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Spatial Rearrangements of Electrons in the 1D to 2D Transition

Spatial Rearrangements of Electrons in the 1D to 2D Transition

When Mar 23, 2018
from 11:30 am to 12:30 pm
Speaker Sanjeev Kumar
Speaker Information London Centre for Nanotechnology, University College London, London WC1H 0AH, United Kingdom
Where 1311 HN
Contact Name Yuhang Ren
Contact Email
Contact Phone 212-772-5258
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An important area of research in mesoscopic physics is the transport properties of one-dimensional (1D) quantum wires. In a 1D quantum wire the conductance takes quantised values in the units of 2e2/h with progressive filling of the sub-bands. However when electron-electron interaction is considered, a number of 1D states are predicted, including a ferromagnetic state and various spin phases, which have aroused considerable interest in the many body effects in quantum wires for spintronics and spin-based logic devices [1-4]. Therefore, a direct measurement of the degree of spin freedom in one-dimension is vital to complement conductance measurements [5].
In this seminar, recent experimental results of a low-density quasi-1D device fabricated using GaAs/AlGaAs heterostructure would be presented. At sufficiently low values of carrier concentration the ground state is no longer represented by a single line of electrons but rather two rows in order to minimise the mutual electron repulsion [2]. At very weak confinement potential the system reverts to a single row and I will discuss the manner in which the formation of this reversion is influenced by the spin-momentum coupling. I will also show how momentum-spin coupling influences the row splitting and the various spin textures. Transconductance results indicate a coupling between the rows and anticrossing, crossing and locking of energy levels can be observed in different regimes of confinement. The most remarkable observation was the interaction combined with weak confinement results in the first excited state becoming the ground state as the two rows are formed, and the ground state moves up and crosses the higher levels. This unexpected manifestation of the electron interaction show the potential of double row or Wigner crystal as a playground for engineering various spin phases.
I will then show results of direct measurement of spin states and signatures of spin repulsion within a 1D system using transverse electron focusing. The electron focusing results show a pronounced splitting of the first focusing peak, where each sub-peak is associated to a spin state. A finite polarization of 20% was recorded when injector conductance was set at the 0.7 structure indicating electrons are spin polarized. It is shown that spin effects can be observed in higher quantum levels and the peak-splitting enhanced by an in-plane magnetic field [5-6].
Finally, I will conclude the presentation by showing results of our recent discovery of fractional quantization in quasi-1D hole quantum wire, where fractional conductance plateaus in units of 2Ne2/h appear at N= 1/2 and N = 1/32 suggesting as if charge was fractionalised [7,8]. Finally before concluding the presentation, I will show very recent results of evidence of fractional quantisation of conductance of 1D electrons [9].

[1]. S. Kumar et al. Phys. Rev. B 90, 201304(R) (2014).
[2]. J. S. Meyer et al., Journal of Physics: Condensed Matter, 21(2), 023203 (2009).
[3]. G. Gumbs, et al. Advances in Physics: X, 2(3), 545-568 (2017).
[4]. B. Antonio et al. Phys. Rev. Lett. 115 216804 (2015).
[5]. C. Yan, S. Kumar et al., Appl. Phys. Lett. 111, 042107 (2017); C. Yan, S. Kumar et al., Journal of Physics: Condensed Matter, 30, 08LT01 (2018).
[6]. C. Yan, S. Kumar et al., Phys. Rev. Lett. (in press 2018).
[7]. Y. Gul, et al. Journal of Physics: Condensed Matter, 30, 09LT01(2018).
[8]. Holes reveal first fractional quantization
[9]. S. Kumar et al. (unpublished).