Strong and Tunable Spin−Orbit Coupling of One-Dimensional Holes in Ge/Si Core/Shell Nanowires

Hao, Xinjun; Tu, Tao; Cao, Gang; Li, Hai-Ou; Guo, Guo-Ping; Fung, Wayne Y.; Ji, Zhongqing; Lü, Wei

doi:10.1021/nl101181e

Cited by 111 publications

(137 citation statements)

References 40 publications

Supporting

Mentioning

126

Contrasting

Order By: Relevance

“…Based on the split-off band in bulk germanium (0.29 eV, compared to 0.38 eV in InAs (ref. 36)), we speculate that the spin-orbit coupling is of comparable strength 14,37 to that in InAs nanowire qubits 38 and, in conjunction with heavy/light hole mixing, may allow rapid electrical spin manipulation techniques that are absent in electron-based qubits, such as rapid direct spin rotation 39 and a recently predicted direct Rashba spin-orbit interaction 14 . In summary, we have observed spin doublets of holes confined in one-dimensional Ge-Si nanowires.…”

mentioning

confidence: 91%

Hole spin relaxation in Ge–Si core–shell nanowire qubits

et al. 2011

View full text Add to dashboard Cite

Controlling decoherence is the biggest challenge in efforts to develop quantum information hardware [1][2][3] . Single electron spins in gallium arsenide are a leading candidate among implementations of solid-state quantum bits, but their strong coupling to nuclear spins produces high decoherence rates [4][5][6] . Group IV semiconductors, on the other hand, have relatively low nuclear spin densities, making them an attractive platform for spin quantum bits. However, device fabrication remains a challenge, particularly with respect to the control of materials and interfaces 7 . Here, we demonstrate state preparation, pulsed gate control and charge-sensing spin readout of hole spins confined in a Ge-Si core-shell nanowire. With fast gating, we measure T 1 spin relaxation times of up to 0.6 ms in coupled quantum dots at zero magnetic field. Relaxation time increases as the magnetic field is reduced, which is consistent with a spin-orbit mechanism that is usually masked by hyperfine contributions.Since the proposal of Loss and DiVincenzo's 1 , the promise of quantum dots for solid-state quantum computation has been underscored by the successful initialization, manipulation and readout of electron spins in GaAs systems 5,[8][9][10] . The electronic wavefunctions in these systems typically overlap with a large number of nuclear spins that are difficult to control and in most cases thermally randomized. The resulting intrinsic spin decoherence rates 4-6 have been successfully reduced by spin-echo techniques 6,11 , but require complex gate sequences that complicate multi-qubit operations 12 . The prospect of achieving long coherence times in group IV materials with few nuclear spins has stimulated many proposals 13,14 and intensive experimental efforts [15][16][17][18][19] , and crucially depends on the development of high-quality host materials. Recent advances regarding single quantum dots have been achieved using Zeeman splitting for readout with a finite magnetic field [19][20][21][22][23] . Coupled quantum-dot devices 13,[15][16][17][18]24 in a nuclear spin-free system are more desirable for flexible quantum manipulation 25 but more challenging, and characterization of the spin lifetime has yet to be completed.Semiconductor nanowires form a favourable platform for quantum devices because of the ability to precisely control their diameter, composition, morphology and electronic properties during synthesis 26 . The prototypical Ge-Si nanowire heterostructure has revealed diverse phenomena at the nanoscale and enabled numerous applications in nanoelectronics. The epitaxial growth of silicon around a single-crystal germanium core (Fig. 1, inset) and the associated valence band offset provide a natural radial confinement of holes that, due to the large sub-band spacing, behave onedimensionally at low temperature 27 . Although the topmost valence band has been predicted to be twofold degenerate and of lighthole character under idealized approximations 28 , it is generally expected that mixing between heavy and light hole...

show abstract

mentioning

confidence: 91%

Hole spin relaxation in Ge–Si core–shell nanowire qubits

et al. 2011

View full text Add to dashboard Cite

show abstract

“…Heavy/light hole degeneracy may also influence the spin blockade regime 12 . On the other hand, spin-orbit interaction is predicted 13 and suggested by experiments [14][15][16][17] to be strong in Ge/Si core/shell nanowires. This offers a path to electrical spin manipulation 18,19 , as well as to realizing Majorana fermions [20][21][22][23] .…”

