Valley splitting control in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">SiO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>/</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mo>/</mml:mo><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mi mathvariant="normal">O</mml:mi></mml:

Takashina, Kei; Fujiwara, Akira; Horiguchi, S.; Takahashi, Yasuo; Hirayama, Y.

doi:10.1103/physrevb.69.161304

Cited by 38 publications

(59 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Many effects are not included, such as strain, interface misorientation [10], atomic scale disorder, lateral confinement, or many-body corrections to the valley splitting. Nonetheless, the splittings 2|V V O | on the order of 0.5 meV we obtained are in fair agreement with available measurements in Si/SiO 2 and Si/SiGe interfaces [8].…”

supporting

confidence: 92%

Physical mechanisms of interface-mediated intervalley coupling in Si

et al. 2009

View full text Add to dashboard Cite

The conduction band degeneracy in Si is detrimental to quantum computing based on spin qubits, for which a nondegenerate ground orbital state is desirable. This degeneracy is lifted at an interface with an insulator, as the spatially abrupt change in the conduction band minimum leads to intervalley scattering. We present a theoretical study of the interface-induced valley splitting in Si that provides simple criteria for optimal fabrication parameters to maximize this splitting. Our work emphasizes the relevance of different interface-related properties to the valley splitting.PACS numbers: 03.67. Lx, 85.35.Gv, 71.55.Cn Semiconductor nanostructures based on GaAs and Si [1,2] are approaching the limit where device functionality relies on degrees of freedom of individual electrons. Recent progress in material processing allows precise controlled doping, band-structure engineering, and fabrication of high quality heterojunctions, which in turn pave the way for challenging applications such as the development of a scalable solid state quantum computer. The past few years witnessed tremendous experimental progress in the study of spin qubits at GaAs/AlGaAs quantum dots [1], which raises intriguing questions on the feasibility of spin qubits in Si quantum dot [3] or donor states [4] at a Si/barrier-material interface.A clear advantage of spin qubits in Si over GaAs is the long spin coherence times in Si [5]. On the other hand bulk Si conduction band edge is six-fold degenerate, a complication not present in GaAs. Near a (001) interface with a barrier material, this degeneracy is partially lifted, with the interface electron ground state remaining doubly degenerate. For electron spin qubits, the residual orbital degeneracy is an important spin decoherence source [6]. This effect can be overcome if the ground state degeneracy is significantly lifted, which occurs close to an interface that can efficiently scatter carriers between the two degenerate valleys that are near opposite ends of the Brillouin zone [7]. Measurements of the doublet splitting, or valley splitting, present significant variations among different Si/barrier samples, ranging from 0 to ∼ 1 meV [8]. In this context, a simple physical model that can help identify the relevant fabrication-related parameters in order to maximize the valley splitting is a valuable tool in assisting current experimental efforts.Theoretical approaches to describe the electronic behavior in the presence of an interface or heterojunction range from the effective mass approximation (EMA) [9,10], tight-binding models [11] to first-principles envelope function approach [12]. The present study, based on the physically motivated EMA [13], aims to identify the relevance of sample-dependent parameters to the valley splitting. Our approach, while simple, is original and permits the study of the intervalley coupling due to a single interface, not employing periodic boundary conditions. The full plane wave expansions of the Bloch functions at the two conduction band minima obtained fro...

show abstract

supporting

confidence: 92%

Physical mechanisms of interface-mediated intervalley coupling in Si

et al. 2009

View full text Add to dashboard Cite

show abstract

“…However, they cannot explain the recent puzzling results of Takashina et al [5]. In an asymmetrically grown Si/SiO 2 quantum well, they observe a large ground state gap of 23 meV at the buried oxide (BOX) barrier, but a more typical valley splitting at the second, thermally grown oxide barrier [12].In this work, we demonstrate that conventional CB electron states tend to hybridize with intrinsic Si/SiO 2 interface states (IS), which form in the gap. Hybridization can produce a conducting ground state that is nondegenerate, due to strong valley orbit coupling.…”

