Ground state properties of disordered spin-1/2 Heisenberg models in low dimensions

Ta-Jung Cheng^1*, Ying-Jer Kao¹, Yu-Cheng Lin²

¹Department of Physics, National Taiwan University, Taipei, Taiwan
²Graduate Institute of Applied Physics, National Chengchi University, Taipei, Taiwan

* Presenter:Ta-Jung Cheng, email:r10222023@ntu.edu.tw

The random-singlet (RS) phase consists of random pairing of spins showing collective and universal critical behavior, which governs low-energy physics of the antiferromagnetic spin-1/2 Heisenberg chain with random couplings. The RS phases are found in a broad class of spin chains, including the spin-1 chain that is gapped in the absence of disorder. On the other hand, the spin-1/2 Heisenberg two-leg ladder, despite its similarity to the spin-1 chain, does not transform to an RS phase by introducing randomness in couplings. Even with extremely weak interchain couplings, the disordered spin ladder remains in a Griffiths phase with short-range correlations. Here we use projector quantum Monte Carlo simulations to study ground state properties of Heisenberg models consisting of two or more chains with sparse connectivities. In particular, we examine whether there is a transition to the RS phase in a two-leg ladder when a fraction of interchain couplings are removed randomly. Our goal is to understand how the RS phase breaks down by increasing connectivities in low-dimensional spin systems.

Keywords: the random-singlet phase, Griffiths phase, antiferromagnetic Heisenberg model, projector quantum Monte Carlo, low-dimensional spin systems