paper

Critical level crossings and gapless spin liquid in the square-lattice spin- - Heisenberg antiferromagnet

arXiv:1702.08197 · doi:10.1103/PhysRevLett.121.107202

Abstract

We use the DMRG method to calculate several energy eigenvalues of the frustrated square-lattice - Heisenberg model on cylinders with . We identify excited-level crossings versus the coupling ratio and study their drifts with the system size . The lowest singlet-triplet and singlet-quintuplet crossings converge rapidly (with corrections ) to different values, and we argue that these correspond to ground-state transitions between the Néel antiferromagnet and a gapless spin liquid, at , and between the spin liquid and a valence-bond-solid at . Previous studies of order parameters were not able to positively discriminate between an extended spin liquid phase and a critical point. We expect level-crossing analysis to be a generically powerful tool in DMRG studies of quantum phase transitions.

14 pages 16 figs, accepted by PRL

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