Unconventional reentrant quantum Hall effect in a HgTe/CdHgTe double quantum well Auteur(s): Yakunin M., Krishtopenko S., Desrat W., Podgornykh S. m., Popov M. r., Neverov V. n., Dvoretsky S. a., Mikhailov N. n., Teppe F., Jouault B. (Article) Publié: Physical Review B, vol. 102 p.165305 (2020) Texte intégral en Openaccess : DOI: 10.1103/PhysRevB.102.165305 WoS: WOS:000576600700006 Résumé: We report on the observation of an unconventional structure of the quantum Hall effect (QHE) in a $p$-type HgTe/Cd$_x$Hg$_{1-x}$Te double quantum well (DQW) consisting of two HgTe layers of critical thickness. The observed QHE is a reentrant function of magnetic field between two $i=2$ states (plateaus at $\rho_{xy}=h/ie^2$) separated by an intermediate $i=1$ state in the shape of a flat-top peak placed on an remarkably long $i=2$ plateau. This anomalous $i=1$ peak separates two different regimes: i) a QHE at low fields corresponding to a small density of mobile holes $p_s$ and ii) a high-field QHE with a $2-1$ plateau--plateau transition corresponding to a much larger $p_s$. The high-field part is strongly sensitive to external influences, like gate voltages, by contrast to the low field part which is much less responsive. We explain the observed behavior by analyzing the trajectories of the Fermi level $E_F(B)$ between hole-like and electron-like LLs. At low fields, below the QHE reentrance, only the 2D holes at the $\Gamma$ point of the first Brillouin zone contribute into the QHE, while the holes of the lateral maximum (LM) of the valence subband are inactive. At the contrary, at fields above the reentrance, $E_F$ comes close to the zero-mode hole LLs and all the holes come into play in the QHE. At intermediate fields, the reentrance itself is caused by a combination of two factors in the specific energy spectrum of this DQW: i) a superposition of electron-like LL and hole-like LLs and ii) a stabilizing influence of the LM reservoir on $E_F(B)$.