Random spin-3/2 antiferromagnetic Heisenberg chains revisited

We revisit the spin-reduction transition in the random spin- 3/2 antiferromagnetic Heisenberg chain using the tensor-network strong-disorder renormalization group (tSDRG). The predicted transition separates two random-singlet (RS) phases: one formed by effective spin- 1/2 moments at weaker disorder and the other by full spin- 3/2 moments at stronger disorder. Within the Damle--Huse classification, this transition corresponds to an emergent permutation-symmetric P 4 multicritical point on a P 2 critical line associated with the RS phases. We first derive the critical exponents governing the disorder-averaged bulk and end-to-end correlation functions in the P n universality classes within the Damle--Huse framework. Using these theoretical predictions, together with a diagnostic constructed from the mean and variance of the energy-gap distribution, we identify the P 4 transition point and the reentrant behavior of the RS phase.