Critical phenomena on a 3D fractal with intermediate dimensionality: tensor-network study
摘要
The critical behavior of spin systems is fundamentally governed by dimensionality and connectivity. Moving beyond translationally invariant lattices, we explore a new paradigm where fractality itself becomes a tunable parameter, engineering magnetic order and critical behavior. By implementing the classical Ising model on a three-dimensional fractal lattice—a static realization of a spin cluster with Hausdorff dimension dH = 2.5 and boundary dimension d = 2—we demonstrate how fractal geometry dictates unique critical phenomena. Using the higher-order tensor renormalization group (HOTRG) method, we identify a finite-temperature phase transition at Tc ≈ 2.65231 with exotic critical exponents (β ≈ 0.059, δ ≈ 35) and a diverging specific heat consistent with a logarithmic singularity (i.e., α = 0) within the present numerical accuracy—a hallmark absent in lower-dimensional fractals. This work establishes that fractal geometry serves as a powerful and untapped degree of freedom for spintronics. It provides a blueprint for designing materials with programmable magnetic phase transitions, paving the way for next-generation, geometry-driven devices in magnonics and neuromorphic computing.