Abstract
The spin-polarized even-denominator fractional quantum Hall (FQH) states in the second Landau level (LL), i.e. 5/2 and 7/2, may possess novel quasi-particle excitations obeying non-Abelian statistics. However, the spin polarization of the 7/2 FQH state has not been investigated experimentally and the spin polarization of the 5/2 FQH state from tilted field experiments remains controversial. Using a piezo-driven sample rotator with the lowest electron temperature down to 25 mK, we studied the energy gap of the even-denominator FQH states in the second LL by precise control of the tilted angles with a resolution less than 0.1{\deg}. We observed two different energy gap dependences on the in-plane magnetic field for 5/2, 7/2, other FQH states (7/3 and 8/3) in the second LL and reentrant integer quantum Hall (RIQH) states in the third LL. Though the transition fields vary from states, their corresponding in-plane magnetic lengths are comparable to the quantum well thickness of the sample, which may result from the influence of the finite-thickness effect. At low in-plane magnetic fields, before the conjectured finite-thickness effect starts to dominate, the energy gaps of both 5/2 and 7/2 states show a non-decreasing behavior, supporting spin-polarized ground states. Our results also suggest that the 7/3, 8/3 FQH states, and the RIQH states in the third LL are spin-polarized or partially spin-polarized.
Highlights
The spin-polarized even-denominator fractional quantum Hall (FQH) states in the second Landau level (LL), i.e., 5/2 and 7/2, may possess novel quasiparticle excitations obeying non-Abelian statistics
Using a piezodriven sample rotator with the lowest electron temperature down to 25 mK, we studied the energy gap of the even-denominator FQH states in the second LL by precise control of the tilted angles with a resolution less than 0.1°
Though the transition fields vary from states, their corresponding in-plane magnetic lengths are comparable to the quantum well thickness of the sample, which may result from the influence of the finite-thickness effect
Summary
Pengjie Wang ,1,2 Jian Sun ,1 Hailong Fu, Yijia Wu ,1 Hua Chen ,1 L. We observed two different energy gap dependences on the in-plane magnetic field for 5/2, 7/2, other FQH states (7/3 and 8/3) in the second LL, and reentrant integer quantum Hall (RIQH) states in the third LL. At low in-plane magnetic fields, before the conjectured finite-thickness effect starts to dominate, the energy gaps of both 5/2 and 7/2 states show a nondecreasing behavior, supporting spin-polarized ground states. The spin polarization at 5/2 has been under intense studies through different experimental techniques, such as optical method [28,29], resistive detected nuclear magnetic resonance (RDNMR) [30,31], geometric resonance [32], and tilted-field experiments [33,34,35,36,37,38]. Calculations [41] examined the wave-function overlap, as a function of quasi-2D layer thickness, between the exact ground
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