CaFeAsF is an ironbased superconductor parent compound whose Fermi surface is quasitwo dimensional, composed of Diracelectron and Schrödingerhole cylinders elongated along the
 NSFPAR ID:
 10381687
 Publisher / Repository:
 Nature Publishing Group
 Date Published:
 Journal Name:
 npj Quantum Materials
 Volume:
 7
 Issue:
 1
 ISSN:
 23974648
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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We report complex magnetotransport patterns of the ν = 1 integer quantum Hall state in a GaAs/AlGaAs sample from the newest generation with a record high electron mobility. The reentrant integer quantum Hall effect in the flanks of the ν = 1 plateau indicates the formation of the integer quantum Hall Wigner solid, a collective insulator. Moreover, at a fixed filling factor, the longitudinal resistance versus temperature in the region of the integer quantum Hall Wigner solid exhibits a sharp peak. Such sharp peaks in the longitudinal resistance versus temperature so far were only detected for bubble phases forming in high Landau levels but were absent in the region of the Anderson insulator. We suggest that in samples of sufficiently low disorder, sharp peaks in the longitudinal resistance versus temperature traces are universal transport signatures of all isotropic electron solids that form in the flanks of integer quantum Hall plateaus. We discuss possible origins of these sharp resistance peaks and we draw a stability diagram for the insulating phases in the νT phase space.more » « less

Abstract The interplay of strong Coulomb interactions and of topology is currently under intense scrutiny in various condensed matter and atomic systems. One example of this interplay is the phase competition of fractional quantum Hall states and the Wigner solid in the twodimensional electron gas. Here we report a Wigner solid at ν = 1.79 and its melting due to fractional correlations occurring at ν = 9/5. This Wigner solid, that we call the reentrant integer quantum Hall Wigner solid, develops in a range of Landau level filling factors that is related by particlehole symmetry to the so called reentrant Wigner solid. We thus find that the Wigner solid in the GaAs/AlGaAs system straddles the partial filling factor 1/5 not only at the lowest filling factors, but also near ν = 9/5. Our results highlight the particlehole symmetry as a fundamental symmetry of the extended family of Wigner solids and paint a complex picture of the competition of the Wigner solid with fractional quantum Hall states.more » « less

The discovery of the fractional quantum Hall state (FQHS) in 1982 ushered a new era of research in manybody condensed matter physics. Among the numerous FQHSs, those observed at evendenominator Landau level filling factors are of particular interest as they may host quasiparticles obeying nonAbelian statistics and be of potential use in topological quantum computing. The evendenominator FQHSs, however, are scarce and have been observed predominantly in lowdisorder twodimensional (2D) systems when an excited electron Landau level is half filled. An example is the wellstudied FQHS at filling factor
$\mathit{\nu}\mathbf{=}$ 5/2 which is believed to be a BardeenCooperSchrieffertype, paired state of fluxparticle composite fermions (CFs). Here, we report the observation of evendenominator FQHSs at$\mathit{\nu}\mathbf{=}$ 3/10, 3/8, and 3/4 in the lowest Landau level of an ultrahighquality GaAs 2D hole system, evinced by deep minima in longitudinal resistance and developing quantized Hall plateaus. Quite remarkably, these states can be interpreted as evendenominator FQHSs of CFs, emerging from pairing of higherorder CFs when a CF Landau level, rather than an electron or a hole Landau level, is halffilled. Our results affirm enhanced interaction between CFs in a hole system with significant Landau level mixing and, more generally, the pairing of CFs as a valid mechanism for evendenominator FQHSs, and suggest the realization of FQHSs with nonAbelian anyons. 
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