$3.$For which parameters $a,b$ the following system has unique rational solution $(x,y)=(0,0)$

$-2y+x(a+2b\sqrt[\phantom{2}]{x^2+y^2}-(x^2+y^2))=0$

$x+y(3a+b\sqrt[\phantom{2}]{x^2+y^2}-(x^2+y^2))=0$