Vertical confinement and evolution of reentrant insulating transition in the fractional quantum Hall regime

Abstract

We have observed an anomalous shift of the high field reentrant insulating phases in a twodimensional electron system (2DES) tightly confined within a narrow GaAs/AlGaAs quantum well. Instead of the well-known transitions into the high field insulating states centered around ν = 1/5, the 2DES confined within an 80Å-wide quantum well exhibits the transition at ν = 1/3.Comparably large quantum lifetime of the 2DES in narrow well discounts the effect of disorder and points to confinement as the primary driving force behind the evolution of the reentrant transition.

Observation of Reentrant Phases Induced by Short-Range Disorder in the Lowest Landau Level ofAlxGa1−xAs/Al0.32Ga0.68AsLi1, Luhman2, Tsui3 et al. 2010Phys. Rev. Lett.Self Cite201200View full textAdd to dashboardCite

“…This reentrant insulating phase near ¼ 1=3 and the observed RIQHE near ¼ 2=3 demonstrate a particlehole symmetry in the insulating phase. These data, along with results from other samples dominated by short-range disorder reported here and elsewhere [11][12][13], indicate that it is the short-range disorder specifically-not just a decrease in mobility-that leads to the emergence of the RIQHE near ¼ 2=3 and the shift of the apparent Wigner crystal phases to higher values of .…”

“…For the x ¼ 0% sample, a reentrant insulating phase is seen between ¼ 2=9 and ¼ 1=5, the usual situation for high quality samples. As x is increased to 0.4%, insulating behavior is beginning to emerge near ¼ 1=3, and by x ¼ 1:2% a reentrant insulating phase is fully developed near A previous experiment using a 2DES confined to a narrow quantum well has also shown a reentrant insulating phase around ¼ 1=3 [11]. In addition, Luhman et al [12] have investigated the emergence of a similar phase around ¼ 1=3 as a function of quantum well width in a series of narrow quantum wells, finding that the reentrant insulating phase emerges as the well width decreases.…”

ν=1/2fractional quantum Hall effect in tilted magnetic fields

“…One possible explanation is that, because d/l B is smaller at the highest B (compared to the highest n), interlayer interactions are preserved and the ground state is a pinned, bilayer Wigner crystal. We note that, in singlelayer 2DESs confined to very narrow GaAs QWs, IPs which are reentrant around ν = 1/3 instead of ν = 1/5 have been reported and interpreted as possible Wigner crystal states [38] although the role of disorder and interface roughness is unclear [39]. In our experiments it is possible that, because the electron layers are pushed closer to the walls of the QW at high B || , we have effectively two narrow 2DESs each exhibiting a pinned Wigner crystal phase near (layer) filling factor ν = 1/3.…”

Connecting the Reentrant Insulating Phase and the Zero-Field Metal-Insulator Transition in a 2D Hole System

“…We believe that the narrow QW width is a key in the formation of this RIP at ν >1. Empirically, it has already been noticed that the RIP in GaAs 2D electron system shifts to higher filling factor as QW width decreases [40]. Another argument is in GaAs hole system, Landau-level mixing is significant and the well width will affect the hole effective mass, which is essential to the Monte Carlo calculation [26].…”