In-operando Angle-Resolved Photoemission Spectroscopy (ARPES) with Spatially High Resolution

Our group utilizes ARPES with focused spot size to directly probe the energy-momentum information of mesoscopic sized high-quality single-layer exfoliated 2D materials, their heterostructures, and devices. We have an approved program (AP) to probe the electronic band structure of 2D based devices using state-of-the-art in-operando nanoARPES (with spatial resolution reaching 120 nm) at the MAESTRO beamline at Advanced Light Source (ALS), Berkeley. With the advent of nano-ARPES, the exploration of exotic physical phenomena in the vast library of emerging 2D materials, van der Waals heterostructures, and devices is just the beginning!

X-ray Magnetic Circular & Linear Dichroism (XMCD & XMLD)

The Katoch–Singh research groups collaborate to utilize state-of-the-art X-ray scattering techniques — specifically photoemission electron microscopy (PEEM) paired with XMCD and XMLD capabilities — to obtain a spatially resolved view of the underlying mechanisms of intriguing magnetic behavior in novel quantum materials.

We are especially interested in studying the thickness- and twist-angle-dependent magnetic behavior in 2D magnets and their heterostructures. This joint experimental platform connects the electronic structure expertise of the Katoch group with the spin and magnetism focus of the Singh group to reveal how magnetic order emerges and can be controlled at the atomic scale.

Synthesis of Topological Materials — Molecular Beam Epitaxy

There is an increasing demand for synthesis of high-quality novel quantum materials with exotic properties. MBE is an excellent technique to grow crystalline thin films by deposition of atoms or molecules layer-by-layer onto a substrate. Advantages include better control of doping, uniformity of epitaxial film thickness, and sharp crystalline interfaces in heterostructures.

Our focus is to grow a variety of materials including: 2D Si/Ge/Sn graphene analogues; topological Dirac 3D semimetals; complex oxide thin films & hetero-interfaces; and magnetic thin films (in collaboration with the Singh group). Some of these materials are predicted to exhibit exotic topological phases, such as near-room-temperature quantum anomalous Hall effect and topological superconductivity. We also tune band gap and spin-orbit coupling by surface functionalization and alloying.

van der Waals Heterostructures and Interfaces

The mechanical assembly of extremely clean interfaces of arbitrary atomically thin sheets of vdW materials provides unprecedented flexibility to control physical properties, modify spin-orbit coupling and band structures, and induce magnetic and topological correlations by proximity effects at the atomic limit.

We use the vdW-based transfer technique in a controlled environment to assemble 2D/2D, 2D/3D, and 2D/1D cross-dimensional heterostructures to study electronic, spin, and optical properties. We are also developing a transfer tool to assemble heterostructures in ultra-high vacuum to fully exploit the intrinsic phenomena at atomically clean interfaces.

In-operando Tuning of Material Properties

Being atomically thin, the effects of surface adsorption, electrostatic gating, Coulomb interactions, strain, and proximity-induced phenomena are more pronounced in 2D materials than in 3D counterparts. However, the "all-surface" nature of 2D materials also makes them extremely sensitive to their environment, which can be detrimental to their intrinsic ground-state properties.

Our research addresses two fundamental questions: (1) What effects do external perturbations — mechanical stress, chemical environment, electrostatic interactions — have on the electronic, optical, valley, and spin-related properties of 2D materials? (2) How can surface modification and substrate engineering be used to alter physical properties? We utilize in-situ magneto-transport and optical measurements to study quantum phenomena in mesoscopic 2D devices while doping with adatoms.