Understanding the anomalous conductance plateau in asymmetrically biased InAs/In0.52Al0.48As quantum point contacts—A step towards a tunable all electric spin valve

Abstract

The appearance and evolution of an anomalous conductance plateau at 0.4(2e2/h) in an In0.52Al0.48As/InAs quantum point contact (QPC), in the presence of lateral spin-orbit coupling, has been studied at T = 4.2 K as a function of the potential asymmetry between the in-plane gates of the QPC. The anomalous plateau, a signature of spin polarization in the channel, appears only over an intermediate range (around 3 V) of bias asymmetry. It is quite robust, being observed over a maximum range of nearly 1 V of the sweep voltage common to the two in-plane gates. The conductance measurements show evidence of surface roughness and dangling bond scattering from the side walls of the QPC.

Intrinsic bistability in quantum point contacts with in-plane side gates

“…Recently, we showed that LSOC in InAs/InAlAs and GaAs/AlGaAs QPCs with in-plane side gates can be used to create a strongly spin-polarized current by purely electrical means in the absence of any applied magnetic field [7][8][9][10]. The use of a Non Equilibrium Green's Function (NEGF) approach to calculate the conductance of QPCs shows that the onset of spin polarization in devices with in-plane side gates required three ingredients: (1) an asymmetric lateral confinement, (2) a LSOC induced by lateral confining potential of the QPC, and (3) a strong electron-electron interaction [11,12].…”

Spin filtering effect generated by the inter-subband spin-orbit coupling in the bilayer nanowire with the quantum point contact

“…In such nanostructures, the spin filtering effect results from the interplay between the SO coupling 18,19 and the quantum confinement. Recent papers [9][10][11][12][13][14][15] have reported the experimental evidence of the spin filtering in QPCs, which manifests itself as the plateau of conductance at 0.5G 0 (G 0 = 2e 2 /h) measured in the absence of the external magnetic field. The 0.5G 0 plateau has been explained as resulting from the combination of the three effects 13,14,17 : an asymmetric lateral confinement, a lateral Rashba SO interaction, and an electron -electron interaction.…”

“…The experimental realizations of spin filters based on QPCs, reported so far, are based on a two-dimensional electron gas (2DEG) confined in the narrow quantum well at the AlGaAs/GaAs or InAs/InAlAs interface 10,11 , in which the electrons occupy the lowest-energy state ("single occupancy"). However, recently, wider or coupled quantum wells with two populated subbands ("double occupancy") have attracted a growing interest of both experimentalists [24][25][26][27][28][29] and theoreticians [30][31][32][33][34][35] .…”

Spin-orbit coupling and resonances in the conductance of quantum wires

“…In the short wire limit, we calculate several e-e collision processes, which give rise to three distinct resonances in conductance as a function of the chemical potential, see dramatically stronger compared to the three-particle collisions in spin-degenerate case 2 . In addition, some of the e-e contributions, including the strongest linear in T negative term, vanish in the case of symmetric transverse confinement potential, providing a tool for a straightforward test of our theory [26][27][28] . Our results may explain the origin of a helical gap-like feature recently observed in a ballistic InAs nanowire 29 and pave the way towards allelectrical control of e-e collisions in clean quantum wires with strong SOC 30,31 .…”