Behavior of Tl(2212)-Normal Metal Point Contacts under Microwave Irradiation

Current-voltage characteristics and their derivatives of S-c-N point contacts formed by Tl₂Ba₂CaCu₂O_8–x anvil - niobium needle have been studied in the temperature range from 4.2 to T_c under microwave irradiation of wide frequency range. At frequencies of order 10¹⁰ Hz two types of excess current (I_exc) dependence on irradiation power level P was observed. In one case at temperatures near T/T_c 0.5 an excess current oscillates with increasing of P as the square of zero order Bessel function. In another case closer to the critical temperature (mainly at T/T_c 0.9) the enhancement of I_exc by the microwave power was revealed. Observed effects demonstrate complicated dynamics of quasiparticles in Tl-based HTS.