Impact of Valley Polarization on the Resistivity in Two Dimensions

Takashina, Kei; Niida, Y; Renard, V.; Fujiwara, Akira; Fujisawa, Toshimasa; Muraki, K.; Hirayama, Y.

doi:10.1103/physrevlett.106.196403

Cited by 10 publications

(13 citation statements)

References 25 publications

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“…Unlike most materials used for qubits, silicon posses a complex momentum space structure, primarily arising due to the six degenerate conduction band (CB) valleys away from the Brillouin Zone center. The CB valley degeneracy provides an extra degree of freedom to the quantum confined orbital states in silicon, and gives rise to a variety of novel phenomena that strongly affect the electronic structure, transport, and relaxation mechanisms [12][13][14][15][16]. It is therefore important to understand and quantify valley physics and its effect on electronic states.In this letter, we report observations of a novel valley induced phenomena in electronic transport in silicon.…”

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confidence: 99%

Lifetime-Enhanced Transport in Silicon due to Spin and Valley Blockade

et al. 2011

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We report the observation of lifetime-enhanced transport (LET) based on perpendicular valleys in silicon by transport spectroscopy measurements of a two-electron system in a silicon transistor. The LET is manifested as a peculiar current step in the stability diagram due to a forbidden transition between an excited state and any of the lower energy states due to perpendicular valley (and spin) configurations, offering an additional current path. By employing a detailed temperature dependence study in combination with a rate equation model, we estimate the lifetime of this particular state to exceed 48 ns. The twoelectron spin-valley configurations of all relevant confined quantum states in our device were obtained by a large-scale atomistic tight-binding simulation. The LET acts as a signature of the complicated valley physics in silicon: a feature that becomes increasingly important in silicon quantum devices. DOI: 10.1103/PhysRevLett.107.136602 PACS numbers: 72.20.Jv, 03.67.Lx, 71.70.Ej, 85.35.Gv Silicon, the most important material in the electronics industry to date, is starting to make its mark in nanoscale quantum electronics. While silicon nanowires are showing promise in thermoelectric applications [1], silicon-based qubits [2-6] have been widely investigated worldwide due to their long spin coherence times [7] and compatibility with the present-day infrastructure of the semiconductor industry. In recent times, both top-down and bottom-up approaches have been successful in building single to few electron silicon devices [8][9][10]. The demonstration of a single-shot readout of an electron spin [11] marks a crucial step towards building a silicon qubit. Unlike most materials used for qubits, silicon possesses a complex momentum space structure, primarily arising due to the six degenerate conduction band (CB) valleys away from the Brillouin zone center. The CB valley degeneracy provides an extra degree of freedom to the quantum confined orbital states in silicon, and gives rise to a variety of novel phenomena that strongly affect the electronic structure, transport, and relaxation mechanisms [12][13][14][15][16]. It is therefore important to understand and quantify valley physics and its effect on electronic states.In this Letter, we report observations of a novel valley induced phenomena in electronic transport in silicon. Through transport spectroscopy measurements of donor states in fin-type field effect transistors (FinFETs), we show that under certain conditions relaxation of excited states into lower manifolds is suppressed due to a combination of both spin and valley blockade. This enhanced lifetime results in an additional transport path through the excited state, and appears as a current step in the stability diagram. The phenomena dubbed ''lifetime-enhanced transport'' (LET) was first observed in a silicon double quantum dot [10] due to a blocked relaxation of a spin triplet into a ground state spin singlet, arising from the long spin relaxation times in silicon. In this experiment, LET enabl...

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confidence: 99%

Lifetime-Enhanced Transport in Silicon due to Spin and Valley Blockade

et al. 2011

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“…In silicon, valley physics determines qubit relaxation rates 13,17,18 and are predicted to strongly influence two qubit gates 6,7 . Moreover, valley degrees of freedom in AlAs 19 , silicon 20 , diamond 21 , and graphene 22 can play a role similar to spin in condensed matter systems. Encoding of information within valley polarization has been proposed in AlAs 23 , silicon 24, 25 and diamond 21 , and within polarization of chiral valley pseudospin in carbon-based nanostructures [26][27][28] .…”

