arXiv subjects

N. T. Bagraev

Publications and source records attributed to N. T. Bagraev.

35 records · Page 2Linked to original sources

arXiv2008

Phase and amplitude response of "0.7 feature" caused by holes in silicon one-dimensional wires and rings

We present the findings of the 0.7(2e2/h) feature in the hole quantum conductance staircase that is caused by silicon one-dimensional channels prepared by the split-gate method inside the p-type silicon quantum well (SQW) on the n-type Si (100) surface. Firstly, the interplay of the spin depolarisation with the evolution of the 0.7(2e2/h) feature from the e2/h to 3/2 e2/h values as a function of the sheet density of holes is revealed by the quantum point contact connecting two 2D reservoirs in the p-type SQW. The 1D holes are demonstrated to be spin-polarised at low sheet density, because the 0.7(2e2/h) feature is close to the value of 0.5(2e2/h) that indicates the spin degeneracy lifting for the first step of the quantum conductance staircase. The 0.7(2e2/h) feature is found to take however the value of 0.75(2e2/h) when the sheet density increases thereby giving rise to the spin depolarisation of the 1D holes. Secondly, the amplitude and phase sensitivity of the 0.7(2e2/h) feature are studied by varying the value of the external magnetic field and the top gate voltage that are applied perpendicularly to the plane of the double-slit ring embedded in the p-type SQW, with the extra quantum point contact inserted in the one of its arms. The Aharonov-Bohm (AB) and the Aharonov-Casher (AC) conductance oscillations obtained are evidence of the interplay of the spontaneous spin polarisation and the Rashba spin-orbit interaction (SOI) in the formation of the 0.7(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 the plateaux and steps as a function of the top gate voltage.

cond-mat.mes-hall↗

arXiv2007

Fractional quantization of ballistic conductance in 1D hole systems

We analyze the fractional quantization of the ballistic conductance associated with the light and heavy holes bands in Si, Ge and GaAs systems. It is shown that the formation of the localized hole state in the region of the quantum point contact connecting two quasi-1D hole leads modifies drastically the conductance pattern. Exchange interaction between localized and propagating holes results in the fractional quantization of the ballistic conductance different from those in electronic systems. The value of the conductance at the additional plateaux depends on the offset between the bands of the light and heavy holes, Δ, and the sign of the exchange interaction constant. For Δ=0 and ferromagnetic exchange interaction, we observe additional plateaux around the values 7e^{2}/4h, 3e^{2}/h and 15e^{2}/4h, while antiferromagnetic interaction plateaux are formed around e^{2}/4h, e^{2}/h and 9e^{2}/4h. For large Δ, the single plateau is formed at e^2/h.

cond-mat.mes-hall↗

arXiv2007

Comment on "Experimental Demonstration of the Time Reversal Aharonov-Casher Effect"

In a recent Letter, Bergsten and co-authors have studied the resistance oscillations with gate voltage and magnetic field in arrays of semiconductor rings and interpreted the oscillatory magnetic field dependence as Altshuler-Aronov-Spivak (AAS) oscillations and oscillatory dependence on gate voltage as the Aharonov-Casher (AC) effect. This Comment shows that Bergsten and co-authors incorrectly identified AAS effect as a source of resistance oscillations in magnetic field, that spin relaxation in their experimental setting is strong enough to destroy oscillatory effects of spin origin, and that the oscillations are caused by changes in carrier density and the Fermi energy by gate, and are unrelated to spin.

cond-mat.mes-hall↗

arXiv2006

Spin-dependent transport in the p-type ultra-narrow silicon quantum well

We present the findings of the spin-dependent transport of the 2D holes in the p-type ultra-narrow self-assembled silicon quantum well (Si-QW) confined by the superconductor barriers on the n-type Si (100) surface. The Aharonov-Casher conductance oscillations caused by the Rashba spin-orbit interaction are found to interplay with the quantization phenomena induced by the creation of the two-dimensional subbands in Si-QW and the quantum subbands due to the Andreev reflection from the superconductor barriers.

