TAILIEUCHUNG - The Discovery of Type II Superconductors Part 14

Tham khảo tài liệu 'the discovery of type ii superconductors part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 316 Superconductor 1 P E lim -1- T4 2nhT e 9o t e-W0 0 e x cos a t t e a cos at e Et di di TO 2 j2 x Po E - nh 0 n -TO 6 Here P0 E is the spectral function in absence of the microwave influence and satisfies the detailed balance P0 -E exp -EkBT P0 E a consequence of thermal equilibrium. We note that equation 6 is an expression of multiple photon absorption and emission with the amplitude of Bessel function Jn x . Fig. 4. The zero-bias resistance as a function of irradiating microwave or RF amplitude at various frequencies. Here the resistances are shifted and the microwave amplitude is rescaled to its period for each curve. The oscillation period is related to the superconducting gap of the electrodes. Adopted from Liou Kuo et al. 2008 Expression 6 gives a supercurrent Is V i J2 x I0 v - n a . n -TO 2 e 7 Here I V is the Cooper-pair tunneling current in absence of the microwaves. When the environmental impedance is much smaller than the quantum resistance the spectral function becomes Delta-function so as to yield a coherent supercurrent IC at zero bias voltage. In turn the microwave-induced supercurrent becomes Is Vn ICjn x at a voltage Vn iJa leading to the structure of Shapiro steps. Ideally each step in IV curves represents a constant-voltage state labeled by n featuring a coherent charge tunneling generated by the mode-locking. When the bias voltage is ramped the junction would switch 317 Phase Dynamics of Superconducting Junctions under Microwave Excitation in Phase Diffusive Regime from one constant-voltage state to another and eventually jumps to the finite-voltage state. It is noteworthy that in the analogy of a driven pendulum described in the previous section the mode-locking should yield Is Vn ICJ x a different result from the incoherent square dependence. CXI 51 01 Õ__ Ơ j 05 -l-J o ỉ-1d Q J RF amplitude eVac 2A Fig. 5. The intensity plots of the dynamical .

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