  We present theoretical calculations and experimental measurements which
reveal the Luttinger-liquid (LL) nature of elementary excitations in a system
consisting of two quantum wires connected by a long narrow tunnel junction at
the edge of a GaAs/AlGaAs bilayer heterostructure. The boundaries of the wires
are important and lead to a characteristic interference pattern in measurements
on short junctions. We show that the experimentally observed modulation of the
conductance oscillation amplitude as a function of the voltage bias can be
accounted for by spin-charge separation of the elementary excitations in the
interacting wires. Furthermore, boundaries affect the LL exponents of the
voltage and temperature dependence of the tunneling conductance at low
energies. We show that the measured temperature dependence of the conductance
zero-bias dip as well as the voltage modulation of the conductance oscillation
pattern can be used to extract the electron interaction parameters in the
wires.
