Perovskite Lanthanum‐Doped Barium Stannate: A Refractory Near‐Zero‐Index Material for High‐Temperature Energy Harvesting Systems oleh Hyebi Kim, Geunpil Kim, Young‐Uk Jeon, Wonjun Lee, Byeong‐Hyeon Lee, In Soo Kim, Kwanil Lee, Soo Jin Kim, Jongbum Kim