Imaging thermoelectric transport through quantum nanostructures
Mardi 5 mars 2019 14:00
- Duree : 1 heure
Lieu : Salle « Remy Lemaire » (K223) de l’Institut Néel – au n°25 de la rue des martyrs, Grenoble.
Orateur : Boris BRUN (UCLouvain, Belgium)
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Resumé/Abstract :
We developed a new scanning probe technique to image thermoelectric transport in two- dimensional devices : Thermoelectric Scanning Gate Microscopy (TSGM). This technique is derived from Scanning Gate Microscopy (SGM), that consists in mapping changes in a device’s electrical conductance induced by a moving electrostatic perturbation, generated with a biased AFM tip [1]. TSGM consists in recording the devices’ Seebeck coefficient instead of its electrical conductance. To perform this measurement, we heat one side of the device and record the thermoelectric voltage arising across the device in response to this temperature difference. We then scan the electrically biased tip above the surface while recording this signal. We apply this technique to investigate the low density regime of quantum point contacts (QPCs), where strong electron-electron interactions give rise to conductance [2,3] and thermoeletcric [4] anomalies. By scanning the polarized tip in front of the QPC, we create a Fabry-Pérot cavity between the QPC channel and the tip-depleted region [5], which induces interference fringes in both the conductance and the thermopower. Surprisingly, the interference in the thermoelectric signal exhibit an abrupt phase shift by π at very low QPC transmission, which is invisible in the conductance. We propose a model to explain these differences, based on the spontaneous localization of electrons in the QPC channel [6,7]. Our work illustrates that the combination of scanning gate microscopy and thermoelectric measurements can unveil elusive phenomena that escape transport measurements [8].
[1] M.A Topinka et al., Nature, 416, 183-186 (2001).
[2] K.J Thomas, Phys. Rev. Lett. 77, 135 (1996).
[3] S. M. Cronenwett, Phys. Rev. Lett. 88, 226805 (2002).
[4] N. J. Appleyard, Phys. Rev. B 62, 8 R16275 (2000)
[5] B. Brun et al., Phys. Rev. Lett. 116, 136801 (2016).
[6] M. J. Iqbal et al. Nature, 501, 79 (2013)
[7] B. Brun et al., Nat. Com., 5, 4290 (2014)
[8] B. Brun et al., arXiv:1804,00075
Contact : equipe-seminaires-nano@fondation-nanosciences.fr
Discipline évènement : (Physique)
Entité organisatrice : (Fondation Nanosciences)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire Nanoélectronique Quantique)
Site de l'évènement : Polygone scientifique
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