Search for the 4f¹⁴6s² ¹S₀-4f¹³5d6s²(J=2) transition in Yb towards a search for the time variation of fine structure constant

The 4f¹⁴6s^{2 1}S₀-4f¹³5d6s²(J=2) transition in ytterbium (Yb) at 431 nm is theoretically predicted as a narrow-linewidth transition that has high sensitivity for the variation of the fine structure constant, and it also has some other interesting features such as a transition with f-orbital electron excited in neutral Yb and large electronic structure difference from known clock transitions. We are searching for this 4f¹⁴6s^{2 1}S₀-4f¹³5d6s²(J=2) transition with Yb atoms laser-cooled by a magneto-optical trap formed by the 4f¹⁴6s^{2 1}S₀-4f¹⁴6s6p ³P₁ transition. The current status of the search with our optical lattice clock system is presented. Establishing the spectroscopy of this transition leads to the more precise test of the time variation of the fine structure constant and the dark matter search with nonlinearity of the King plot.