Crystal-field excitations in the spin-liquid candidate on a rare-earth based Jeff=1/2 square lattice antiferromagnet NaNdTiO4

Quantum spin-liquid (QSL) refers to a highly entangled state wherein strong frustration-induced quantum fluctuations prevent phase transitions at T→0 in magnetic materials despite strong exchange interactions between spins. QSLs are ideal hosts of exotic fractional quantum numbers coupled to emergent gauge fields and hold tantalizing prospects for applications in fault-tolerant quantum computing. The experimental realization of QSLs in two-dimensional spin-lattice remains elusive in view of the presence of defects and anti-site disorder in real materials. Rare-earth-based frustrated magnets provide a novel route for exploring the enigmatic QSL state with fractional magnetic excitations. The recently synthesized structurally perfect square lattice antiferromagnet NaNdTiO4 seems a very promising QSL candidate, as confirmed by a series of macroscopic measurements. The localized Nd3+ spins show neither magnetic order nor spin-freezing state down to 1.9 K. Thermodynamic data reveal an effective Jeff = 1/2 (Nd3+) in the Kramers doublet state and an antiferromagnetic interaction between Jeff = 1/2 moments. This calls for a very sensitive local probe such as inelastic neutron scattering that could unambiguously establish the ground state and associated magnetic excitations. We propose to carry out INS studies to study the crystal field excitations, single-ion anisotropy and to probe the energy and wavevector dependence of the dynamic structure factor in NaNdTiO4.