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Bulletin of the American Physical Society

Quantum Criticality in Coupled Spin-Dimer Systems

Stefan Weßel, S. C. Wenzel

Published Mar 17, 2010• 0 citations
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Spin-dimer systems are a versatile playground for the detailed study of quantum phase transitions. Using the magnetic field as the tuning parameter, it is possible to observe a crossover from the characteristic scaling near critical points to the behavior of a finite-temperature phase transition. In this work we study two-dimensional coupled spin-dimer systems by comparing numerical quantum Monte Carlo simulations with analytical calculations of the susceptibility, the magnetocaloric effect, and the helicity modulus. The magnetocaloric behavior of the magnetization with temperature can be used to determine the critical fields with high accuracy, but the critical scaling does not show the expected logarithmic corrections. The zeros of the cooling rate are an excellent indicator of the competition between quantum criticality and vortex physics, but they are not directly associated with the quantum phase transition or the finite-temperature Berezinsky-Kosterlitz-Thouless transition. The results give a unified picture of the full quantum and finite-temperature phase diagram.
The spin-12\frac{1}{2}21​ Heisenberg antiferromagnet on the distorted honeycomb (DHC) lattice is studied by means of the tensor renormalization-group method. It is unveiled that the system has a quantum phase transition of second order between the gapped quantum dimer phase and a collinear N\'eel phase at the critical point of coupling ratio ${\ensuremath{\alpha}}_{c}\ensuremath{\simeq}0.54$, where the quantum critical exponents $\ensuremath{\nu}\ensuremath{\simeq}0.69(2)$ and $\ensuremath{\gamma}\ensuremath{\simeq}1.363(8)$ are obtained. The quantum criticality is found to fall into the O(3)O(3)O(3) universality class. A ground-state phase diagram in the field-coupling ratio plane is proposed, where the phases such as the dimer, semiclassical N\'eel, and polarized phases are identified. A link between the present spin system to the boson Hubbard model on the DHC lattice is also discussed.