cond-mat.mes-hall↗

arXiv2006

ODMR Of Impurity Centers Embedded In Silicon Microcavities

We present the findings of high efficient light absorption in self-assembled quantum wells (SQW) embedded in silicon microcavities that exhibit a distributed feedback identified by the FIR transmission spectra. The excitonic normal-mode coupling (NMC) is found to result in high efficient bound exciton photoluminescence in the range of the Rabi splitting. The bound excitons at the iron-boron pair and the erbium-related centers inserted in SQW are shown to cause giant exchange splitting of the center multiplets as a result of the strong sp-d and sp-f mixing in the absence of the external magnetic field. The NMC regime is observed to reveal this exchange splitting in the angular dependencies of the transmission spectra measured in the range of the Rabi splitting that are evidence of the ODMR of the trigonal iron-boron pairs and trigonal erbium-related centers.

cond-mat.mes-hall↗

arXiv2006

Fractional form of the 0.7(2e2/h) feature

We present the first findings of the spin transistor effect in the Rashba gate-controlled 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 spin-dependent transport of holes are studied by varying the value of the external magnetic field and the top gate voltage that are applied perpendicularly to the plane of the double-slit ring and revealed by the Aharonov-Bohm (AB) and Aharonov-Casher (AC) conductance oscillations, respectively. Firstly, the amplitude and phase sensitivity of the 0.7(2e2/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 (SOI). Secondly, the values of the AC conductance oscillations caused by the Rashba SOI are found to take the fractional form with both the plateaus and steps as a function of the top gate voltage.

cond-mat.mes-hall↗

arXiv2006

The conductance of the quantum wire touching the gated Aharonov-Bohm ring

We analyse the conductance of the Aharonov - Bohm (AB) one- dimensional quantum ring touching a quantum wire. The period of the AB oscillations is shown to be dependent strongly on the chemical potential and the Rashba coupling parameter that is in a good agreement with the studies of such a device prepared on the Si(100) surface.

cond-mat.mes-hall↗

arXiv2006

Spin-dependent transport in p+-CdBxF2-x - n-CdF2 planar structures

The CV measurements and tunneling spectroscopy are used to study the ballistic transport of the spin-polarized holes by varying the value of the Rashba spin-orbit interaction (SOI) in the p-type quantum well prepared on the surface of the n-CdF2 bulk crystal. The findings of the hole conductance oscillations in the plane of the p-type quantum well that are due to the variations of the Rashba SOI are shown to be evidence of the spin transistor effect, with the amplitude of the oscillations close to e2/h.

cond-mat.mes-hall↗

arXiv2006

The conductance of the gated Aharonov - Bohm ring touching a quantum wire

We analyse the conductance of the Aharonov-Bohm one-dimensional quantum ring touching a quantum wire. It is shown that in accordance with experimental data the period of the AB oscillations strongly depends on the chemical potential and the Rashba coupling parameter. The dependence of the conductance on the carrier's energy is shown to reveal the Fano resonances.

cond-mat.mes-hall↗

arXiv2006

Spin interference in silicon three-terminal one-dimensional rings

We present the first findings of the spin transistor effect in the Rashba gate-controlled 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 spin-dependent 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.

cond-mat.mes-hall↗

arXiv2006

Quantum point contact with large localized spin: fractional quantization of the ballistic conductance

We analyze the conductance of the quantum point contact containing large localized spin J. The additional plateau is formed on a ballistic conductance staircase if only one propagating channel is rendered conducting. The conductance value at this plateau is shown to depend strongly on J and decrease from 3e^2/2h to e^2/h when J increases from 1/2 to infinity, which is in a good agreement with the experimental observations [D.J. Reilly, et al, Phys. Rev. B 63, 121311 (2001)].

cond-mat.mes-hall↗

arXiv2006

Superconductivity in silicon nanostructures

We present the findings of the superconductivity observed in the silicon nanostructures prepared by short time diffusion of boron on the n-type Si(100) surface. These Si-based nanostructures represent the p-type ultra-narrow self-assembled silicon quantum wells, 2nm, confined by the delta - barriers heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the delta - barriers appear to consist of the trigonal dipole centres, which are caused by the negative-U reconstruction of the shallow boron acceptors. Using the CV and thermo-emf techniques, the transport of two-dimensional holes inside SQW is demonstrated to be accompanied by single-hole tunneling through these negative-U centres that results in the superconductivity of the delta - barriers. The values of the correlation gaps obtained from these measurements are in a good agreement with the data derived from the temperature and magnetic field dependencies of the magnetic susceptibility, which reveal a strong diamagnetism and additionally identify the superconductor gap value.

