Matrix t2*K(2) in Subspace 141 with Dimension 3

(K(2) is the second-order Grosse operator)

-3*t*U (((3*I)/2)*(I + Sqrt[3])*t*U)/Sqrt[2] 0
(((-3*I)/2)*(-I + Sqrt[3])*t*U)/Sqrt[2] (-9*t*U)/2 (I/4)*(3*I + Sqrt[3])*U^2
0 (-I/4)*(-3*I + Sqrt[3])*U^2 (-3*t*U)/2