Fractional quantum Hall effect of two-dimensional electrons in high-mobility Si/SiGe field-effect transistors

Abstract

The fractional quantum Hall (FQH) regime of the Si two-dimensional electron system (2DES) in enhancement-mode field-effect transistors of Si/SiGe heterostructures was probed via electrical transport measurements. At n ∼ 2.6 × 10 11 /cm 2 with µ = 1.6 × 10 6 cm 2 /V s, signatures of FQH states at filling factors ν = 4/5, 6/5, and 10/7 were observed, in addition to the FQH states reported in previous studies. The temperature dependence of the FQH states is investigated and comparison is made with previous work done on modulation-doped samples. Results indicate that robustness of the FQH states is dependent on the nature of disorder in the 2DES. 1The discoveries of the integer quantum Hall (IQH) effect[1] and the fractional quantum Hall (FQH) effect [2] have spurred much research on the ground states of two-dimensional (2D) electrons in the presence of strong magnetic fields over the past 30 years. Thanks to to the constantly refined III-V epitaxial technology, the quality of GaAs/AlGaAs heterostructures has been continually improving, leading to the observation of a few tens of FQH states in GaAs [3]. While large in number, most of the FQH states can be understood within the theoretical framework of composite fermions (CFs) [4]. In the CF model, the FQH effect, originally arising from electron-electron interaction, is mapped to the IQH effect arising from Landau quantization of the orbital motion of CFs.Soon after the discoveries of the IQH and FQH effects, it was realized that additional degrees of freedom of 2DESs such as spins, layers, subbands, and valleys, may produce new correlated states which do not exist in a one-component 2DES [5]. Celebrated examples include Skyrmions in systems with small Zeeman splitting [6,7], even-denominator FQH states [8,9], and the excitonic superfluid in bilayer systems [10]. While much effort towards the understanding of the roles of spins, layers, and subbands in the FQH regime has been made using high-quality GaAs quantum wells, experimental studies on the effects of valleys have been relatively sparse, only a few reports on 2D electrons in Si [11,12] and AlAs [13][14][15][16] available, partly due to the less impressive material quality of multi-valley semiconductors.Indeed, the electron mobilities of the devices used in these studies were smaller than that of GaAs by almost two orders of magnitude [3,17]. Nevertheless, looking back at the history of discoveries of new states in GaAs, we may expect that more interesting physical phenomena in multi-valley systems will emerge, once materials with higher mobility are available.Recently, we reported a fabrication process for making undoped (100)-oriented Si/SiGe FETs and observed an electron mobility of 1.6 × 10 6 cm 2 /V s [18], approximately eight times higher than that of typical modulation-doped Si/SiGe quantum wells [19]. Such improvement in material quality naturally prompted us to perform magneto-transport experiments and search for new states in Si 2DESs. In this paper, we focus on the FQH regime ν < 2, where the...

Multivalley two-dimensional electron system in an AlAs quantum well with mobility exceeding 2×106cm2V−1Chung1, Rosales2, Deng3 et al. 2018Phys. Rev. Materials210160View full textAdd to dashboardCite

“…This conjecture is consistent with the fact that while the Si 2DES data in Ref. [4] show high-order FQHE minima up to ν = 4/9 in the extreme quantum limit, our samples exhibit FQHE features up to ν = 8/17 even at lower densities ( Fig. 4(a)).…”

“…It is worthwhile to compare our results to those for other multivalley 2DESs such as Si or monolayer graphene. In a Si/SiGe field-effect transistor structure, it has been reported that Si 2DESs which occupy two out-of-plane valleys can achieve a mobility of 1.6 × 10 6 cm 2 V −1 s −1 at n 2.6 × 10 11 cm −2 and T = 30 mK [4]. Since the transport effective mass for this case (m * = m t = 0.19) is smaller than our AlAs 2DESs, we expect that our samples have higher quality.…”

Recent experimental progress of fractional quantum Hall effect: 5/2 filling state and graphene

“…For example, 2DEG based on MgZnO/ZnO heterostructure reached the mobility of 7×10 5 cm 2 /(V•s) only 4 years after its first demonstration as a host for 2DEG [189,190] and many FQH states have been observed in ZnO system [191,192]. FQHE has been also observed in Si/SiGe heterostructure [193,194] with mobility in the order of 10 6 cm 2 /(V•s) nowadays. Besides the familiar heterostructure, two-dimensional materials can also host FQHE.…”

Composite Fermion Theory of Exotic Fractional Quantum Hall Effect

“…[as was also found in graphene (35)]. The FQHE has been seen in high-mobility Si/SiGe field-effect transistors (125). Here also, the observations are consistent with CFs in the SU(2) limit, with strong FQHE at 2/3, 4/3, 2/5, 8/5, 4/7, and 4/9, and a weak FQHE at 1/3; indications are also seen for FQHE at 10/ 7, 6/5, and 4/5.…”