics on fractal lattices [18]. An exact parent Hamiltonian for (1) can be found in [18,24], and [21] made a systematic search for simpler, approximate parent Hamiltonians.…”