Chemical potential offset.

        The distance of the chemical potential
        from the top of the upper valence band.

        :return: :math:`Δμ`
        :rtype: float
        :default: :math:`-λ`

def Δμ(self):
        """Chemical potential offset.

        The distance of the chemical potential
        from the top of the upper valence band.

        :return: :math:`Δμ`
        :rtype: float
        :default: :math:`-λ`
        """
        if not hasattr(self, '_Δμ'): self.Δμ = -self._dichalcogenide.λ
        return self._Δμ