Abstract
By exploiting density-matrix renormalization group techniques, we investigate the spin dynamics of a spin-1/2 one-dimensional J1-J2 XXZ model with competing ferromagnetic J1 and antiferromagnetic J2 exchange couplings under applied magnetic fields. Numerical results of spin excitation spectra show that in the field-induced spin quadrupole regime, the longitudinal component has a gapless mode and the transverse component has a gapped mode irrespective of the exchange anisotropy. The excitation gap of the transverse spin excitation increases as the exchange anisotropy increases over the XY-like and Ising-like regions, demonstrating that two-magnon bound states are stabilized due to the easy-axis anisotropy.
Highlights
Frustrated quantum spin systems in low dimensions have provided a fascinating playground to explore strange new phases that have no classical analogue, and rich physics of quantum phase transitions between them
Recent studies on the ferromagnetic J1 case in a magnetic field have revealed that the ground state is a vector chiral (VC) state in low magnetic fields, while it turns to an exotic Tomonaga-Luttinger-liquid state in high magnetic fields [1, 2, 3, 4]
The so-called spin nematic (SN) state is realized in the vicinity of the saturation, while the ground state shows a crossover to a spin-density-wave (SDW) state with lowering the magnetic field
Summary
Frustrated quantum spin systems in low dimensions have provided a fascinating playground to explore strange new phases that have no classical analogue, and rich physics of quantum phase transitions between them. To clarify the property of the field-induced quadrupole state from the viewpoint of the spin dynamics, we have studied the dynamical spin structure factor of the spin-1/2 one-dimensional J1-J2 Heisenberg model by exploiting numerical methods such as a dynamical density-matrix renormalization group [8]. We present numerical results on the anisotropic behavior of longitudinal and transverse spin excitation spectra, and discuss the dependence on the exchange anisotropy.
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