Mutual friction between parallel two-dimensional electron systems

Gramila, T. J.; Eisenstein, J. P.; MacDonald, Allan H.; Pfeiffer, L. N.; West, K.W.

doi:10.1103/physrevlett.66.1216

Cited by 498 publications

(680 citation statements)

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“…Paradigmatic examples in the field of superconductivity include the high temperature superconducting cuprates [1, 2], and the iron pnictides [3], as well as artificially created superlattices, in which the Josephson coupling between the layers can be tunable continuously using thin film control [4,5]. There have also been extensive studies of coupled bilayer 2D systems, where exotic phases arise from the interlayer interactions [6][7][8][9][10][11][12].Among the various 2D systems currently under investigation, SrTiO 3 (STO) is of particular interest since it is a rare example of a high mobility doped semiconductor that is simultaneously superconducting. By confining electrons in STO two-dimensionally using field effect gating [13], heterointerfaces with LaTiO 3 [14], or LaAlO 3 [15,16], and δ-doping [17], the interplay between subband quantization and superconductivity can be investigated.…”

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Tunable coupling of two-dimensional superconductors in bilayer SrTiO3heterostructures

et al. 2013

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Interlayer coupling effects between high mobility two-dimensional superconductors are studied in bilayer δ-doped SrTiO3 heterostructures. By tuning the undoped SrTiO3 spacer layer between the dopant planes, clear tunable coupling is demonstrated in the variation of the sheet carrier density, Hall mobility, superconducting transition temperature, and the temperature-and angle-dependences of the superconducting upper critical field. Systematic variation is found between one effective (merged) two-dimensional superconductor to two decoupled two-dimensional superconductors. In the intermediate coupled regime, a crossover is observed due to coupling arising from inter-sub-band interactions.Interlayer coupling between two-dimensional (2D) planes in layered materials is a key parameter which dramatically influences their physics and functionality. Paradigmatic examples in the field of superconductivity include the high temperature superconducting cuprates [1, 2], and the iron pnictides [3], as well as artificially created superlattices, in which the Josephson coupling between the layers can be tunable continuously using thin film control [4,5]. There have also been extensive studies of coupled bilayer 2D systems, where exotic phases arise from the interlayer interactions [6][7][8][9][10][11][12].Among the various 2D systems currently under investigation, SrTiO 3 (STO) is of particular interest since it is a rare example of a high mobility doped semiconductor that is simultaneously superconducting. By confining electrons in STO two-dimensionally using field effect gating [13], heterointerfaces with LaTiO 3 [14], or LaAlO 3 [15,16], and δ-doping [17], the interplay between subband quantization and superconductivity can be investigated. Here we exploit interlayer coupling in a δ-doped bilayer system to spatially and flexibly control the subbands. By systematically tuning the interlayer coupling by varying the spacer layer thickness, we can examine the effects of the sub-band quantization on superconductivity.The bilayer samples consist of two Nb:STO δ-doped layers, with an undoped STO spacer of thickness d inter , as well as 100 nm thick undoped STO cap and buffer layers. All samples were fabricated using pulsed laser deposition using growth conditions as reported elsewhere [18]. The thickness of each of the two δ-layers was fixed at a constant value of d doped = 5.4 ± 1 nm, as calibrated from the total thickness and the laser pulse count. The interlayer undoped STO thickness d inter was varied in the range 3.7 ≤ d inter ≤ 272 nm. The dopant concentration of the δ-doped layers was 1 at.%. A schematic of the bilayer samples is shown in Fig.

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Tunable coupling of two-dimensional superconductors in bilayer SrTiO3heterostructures

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“…For layer densities higher than 6 Â 10 10 cm À2 , the h-h drag approaches a q D / T 2 regime, as expected for bilayers with sufficiently high density and large interlayer separation. 34,36 However, at the lowest density, the temperature dependence becomes slightly weaker, with c in the range 1.5-1.8. This is similar to previous results for low-density h-h bilayers, where a stronger than T 2 -dependence was observed at low temperature, crossing over to a weaker than T 2 -dependence at higher temperature.…”

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“…Low-frequency ac (12 Hz) four-terminal Coulomb drag and magnetotransport measurements in a constant-current (5 or 10 nA) set-up were used to investigate the state of the system as a function of the temperature and density of the layers. The usual consistency checks for a linear relationship between drag voltage and drive current, scaling of the drag voltage with the Hall bar length-to-width ratio, and the effects of interlayer leakage 16,34 have been performed to exclude the contribution of spurious signals to the measured drag voltage (normally in the range of $nV). Onsager's reciprocity theorem, applied to bilayer systems in the linear response regime, predicts that the interchanging voltage and current probes in a Coulomb drag set-up at zero magnetic field should not affect the value of the drag resistivity.…”

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A complete laboratory for transport studies of electron-hole interactions in GaAs/AlGaAs ambipolar bilayers

