The notes are available on the websitehttp://stanford.edu/~nap/files/02-03-2021-ben.pdf
Title: The Yang-Baxter equation, symmetric functions, and Schubert polynomials
Fomin, Kirillov: The Yang-Baxter equation, symmetric functions and Schubert polynomials (maybe?)
They also have an ArXiv follow-up called "YANG-BAXTER EQUATION, SYMMETRIC FUNCTIONS AND GROTHENDIECK POLYNOMIALS" (sorry for the all-caps)
What would be a good reference about these standard intertwiners?
Ben is referencing Casselman, Compositio (1980) and Casselman-Shalika (1980). There is also a book by Casselman available on his web page