1 / 21

210 likes | 418 Vues

Effect of density gradients on magnetotransport of quantum Hall systems. L. Ponomarenko. Participants:. Anne de Visser and Dennis de Lang A. Pruisken (ITF, UvA) G. Galeev (IRE, Moscow) H. Kunzel (HHIN, Berlin). Outline:. Introduction Quantum Hall Effect Quantum Critical Point

Télécharger la présentation
## Effect of density gradients on magnetotransport of quantum Hall systems

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**Effect of density gradients on magnetotransport of quantum**Hall systems L. Ponomarenko**Participants:**• Anne de Visser and Dennis de Lang • A. Pruisken (ITF, UvA) • G. Galeev (IRE, Moscow) • H. Kunzel (HHIN, Berlin)**Outline:**• Introduction • Quantum Hall Effect • Quantum Critical Point • Motivation • Results • Experiment • Explanation • Outlook**Introduction**• Two-dimensional electron gas (2DEG) • applications: • high frequency devices • fundamental research: • Quantum Hall Effect • Weak localization problem**Vxy**Vxx Quantum Hall Effect**B 0**Band Structure B = 0**Effect of Disorder (T = 0)**• Order • Disorder Filling factor:**Quantum Phase Transition**• Takes place at T = 0 • Critical behavior • Localization length • For non-interacting electrons**Criticality**• InGaAs/InP (H.P.Wei et al., PRL, 1988) • half width of rxx scales as • maximum slope of rxy scales as • = 0.42 • Localization length exponent and critical exponent :**However…**• AlGaAs/GaAs • S.Koch et al. (PRB, 1991): ranges from 0.36 to 0.81 • H.P.Wei et al. (PRB, 1992): scaling only below 0.2 K • Semicircle relation**Introduction (Summary):**• Transition between two plateaus is a quantum phase transition • Critical exponent is not universal • Experimental data do not obey “semicircle” law**Different contacts and field polarity**• Antisymmetry:**Vxy**Vxy Hall Resistance • Same for both field polarities, but PP transitions on different contacts take place at different fields**How to obtain correct data?**• Illumination • Averaging data from different contacts and for both field polarities Gradient is 0.25 %**Recovered semicircle**• By proper averaging a “semicircle” behavior can be obtained from slightly inhomogeneous sample**Summary**• Antisymmetry effect • Explained by density gradient • Criterion for sample selection and reliable temperature range • Semicircle recovered**Outlook**• Reliable scaling experiment on plateau-plateau transition • Plateau-insulator transition

More Related