def get_hall_carrier_concentration(self):
        """
        gives the Hall carrier concentration (in cm^-3). This is the trace of
        the Hall tensor (see Boltztrap source code) Hall carrier concentration
        are not always exactly the same than carrier concentration.

        Returns
            a dictionary {temp:[]} with an array of Hall carrier concentration
            (in cm^-3) at each temperature The array relates to each step of
            electron chemical potential
        """
        result = {temp: [] for temp in self._hall}
        for temp in self._hall:
            for i in self._hall[temp]:
                trace = (i[1][2][0] + i[2][0][1] + i[0][1][2]) / 3.0
                if trace != 0.0:
                    result[temp].append(1e-6 / (trace * constants.e))
                else:
                    result[temp].append(0.0)
        return result