Non-Magnetic Fractionally Quantized Conductance in Quasi-One Dimensional Semiconductor Structures

We have investigated quasi-one dimensional carrier transport using holes, (electrons), in Ge-SiGe, (GaAs-AlGaAs), heterostructures in the ballistic regime. At values of carrier concentration below about 5.1010 cm-2 the integer ground state disappears to be replaced by fractional values of conductance. This occurs when the confinement of the carriers is relaxed to be on the verge of two-dimensionality. For holes in Ge we find that, in units of e2/h, the fractional values of conductance are 1/2, spin degenerate, dropping to 1/4 in the presence of a parallel magnetic field and 1/16 which is spin polarized at zero field, (1). The accuracy of the quantization was 0.5%, possibly corresponding to fractional charges of e/2 and e/4.
For electrons in GaAs we find a rich structure, the dominant fractional values of conductance, consistently observed, are in the presence of a weak, asymmetric confinement. The values found are 2/5, 1/2 and 1/6. In the presence of a parallel magnetic field a number of other fractions started to appear, (2). These results will be discussed in relation to the formation of a zig-zag electron configuration with strong interactions between the two rows.
1.Y.Gul et al, J.Phys. Cond. Matt. 30, 09LT01, 2018
2. S. Kumar et al, to be published