Spin interference in silicon one-dimensional rings

Abstract

Abstract. We present the first findings of the spin transistor effect in the Rashba gatecontrolled ring embedded in the p-type self-assembled silicon quantum well that is prepared on the n-type Si (100) surface. The coherence and phase sensitivity of the spindependent transport of holes are studied by varying the value of the external magnetic field and the bias voltage that are applied perpendicularly to the plane of the double-slit ring. Firstly, the amplitude and phase sensitivity of the 0.7·(2e 2 /h) feature of the hole quantum conductance staircase revealed by the quantum point contact inserted in the one of the arms of the double-slit ring are found to result from the interplay of the spontaneous spin polarization and the Rashba spin-orbit interaction. Secondly, the quantum scatterers connected to two one-dimensional leads and the quantum point contact inserted are shown to define the amplitude and the phase of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations.The spin-correlated transport in low-dimensional systems was in focus of both theoretical and experimental activity in the last decade [1,2]. The studies of the Rashba spin-orbit interaction (SOI) that results from the structure inversion asymmetry in mesoscopic nanostructures have specifically attracted much of the efforts [1,3,4]. The variations in the Rashba SOI value appeared to give rise to the developments of spintronic devices based on the spin-interference phenomena that are able to demonstrate the characteristics of the spin field-effect transistor (FET) even without ferromagnetic electrodes and external magnetic field [4,5]. For instance, the spin-interference device shown schematically in figure 1a represents the Aharonov-Bohm (AB) ring covered by the top gate electrode, which in addition to the geometrical Berry phase provides the phase shift between the transmission amplitudes for the particles moving in the clockwise and anticlockwise direction [4]. This transmission phase shift (TPS) seems to be revealed by the Aharonov-Casher oscillations of the conductance measured under the top gate voltage applied to the two-terminal device, with the only drain and source constrictions [5]. However, the variations in the density of carriers that accompany the application of the top gate voltage are also able to result in the conductance oscillations. Therefore the three-terminal device with the quantum dot (QD) [6] or the quantum point contact (QPC) [7] inserted in one of the ring's arms using the split-gate technique [8] could be more appropriate to divide the relative contribution of the Aharonov-Casher (AC) effect in the conductance oscillations (see figure 1a).Since the AB ring's conductance has to be oscillated with the periodicity of a flux quantum h/e when a variable magnetic field threads its inner core, these AB oscillations have been shown to be persisted, if the transport through the QD [6] or QPC [7] inserted is coherent. The TPS caused by the QD or QPC has been found to be equal to π in the absence of the spin polarisa...

Quantum Supercurrent Transistors in Silicon Quantum Wells Confined by Superconductor Barriers

“…The energy positions of two-dimensional subbands for the light and heavy holes in the Si-QW studied were determined by studying the far-infrared electroluminescence spectra obtained with the infrared Fourier spectrometer IFS-115 Brucker Physik AG (Figure 3(a)) [3,13]. The results obtained are in a good agreement with corresponding calculations following by Ref [14] if the width of the Si-QW, 2nm, is taken into account ( Figure 3(b)).…”

Superconductor Properties for Silicon Nanostructures

“…Within frameworks of this mechanism of the coherent tunneling, the spin projection of 2D holes that take part in the MAR processes is conserved in the Si-QW plane (Klapwijk, 2004) and its precession in the Rashba effective field is able to give rise to the reproduction of the MAR peaks in the oscillations of the longitudinal conductance. Thus, the interplay of the MAR processes and the Rashba SOI appears to reveal the spin transistor effect (Bagraev et al, 2005;2006b;2008a;2008c) without the injection of the spinpolarized carriers from the iron contacts as proposed in the classical version of this device. Fig.…”

“…The conductance of these silicon nanostructures appeared to be determined by the parameters of the 2D gas of holes in the Si-QW (Bagraev et al 2002;2004b;2006b). However, here we demonstrate using the electrical resistance, thermo-emf, specific heat magnetic susceptibility and local tunnelling spectroscopy techniques that the high sheet density of holes in the Si-QW (>10 15 m -2 ) gives rise to the superconductor properties for the δ -barriers which result from the transfer of the small hole bipolarons through the negative-U centers (Šimánek, 1979;Ting et al, 1980;Alexandrov & Ranninger, 1981;Chakraverty, 1981;Alexandrov & Mott, 1994) in the interplay with the multiple Andreev reflections inside the Si-QW (Andreev, 1964;Klapwijk, 2004;Jarillo-Herrero et al, 2006;Jie Xiang et al, 2006).…”

“…If a negative bias voltage is applied to the δ-barriers, holes will tunnel into unoccupied sample states, whereas at a positive bias voltage they will tunnel out of occupied sample states. Since the transport conditions inside the 'sandwich' structures, S-Si-QW-S, are close to ideal (Bagraev et al, 2002;2004b;2005;2006b), the tunnelling conductance, dI/dV(V), provides the measurements of the LDOS thereby allowing the precise definition of the superconductor energy gap. The LTS current-voltage characteristic shown in Fig.…”

“…The resonance behaviour of the U xx (H) and U xy (H) dependences in the anti-crossing points of the triplet sublevels (T + -T 0 ) is evidence of the spin polarization that results from the selective population or depopulation of the T + and T -states relatively to the T 0 state in consequence of the partial removal of a ban on the forbidden triplet-singlet transitions (Laiho et al, 1998). The spin polarization of the bipolarons in the triplet state in the S-Si-QW-S structures should be of importance in the studies of the spin interference caused by the Rashba spin-orbit interaction in the quantum wires and rings (Bagraev et al, 2006b;2008a). The creation of the excited singlet states in the processes of the bipolaronic transport is also bound to be noticed, because owing to the transitions from the excited to the ground singlet state of the small hole bipolarons these 'sandwich' structures seem to be perspective as the sources and recorders of the THz and GHz emission that is revealed specifically in the www.intechopen.com electroluminescence spectra as a low frequency modulation (see Fig.…”