Recent experiments (Yacoby et al., Phys. Rev. Lett. 77 (1996) 4612; Solid State Commun. 101 (1997) 77; M. Rother et al., ICPS-24, Th-P137) have shown non-universal conductance quantization in one-dimensional wires that are fabricated using the cleaved edge overgrowth technique (L.N. Pfei er et al., Microelectronics J. 28 (1997) 817). In one of the papers (Yacoby et al., Phys. Rev. Lett. 77 (1996) 4612), it was speculated that the origin of the reduced conductance lies in the interface between the one-dimensional wire and the two-dimensional electron gas regions, which serve as ohmic contacts and thermal reservoirs. Here we report the results of a systematic study of such 2D-1D interfaces. By embedding a 2D-1D interaction section region of controllable length inside an otherwise isolated wire, we were able to study the properties of the coupling between these two subsystems. Our results show that 2D-1D interface is in fact the origin of the non-universal conductance. ? 2000 Elsevier Science B.V. All rights reserved. One-dimensional electronic systems, the so-called Luttinger-liquids, are expected to show unique transport properties as a consequence of the Coulomb interaction between carriers [1][2][3][4][5][6][7]. In contrast to Fermi liquid theory [8][9][10][11][12], the Luttinger model predicts that even the weakest impurity embedded in an otherwise perfectly clean 1D wire will completely suppress its conductance at zero temperature. Furthermore, the tunneling conductance into such a perfect wire will also be completely suppressed at zero temperature. * Corresponding author.One of the ÿngerprints of a clean non-interacting 1D conductor is its quantized conductance in multiples of the universal value g 0 = 2e 2 =h. This quantization results from an exact cancellation of the increasing electron velocity and the decreasing density of states as the carrier density increases [13][14][15][16]. Therefore, as subsequent 1D electronic subbands are ÿlled with electrons the conductance increases in a series of plateaus (or steps) with values equal to g 0 multiplied by the number of occupied wire modes. Surprisingly, the inclusion of interactions does not alter this prediction. Early papers [4 -7], considering inÿnitely long wires, did in fact predict quantization 1386-9477/00/$ -see front matter ? 2000 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 6 -9 4 7 7 ( 9 9 ) 0 0 0 9 7 -1