Quasiparticle tunneling in the lowest Landau level

Abstract

We measure quasiparticle tunneling across a constriction in the first Landau level. In the limit of weak backscattering, the dependence of the tunneling conductance on temperature and dc-bias is in qualitative disagreement with existing theories. For stronger backscattering, data obtained in the ν = 1/3 state can be fitted to weak backscattering theory with the predicted effective fractional charge of e * = e/3. The scaling parameter g is however not universal and depends strongly on the gate voltage applied to the constriction. At ν = 4/3, a more complex picture emerges. We propose an interpretation in terms of selective tunneling between the multiple modes present at the edge.

Quasiparticle Tunneling across an Exciton Condensate

“…A deep minimum around zero bias is observed when V g is set to 0.9 and 0.95 V. The tunnel conductance suddenly transforms into a peak at V g ¼ 1 V. The background conductance g ∞ , which serves as a measure of the transmission through the QPC, stays almost the same across this gate voltage interval. This is very different from previous experiments [37,47] showing dip-to-peak transitions. We assign this observed behaviour to a crossover from the breakdown of the quantum Hall effect to interedge tunneling.…”

“…[38,[40][41][42] and for ν ¼ 1=3 from Ref. [37] are also shown. The error bar for one of the ν ¼ 5=2 data points stems from a variation of the confinement while fixing e à =e ¼ 1=4 during fitting [42].…”

“…With the advent of lowdensity (< 2 × 10 10 cm −2 ) GaAs bilayer samples with high quality (μ ≥ 1 × 10 6 cm 2 =V s), it has become possible to enter the ν tot ¼ 1 state by only tuning a back gate [36], leaving the top surface available to deploy the split gate technique for edge manipulation. The latter has been widely used to address interedge tunneling for instance in single layer electron systems at fractional filling factors with both odd [37] and even [38][39][40][41][42] denominators. These studies extracted effective charges that are overall close to the theoretical expectations, although the extracted Coulomb interaction strength may be influenced by the device geometry [43].…”

“…The peak feature depends sensitively on the magnetic field and appears only around ν tot ¼ 1 [45]. The dip at ν tot ¼ 4=3 may stem from weaker interedge coupling [37]. Figure 1(d) addresses the temperature dependence of the peak at ν tot ¼ 1.…”

“…We also note that the influence from the neighboring FQHS should be minimal in the balanced situation as the individual layer is at ν ¼ 1=2. Figure 4 also includes previous experimental results gathered on single layer systems at ν ¼ 5=2 [38,[40][41][42] and ν ¼ 1=3 [37] with the same approach. Analogously, for those works the extracted g spans a wide range of values and exhibits a strong dependence on the transmission through the QPC [37,41,42], possibly via the device geometry effect [43].…”