Ryota Eguchi’s research while affiliated with Tokyo Institute of Technology and other places

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Publications (3)


(Color online) (a) The schematic device layout and the measurement setup for n (=2) edge channels. The airbridge gate with the central pillar is used to define bound states in n ′ (=2) channels. Tunneling current Ii to the north (i = N), south (S), east (E), and west (W) contact is detected by measuring voltage drop Vi between the nearby voltage terminals. (b) Schematic cross section of the airbridge gate. (c) A scanning electron micrograph of a test device with D = 0.4 μm and ℓ = 0.8 μm.
(Color online) (a) Color-scale plot of VW measured with V ac = 30 μ V and Vdc = 0 as a function of B and V GB in the upper panel, and a single trace taken at V GB = − 0.75 V (along the long dashed line). The number of edge channels, n, in the insulating region (VW ∼ 0 in blue) is shown. The dotted line shows the definition voltage Vdef for electrons underneath the directly metalized gates. (b) Coulomb blockade oscillations of the QAD. Some jumps (marked by thin vertical lines) in the peak positions may be associated with changes in nearby impurity states.
(Color online) (a)–(c) Color-scale plots of VW as a function of B and VGB for (a) n = 1, (b) n = 2, and (c) n = 4. The faint peaks in (c) are marked by the arrows. (d) Coulomb diamonds of the QAD seen in the color-scale plot of ΔVW with linear background subtracted, measured with Vac = 10 μ V at V GB = − 1 V. Extra peaks associated with the excited states are marked by the arrows.
(Color online) (a) Color-scale plot of VN as a function of V GS and VGN at VGB = −400 mV, showing CB oscillations in the presence of a partially depleted region. As depicted in the inset, spin-up electrons are partially depleted with impurity potential, whereas spin-down electrons are fully depleted under the pillar. (b) Color-scale plot of VN as a function of VGB and B with VGN and VGS set at point P in (a). (c) Color-scale plot of VN at VGB = −220 mV. The inset shows a possible multi-dot configuration of partially depleted spin-down regions. (d) Color-scale plot of VN with V GN and VGS set at point Q in (c).
Quantum anti-dot formed with an airbridge gate in the quantum Hall regime
  • Article
  • Publisher preview available

May 2019

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12 Reads

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3 Citations

Ryota Eguchi

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Eiki Kamata

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Chaojing Lin

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Toshimasa Fujisawa

We demonstrate a quantum antidot (QAD) formed with an airbridge gate on an AlGaAs/GaAs heterostructure, where a sub-micron pillar-shaped surface gate is biased via the bridge. We study transport through the QAD in the two regimes; one with a fully depleted region and the other with a partially depleted region at the center of the QAD. While standard Coulomb blockade (CB) oscillations with discrete levels are observed in the fully depleted region, short-period CB oscillations and more complicated patterns with multiple QADs are seen in the partially depleted region. The device is promising for investigating the few-particle regime.

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Charge equilibration in integer and fractional quantum Hall edge channels in a generalized Hall-bar device

May 2019

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26 Reads

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32 Citations

Charge equilibration between quantum Hall edge states can be studied to reveal the geometric structure of edge channels not only in the integer quantum Hall (IQH) regime but also in the fractional quantum Hall (FQH) regime, particularly for hole-conjugate states. Here we report on a systematic study of charge equilibration in both IQH and FQH regimes by using a generalized Hall bar, in which a quantum Hall state is nested in another quantum Hall state with different Landau filling factors. This provides a feasible way to evaluate equilibration in various conditions even in the presence of scattering in the bulk region. The validity of the analysis is tested in the IQH regime by confirming consistency with previous works. In the FQH regime, we find that the equilibration length for counterpropagating δν=1 and δν=−1/3 channels along a hole-conjugate state at Landau filling factor ν=2/3 is much shorter than that for copropagating δν=1 and δν=1/3 channels along a particle state at ν=4/3. The difference can be associated with the distinct geometric structures of the edge channels. Our analysis with generalized Hall-bar devices would be useful in studying edge equilibration and edge structures.


Charge equilibration in integer and fractional quantum Hall edge channels in a generalized Hall-bar device

May 2019

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38 Reads

Charge equilibration between quantum-Hall edge states can be studied to reveal geometric structure of edge channels not only in the integer quantum Hall (IQH) regime but also in the fractional quantum Hall (FQH) regime particularly for hole-conjugate states. Here we report on a systematic study of charge equilibration in both IQH and FQH regimes by using a generalized Hall bar, in which a quantum Hall state is nested in another quantum Hall state with different Landau filling factors. This provides a feasible way to evaluate equilibration in various conditions even in the presence of scattering in the bulk region. The validity of the analysis is tested in the IQH regime by confirming consistency with previous works. In the FQH regime, we find that the equilibration length for counter-propagating δν\delta \nu = 1 and δν\delta \nu = -1/3 channels along a hole-conjugate state at Landau filling factor ν\nu = 2/3 is much shorter than that for co-propagating δν\delta \nu = 1 and δν\delta \nu = 1/3 channels along a particle state at ν\nu = 4/3. The difference can be associated to the distinct geometric structures of the edge channels. Our analysis with generalized Hall bar devices would be useful in studying edge equilibration and edge structures.

Citations (2)


... The experimental progress in the field of hybrid mesoscale systems based on chiral quantum Hall (QH) edge states has triggered renewed interest in the phenomena of phase coherence [1][2][3][4], charge and heat quantization [5][6][7][8][9][10][11], relaxation and equilibration [12][13][14][15][16][17][18][19], and entanglement [20][21][22][23], which are related to the fundamental problems of mesoscopic physics. In QH systems these phenomena are often observed by injecting electrons into a QH edge state using a quantum point contact (QPC) [24,25], quantum dot (QD) [26], or a mesoscopic Ohmic contact (a metallic reservoir of finite charge capacitance) [8,11] [see Fig. 1(a)] and detecting the charge current, heat current, current noise, or an electron distribution function [24,25] downstream of the injection point. ...

Reference:

Charge-conserving equilibration of quantum Hall edge states
Charge equilibration in integer and fractional quantum Hall edge channels in a generalized Hall-bar device
  • Citing Article
  • May 2019

... Our sample was fabricated in a standard Al-GaAs/GaAs heterostructure with two-dimensional electron gas located at 100 nm below the surface. With an electron density of ∼ 2.75 × 10 15 m −2 , a QH state at ν B = 2 can be prepared by applying perpendicular magnetic field B ≃ 5 T. Two airbridge gates with Ti (thickness of 30 nm) and Au (270 nm) layers were fabricated by using electron-beam lithography with a triple layer resist 24,25 . Each gate has a small pillar of diameter D = 300 nm and is connected to the lead electrode through the bridge of length L = 3 µm, width W = 300 nm, and bridge height h = 150 nm, as shown in Fig. 2(a). ...

Quantum anti-dot formed with an airbridge gate in the quantum Hall regime