Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu₂Si₂

Takuya Yamashita, Takaaki Takenaka, Yoshifumi Tokiwa, Joseph A. Wilcox, Yuta Mizukami, Daiki Terazawa, Yuichi Kasahara, Shunichiro Kittaka, Toshiro Sakakibara, Marcin Konczykowski, Silvia Seiro, Hirale S. Jeevan, Christoph Geibel, Carsten Putzke, Takafumi Onishi, Hiroaki Ikeda, Antony Carrington, Takasada Shibauchi, Yuji Matsuda