Metastable 1T-RhO2 with a Triangular Lattice: A Possible Quantum Spin Liquid Candidate.

The discovery of intrinsic magnetism in layered van der Waals (vdW) magnets has received intensive attention due to their fundamental importance in low-dimensional magnetism and potential device applications. To date, most vdW magnets contain 3d transition metals. Extending vdW magnetism to 4d and 5d transition metal systems is therefore of great interest as it offers opportunities to explore exotic magnetic behaviors arising from the interplay between electronic correlations and strong spin-orbit coupling (SOC). Here, we report the successful synthesis of a metastable layered vdW triangular lattice crystal, 1T-RhO2, through the topochemical reaction from Cs0.5RhO2 single crystals. Electrical transport measurements reveal that 1T-RhO2 is an insulator, while magnetic susceptibility and alternating current susceptibility confirm the absence of long-range magnetic order or spin glass behavior down to 2 K. Raman spectroscopy indicates fermionic excitations consistent with fractionalized Majorana fermions. Angle-resolved photoemission spectroscopy, supported by hybrid functional calculations, reveals a band gap of about 1.0 eV, further confirming the insulating nature. These results collectively suggest that 1T-RhO2 is a possible quantum spin liquid (QSL) candidate. Our work not only sheds light on the research fields of 4d and 5d transition metal vdW magnets but also significantly expands the pathways for discovering QSL candidates in metastable materials.