“…In this paper we propose how to realize the qq-character in refined topological string by the brane insertion, analyzed using the refined geometric transition. In particular, the codimension-2 defect operator, corresponding to the surface operator in gauge theory, is obtained by inserting a defect brane to the Lagrangian submanifold of the Calabi-Yau threefold [34,16,35,36,37,38]. We show that the Y-operator, which is a codimension-4 building block of the qq-character, can be constructed by inserting two codimension-2 defect operators.…”