Center for Functional Nanomaterials Seminar

"Scanning probe microscopy of van der Waals heterostructure and magnetotransport in graphene and magic angle twisted bilayer graphene"

Presented by Mrityunjay Pandey, Indian Institute of Science, India

Wednesday, September 14, 2022, 10:45 am — Videoconference / Virtual Event (see link below)

In first part of the presentation, I will talk about Electrostatic force microscopy which has been used as a non-invasive, time and cost efficient method to identify the geometrical extent of the graphene and TMDCs encapsulated by boron nitride. This technique has further exploited to understand the doping and charge transfer in graphene, TMDCs and estimating the electrical barrier height at nano-junctions of different materials.

In second part of the presentation, I will discuss about the magneto transport in graphene under large dc current. We explore the non-equilibrium transport regime in graphene using a large dc current in combination with a perpendicular magnetic field. The strong in-plane Hall field that is generated in the bulk of the graphene channel results in Landau levels that are tilted spatially. The energy of cyclotron orbits in the bulk varies as a function of the spatial position of the guiding center, enabling us to observe a series of compelling features. While Shubnikov-de Haas oscillations are predictably suppressed in the presence of the Hall field, a set of fresh magnetoresistance oscillations emerge near the charge neutrality point as a function of dc current. Two branches of oscillations with linear dispersions are evident as we vary carrier density and dc current, the velocity of which closely resembles the TA and LA phonon modes, suggestive of phonon-assisted intra-Landau level transitions between adjacent cyclotron orbits.

In third and final part I will discuss about the broken symmetry states in magic angle twisted bilayer graphene in proximity to tungsten diselenide. Magic angle twisted bilayer graphene (TBG) has demonstrated exotic phases like correlated insulators, superconductivity, ferromagnetism, nematic phases, and Chern insulators. These phases have been realized at the integer filling of the moiré. Recent experiments have revealed many broken-symmetry phases in TBG and related moiré materials, where the external tuning of several parameters leads to the desired symmetry breaking. For example, C2 inversion symmetry can be broken by aligning the TBG layers with hexagonal boron nitride (hBN), and applying a B field breaks time-reversal symmetry T. However, demonstrating ordered states at fractional moiré band fillings at zero applied magnetic field is more challenging. Here, I will discuss the observation of states near half-integer band fillings 0.5 and ±3.5 at a near-zero magnetic field in TBG proximitized by tungsten diselenide.

Hosted by: Gregory Doerk

Videoconference Instructions

Meeting ID: 161 649 6610 Passcode: 551420

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