Ballistic transport in induced one-dimensional hole systems

Klochan, O.; Clarke, W.A.; Danneau, R.; Micolich, A. P.; Ho, L. H.; Hamilton, A. R.; Muraki, K.; Hirayama, Y.

doi:10.1063/1.2337525

Cited by 62 publications

(60 citation statements)

References 20 publications

(17 reference statements)

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“…In contrast to electrons, we find that the field splitting of the zero-bias peak is highly anisotropic. We used a heterostructure consisting of the following layers grown on a (100)-oriented substrate: 1 µm undoped GaAs, 160 nm undoped AlGaAs barrier, 10 nm undoped GaAs spacer and a 20 nm GaAs cap degenerately doped with carbon for use as a metallic gate [24,25]. A (100) heterostructure was used to avoid the crystallographic asymmetries that plague (311)A heterostructures [16,17].…”

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confidence: 99%

Observation of the Kondo effect in a spin-32 hole quantum dot

Klochan

Micolich

Hamilton

et al. 2013

AIP Conference Proceedings

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We report the observation of Kondo physics in a spin-3 2 hole quantum dot. The dot is formed close to pinch-off in a hole quantum wire defined in an undoped AlGaAs/GaAs heterostructure. We clearly observe two distinctive hallmarks of quantum dot Kondo physics. First, the Zeeman spin-splitting of the zero-bias peak in the differential conductance is independent of gate voltage. Second, this splitting is twice as large as the splitting for the lowest one-dimensional subband. We show that the Zeeman splitting of the zero-bias peak is highly-anisotropic, and attribute this to the strong spin-orbit interaction for holes in GaAs.PACS numbers: 72.15. Qm, 75.70.Tj The observation of an unexpected minimum in the low temperature resistance of metals by de Haas in 1933 was ultimately explained thirty years later by Kondo as being due to interactions between a single magnetic impurity and the sea of conduction electrons in a metal [1,2]. More recently there has been a resurgence of interest in the Kondo effect, following the discovery that the conductance of a few electron quantum dot in the Coulomb blockade regime is enhanced when the dot contains an odd number of electrons [3][4][5]. There is a direct analogy with the Kondo effect in metals, with the localized electron in the quantum dot acting as a magnetic impurity that interacts with the two-dimensional sea of electrons in the source and drain reservoirs.Studies of the Kondo effect in bulk systems have progressed since the 1960s, with the focus shifting towards manifestations of Kondo physics in the strongly correlated electron systems formed in cuprates and heavyfermion metals [6]. More precise control via improved electrostatic gate design has similarly allowed progress towards the study of more exotic manifestations of Kondo phenomena in quantum dots such as the integer-spin [7][8][9], two-impurity [10], and orbital Kondo effects [11]. Thus far all quantum dot Kondo studies have involved electrons, and GaAs hole quantum dots present an interesting next step. Holes in GaAs originate from p-like orbitals and behave as spin-3 2 particles due to strong spinorbit coupling [12]. In two-and one-dimensional systems, the spin-3 2 nature of holes leads to remarkable, highlyanisotropic phenomena [13-17] not observed in electron systems, and new physics is expected for hole quantum dots also [18]. Studies of Kondo physics in hole quantum dots may also provide useful connections to recent studies in bulk strongly correlated systems [19,20].Here we report the observation of the Kondo effect in a GaAs hole quantum dot. Due to the poor stability of conventional gate-defined modulation doped struc- * klochan@phys.unsw.edu. A key advantage to this approach is the ability to obtain an independent estimate of the effective Landé g-factor g * . Using this we have fabricated a small hole quantum dot and conclusively demonstrate the "smoking gun" for Kondo physics [23] -a splitting of the zero-bias peak in the differential conductance that opens as 2g * µ B B in response to an in-plane...

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Observation of the Kondo effect in a spin-32 hole quantum dot

Klochan

Micolich

Hamilton

et al. 2013

AIP Conference Proceedings

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“…The degeneracy of heavy-hole (HH) and light-hole (LH) bulk dispersions at the zone center makes the spin properties of valence-band states especially susceptible to such confinement engineering. 4,5,6,7 Recent advances in fabrication technology 8,9,10,11,12,13,14,15,16 have created opportunities to investigate hole spin physics in semiconductor nanowires made from a range of different materials.In contrast to previous theoretical work 17,18,19,20 on hole spin splitting in quantum wires, we focus here on the influence of the spin-orbit coupling strength on Zeeman splitting of wire-subband edges. A suitable parameter γ quantifying spin-orbit coupling in the valence band can be defined in terms of the effective masses m HH and m LH associated with the HH and LH bands, 21 respectively: 2γ = (m HH − m LH )/ (m HH + m LH ).…”

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confidence: 99%

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Tailoring hole spin splitting and polarization in nanowires

