Specific heat and thermal conductivity of the triangular-lattice rare-earth material KBaYb(BO3)2 at ultralow temperature

We present the ultralow-temperature specific-heat and thermal-conductivity measurements on single crystals of the triangular rare-earth lattice material $\mathrm{KBaYb}{({\mathrm{BO}}_{3})}_{2}$. Our experiments show the absence of long-range magnetic order down to 50 mK, giving the possibility of a quantum spin liquid ground state in this frustrated compound. Furthermore, no signature of spin freezing is observed down to 50 mK in the ac susceptibility measurements. However, no notable contributions from gapless magnetic excitations, but only a Schottky anomaly is observed in the specific-heat data. The ultralow-temperature thermal-conductivity data show that the residual linear term at zero field is negligible, and the thermal conductivity is insensitive to the magnetic field up to 9 T. The ground state of this frustrated triangular rare-earth lattice material is discussed.