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Ultra-Clean Mesoscopic Devices in Gr...

Cohen, Liam Augustus,

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Ultra-Clean Mesoscopic Devices in Graphene van der Waals Heterostructures in the Quantum Hall Regime /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Ultra-Clean Mesoscopic Devices in Graphene van der Waals Heterostructures in the Quantum Hall Regime // Liam Augustus Cohen.
Author:	Cohen, Liam Augustus,
Description:	1 electronic resource (172 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-11, Section: B.
Contained By:	Dissertations Abstracts International85-11B.
Subject:	Condensed matter physics. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31140940
ISBN:	9798382342740

Ultra-Clean Mesoscopic Devices in Graphene van der Waals Heterostructures in the Quantum Hall Regime /
Cohen, Liam Augustus,

Ultra-Clean Mesoscopic Devices in Graphene van der Waals Heterostructures in the Quantum Hall Regime /Liam Augustus Cohen. - 1 electronic resource (172 pages)

Source: Dissertations Abstracts International, Volume: 85-11, Section: B.

A successful program for improving the quality of graphene based 2DEGs has been the steady removal of charged impurities near the graphene surface. This was first accomplished by using hBN as a substrate and encapsulant, and then further improved by using atomically uniform graphite as a gate electrode instead of amorphous evaporated metal, resulting in the first all `van der Waals' heterostructure. These improvements lead to the robust observation of even-denominator fractional quantum Hall states in bilayer graphene, as well as many other interesting correlated ground states at zero magnetic field such as superconductivity and ferromagnetism in both twisted and un-twisted graphene multi-layers. Moreover, as many of these states occur at an electron density near charge neutrality, they may be accessed within a single device simply by field-effect gating. However, engineering more complex mesoscopic devices which are designed to interface these exotic phases of electronic matter require fabricating spatially varying potential profiles on the order of the correlation lengths in these systems, typically around 100nm. Additionally, these manufactured potentials need to be energetically uniform, i.e., they must not introduce uncontrolled disorder potentials on the order of the energy gaps of the systems of interest, again typically around 1meV, on the requisite length scales. Here we report on a novel fabrication technique, AFM based local anodic oxidation gate lithography, to pre-pattern graphite gates with critical feature sizes smaller than 100nm which does not introduce any unwanted contaminants or damage to the underlying van der Waals heterostructure. We then use this technique to fabricate two types of mesoscopic devices operated in the fractional quantum Hall regime, a quantum point contact and an edge-state Fabry-Perot interferometer. We show that our quantum point contact nearly perfectly mimics a simple model which characterizes electron tunneling between ν = 1/3 and ν = 1 edge modes at any tunneling strength. This indicates that these junctions are nearly disorder-free validating our novel fabrication technique. Moreover, we use our nearly defect free junctions to create an edge-state Fabry-Perot interferometer operating in ν = 1/3. Here we observe sharp phase jumps in the interference pattern consistent with the expected braiding phase of anyons in the ν = 1/3 state. These results taken together show that our method for fabricating mesoscopic devices within the graphene based van der Waals heterostructure platform, developed over the last four years, makes these devices comparable to the most modern III-V semiconductor quantum wells, which took over 30 years of refinement.

English

ISBN: 9798382342740Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Fractional quantum Hall

Ultra-Clean Mesoscopic Devices in Graphene van der Waals Heterostructures in the Quantum Hall Regime /
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500 $a Advisors: Young, Andrea Committee members: Nayak, Chetan; Wang, Zhenghan; Jin, Chenhao.
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520 $a A successful program for improving the quality of graphene based 2DEGs has been the steady removal of charged impurities near the graphene surface. This was first accomplished by using hBN as a substrate and encapsulant, and then further improved by using atomically uniform graphite as a gate electrode instead of amorphous evaporated metal, resulting in the first all `van der Waals' heterostructure. These improvements lead to the robust observation of even-denominator fractional quantum Hall states in bilayer graphene, as well as many other interesting correlated ground states at zero magnetic field such as superconductivity and ferromagnetism in both twisted and un-twisted graphene multi-layers. Moreover, as many of these states occur at an electron density near charge neutrality, they may be accessed within a single device simply by field-effect gating. However, engineering more complex mesoscopic devices which are designed to interface these exotic phases of electronic matter require fabricating spatially varying potential profiles on the order of the correlation lengths in these systems, typically around 100nm. Additionally, these manufactured potentials need to be energetically uniform, i.e., they must not introduce uncontrolled disorder potentials on the order of the energy gaps of the systems of interest, again typically around 1meV, on the requisite length scales. Here we report on a novel fabrication technique, AFM based local anodic oxidation gate lithography, to pre-pattern graphite gates with critical feature sizes smaller than 100nm which does not introduce any unwanted contaminants or damage to the underlying van der Waals heterostructure. We then use this technique to fabricate two types of mesoscopic devices operated in the fractional quantum Hall regime, a quantum point contact and an edge-state Fabry-Perot interferometer. We show that our quantum point contact nearly perfectly mimics a simple model which characterizes electron tunneling between ν = 1/3 and ν = 1 edge modes at any tunneling strength. This indicates that these junctions are nearly disorder-free validating our novel fabrication technique. Moreover, we use our nearly defect free junctions to create an edge-state Fabry-Perot interferometer operating in ν = 1/3. Here we observe sharp phase jumps in the interference pattern consistent with the expected braiding phase of anyons in the ν = 1/3 state. These results taken together show that our method for fabricating mesoscopic devices within the graphene based van der Waals heterostructure platform, developed over the last four years, makes these devices comparable to the most modern III-V semiconductor quantum wells, which took over 30 years of refinement.
546 $a English
590 $a School code: 0035
650 4 $a Condensed matter physics. $3 3173567
650 4 $a Physics. $3 516296
653 $a Fractional quantum Hall
653 $a Graphene
653 $a Interferometer
653 $a Mesoscopic devices
690 $a 0611
690 $a 0605
710 2 $a University of California, Santa Barbara. $b Physics. $e degree granting institution. $3 3771780
720 1 $a Young, Andrea $e degree supervisor.
773 0 $t Dissertations Abstracts International $g 85-11B.
790 $a 0035
791 $a Ph.D.
792 $a 2024
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31140940