code: def plot_seebeck_mu(self, temp=600, output='eig', xlim=None):
          
          import matplotlib.pyplot as plt
          plt.figure(figsize=(9, 7))
          seebeck = self._bz.get_seebeck(output=output, doping_levels=False)[
              temp]
          plt.plot(self._bz.mu_steps, seebeck,
                   linewidth=3.0)
  
          self._plot_bg_limits()
          self._plot_doping(temp)
          if output == 'eig':
              plt.legend(['S$_1$', 'S$_2$', 'S$_3$'])
          if xlim is None:
              plt.xlim(-0.5, self._bz.gap + 0.5)
          else:
              plt.xlim(xlim[0], xlim[1])
          plt.ylabel("Seebeck \n coefficient  ($\\mu$V/K)", fontsize=30.0)
          plt.xlabel("E-E$_f$ (eV)", fontsize=30)
          plt.xticks(fontsize=25)
          plt.yticks(fontsize=25)
          plt.tight_layout()
          return plt
docs: Plot the seebeck coefficient in function of Fermi level
  
          Args:
              temp:
                  the temperature
              xlim:
                  a list of min and max fermi energy by default (0, and band gap)
          Returns:
              a matplotlib object