Csontos

Zülicke

2008

Applied Physics Letters

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Spin splitting in p-type semiconductor nanowires is strongly affected by the interplay between quantum confinement and spin-orbit coupling in the valence band. The latter's particular importance is revealed in our systematic theoretical study presented here, which has mapped the range of spin-orbit coupling strengths realized in typical semiconductors. Large controllable variations of the g-factor with associated characteristic spin polarization are shown to exist for nanowire subband edges, which therefore turn out to be a versatile laboratory for investigating the complex spin properties exhibited by quantum-confined holes.Engineering spin splitting of charge carriers in semiconductor nanostructures may open up intriguing possibilities for realizing spin-based electronics 1 and quantum information processing. 2 Due to the generally strong dependence of g-factors on band structure, 3 it is expected that spatial confinement will have an important effect on Zeeman splitting when bound-state quantization energies are no longer negligible compared with the separation of bulk-material energy bands. The degeneracy of heavy-hole (HH) and light-hole (LH) bulk dispersions at the zone center makes the spin properties of valence-band states especially susceptible to such confinement engineering. 4,5,6,7 Recent advances in fabrication technology 8,9,10,11,12,13,14,15,16 have created opportunities to investigate hole spin physics in semiconductor nanowires made from a range of different materials.In contrast to previous theoretical work 17,18,19,20 on hole spin splitting in quantum wires, we focus here on the influence of the spin-orbit coupling strength on Zeeman splitting of wire-subband edges. A suitable parameter γ quantifying spin-orbit coupling in the valence band can be defined in terms of the effective masses m HH and m LH associated with the HH and LH bands, 21 respectively: 2γ = (m HH − m LH )/ (m HH + m LH ). Table I lists values for γ in common semiconductors and states its relation to basic bandstructure parameters. 22 A large part of the theoretically possible range 0 ≤ γ ≤ 1/2 is covered by available materials, 23 enabling a detailed study of the interplay between spin-orbit coupling in the valence band and nanowire confinement. Our theoretical investigation reveals surprising qualitative differences in the hole spin properties of nanowires depending on the value of γ, showing that spin splitting (and polarization) of zone-center valence-band edges in nanowires is highly tunable and has a complex materials dependence. A detailed understanding of these properties is vital for proper interpretation of optical and transport measurements as well as for the design of spintronic applications involving p-doped semiconductor nanowires.We use the Luttinger model 22 in the spherical approximation 26 for the top-most bulk valence bands. Including the bulk Zeeman term H Z = −2κµ B BĴ z , the Hamiltonian is given byHere p is the linear orbital momentum,Ĵ the vector of spin-3/2 matrices, m 0 the electron mass in vacuum, γ ...

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“…Field-effect-induced 2DEG transistors (FETs) in GaAs/AlGaAs heterostructures have been investigated extensively [14][15][16][17][18][19][20][21][22][23][24][25][26][27] and might find utility as a platform to investigate nanoscale phenomena in a low-noise environment if certain limitations can be overcome. The most widely studied device is the heterostructure-insulated-gate field-effect transistor (HIGFET), in which a highly-conducting n+ GaAs gate is grown on top of an insulating Al x Ga 1−x As barrier layer by molecular beam epitaxy (MBE) [14-16, 18, 22].…”

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“…The most widely studied device is the heterostructure-insulated-gate field-effect transistor (HIGFET), in which a highly-conducting n+ GaAs gate is grown on top of an insulating Al x Ga 1−x As barrier layer by molecular beam epitaxy (MBE) [14-16, 18, 22]. HIGFET fabrication requires placing ohmic contacts in intimate contact with the primary AlGaAs/GaAs interface where the 2DEG will reside without shorting the ohmic contact to the n+ GaAs gate [17,18]. This challenging task becomes increasingly difficult for shallow 2DEG structures required for many nanostructure devices [15].…”

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Field-effect-induced two-dimensional electron gas utilizing modulation-doped ohmic contacts

Mondal

Gardner

Watson

et al. 2014

Solid State Communications

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Modulation-doped AlGaAs/GaAs heterostructures are utilized extensively in the study of quantum transport in nanostructures, but charge fluctuations associated with remote ionized dopants often produce deleterious effects. Electric field-induced carrier systems offer an attractive alternative if certain challenges can be overcome. We demonstrate a field-effect transistor in which the active channel is locally devoid of modulation-doping, but silicon dopant atoms are retained in the ohmic contact region to facilitate reliable lowresistance contacts. A high quality two-dimensional electron gas is induced by a field-effect and is tunable over a wide range of density. Device design, fabrication, and low temperature (T= 0.3K) transport data are reported.Nanostructures such as quantum point contacts and quantum dots fabricated on modulation-doped AlGaAs/GaAs heterostructures are widely used to explore nanoscale electron transport and are utilized extensively in spin-based approaches to quantum computing [1][2][3][4][5][6][7][8]. Modulation-doped GaAs/AlGaAs heterostructures possess several desirable attributes including very high mobility of the underlying two-dimensional electron gas (2DEG) and the relative ease of nanostructure fabrication. However, the presence of ionized dopants inherent to modulationdoping can have adverse effects on the behavior of nanostructures and are a possible source of decoherence for spin-qubits [9,10]. Ionized dopants can act as active trapping sites for electrons injected from the metal surface gate through the Schottky barrier [11], giving rise to random switching of the charge state of the impurities. These fluctuations cause instability through a time-dependent potential landscape [10][11][12][13]. Methods such as 'bias cooling' in which nanostructures are cooled while a positive bias applied to the gates aid in reducing fluctuations [11], but charge noise is still believed to a dominant mechanism limiting gate fidelities in spin qubits [9].

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Ballistic transport in induced one-dimensional hole systems

Cited by 62 publications

References 20 publications

Observation of the Kondo effect in a spin-32 hole quantum dot

Observation of the Kondo effect in a spin-32 hole quantum dot

Tailoring hole spin splitting and polarization in nanowires

Field-effect-induced two-dimensional electron gas utilizing modulation-doped ohmic contacts

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