The nature of the fractional quantum Hall state with filling factor ν = 2/3 and its edge modes continues to remain an open problem in low-dimensional condensed matter physics. Here, we suggest an experimental setting to probe the ν = 2/3 edge by tunnel-coupling it to a ν = 1 integer quantum Hall edge in another layer of a two-dimensional electron gas (2DEG). In this double-layer geometry, the momentum of tunneling electrons may be boosted by an auxiliary magnetic field parallel to the two planes of 2DEGs. The threshold behavior of the current as a function of bias voltage and the boosting magnetic field yields information about the spectral function of the ν = 2/3 edge, and in particular about the nature of the chiral edge modes. Our theoretical analysis accounts also for the effects of Coulomb interaction and disorder.Introduction. In the conditions of quantum Hall effect, the compressible regions remain only at the edges of a sample and are known as edge states [1,2]. Edges of fractional Hall states are strongly-correlated chiral electron liquids [3]. The situation becomes even more intriguing for systems with filling factors different from those of Laughlin states, for which ν = 1/m with odd integer m > 0. Here we consider the particular case of a quantum Hall system with filling factor ν = 2/3.A prominent conjecture [4,5] considers the ν = 2/3 edge [6,7] as composed of two spatially separated edge channels: an outer channel with filling factor ν = 1 and an inner counter-propagating one corresponding to a ν = 1/3 liquid of hole states. Coulomb interactions between the two channels and backscattering off disorder enrich the physical picture and in the low-energy limit drive the system into a state with universal twoterminal and Hall conductance G = 2e 2 /3h [8]. Theory [8] predicts two effective edge modes, a charge-carrying mode and a counter-propagating neutral one. Recent shot noise measurements at a quantum point contact [9] have provided indirect evidence for the existence of such a neutral mode and a mechanism of upstream heating by neutral currents [9][10][11]. However, two observations put the picture of two counter-propagating modes in question and favor the possibility of two co-propagating ν = 1/3 modes as alternatively suggested long ago [12]. One is the observation of a G = e 2 /3h plateau [13,14] in the conductance through quantum point contacts. The second is the effective charge, detected through shot noise measurements [14], which crosses over from e/3 at higher temperature to 2e/3 at lower ones. A "unified" theory has recently [15] been proposed in terms of a four-channel model for a reconstructed edge. In this situation of competing theories, direct experimental evidence about the internal structure of the ν = 2/3 edge is called for.In this paper, we are suggesting a bilayer experiment to investigate the spectral function and, in particular, the nature of the chiral modes of the ν = 2/3 edge. In this experiment, the fractional quantum Hall edge is probed by momentum-resolved tunneling into o...