Fig. 2: Observation of terahertz BPVE.

a Schematics of experimental setup and of ab-plane spin spiral. Terahertz light-polarization is rotated by rotating the wire grid polarizer. The photocurrent flowing along the a axis is measured by the oscilloscope. b Time profile of photocurrent generated by terahertz pulses at the ferroelectric phase with \(\pm P\) (5 K) and at the paraelectric phase (30 K). c Terahertz power dependence of photocurrent. Amplitude of photocurrent is plotted (see (b)). The blue line is a linear fit. d Terahertz light-polarization dependence of photocurrent flowing along the a axis at 5 K. The signal at 0° and 180° represents the photocurrent arising from electromagnon, while the signal at 90° and 270° represents the photocurrent arising from AFMR (see right upper panel). The amplitude of photocurrent is normalized by the energy of light inside the sample by considering the reflection loss at the sample surface.