Charge, spin, and heat shot noises in the absence of average currents: Conditions on bounds at zero and finite frequencies

Nonequilibrium situations where selected currents are suppressed of interest in fields like thermoelectrics and spintronics, raising the question how related noises behave. We study such zero-current charge, spin, heat a two-terminal mesoscopic conductor. In presence voltage, temperature biases, nonequilibrium (shot) can be arbitrarily large, even if their average vanish. However, as soon bias is present, additional equilibrium (thermal-like) noise necessarily occurs. show that this sets an upper bound on charge spin shot noises, voltage or biases present. demonstrate these bounds overcome for transport by breaking electron-hole symmetries, respectively. By contrast, we strictly conductors extends into finite-frequency regime.