mentioning

confidence: 56%

Extended interface states enhance valley splitting inSi/SiO2

2010

View full text Add to dashboard Cite

Interface disorder and its effect on the valley degeneracy of the conduction band edge remains among the greatest theoretical challenges for understanding the operation of spin qubits in silicon. Here, we investigate a counterintuitive effect occurring at Si/SiO2 interfaces. By applying tight binding methods, we show that intrinsic interface states can hybridize with conventional valley states, leading to a large ground state energy gap. The effects of hybridization have not previously been explored in details for valley splitting. We find that valley splitting is enhanced in the presence of disordered chemical bonds, in agreement with recent experiments.PACS numbers: 03.67. Lx, 85.35.Gv, 71.55.Cn Introduction.-The transistor revolution has granted silicon heterostructures a special status amongst materials platforms. Yet after many years of intense study, this system still reveals new and intriguing features. This is due in part to technological advances that open the door to new physical regimes. However, the interest in Si has also been stirred by its unusual materials properties. The Si conduction band (CB) possesses six degenerate minima in the first Brillouin zone, known as valleys. Quantum well confinement and/or the application of uniaxial strain (e.g., in the case of Si/SiGe heterostructures) in the [001] direction reduces the bulk, cubic symmetry, and raises the energy levels associated with the transverse x and y valleys [1]. At very low temperatures, the CB physics is therefore governed by the spin and the z valley degrees of freedom. Control over valley degeneracy is a key concern for Si spin qubits [2][3][4].Experimental [1,5,6] and theoretical [1,7,8] investigations of the physical mechanisms of valley coupling reveal that a sharp interface between a quantum well and a quantum barrier (most commonly SiGe or SiO 2 ) can produce a sizable energy splitting between the valley states, and that roughness can suppress this effect [9,10]. Realistic theoretical estimates for the interface-induced valley splitting are on the order of 0.1-1 meV [11], in agreement with many experiments. However, they cannot explain the recent puzzling results of Takashina et al. [5]. In an asymmetrically grown Si/SiO 2 quantum well, they observe a large ground state gap of 23 meV at the buried oxide (BOX) barrier, but a more typical valley splitting at the second, thermally grown oxide barrier [12].In this work, we demonstrate that conventional CB electron states tend to hybridize with intrinsic Si/SiO 2 interface states (IS), which form in the gap. Hybridization can produce a conducting ground state that is nondegenerate, due to strong valley orbit coupling. The resulting ground state gap can be tens of meV larger than the valley splitting between pure CB states, which could explain the large values measured in Ref. 5. Such a gap would be ideal for controlling spin qubits in Si.

show abstract

“…41 In Si/SiO 2 systems, the splitting can even be tens of meV. [48][49][50] Here we assume that the splitting is at least 1 meV and we can use the effective singlevalley approximation, 28,51 in which only the lowest valley eigenstate is considered. This choice is strengthened by the fact that electron spins in valley-degenerate dots would not be viable qubits.…”

Section: -15mentioning

confidence: 99%

Theory of single electron spin relaxation in Si/SiGe lateral coupled quantum dots

2011

View full text Add to dashboard Cite

We investigate the spin relaxation induced by acoustic phonons in the presence of spin-orbit interactions in single electron Si/SiGe lateral coupled quantum dots. The relaxation rates are computed numerically in single and double quantum dots, in in-plane and perpendicular magnetic fields. The deformation potential of acoustic phonons is taken into account for both transverse and longitudinal polarizations and their contributions to the total relaxation rate are discussed with respect to the dilatation and shear potential constants. We find that in single dots the spin relaxation rate scales approximately with the seventh power of the magnetic field, in line with a recent experiment. In double dots the relaxation rate is much more sensitive to the dot spectrum structure, as it is often dominated by a spin hot spot. The anisotropy of the spin-orbit interactions gives rise to easy passages, special directions of the magnetic field for which the relaxation is strongly suppressed. Quantitatively, the spin relaxation rates in Si are typically 2 orders of magnitude smaller than in GaAs due to the absence of the piezoelectric phonon potential and generally weaker spinorbit interactions.

show abstract

Valley splitting control inSiO2/Si/SiO

Cited by 38 publications

References 23 publications

Physical mechanisms of interface-mediated intervalley coupling in Si

Physical mechanisms of interface-mediated intervalley coupling in Si

Extended interface states enhance valley splitting inSi/SiO2

Theory of single electron spin relaxation in Si/SiGe lateral coupled quantum dots

Contact Info

Product

Resources

About