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perature ( T$_{D}$ ∝ τ $^{$_{−}$1}$) and α = 2 π $^{2}$k$_{B}$ m$_{0}$/e ℏ ( ∼ 14 . 69 T/K). 

Fourier analysis of the oscillatory part of the QO all give a single peak at about F = 530 ± 10 T, which is also consistent with the previous study [1]. The ampli- tude of the oscillations in R$_{xx}$ is large enough in the present study to deduce reliable parameters from the Fourier analysis. In particular, it is clear from Fig. 1 that the phase shift between the transverse magnetore- sistance R$_{xx}$ and the Hall resistance R$_{xy}$ is about π , as expected in the case of an electron pocket. Such a pocket in the FS of underdoped YBa$_{2}$Cu$_{3}$O$_{y}$ has been inferred from Hall effect measurements [15] and confirmed in the present study in a different sample. 

Fig. 2 displays the temperature dependence of the os- cillation amplitudes. Good agreement with the LK the- ory is observed, giving an effective mass m ∗ = 1 . 8 ± 0 . 1 m$_{0}$ . The inset of Fig. 2 shows the effective mass deduced from dHvA and SdH in different field windows. 

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Within our experimental resolution, we can conclude that the effective mass is field-independent, as expected in the standard LK theory [14]. 

The field dependence of the amplitude of the oscilla- tions leads to a Dingle temperature T$_{D}$ = 6 . 2 ± 1 . 2 K for dHvA data and converts to a mean free path of l ∼ 160 ˚ A and w$_{c}$τ = 0 . 7 ± 0 . 2 at 35 T. Within our experimental res- olution, it is not possible to resolve an extra attenuation corresponding to the effect of superconductivity on the dHvA amplitude. Note that the field range in which R$_{xy}$ 

