I shall review the recent studies conducted in Yb-based delafossite AYbSe2 (A = Cs, Na, K, Tl, etc.), a two-dimensional triangular antiferromagnet (TLAF).
The search for a quantum spin liquid (QSL) – a highly-entangled quantum state of spins – has been a central issue in the condensed-matter physics. The primary motivation lies in the search for entangled states of quantum spins and novel elementary excitations such as spinons, visons, Majorana fermions, etc. Experimentally, to discover a QSL state, research has been conducted in materials having a geometrical frustration, such as a triangular, kagome, or pyrochlore lattice, or anisotropic interactions such as a Kitaev material.
Recently, there has been a surge of research done in two-dimensional TLAF materials known as delafossite AYbSe2, in which the rare-earth ion Yb3+ serves as an effective spin 1/2 due to the crystal electric field effect.
In a TLAF, it has been shown that the ground state is not a QSL, but a long-range ordered state (120-degree structure) if the spin interaction is limited to the nearest-neighbor Heisenberg interaction (J1). One needs to suppress this ordered state by introducing a next-nearest neighbor (J2) to realize a QSL state. Researchers hope that replacing the A site ion of delafossite allows us to tune the J2/J1 ratio, which may achieve a QSL state.
I shall provide a brief review of the research background of the TLAF and the experimental results obtained in several delafossite materials.