Hall field-induced resistance oscillations in ap-type Ge/SiGe quantum well

Abstract

We report on Hall field-induced resistance oscillations (HIRO) in a 60 nm-wide GaAs/AlGaAs quantum well with an in situ grown back gate, which allows tuning the carrier density n. At low n, when all electrons are confined to the lowest subband (SB1), the HIRO frequency, proportional to the product of the cyclotron diameter and the Hall field, scales with n −1/2 , as expected. Remarkably, population of the second subband (SB2) significantly enhances HIRO, while their frequency now scales as n −1. We demonstrate that in this two-subband regime HIRO still originate solely from backscattering of SB1 electrons. The unusual density dependence occurs because the population of SB2 steadily increases, while that of SB1 remains essentially unchanged. The enhancement of HIRO manifests an unexpected, step-like increase of the quantum lifetime of SB1 electrons, which reaches a record value of 52 ps in the two-subband regime. Continuous developments [1-8] in the molecular beam epitaxy and heterostructure design of 2D electron systems (2DES) have led to discoveries of a plethora of novel phenomena , especially in the field of low-temperature magnetotrans-port. Apart from the extremely rich quantum Hall physics in strong magnetic fields [9, 10], high-mobility 2DES display many prominent transport phenomena in low fields. Two salient examples of such phenomena are microwave-(MIRO) [11-16] and Hall field-induced resistance oscillations (HIRO) [17-26] which emerge when a 2DES is driven by microwave radiation and direct current, respectively. HIRO emerge due to elastic electron transitions between Landau levels, tilted by the Hall field, as a result of backscat-tering off short-range impurities [17, 27, 28]. The probability of these transitions is maximized each time the Hall voltage drop across the cyclotron diameter matches an integer multiple of the cyclotron energy. As a result, the differential re-sistivity acquires a 1/B-periodic correction δr which can be described by [27] δr/ρ 0 ≈ (16τ /πτ π)λ 2 cos(2πB 1 /B) , (1) where ρ 0 = m ⋆ /e 2 nτ is the resistivity at zero magnetic field B, m ⋆ ≈ 0.07m 0 is the effective mass, n is the electron density , λ = exp(−π/ω c τ q) is the Dingle factor, ω c = eB/m ⋆ is the cyclotron frequency, and τ, τ π , τ q are transport, backscat-tering, and quantum lifetimes, respectively [29]. The HIRO frequency (inverse period) B 1 is given by B 1 B ≡ eE(2R c) ω c ⇒ B 1 = 8π n m ⋆ e 2 j , (2) where E = Bj/ne is the Hall field and R c = √ 2πn/eB is the cyclotron radius. It is well known that in systems with several populated subbands, MIRO and HIRO often mix with magneto-intersubband oscillations (MISO) [30-36]. However, it is also important to examine how MIRO and HIRO are affected by the population of the second subband in the absence of such mixing. For example, capacitance measurements in a wide quantum well provided direct evidence of microwave-induced non-equilibrium redistribution of electrons between two subbands but no significant change in MIRO upon second subband population [37]. However, ...

Microwave photoresistance in an ultra-high-quality GaAs quantum well

“…Here, we report on MIRO in an ultrahigh mobility (µ > 3×10 7 cm 2 /Vs) 2D electron gas at T between 0.3 K and 1.8 K. In contrast to theoretical predictions, the quantum lifetime is found to be T -independent in the whole temperature range studied. At the same time, the T -dependence of the inelastic lifetime is much stronger than can be expected from electron-electron interactions.Microwave-induced resistance oscillations (MIRO) appear in two-dimensional electron [1,2] or hole systems [3,4] subjected to low temperature T , weak magnetic field B, and radiation of frequency f = ω/2π. When the MIRO amplitude exceeds dark resistance, the oscillation minima evolve into zero-resistance states [5][6][7][8][9][10][11][12][13][14], understood in terms of formation of current domains [15][16][17][18][19][20].When the microwave power is not too high and Landau levels are overlapping, away from the cyclotron resonance MIRO can be described by [21] δR ≈ −A sin 2πǫ , A = ǫp(ǫ)λ 2 A 0 ,…”

Hall field-induced resistance oscillations in a tunable-density GaAs quantum well

“…Apart from the extremely rich quantum Hall physics in strong magnetic fields [9,10], high-mobility 2DES display many prominent transport phenomena in low fields. Two salient examples of such phenomena are microwave-(MIRO) [11][12][13][14][15][16] and Hall field-induced resistance oscillations (HIRO) [17][18][19][20][21][22][23][24][25][26] which emerge when a 2DES is driven by microwave radiation and direct current, respectively.HIRO emerge due to elastic electron transitions between Landau levels, tilted by the Hall field, as a result of backscattering off short-range impurities [17,27,28]. The probability of these transitions is maximized each time the Hall voltage drop across the cyclotron diameter matches an integer multiple of the cyclotron energy.…”

Hall field-induced resistance oscillations in MgZnO/ZnO heterostructures

“…To date, HIRO have been studied in modulation-doped systems based on either GaAs/AlGaAs [4][5][6][22][23][24][25][26][27] or, more recently, on Ge/SiGe [28] heterostructures. Both of the studied systems are characterized by very high mobility (µ ∼ 10 6 − 10 7 cm 2 /Vs), low effective mass (m ⋆ ≈ 0.06 − 0.09m 0 ), and moderate carrier density (typically n e ∼ 10 11 cm −2 ).…”