ABSTRACT
Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (µSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state.
ABSTRACT
The magnetization M(H), magnetic susceptibility χ(T), electrical resistivity ρ(T) and specific heat C(T) properties of PrCu(4)Au have been investigated. A clear antiferromagnetic transition T(N) is observed at 2.5 K in C(T) and χ(T). The internal magnetic field at the Pr nucleus, H(HF), is obtained to be 195 T from the nuclear specific heat observed in C(T) below 0.7 K. The ground state of Pr 4f(2) in the cubic crystalline electric field is inferred to be a magnetic triplet Γ(5) from the magnitude of the magnetization at 2 K, which coincides with the value of the 4f(2) magnetic moments deduced from H(HF). The large value of the electronic specific heat coefficient, γ, remains at the zero-temperature limit even in external magnetic fields. On the other hand, the entropy up to T(N) is somewhat less than Rln3. These anomalous heavy-electron-like behaviors probably originate in the fact that both the magnetic moments and the quadrupole moments are involved in the ground state of Pr 4f(2).
