Itamar Gurman, Ron Sabo, Moty Heiblum, Vladimir Umansky, Diana Mahalu
Thirty years after the discovery of the celebrated fractional quantum Hall effect (FQHE) there are still open questions regarding electronic characteristics in this regime; one is the formation and nature of the upstream chiral neutral modes. These modes, which usually appear at hole-conjugate states (such as 1/2<{\nu}<1, {\nu} being the filling factor), counter propagate to the direction of the charge modes and carry energy without net current. Following their early predication by Kane et al., they were only recently observed via noise measurements . In this work, performed mainly at {\nu}=2/3, we placed a 'metallic' quantum dot (QD) in the Coulomb blockade (CB) regime a few micrometers upstream a 'hot spot' of a biased ohmic contact. A temperature gradient, which was consequently developed across the dot, led to a fast responding (~1uS) net thermoelectric current in the circuit. Increasing the 2D electron temperature to 100mK quenched strongly the net current, indicating a strong drop of the energy carried by the neutral mode. This method provides a straightforward procedure to detect and study upstream neutral modes without turning to the more complex noise measurements.
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http://arxiv.org/abs/1205.2945
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