Phys.org  September 27, 2024 Excitons in monolayer semiconductors offer strong light–matter coupling, spin–valley locking and exceptional tunability allowing electrical switching of their optical response due to efficient interactions of excitonic emitters with free charge carriers forming trions and Fermi polarons. However, there are major limitations to how fast the light emission of these states can be tuned, restricting most applications to an essentially static regime. An international team of researchers (Italy, Sweden, Germany, Japan) demonstrated switching of excitonic light emitters in monolayer semiconductors on ultrafast picosecond time scales by applying short pulses in the terahertz spectral range following optical injection. […]