CaFeAsF is an ironbased superconductor parent compound whose Fermi surface is quasitwo dimensional, composed of Diracelectron and Schrödingerhole cylinders elongated along the
 Publication Date:
 NSFPAR ID:
 10381687
 Journal Name:
 npj Quantum Materials
 Volume:
 7
 Issue:
 1
 ISSN:
 23974648
 Publisher:
 Nature Publishing Group
 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.

Abstract The formation of a “spin polaron” stems from strong spinchargelattice interactions in magnetic oxides, which leads to a localization of carriers accompanied by local magnetic polarization and lattice distortion. For example, cupric oxide (CuO), which is a promising photocathode material and shares important similarities with high
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Abstract Twodimensional electron systems subjected to high transverse magnetic fields can exhibit Fractional Quantum Hall Effects (FQHE). In the GaAs/AlGaAs 2D electron system, a double degeneracy of Landau levels due to electronspin, is removed by a small Zeeman spin splitting,
, comparable to the correlation energy. Then, a change of the Zeeman splitting relative to the correlation energy can lead to a reordering between spin polarized, partially polarized, and unpolarized many body ground states at a constant filling factor. We show here that tuning the spin energy can produce fractionally quantized Hall effect transitions that include both a change in$$g \mu _B B$$ $g{\mu}_{B}B$ for the$$\nu$$ $\nu $ minimum, e.g., from$$R_{xx}$$ ${R}_{\mathrm{xx}}$ to$$\nu = 11/7$$ $\nu =11/7$ , and a corresponding change in the$$\nu = 8/5$$ $\nu =8/5$ , e.g., from$$R_{xy}$$ ${R}_{\mathrm{xy}}$ to$$R_{xy}/R_{K} = (11/7)^{1}$$ ${R}_{\mathrm{xy}}/{R}_{K}={(11/7)}^{1}$ , with increasing tilt angle. Further, we exhibit a striking size dependence in the tilt angle interval for the vanishing of the$$R_{xy}/R_{K} = (8/5)^{1}$$ ${R}_{\mathrm{xy}}/{R}_{K}={(8/5)}^{1}$ and$$\nu = 4/3$$ $\nu =4/3$ resistance minima, including “avoided crossing” type lineshape characteristics, and observable shifts of$$\nu = 7/5$$ $\nu =7/5$ at the$$R_{xy}$$ ${R}_{\mathrm{xy}}$ minima the latter occurring for$$R_{xx}$$ ${R}_{\mathrm{xx}}$ and the 10/7. The results demonstrate both size dependence and the possibility, not just of competition between different spin polarized states at the same$$\nu = 4/3, 7/5$$ $\nu =4/3,7/5$ and$$\nu$$ $\nu $ , but also the tilt or Zeemanenergydependent crossover between distinct FQHE associated withmore »$$R_{xy}$$ ${R}_{\mathrm{xy}}$ 
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