Quantum magnetism and quantum phase transitions

Abstract:

Inelastic neutron scattering is used to study the magnetic excitations of the S=1 square-lattice antiferromagnet La₂NiO₄. We find that the spin waves cannot be described by a simple classical (harmonic) Heisenberg model with only nearest-neighbor interactions. The spin-wave dispersion measured along the antiferromagnetic Brillouin-zone boundary shows a minimum energy at the (1/2,0) position as is observed in some S=1/2 square-lattice antiferromagnets. Thus, our results suggest that the quantum dispersion renormalization effects or longer-range exchange interactions observed in cuprates and other S =1/2 square-lattice antiferromagnets are also present in La₂NiO₄. We also find that the overall intensity of the spin-wave excitations is suppressed relative to linear spin-wave theory, indicating that covalency is important. Two-magnon scattering is also observed.

Abstract:

This corrects the article DOI: 10.1103/PhysRevLett.127.037201.

Abstract:

The deposited package contains experimental single crystal inelastic neutron scattering data probing the spin dynamics in the quantum Ising chain magnet CoNb2O6 in applied transverse magnetic field together with corresponding theoretical calculations of the spin dynamics. A matlab script to read and plot all data in ASCII files is also supplied.

Abstract:

Neutron diffraction and nuclear magnetic resonance (NMR) measurements have been used to analyze the magnetic structure in the S = 1 2 kagome antiferromagnet CdCu 3 ( OH ) 6 ( NO 3 ) 2 ⋅ H 2 O . Below the magnetic ordering temperature T N ≃ 4 K , magnetic Bragg reflections at (101) and (100) were found in the neutron diffraction pattern, which suggests a q = 0 magnetic structure. Furthermore, the vector spin chirality for the q = 0 structure was successfully identified from the internal field direction obtained by the 14 N -NMR measurement, previous magnetization measurements, and magnetic symmetry analysis. Our findings point to a chirality-ordered magnetic structure with negative vector chirality and ⟨ 100 ⟩ anisotropy.