An electron with mass $ m $ with an initial velocity $ (t = 0) \, \vec{v} = \vec{v_0} \, (v_0>0) $ enters a magnetic field $ \vec{B} = B \hat{j} $. If the initial de-Broglie wavelength at $ t = 0 $ is $ \lambda_0 $, then its value after time $ t $ would be: