plot dos

        Args:
            sigma: a smearing

        Returns:
            a matplotlib object

def plot_dos(self, sigma=0.05):
        """
        plot dos

        Args:
            sigma: a smearing

        Returns:
            a matplotlib object
        """
        plotter = DosPlotter(sigma=sigma)
        plotter.add_dos("t", self._bz.dos)
        return plotter.get_plot()