docs: 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