Sprecher
Beschreibung
Rare earth pyrochlores offer a rich landscape for discovering and studying new states of matter due to the geometrical frustration imposed by their lattice structure. A notable example is the classical spin ice state found in Dy₂Ti₂O₇ and Ho₂Ti₂O₇, which exhibits infinite degeneracy.
Even more intriguing is the concept of Quantum Spin Ice (QSI), where quantum tunneling between degenerate ice states realizes quantum electrodynamics. Quantum effects in QSI can be introduced through transverse interactions between Ising spins. Pyrochlore compounds containing elements such as Ce, Pr, Nd, and Yb are proposed candidates for exhibiting such behaviors. Another promising route to achieving QSI is by introducing effective transverse fields. These fields arise from lifting the accidental doublet degeneracy of the crystal field ground state of non-Kramers ions, such as Ho³⁺.
Ho₂GaSbO₇, characterized by Ga/Sb disorder, is an ideal candidate for exploring this second route. Here, we report our studies on Ho₂GaSbO₇ using both macroscopic measurements and neutron scattering methods. The specific heat capacity of Ho₂GaSbO₇ shows a broad peak at 1.5 K, accompanied by a nuclear Schottky anomaly at lower temperatures, suggesting an absence of a transition to long-range magnetic order. This behavior is very similar to that observed in Ho₂Ti₂O₇.
Furthermore, crystal field excitations in Ho₂GaSbO₇ were observed to be significantly broader than the instrument resolution, a consequence of the structural disorder. The elastic scattering profile shows intensity modulation characteristic of spin ice, while broad low-energy magnetic excitations below 0.8 meV were observed at 1.5 K. This observation starkly contrasts with classical spin ice and hints at the presence of quantum dynamics within the system.
