An electron of mass \( m \) is moving in an electric field \( \vec{E} = -2E_0 \, \hat{j} \) \( (E_0 = \text{constant} > 0) \), with an initial velocity \( \vec{V} = v_0 \, \hat{i} \) \( (v_0 = \text{constant} > 0) \). If \( \lambda_0 = \dfrac{h}{4 m v_0} \), its de Broglie wavelength at time \( t \) is ______; \( (e = \text{charge of electron}) \).
