Recently, a class of Ising anisotropic antiferromagnetic screw chain compounds ACo 2 V 2 O 8 (A =Ba,Sr) [16,17] attracts a lot of research attention. In these compounds, the easy-axis is along the chain direction (c-axis), and the intrachain exchange coupling J z ≈ 5-7 meV [18,19]. Both compounds order at fairly low temperatures (about 5 K), which implies the interchain exchange coupling J ′ ≪ J [20][21][22]. The magnetic order can be suppressed by a transverse field applied in the ab-plane [16,17]. Interestingly, the critical field values and the quantum critical behaviors are very different for fields applied along the [100] and the [110] direction [19,[23][24][25][26][27][28][29]. In BaCo 2 V 2 O 8 , separated 3D and 1D QCPs were suggested with field along the [110] direction at H 20 T [28]. For the field along the [100] direction, H C ∼ 10 T [24], much lower

We study the ground state phase diagram of the Shastry-Sutherland model by using the variational optimization of the infinite tensor network states, and find a weakly first-order transition between the plaquette and the antiferromagnetic states. The full plaquette state strongly competes with the empty plaquette ground state, with an energy difference less than 10 −4 J. We show a staggered ring exchange interaction that preserves the Shastry-Sutherland lattice symmetry can stabilize the full plaquette ground state. In light of this, we propose the triple point where the full plaquette, empty plaquette, and antiferromagnetic phases meet as a deconfined quantum critical point.

The deconfined quantum critical point (DQCP) represents a paradigm shift in theories of quantum matter, presenting a "beyond Landau" scenario for order-order transitions. Its experimental realization, however, has remained elusive. Here we demonstrate by high-pressure 11 B NMR measurements on the quantum magnet SrCu2(BO3)2 that the magnetic field induced plaquette-singlet to antiferromagnetic transition above 1.8 GPa is proximate to a DQCP. We find a weak first-order transition between the two phases at a remarkably low temperature, Tc 0.07 K. Above Tc we observe quantum critical scaling at the highest pressure, 2.4 GPa. We explain the low first-order Tc values by a DQCP-induced emergent O(3) symmetry that is broken in the coexistence state. Our findings take the DQCP from a theoretical concept to a concrete experimental platform.

We study the critical scaling and dynamical signatures of fractionalized excitations at two different deconfined quantum critical points (DQCPs) in an S = 1/2 spin chain by using the time evolution of infinite matrix product states. The scaling of the correlation functions and the dispersion of the conserved current correlations explicitly show the emergence of enhanced continuous symmetries at these DQCPs. The dynamical structure factors in several different channels reveal the development of deconfined fractionalized excitations at the DQCPs. Furthermore, we find an effective spin-charge separation at the DQCP between the ferromagnetic (FM) and valence bond solid (VBS) phases, and identify two continua associated to different types of fractionalized excitations at the DQCP between the X-direction and Z-direction FM phases. Our findings not only provide direct evidence for the DQCP in one dimension but also shed light on exploring the DQCP in higher dimension.

No abstract