Fig. 2

IR reflectance spectra in magnetic fields. a, b Reflectance spectra R(ω, B) in several magnetic fields at T~4.5 K. For clarity the spectra in b are displaced from one another by 0.01 with the spectrum at B = 17.5 T shown at its actual value. The gray area around 175 meV is the energy range in which no data can be obtained due to the absorption of the optical window in our setup