cond-mat.supr-con↗

arXiv2005

Quantum splitter controlled by Rashba spin-orbit interaction

We propose the mesoscopic device based on the Rashba spin orbit interaction (SOI) that contains a gated ballistic Aharonov-Bohm (AB) ring with incoming lead and two asymmetrically situated outgoing leads. The variations of the Rashba coupling parameter induced by the gate voltage applied to the AB ring is shown to cause the redistribution of the carrier flux between the outgoing leads and spin polarization of the outgoing currents, thus allowing the system to manifest the properties of the quantum splitter and spin filter.

cond-mat.mes-hall↗

arXiv2005

Spin interference in silicon one-dimensional rings

We present the first findings of the spin transistor effect caused by the Rashba gate-controlled ring embedded in the p-type self-assembled silicon quantum well that is prepared on the Si (100) surface. The coherence and phase sensitivity of the spin-dependent transport of holes are studied by varying the value of the external magnetic field and the gate voltage that are perpendicular to the plane of the double-slit ring. Firstly, the quantum scatterers connected to two one-dimensional leads and the quantum point contact inserted in the one of the arms of the double-slit ring are shown to define the amplitude and the phase of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations. Secondly, the amplitude and phase sensitivity of the 0.7 feature of the hole quantum conductance staircase revealed by the quantum point contact inserted are found to result from the interplay of the spontaneous spin polarization and the Rashba spin-orbit interaction.

cond-mat.mes-hall↗

arXiv2004

Fractal Self-Assembled Nanostructures on Monocrystalline Silicon Surface

We present ultra-shallow diffusion profiles performed by short-time diffusion of boron from the gas phase using controlled surface injection of self-interstitials and vacancies into the n-type Si(100) wafers. The diffusion profiles of this art are found to consist of both longitudinal and lateral silicon quantum wells of the p-type that are self-assembled between the alloys of microdefects, which are produced by previous oxidation. These alloys appear to be passivated during short-time diffusion of boron thereby forming neutral del'ta barriers. The fractal type self-assembly of microdefects is found to be created by varying the thickness of the oxide overlayer, which causes the system of microcavities embedded in the quantum well plane.

cond-mat.mes-hall↗

arXiv2004

Interplay of h/e and h/2e Oscillations in Gate-Controlled Aharonov-Bohm Rings

The spin-interference that is caused by the Rashba spin-orbit interaction in a gate-controlled Aharonov-Bohm ring is studied by the analysis of the conductance oscillations as a function of both the gate voltage and magnetic field. The scattering matrix approach is used to reveal the effect of the quantum scatterers connected to two one-dimensional leads on the phase of the transmission and reflection amplitudes. The variations of the transmission and reflection amplitudes that are caused by the quantum scatterers for the particles moving inside and outside rings are shown to define a parity of the and conductance oscillations.

cond-mat.mes-hall↗

arXiv2004

Spin Depolarization in Quantum Wires Polarized Spontaneously in a Zero Magnetic Field

The conditions for a spontaneous spin polarization in a quantum wire positioned in a zero magnetic field are analyzed under weak population of one-dimensional subbands that gives rise to the efficient quenching of the kinetic energy by the exchange energy of carriers. The critical linear concentration of carriers above which the quasi one-dimensional gas undergoes a complete spin depolarization is determined by the Hartree-Fock approximation. The dependence of the critical linear concentration on the concentration of carriers is defined to reveal the interplay of the spin depolarization with the evolution of the 0.7 (2e2/h) feature in the quantum conductance staircase from the e2/h to 3/2 (e2/h) values. This dependence is used to study the effect of the hole concentration on the 0.7 (2e2/h) feature in the quantum conductance staircase of the quantum wire prepared inside the p-type silicon quantum well using the split-gate technique. The 1D channel is demonstrated to be spin-polarized at the linear concentration of holes lower than the critical linear concentration, because the 0.7 (2e2/h) feature is close to the value of 0.5 (2e2/h) that indicates the spin degeneracy lifting for the first step of the quantum conductance staircase. The 0.7 (2e2/h) feature is found to take however its normal magnitude when the linear concentration of holes attains the critical value corresponding to the spin depolarization. The variations in the height of the 0.7 (2e2/h) feature observed in the hole quantum conductance staircase that is revealed by the p-type silicon quantum wire seem to be related to the evidences of the quantum conductance staircase obtained by varying the concentration of electrons in the 1D channel prepared inside the GaAs-AlGaAs heterojunction.

cond-mat.mes-hall↗