Section: Fabrication Of Devicesmentioning

confidence: 99%

Spatially resolving valley quantum interference of a donor in silicon

Salfi¹,

Mol²,

Rahman³

et al. 2014

Nature Mater

105

187

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Electron and nuclear spins of donor ensembles in isotopically pure silicon experience a vacuum-like environment, giving them extraordinary coherence. However, in contrast to a real vacuum, electrons in silicon occupy quantum superpositions of valleys in momentum space. Addressable single-qubit and two-qubit operations in silicon require that qubits are placed near interfaces, modifying the valley degrees of freedom associated with these quantum superpositions and strongly influencing qubit relaxation and exchange processes. Yet to date, spectroscopic measurements only indirectly probe wavefunctions, preventing direct experimental access to valley population, donor position, and environment. Here we directly probe the probability density of single quantum states of individual subsurface donors, in real space and reciprocal space, using scanning tunneling spectroscopy. We directly observe quantum mechanical valley interference patterns associated with linear superpositions of valleys in the donor ground state. The valley population is found to be within 5% of a bulk donor when 2.85 ± 0.45 nm from the interface, indicating that valley perturbation-induced enhancement of spin relaxation will be negligible for depths > 3 nm. The observed valley interference will render two-qubit exchange gates sensitive to atomic-scale variations in positions of subsurface donors. Moreover, these results will also be of interest to emerging schemes proposing to encode information directly in valley polarization. Fabrication of devices1,2 , spin readout 1 , and quantum control of spins 3,4 in silicon has been accomplished at the single-donor level. However, addressable control and coupling within qubit arrays requires local gates and control interfaces, whose atomic-scale potentials strongly influence electronic valley degrees of freedom [5][6][7][8][9][10][11][12][13][14][15][16] . While these unconventional orbital degrees of freedom play no role in conventional silicon microelectronics, they invariably arise in quantized states in indirect gap materials, and are pervasive in quantum electronics. In silicon, valley physics determines qubit relaxation rates 13,17,18 and are predicted to strongly influence two qubit gates Here, individual states of subsurface donors were measured using cryogenic scanning tunneling spectroscopy. Quantum mechanical valley interference patterns were observed in real space, associated with linear quantum superpositions of wavevectors in the six conduction band valleys of silicon. Enabled by high-accuracy empirical determination of donor depth and electric field, we perform a parameter-free comparison with atomistic theory establishing that the z-valley population is ∼ 38 ± 2% for a 2.85 ± 0.45 nm deep donor, perturbed by only ∼ 5% compared with ∼ 33.3% for a donor in bulk silicon. Consequently, donors more than 3 nm deep should not experience a significant valley-repopulation induced increase in spin-lattice relaxation. Moreover, the nearly bulklike valley interference observed will render two-qubit excha...

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“…The data described here were measured at a back gate voltage of 2 V at which the metallic behavour is maximum (See Ref. 29). At this gate voltage, valley splitting is small3 and was therefore neglected.…”

Section: Methodsmentioning

confidence: 99%

“…However, previous studies in which the role of intervalley scattering on interactions has been analysed had been limited to systems where this scattering is only weak or moderate so that its effect on the metallic behavour is either absent or restricted to the lowest temperatures232425. Here, we investigate two-dimensionnal electron gases confined in a SOI quantum well2329 (See Methods) where intervalley scattering is an order of magnitude stronger than previously studied so that it modifies the interaction at temperatures up to about 10 K. In addition, compared to Si MOSFETs, interactions are particularly strong in SOI quantum wells because of the reduced dielectric constant of the surrounding SiO 2 . For example, the Wigner-Seitz parameter at the density n = 3.9 × 10 15 m −2 is r s = 8.2 compared to r s = 4.2 in MOSFETs (in Si MOSFETs, while in SOI quantum wells ).…”

mentioning

confidence: 99%

Metallic behaviour in SOI quantum wells with strong intervalley scattering

Renard

Duchemin

Niida

et al. 2013

Sci Rep

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The fundamental properties of valleys are recently attracting growing attention due to electrons in new and topical materials possessing this degree-of-freedom and recent proposals for valleytronics devices. In silicon MOSFETs, the interest has a longer history since the valley degree of freedom had been identified as a key parameter in the observation of the controversial “metallic behaviour” in two dimensions. However, while it has been recently demonstrated that lifting valley degeneracy can destroy the metallic behaviour, little is known about the role of intervalley scattering. Here, we show that the metallic behaviour can be observed in the presence of strong intervalley scattering in silicon on insulator (SOI) quantum wells. Analysis of the conductivity in terms of quantum corrections reveals that interactions are much stronger in SOI than in conventional MOSFETs, leading to the metallic behaviour despite the strong intervalley scattering.

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Impact of Valley Polarization on the Resistivity in Two Dimensions

Cited by 10 publications

References 25 publications

Lifetime-Enhanced Transport in Silicon due to Spin and Valley Blockade

Lifetime-Enhanced Transport in Silicon due to Spin and Valley Blockade

Spatially resolving valley quantum interference of a donor in silicon

Metallic behaviour in SOI quantum wells with strong intervalley scattering

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