mentioning

confidence: 93%

Magnetic field evolution of spin blockade in Ge/Si nanowire double quantum dots

Zarassi

Danon

et al. 2017

Phys. Rev. B

View full text Add to dashboard Cite

We perform transport measurements on double quantum dots defined in Ge/Si core/shell nanowires and focus on Pauli spin blockade in the regime where tens of holes occupy each dot. We identify spin blockade through the magnetic field dependence of leakage current. We find both a dip and a peak in the leakage current at zero field. We analyze this behavior in terms of the quantum dot parameters such as coupling to the leads, interdot tunnel coupling as well as spin-orbit interaction. We find a lower bound for spin-orbit interaction with lso = 500 nm. We also extract large and anisotropic effective Landé g-factors, with larger g-factors in the direction perpendicular to the nanowire axis in agreement with previous studies and experiments but with larger values reported here.Studies of spin blockade in quantum dots are largely motivated by the proposals to build a spin-based quantum computer 1 , as spin blockade can be used for qubit initialization and readout 2,3 . At the same time, spin blockade and its lifting mechanisms offer a direct insight into spin relaxation and dephasing processes in semiconductors and provide deeper understanding of interactions between spin localized in a quantum dot and its environment, be it the lattice and its vibrations or nuclear spins, spin-orbit interaction, or coupling to spins in nearby dots or in the lead reservoirs 4-8 .Holes in Ge/Si nanowires offer a relatively unexplored platform for such studies 9 . On the one hand, hyperfine interaction is expected to be greatly reduced owing to the low abundance of nonzero nuclear spin isotopes in the group IV materials 10 . Moreover, holes weakly couple to nuclear spins due to their p-wave Bloch wave symmetry, thus they are expected to come with longer spin relaxation times 11 . Heavy/light hole degeneracy may also influence the spin blockade regime 12 . On the other hand, spin-orbit interaction is predicted 13 and suggested by experiments 14-17 to be strong in Ge/Si core/shell nanowires. This offers a path to electrical spin manipulation 18,19 , as well as to realizing Majorana fermions [20][21][22][23] .In this work we perform transport measurements on electrostatically defined double quantum dots 2 made in Ge/Si core/shell nanowires, and detect Pauli spin blockade at several charge degeneracy points. We expand and adapt a previously developed rate equation model to analyze the magnetic-field evolution of the leakage current 24 . We also observe large and anisotropic g-factors in these dots, which supports recent theoretical predictions 25 and experimental observations 26,27 .The devices are fabricated on n-doped Si substrates covered with 500 nm of thermal SiO 2 and patterned with local gate arrays of Ti/Au stripes with center to center distance of 60 nm. The gates are covered by a 10 nm layer of HfO 2 dielectric. Using a micromanipulator 28 the nanowires with a typical length of 4 µm and diameter of 30 nm are placed on top of these gates as shown in the inset of Fig. 1. After wet etching with buffered hydrofluoric acid, we sputter 15...

show abstract

“…[21][22][23][24][25] Magneto-transport study of the weak anti-localization (WAL) effect was performed in InAs [21][22][23] and InN nanowires 24 where short spin relaxation times were found, showing the existence of strong SOI. In some experiments, 21,22 electron spin relaxation length was also found to be tunable by a factor of two via back gate.…”

mentioning

confidence: 99%

“…Magneto-conductance, G(B)=G(B)-G(B=0), measured at various V (t-b)g 's within ±1 Tesla perpendicular magnetic field B, are shown in Fig.1c for T=2 K. At small V (t-b)g 's, a positive magneto-conductance due to weak localization (WL) is observed. 28,29 At large positive or negative voltages between the two gates, a negative magneto-conductance emerges around B=0, indicating the WAL effect [21][22][23]25 where the strong SOI gives rise to a spin-orbit relaxation length (l so ) shorter than the phase coherence length (l  ) of electrons. This evolution from WL to WAL as |V (t-b)g | increases clearly shows the increased SOI at larger E in our study.…”

mentioning

confidence: 99%

Strong Tuning of Rashba Spin–Orbit Interaction in Single InAs Nanowires

2012

View full text Add to dashboard Cite

A key concept in the emerging field of spintronics is the gate voltage or electric field control of spin precession via the effective magnetic field generated by the Rashba spin orbit interaction. Here, we demonstrate the generation and tuning of electric field induced Rashba spin orbit interaction in InAs nanowires where a strong electric field is created either by a double gate or a solid electrolyte surrounding gate. In particular, the electrolyte gating enables six-fold tuning of Rashba coefficient and nearly three orders of magnitude tuning of spin relaxation time within only 1 V of gate bias. Such a dramatic tuning of spin orbit interaction in nanowires may have implications in nanowire based spintronic devices.Nanowires of small band gap III-V semiconductors such as indium arsenide (InAs) have recently attracted significant interest in nanoelectronic device research.1-10 With high electron mobility, nanostructures of InAs have appealing potential for high speed electronics such as field effect transistor (FET). [3][4][5][6][7][8] In addition to high electron mobility that is important for charge transport based electronic devices, InAs also has strong spin-orbit interaction (SOI) and was proposed to be an essential material for spintronic devices such as spin FET in which controlling the electrons' spin degree of freedom renders the device's functionality. 11-13 Therefore, InAs nanowire appears to be also an interesting quasi-one dimensional (1D) platform to explore spintronic devices such as 1D spin-FET which exploits the SOI effect to control electrons' spin. SOI is a relativistic effect experienced by electrons (or any charge particles) moving in an electric field E. In the rest frame of the electron, E is Lorentz transformed into an effective magnetic field which couples to the electron's spin and consequently induces spin precession and relaxation. The electric field in this SOI effect could be from the asymmetry in the intrinsic crystal structure, the asymmetric confinement potential in heterostructure interface, or simply an externally applied

show abstract

Strong and Tunable Spin−Orbit Coupling of One-Dimensional Holes in Ge/Si Core/Shell Nanowires

Cited by 111 publications

References 40 publications

Hole spin relaxation in Ge–Si core–shell nanowire qubits

Hole spin relaxation in Ge–Si core–shell nanowire qubits

Magnetic field evolution of spin blockade in Ge/Si nanowire double quantum dots

Strong Tuning of Rashba Spin–Orbit Interaction in Single InAs Nanowires

Contact Info

Product

Resources

About