Cumis

Waldie

Croxall

et al. 2017

Applied Physics Letters

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We present GaAs/AlGaAs double quantum well devices that can operate as both electron-hole (e-h) and hole-hole (h-h) bilayers, with separating barriers as narrow as 5 nm or 7.5 nm. With such narrow barriers, in the h-h configuration, we observe signs of magnetic-field-induced exciton condensation in the quantum Hall bilayer regime. In the same devices, we can study the zero-magnetic-field e-h and h-h bilayer states using Coulomb drag. Very strong e-h Coulomb drag resistivity (up to 10% of the single layer resistivity) is observed at liquid helium temperatures, but no definite signs of exciton condensation are seen in this case. Self-consistent calculations of the electron and hole wavefunctions show this might be because the average interlayer separation is larger in the e-h case than the h-h case.

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“…17͒: within the vortex paradigm, vortices in one layer drag the vortices in the other, but within the percolation picture, the drag resistance is solely due to interlayer "Coulomb drag," as studied in semiconductor heterostructures. 18 The sign and the magnitude of the drag within the two paradigms are different: vortex drag implies the same sign for the voltage drops in the two layers, sign͑V 1 ͒ = sign͑V 2 ͒, but the Coulomb drag yields an opposite sign for V 2 and V 1 . In addition, a vortex drag would be much stronger than a Coulomb drag, because the films' charge carrier density is orders of magnitude larger As the magnetic field B increases, the superconducting phase is destroyed, and a possible metallic phase emerges.…”

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Investigating the superconductor-insulator transition in thin films using drag resistance: Theoretical analysis of a proposed experiment

2009

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The magnetically driven superconductor-insulator transition in amorphous thin films ͑e.g., InO and Ta͒ exhibits several mysterious phenomena, such as a putative metallic phase and a huge magnetoresistance peak. Unfortunately, several conflicting categories of theories, particularly quantum-vortex condensation, and normal region percolation, explain key observations equally well. We present a experimental setup, an amorphous thin-film bilayer, where a drag resistance measurement would clarify the role quantum vortices play in the transition, and hence decisively point to the correct picture. We provide a thorough analysis of the device, which shows that the vortex paradigm gives rise to a drag with an opposite sign and orders of magnitude larger than the drag measured if competing paradigms apply. DOI: 10.1103/PhysRevB.80.180503 PACS number͑s͒: 74.78.Db, 73.43.Nq, 74.25.Fy, 74.78.Fk The superconducting state and the metallic Fermi-liquid form the very basis of our understanding of correlated electron systems. Nevertheless, the transition between these two phases in disordered films is shrouded in mystery. Experiments probing this transition in amorphous thin films such as Ta, MoGe, InO, and TiN used a perpendicular magnetic field and disorder ͑tuned through film thickness͒ to destroy superconductivity. But instead of a superconductor-metal transition, they observed in many cases a superconductor-insulator transition ͑SIT͒. 1 The "dirty boson" model 2 propounded the notion that the insulator is the mark of vortex condensation, and that the SIT occurs at a universal critical resistance, R ᮀ = h / 4e 2 . More recent experiments, however, showed the critical resistance to be nonuniversal. 3 Furthermore, in many field tuned experiments, a surprising metallic phase intervenes between the superconductor and insulator, 4-6 with a temperature-independent resistance below T ϳ 50 mK, and ͑at least in Ta films͒ a distinct nonlinear I-V characteristics. 7 Quite generically, 5,6,8 these films exhibit a peak in the magnetoresistance ͑MR͒ curve ͑particularly strong in InO and TiN͒ as in Fig. 1͑a͒.Two competing categories of theories may account for these phenomena. On one hand, within the quantum vortex pictures, 2,9,10 the insulating phase implies vortex condensation, the intervening metallic phase is described as uncondensed vortex liquid ͑e.g., vortex Fermi liquid͒, and the high field nonmonotonic MR indicates the appearance of a finite electronic density of states ͑DOS͒ at the Fermi level. On the other hand, the percolation paradigm 11,12 describes the films as consisting of superconducting ͑SC͒ and normal puddles; at the MR peak SC puddles exhibit a Coulomb blockade, and the percolating normal regions consist of narrow conduction channels. Yet a third theory tries to account for the low field SC-metal transition using a phase glass model 13 ͑see, however, Ref. 14 which argues against these results͒ but does not address the full MR curve. Qualitatively, both paradigms above are consistent with MR observations, and recent...

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Mutual friction between parallel two-dimensional electron systems

Cited by 498 publications

References 10 publications

Tunable coupling of two-dimensional superconductors in bilayer SrTiO3heterostructures

Tunable coupling of two-dimensional superconductors in bilayer SrTiO3heterostructures

A complete laboratory for transport studies of electron-hole interactions in GaAs/AlGaAs ambipolar bilayers

Investigating the superconductor-insulator transition in thin films using drag resistance: Theoretical analysis of a proposed experiment

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