Quantized conductance in quantum wires with gate-controlled width and electron density

Kane, B. E.; Facer, G. R.; Dzurak, Andrew S.; Lumpkin, N. E.; Clark, R. G.; Pfeiffer, L. N.; West, K. W.

doi:10.1063/1.121642

Cited by 131 publications

(155 citation statements)

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“…The structure at G = 0.7͑2e 2 / h͒ was already observed in low-disorder quantum point contacts ͑quantum wires of zero length͒ by several authors. [15][16][17][18][19][20] In particular, it has been argued 17 that this structure is a manifestation of electron-electron interactions involving spin. Theoretically, the structure is interpreted as some form of spontaneous spin polarization of the system mediated through the exchange interaction.…”

Section: Introductionmentioning

confidence: 99%

Ground state structure and conductivity of quantum wires of infinite length and finite width

et al. 2005

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We have studied the ground state structure of quantum strips within the local spin-density approximation, for a range of electronic densities between ϳ5 ϫ 10 4 and 2 ϫ 10 6 cm −1 and several strengths of the lateral confining potential. The results have been used to address the conductance G of quantum strips. At low density, when only one subband is occupied, the system is fully polarized and G takes a value close to 0.7͑2e 2 / h͒, decreasing with increasing electron density in agreement with experiments. At higher densities the system becomes paramagnetic and G takes a value near ͑2e 2 / h͒, showing a similar decreasing behavior with increasing electron density. In both cases, the physical parameter that determines the value of the conductance is the ratio K / K 0 of the compressibility of the system to the free one.

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Section: Introductionmentioning

confidence: 99%

Ground state structure and conductivity of quantum wires of infinite length and finite width

et al. 2005

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“…A new generation of experiments in quantum wires has revealed an unexpected structure at low electron densities: a plateau at about 0.7 G 0 for short [6,7,8,9,10] and at 0.5 G 0 for long quantum wires [11,12,13,14]. These new features have generated much interest as they are likely caused by electron correlation effects.…”

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confidence: 99%

“…The phenomenon presents itself as very flat plateaus of linear conductance G at integer multiples of G 0 = 2e 2 /h, as a function of gate voltage which tunes the electron density in the wire. Since the first observation of the phenomenon, its various facets have been studied by measurements of thermal transport [2,3], noise [4], and experiments on systems with superconducting elements [5].A new generation of experiments in quantum wires has revealed an unexpected structure at low electron densities: a plateau at about 0.7 G 0 for short [6,7,8,9, 10] and at 0.5 G 0 for long quantum wires [11,12,13,14]. These new features have generated much interest as they are likely caused by electron correlation effects.…”

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confidence: 99%

“…As a result, J is expected to be small compared to the Fermi energy E F , and qualitatively new transport properties of the quantum wires, such as the plateau at 0.5 G 0 , are expected [16,17] at temperatures in the range J ≪ T ≪ E F . In addition to conductance measurements [11,12,13,14], the smallness of J should have a strong effect on the velocity of the spin excitations in the wire measured in Ref. 15 and on transport properties of quantum wires in the in-plane magnetic field.…”

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confidence: 99%

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Exchange coupling in a one-dimensional Wigner crystal

2005

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We consider a long quantum wire at low electron densities. In this strong interaction regime a Wigner crystal may form, in which electrons comprise an antiferromagnetic Heisenberg spin chain. The coupling constant J is exponentially small, as it originates from tunneling of two neighboring electrons through the segregating potential barrier. We study this exponential dependence, properly accounting for the many-body effects and the finite width of the wire.PACS numbers: 73.21. Hb,75.10.Pq,75.30.Et,71.70.Gm Quantum wires exhibit a plethora of interesting phenomena. In particular, quantization of conductance, which is a fundamental manifestation of the quantum nature of the electron, has been actively studied ever since its first observation in quantum point contacts [1]. The phenomenon presents itself as very flat plateaus of linear conductance G at integer multiples of G 0 = 2e 2 /h, as a function of gate voltage which tunes the electron density in the wire. Since the first observation of the phenomenon, its various facets have been studied by measurements of thermal transport [2,3], noise [4], and experiments on systems with superconducting elements [5].A new generation of experiments in quantum wires has revealed an unexpected structure at low electron densities: a plateau at about 0.7 G 0 for short [6,7,8,9, 10] and at 0.5 G 0 for long quantum wires [11,12,13,14]. These new features have generated much interest as they are likely caused by electron correlation effects. The origin of the new plateau has not yet been established; however, the experiments [6,7,8] point to the important role played by the electron spins.In recent experiments of a different kind, involving tunneling between two parallel ballistic quantum wires, mapping of the spectrum of spin and charge excitations was achieved [15]. In addition, unexpected behavior indicating electron localization was observed at low densities. Of particular interest is the concurrence of the localization with the drops in the conductance steps, which indicates [15] a possible connection with the 0.7 structure [6,7,8,9,10].Recent theoretical work suggests that qualitatively new transport properties of quantum wires at low electron densities may be due to the formation of a Wigner crystal state of electrons. The latter is expected to occur when the density is low enough for the potential energy of the Coulomb repulsion to overwhelm the kinetic energy of the electrons in the wire. In the crystalline configuration, the electron spins form an antiferromagnetic Heisenberg spin chain, with the exchange coupling constant J emerging as a new energy scale. The Heisenberg exchange can be viewed as arising from tunneling of two neighboring electrons through the potential barrier created by their mutual repulsion, and by the repulsion from all other electrons of the wire. As a result, J is expected to be small compared to the Fermi energy E F , and qualitatively new transport properties of the quantum wires, such as the plateau at 0.5 G 0 , are expected [16,17] at tempera...

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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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confidence: 99%

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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Quantized conductance in quantum wires with gate-controlled width and electron density

Cited by 131 publications

References 10 publications

Ground state structure and conductivity of quantum wires of infinite length and finite width

Ground state structure and conductivity of quantum wires of infinite length and finite width

Exchange coupling in a one-dimensional Wigner crystal

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

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