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arxiv: 2606.23990 · v1 · pith:VCWZE4LOnew · submitted 2026-06-22 · ❄️ cond-mat.mes-hall

Observation of even-denominator fractional quantum Hall states at ν = 3/4 and 5/4 in the lowest Landau level

Siddharth Kumar Singh , Chengyu Wang , Adbhut Gupta , Kirk W. Baldwin , Loren N. Pfeiffer , Mansour Shayegan This is my paper

Pith reviewed 2026-06-26 06:34 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall
keywords even-denominator FQHSlowest Landau levelbilayer 2DESGaAs quantum wellcomposite fermionsparticle-hole symmetryHalperin 331 stateinterlayer tunneling
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The pith

Even-denominator fractional quantum Hall states appear at filling factors 3/4 and 5/4 in the lowest Landau level.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper reports the observation of even-denominator fractional quantum Hall states at ν = 3/4 and 5/4 inside the lowest Landau level of a wide GaAs quantum well. These states form only after the electron density is raised enough to weaken interlayer tunneling and turn the system into a two-component bilayer. The states vanish under tiny charge asymmetry and are interpreted as particle-hole symmetric partners described by a bilayer composite-fermion construction that extends the Halperin 331 wave function. The result shows how tuning the relative strength of tunneling and Coulomb energy in wide wells can produce new incompressible states that do not appear in single-layer systems.

Core claim

Even-denominator FQHSs are observed at ν = 3/4 and 5/4 in the N = 0 Landau level. As density is increased the ground states evolve from composite-fermion Fermi seas into incompressible states once interlayer tunneling drops and the 2DES becomes two-component, a change also marked by the flanking FQHSs. Both states are extremely sensitive to bilayer symmetry, disappearing when the charge distribution is made asymmetric by only about 2 percent. The states are accounted for as a particle-hole conjugate pair within the Scarola-Jain bilayer composite-fermion framework that generalizes the two-component Halperin Ψ331 state.

What carries the argument

Scarola-Jain bilayer composite-fermion framework that generalizes the Halperin Ψ331 state to produce particle-hole symmetric even-denominator states at 3/4 and 5/4.

If this is right

  • The 3/4 and 5/4 states are two-component and linked by particle-hole symmetry.
  • Both states disappear rapidly once the bilayer charge distribution is made asymmetric.
  • Competing tunneling and Coulomb energy scales in wide wells can stabilize even-denominator states inside the lowest Landau level.
  • The bilayer composite-fermion construction accounts for the observed states and their symmetry properties.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar even-denominator states could appear at other fractions if the interlayer tunneling and layer separation are tuned independently in other wide-well samples.
  • The same density-tuning method might reveal whether the Scarola-Jain framework also describes states at higher Landau levels or in different host materials.
  • Precise control of bilayer asymmetry could be used to switch the 3/4 and 5/4 states on and off in a single device.

Load-bearing premise

The states at 3/4 and 5/4 become two-component FQHSs only after density is raised enough to reduce interlayer tunneling, as signaled by the behavior of the states that flank them.

What would settle it

Measurement of the 3/4 and 5/4 states in the same sample after the charge distribution is deliberately made asymmetric by 2 percent, or after the density is lowered back into the single-component regime.

Figures

Figures reproduced from arXiv: 2606.23990 by Adbhut Gupta, Chengyu Wang, Kirk W. Baldwin, Loren N. Pfeiffer, Mansour Shayegan, Siddharth Kumar Singh.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) Device schematic. (b) Self-consistent Schr¨odinger [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. (a,b) [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Arrhenius plots of the [PITH_FULL_IMAGE:figures/full_fig_p002_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Evolution of the ground state at [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Evolution of the 2DES around [PITH_FULL_IMAGE:figures/full_fig_p003_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6 [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
read the original abstract

