Collective Nature of the Reentrant Integer Quantum Hall States in the Second Landau Level

Abstract

We report an unexpected sharp peak in the temperature dependence of the magnetoresistance of the reentrant integer quantum Hall states in the second Landau level. This peak defines the onset temperature of these states. We find that in different spin branches the onset temperatures of the reentrant states scale with the Coulomb energy. This scaling provides direct evidence that Coulomb interactions play an important role in the formation of these reentrant states evincing their collective nature.The second Landau level (SLL) of the two-dimensional electron gas (2DEG) is astonishingly rich in novel ground states [1][2][3]. Recent experiments [3][4][5][6][7][8][9] suggest that there are both conventional [10,11] as well as exotic fractional quantum Hall states (FQHSs) [12,13] in this region. The study of the latter has enriched quantum many-body physics with numerous novel concepts such as paired composite fermion states with Pfaffian correlations, non-Abelian quasiparticles [12][13][14][15][16][17][18][19], topologically protected quantum computing [20], and established connections between the 2DEG and p-wave superconductivity in Sr 2 RuO 4 and fermionic atomic condensates.The eight reentrant integer quantum Hall states (RIQHSs) form another set of prominent ground states in the SLL [1]. The transport signatures of the RIQHSs are consistent with electron localization in the topmost energy level [1]. However, the nature of the localization is not yet well understood. Depending on the relative importance of the electron-electron interactions, the ground state can be either an Anderson insulator or a collectively pinned electron solid.FQHSs owe their existence to the presence of the interelectronic Coulomb interactions [10,11]. Since FQHSs and RIQHSs alternate in the SLL, it was argued that Coulomb interactions must be important and, therefore, the RIQHSs in the SLL must be electron solids [1]. Subsequent density matrix renormalization group [21] and Hartree-Fock calculations [22] also favored the electron solid picture and predicted the solid phase similar to the Wigner crystal, but having one or more electrons in the nodes of the crystal [22]. Recently reported weak microwave resonances in one such RIQHS are suggestive of but are far from being conclusive on the formation of a collective insulator [23]. Our understanding of the RIQHSs in the SLL, therefore, is still in its infancy and the collective nature of these states has not yet been firmly established.We report a feature in the temperature dependent magnetoresistance unique to the the RIQHSs in the SLL, a feature which is used to define the onset temperature of these states. The scaling of onset temperatures with the Coulomb energy reveals that Coulomb interactions play a central role in the formation of RIQHSs and, therefore, these reentrant states are exotic electronic solids rather than Anderson insulators. We also report an unexpected trend of the onset temperatures within each spin branch. This trend is inconsistent with current theories and can be unde...

Spin and Charge Ordering in the Quantum Hall Regime

“…2.19 shows four reentrant states per spin branch, interposed by different FQHS. They appear at partial filling˜= 0.29, 0.43, 0.57, and 0.70, in agreement with previous publications [116][117][118]. That raises the question whether the reentrant states in the second Landau level are of equal nature as the bubble phases in higher levels.…”

“…Indeed, besides the IQHE transport behavior, other similarities to the bubble phases in higher Landau levels are present, such as sharp and hysteretic features in the -characteristics [116] as well as pinning modes in microwave absorption [120]. In addition, it has been demonstrated that the onset temperatures of the RIQHS in the second Landau level scale with the Coulomb energy, which highlights the importance of electron-electron interactions for the origin of these states [118]. However, also discrepancies to the bubble phases in higher Landau levels are evident.…”

Observation of an anomalous density-dependent energy gap of the ν=5/2 fractional quantum Hall state in the low-density regime

“…Besides the FQHS at ν = 5/2, we also observe strong FQHSs at ν = 7/3 and 11/5, and there are indications of developing FQHSs at ν = 8/3, and 14/5. Furthermore, in Fig.2a we notice three peaks in R xx at B = 1.10, 1.04, and 0.98 T. We associate these peaks with precursors at temperatures above the onset temperature of the reentrant integer quantum Hall states R2a, R2b, and R2c, respectively 80 .…”

Optical Emission Spectroscopy Study of Competing Phases of Electrons in the Second Landau Level

“…It has been predicted that the less studied FQHE state at ν = 2 + 1/3 = 7/3 could possess exotic quasiparticles in which composite fermions are dressed by a cloud of neutral excitations [20]. Since FQHE liquids as well as bubble and stripe phases can serve as ground states, the N=1 LL is home to a striking competition between quantum phases [21].The interplay of anisotropic phases with FQHE liquids in the second LL has been studied by introduction of in-plane magnetic fields [3,[22][23][24][25]. These experiments provide evidence that anisotropic smectic-or nematic-like phases with broken full rotational invariance coexist with quantum Hall liquids [26][27][28][29][30].…”

“…It has been predicted that the less studied FQHE state at ν = 2 + 1/3 = 7/3 could possess exotic quasiparticles in which composite fermions are dressed by a cloud of neutral excitations [20]. Since FQHE liquids as well as bubble and stripe phases can serve as ground states, the N=1 LL is home to a striking competition between quantum phases [21].…”