Effects of microwave radiation on the noise in high-Tc YBa2Cu3O7 dc SQUID magnetometer

With a properly fabricated low-noise SQUID, we have studied the effects of microwave radiation on the noise behavior. Under an ac bias, with increasing microwave power, the critical current and the voltage modulation depth ΔV=Φ0VΦ/π decrease, but the SQUID resistance Rs increases, suggesting a dynamical interaction between the charge carriers and the electromagnetic wave. Furthermore, the microwave radiation modifies drastically the functional dependence of SΦ and ΔV on ac bias current.