Dr. Mohammed Ali Aamir
Research student
I am an experimental physicist. My research focusses on electronic transport in mesoscopic devices. These are micron-scale structures defined on a semiconductor platform which, in my case, are GaAs/AlGaAs heterostructure or bilayer graphene. In my pursuit, I have become well versed with fabrication, measurements, data acquisition and analysis. I design and fabricate most of these devices myself, starting from base materials to several processes such as electron beam lithography, etching recipes, and metallization, all the way to device packaging. One of my distinguished experience in fabrication is in the assembly of heterostructures of 2D crystals, such as graphene, boron nitride and transition metal dichalcogenides.
My experiments on these devices are mainly in two low temperature set-ups that I operate, dilution refrigerator and He3 cryostat which can cool my devices down to 20 mK and 265 mK respectively. The experiments involve sensitive measurements of electrical signals in the nano-amperes and micro-volts range, which require careful optimizations with measuring instruments. My thesis work has been mainly to study the low carrier density regime in these devices. A significant aspect of my investigations have been to study the intrinsic electrical noise in the system (that’s why the sensitivity of measurements are important) and extract information about the nature of electronic transport.
Dissertation – Impact of disorder and topology in two dimensional systems at low carrier densities
Personal webpage
Tel: +91 (0)80 2293 2726
Email: mdaliaamir@gmail.com
My device gallery
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My research gallery
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My research
GaAs/AlGaAs heterostructures
A two-dimensional electron system (2DES) formed in a GaAs/AlGaAs heterostructure offers an avenue to build a variety of mesoscopic devices, much of which is achieved by the capability to construct complex potential landscapes using surface gates. Trapping charge carriers in low densities on them gives the prospects for a broad range of phenomena to emerge. This was the central idea behind my studies in these systems.
Linear magnetoresistance in two-dimensional electron systems
- Linear magnetoresistance in strongly inhmogeneous regime
- Colossal magnitude of about 10,000% by 8 T
- Mobility dependent but temperature independent
- Classical phenomenon
Quantum dot lattice in two-dimensional electron systems
- Periodic potential form both antidot lattice and quantum dot lattice
- Quantum dot lattice with electrostatically tunable energy scales
- Non-equilibrium transport reveals its formation
- Can be used to simulate solid-state systems artificially
Bilayer graphene
Bilayer graphene (BLG), made of two layers of graphene sheets in Bernal stacking, is fundamentally different from an individual graphene layer. The most striking property is that a tunable band gap can be induced in BLG by applying an electric field perpendicular to its plane. As a result, BLG can be electrically driven from a metallic state, with high carrier mobility, to a strongly insulating state, thus being suitable for a diverse range of novel device applications. However, experiments revealed that a significant density of states exist inside the band gap, which leads to new transport mechanisms. My goal has been to understand its true nature by examining noise in the form of flicker noise and mesoscopic conductance fluctuations when it is strongly gapped.
Percolative and edge transport in gapped bilayer graphene
- Random potential fluctuations enable percolative paths in gapped bilayer graphene
- Observable by both standard electrical and flicker noise measurements
- Possible evidence for edge transport
Publications are in preparation.
Mesoscopic conductance statistics in gapped bilayer graphene
- Mesoscopic conductance fluctuations in gapped bilayer graphene
- Anomalous increase in conductance variance near metal-insulator transition
- Exploration of the scaling theory of localization in strongly gapped regime
- Observation of log-normal spectrum of conductance in strong disorder
Publications are in preparation.