Two-dimensional electron systems (2DESs) confined to wide GaAs quantum wells provide a unique platform to study exotic fractional quantum Hall states (FQHSs) because the 2DES has a bilayer charge distribution with significant interlayer tunneling. Precise control over the 2DES density allows the tuning of the interlayer tunneling over a wide range. Here, we present our discovery of new even-denominator FQHSs in the lowest Landau level (orbital index \textit{N} = 0) at filling factors $\nu = 3/4$ and 5/4 in an ultrahigh-quality 2DES confined to a 72.5-nm-wide GaAs quantum well. The ground states at $\nu = 3/4$ and 5/4 both evolve from composite fermion Fermi seas to FQHSs as the density is raised so that interlayer tunneling is sufficiently reduced and the 2DES becomes two-component, signaled by the behavior of the FQHSs flanking $\nu = 3/4$ and 5/4. The two-component nature of the $\nu=3/4$ and 5/4 FQHSs is also evident from their extreme sensitivity to the bilayer charge distribution symmetry: both states disappear quickly when the charge distribution is made asymmetric by only $\simeq 2\%$. We find a natural explanation for the 3/4 and 5/4 FQHSs in terms of two states linked by particle-hole symmetry, and using the Scarola-Jain bilayer composite fermion framework which is a generalization of the well-known, two-component, Halperin state ($\Psi_{331}$ state). Our observations elucidate the crucial role of competing energy and length scales in wide quantum wells in stabilizing new ground states.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript reports the experimental discovery of even-denominator FQHSs at filling factors ν = 3/4 and 5/4 in the lowest Landau level (N=0) of an ultrahigh-quality 2DES confined to a 72.5-nm-wide GaAs quantum well. The ground states at these fillings are claimed to evolve from composite-fermion Fermi seas to FQHSs as density is increased (reducing interlayer tunneling and rendering the 2DES two-component), with this transition signaled by the evolution of flanking FQHSs; the states are further reported to be extremely sensitive to ~2% asymmetry in the bilayer charge distribution and are interpreted within the Scarola-Jain bilayer composite-fermion framework as particle-hole conjugates linked to the Halperin 331 state.

Significance. If the observations hold, the work identifies new even-denominator states in the LLL, a regime where such states are uncommon, and demonstrates density-tuned control over bilayer character in wide wells. This could extend the applicability of bilayer CF constructions and provide a platform for studying competing energy scales in two-component systems.

major comments (1)
  1. [Abstract] Abstract: the central interpretive step—that raising density reduces interlayer tunneling sufficiently for the 2DES to become two-component, with this transition signaled by the behavior of the FQHSs flanking ν = 3/4 and 5/4—is not uniquely established. Density variation simultaneously alters mobility, screening, and subband occupation in a wide well; the manuscript must supply quantitative controls or additional measurements (e.g., tunneling gap vs. density, or direct comparison of mobility-screening effects) to isolate tunneling as the dominant driver.
minor comments (1)
  1. [Abstract] The abstract states the states 'disappear quickly' under ~2% asymmetry; a quantitative plot or table of the asymmetry dependence (e.g., gap vs. asymmetry parameter) would strengthen the two-component claim.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for highlighting the need to strengthen the interpretation of the density-driven transition. We respond to the major comment below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the central interpretive step—that raising density reduces interlayer tunneling sufficiently for the 2DES to become two-component, with this transition signaled by the behavior of the FQHSs flanking ν = 3/4 and 5/4—is not uniquely established. Density variation simultaneously alters mobility, screening, and subband occupation in a wide well; the manuscript must supply quantitative controls or additional measurements (e.g., tunneling gap vs. density, or direct comparison of mobility-screening effects) to isolate tunneling as the dominant driver.

    Authors: We acknowledge that varying density in a wide well simultaneously affects mobility, screening, and subband occupation, so tunneling is not isolated by density alone. Our central evidence for the two-component regime remains the evolution of the flanking FQHSs (whose bilayer character is established in the literature) together with the extreme ~2% asymmetry sensitivity of the 3/4 and 5/4 states themselves. These observables are known to track the interlayer tunneling strength more directly than mobility or screening in this geometry. We will revise the manuscript to add a dedicated paragraph that (i) estimates the relative magnitudes of the competing energy scales with density and (ii) explicitly states that the transition is inferred from the collective behavior of multiple indicators rather than from tunneling in isolation. No new experimental data are available, but the added discussion will make the interpretive logic clearer. revision: partial

Circularity Check

0 steps flagged

No circularity: experimental observation grounded in data

full rationale

The paper reports direct experimental observations of FQHSs at ν=3/4 and 5/4 via transport measurements in a tunable-density GaAs quantum well. All central claims (evolution with density, two-component character, sensitivity to asymmetry) are tied to measured quantities such as resistance minima and their response to external parameters. The interpretive reference to the Scarola-Jain framework is an external citation, not a self-citation chain or self-definitional reduction. No equations, fitted parameters, or uniqueness theorems are invoked that collapse back to the paper's own inputs by construction. The derivation chain is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The work is experimental with interpretation based on existing theoretical models; no new free parameters or entities introduced in the abstract.

axioms (2)
  • standard math Physics of two-dimensional electron systems in magnetic fields follows Landau level quantization.
    Standard background for quantum Hall effect.
  • domain assumption The Scarola-Jain bilayer composite fermion framework applies to this system.
    Used to explain the states.

pith-pipeline@v0.9.1-grok · 5888 in / 1224 out tokens · 36589 ms · 2026-06-26T06:34:33.620854+00:00 · methodology

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Reference graph

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