Dimensional crossover in a spin-liquid-to-helimagnet quantum phase transition

Abstract

Neutron scattering is used to study magnetic-field-induced ordering in the quasi-one-dimensional quantum spin-tube compound Sul-Cu 2 Cl 4 that in zero field has a nonmagnetic spin-liquid ground state. The experiments reveal an incommensurate chiral high-field phase stabilized by a geometric frustration of the magnetic interactions. The measured critical exponents ␤ Ϸ 0.235 and Ϸ 0.34 at H c Ϸ 3.7 T point to an unusual subcritical scaling regime and may reflect the chiral nature of the quantum critical point.

Dimerized ground states inspin−Sfrustrated systems

“…As an example, we will consider the case in which the interaction between ladders are given between correspondent spins on each ladder and on one of the diagonals of each plaquette (see the inset of Figure 7), calling J ⊥ and J d the respective coupling constants. This case is interesting since recently, a similar topology was proposed (but for J d = 0) as the appropriate model describing the compound Cu 2 Cl 4 D 8 C 4 SO 2 25,26 . Despite this case does not satisfy the exact dimerization condition for tubes, it is interesting to find out if it could support dimer order.…”

“…Besides, we analyze the relationship between these exactly solvable models and the case of frustrated spin tubes, which has been recently proposed as a model for the magnetic behavior of the compound Cu 2 Cl 4 D 8 C 4 SO 2 . This compound seems to present frustrating anti-ferromagnetic next-nearestneighbor exchange 25,26 and inelastic neutron scattering experiments reveal that it presents gapped and strongly one-dimensional excitations 27 . So far, there are very few theoretical studies of this frustrated model.…”

“…Now, we are going to discus which are the common features between these results and the behavior of a more realistic family of tubes. In particular, we consider the model proposed by Garlea et al in 25,26 for the Cu 2 Cl 4 D 8 C 4 SO 2 compound. In order to see what features are shared between our exactly solvable model and the model proposed in 25,26 , we explore numerically the ground state of Hamiltonians on the family J > J 2 , J ′ , corresponding to the tube in the figure 8-a, looking for common features.…”

Crystals for neutron scattering studies of quantum magnetism

“…Recent breakthroughs were therefore achieved in studies of organic quantum magnets, particularly in transition metal complexes. Among these compounds, for neutron experiments, one finds excellent one-dimensional [10][11][12][13][14] and two-dimensional [15][16][17] spin networks with varying degrees of geometric frustration [15,18] and typical magnetic energy scales of 1 meV. These energies correspond to temperatures [19][20][21][22] and magnetic fields [23][24][25][26][27] that can be realized in neutron experiments.…”

“…It was later shown that the the system is best described in terms of a pair of coupled frustrated 2-leg ladders [64], and that incommensurability is a direct consequence of frustration. Furthermore, elastic neutron scattering experiments revealed that in an applied magnetic field H c = 3.75 T, the material goes through a quantum phase transition that is a Bose-Einstein condensation of magnons [18]. The high-field phase is an incommensurate quantum helimagnet.…”