Phase and amplitude response of the ‘0.7 feature’ caused by holes in silicon one-dimensionalwires and rings

Abstract

We present findings for the 0.7(2e2/h) feature in the hole quantum conductance staircase that is caused by silicon one-dimensionalchannels prepared by the split-gate method inside the p-type silicon quantum well (SQW) on then-type Si(100) surface. Firstly, the interplay of the spin depolarization with the evolution of the0.7(2e2/h) featurefrom the e2/h to 3/2 e2/h values as a function of the sheet density of holes is revealed by the quantumpoint contact connecting two 2D reservoirs in the p-type SQW. The 1D holesare demonstrated to be spin polarized at low sheet density, because the0.7(2e2/h) feature is closeto the value of 0.5(2e2/h) that indicates the spin degeneracy lifting for the first step of the quantum conductance staircase. The0.7(2e2/h) feature is found to take, however, the value of0.75(2e2/h) when the sheet density increases, thereby giving rise to the spin depolarizationof the 1D holes. Secondly, the amplitude and phase sensitivity of the0.7(2e2/h) feature are studied by varying the value of the external magnetic field and thetop-gate voltage that are applied perpendicularly to the plane of the double-slit ringembedded in the p-type SQW, with the extra quantum point contact inserted in theone of its arms. The Aharonov–Bohm and the Aharonov–Casher conductanceoscillations obtained are evidence of the interplay of the spontaneous spinpolarization and the Rashba spin–orbit interaction (SOI) in the formation of the0.7(2e2/h) feature. Finally,the variations of the 0.7(2e2/h) feature caused by the Rashba SOI are found to take in the fractional form with both theplateaus and steps as a function of the top-gate voltage.