## 1 Introduction  
Anderson insulators [1] describe a quantum localization effect of non-interacting electrons due to random disorders. Such an insulator is expected to prevail in two-dimensional (2D) systems even in the low disorder limit [2], as long as the sample size \(L\) and the electron coherence length \(l_{\phi}\) are beyond the localization length \(\zeta\). As far as the experimental results are concerned, Anderson localization provides a partial description of the transport behaviors because a 2D system can be a metal or an insulator as demonstrated extensively via the metal-insulator transition (MIT) [3, 4] when the carrier density \(n\) is reduced below a critical value \(n_{c}\). While the disorder manifests in metals via the weak-localization (WL) [5] (with perturbation corrections from interaction [6, 7]), it usually, as most results support, drives an Anderson insulator for \(n<n_{c}\) where the low-\(T\) conduction is realized through hopping [7, 8] among the localized states. Thus, this scenario of MIT is characterized by the prominent disorder effect, with perturbation influences from interaction. However, this picture is radically altered if disorder is sufficiently reduced. This paper is aimed to demonstrate an MIT arising from strong interaction effects. Strong interaction in the low disorder limit causes correlated electron states to emerge. Examples range from the long sought-after Wigner crystal (WC) [9] to the non-Fermi liquids [10]. The effect of interaction is reflected in a ratio \(r_{s}=E_{ee}/E_{F}\) as a function of the carrier density \(n\): \(r_{s}=m^{+}e^{2}/\epsilon\hbar^{2}\sqrt{\tau n}\). \(E_{ee}=e^{2}/\epsilon a\) is the Coulomb energy, \(E_{F}=n\pi\hbar^{2}/m^{+}\) is the Fermi energy, and \(m^{+}\) is the effective mass. Continuous increase of \(r_{s}\) should eventually cause a liquid-solid phase transition (LSPT). Since a WC is always pinned by disorder [11], this LSPT manifests a distinctive MIT accompanied by a symmetry breaking. The predicted critical point for the LSPT is \(r_{s}^{WC}\approx 37\)[12]. Therefore, it implies a considerable range for a strongly correlated non-Fermi liquid (non-FL) [10] and even possible intermediate phases (i.e. liquid crystals [13]) whose breakdown precedes the onset of a WC. Such an LSPT composes unknown manybody effects that are fundamentally important to a broad spectrum of strongly correlated phenomena. However, rigorous demonstration of a WC state and the LSPT are still lacking. Realization of a large \(r_{s}\) in a zero magnetic field requires the lowering of \(n\) which necessarily reduces both \(E_{ee}\) and \(E_{F}\). The rising effect from disorder at dilute \(n\) tends to drive an Anderson localization (or percolation transition depending on the nature and the amount of the disorders) and breaks long-range orders. Most systems do not have sufficiently low disorders so that they become Anderson insulators (or a glass or mixed phases) before reaching \(r_{s}^{WC}\). This is evidenced by the activated low-\(T\) conductivity \(\sigma(T)=\sigma_{0}\exp{(-T^{*}/T)^{1/7}}\) (\(\gamma=2,3\)) occurs whenever \(r_{s}\) is raised beyond 20. Consequently, the value of \(n_{c}\) (or \(r_{s}^{c}\)) is sensitive to the disorder levels [14; 15]. Adoption of ultra-clean 2D systems is crucial to avoid disorder-driven localization at large \(r_{s}\). For this study, the samples are \(p\)-type 2D systems in (100) GaAs/AlGaAs heterojunction-insulated-gate field-effect-transistors (HIGFETs). The carrier density \(p\) is tunable between \(7\times 10^{8}\) cm\({}^{-2}\) to \(3\times 10^{10}\) cm\({}^{-2}\), corresponding to \(70>r_{s}>25\). Without any intentional doping, the carriers accumulate at the hetero-interface in response to a voltage bias on the metal gate beyond a threshold (\(V_{th}\sim-1.3\) V). The sample contains a 6 mm\(\times\)0.8 mm Hallbar fabricated with a self-align technique [16; 17]. Ohmic contacts are realized via annealing AuBe alloys. Measurement is made inside a dilution refrigerator.