Magnetic frustration in the Yb-based triangular lattice compound <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi mathvariant="normal">CuYbSe</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math>

The Yb-based triangular lattice delafossites $A\mathrm{Yb}{X}_{2}$ ($A=\text{alkali}$ metal, $X=\text{O}$, S, Se) have recently been studied as quantum spin liquid candidates. We report the synthesis of powders and single crystals of ${\mathrm{CuYbSe}}_{2}$ with a perfect triangular lattice of ${\mathrm{Yb}}^{3+}$ moments. Magnetic susceptibility and heat capacity measurements reveal no evidence of long-range magnetic ordering down to 1.8 K in spite of a significant antiferromagnetic exchange between ${\mathrm{Yb}}^{3+}$ moments, suggesting a frustrated magnetic system. Electrical resistivity measurements indicate insulating behavior, consistent with the localized nature of magnetic moments. Heat capacity reveals that ${\mathrm{CuYbSe}}_{2}$ can be treated as an effective spin $S=1/2$ triangular lattice antiferromagnet below $\ensuremath{\sim}50$ K. Magnetic susceptibility measurements on single crystals reveal weak magnetic anisotropy. These properties position ${\mathrm{CuYbSe}}_{2}$ as another platform for exploring exotic magnetic ground states in triangular lattice systems.