Seminar Series on Quantum Materials
Talk 1: Creating and Measuring Useful Defects in 2D Materials
by Asst. Prof. Akshay Singh from Indian Institute of Science
Abstract:
Two-dimensional (2D) materials are next-generation materials relevant for optoelectronics, electronics, and quantum technologies. I will first present a broad overview of why 2D materials are fascinating for both fundamental physics and emerging technologies.
I will present our group’s work on uncovering an ultralow energy regime of electron-matter interactions, which is used for creation of single photon emitters (SPEs) in monolayer MoS2. Then, I will present our group’s work on SPEs in WSe2 created via AFM nanoindentation on rigid substrates, where we take a deep dive into tunability of SPE dynamics via electrical gating. If time permits, I will present our group’s progress in creating air- and light-sensitive 2D magnetic materials, solving a long-standing problem in the 2D magnetic materials field.
About the Speaker:
Akshay Singh (AS) is an Assistant Professor at the Department of Physics at Indian Institute of Science (IISc), Bengaluru, and Associate of Indian Academy of Sciences, Bengaluru. He received his undergraduate degree in Engineering Physics (2010) from Indian Institute of Technology, Delhi. He pursued his PhD in physics (2016) from University of Texas at Austin, followed by a postdoc in material science at Massachusetts Institute of Technology, Cambridge. He was an Infosys Young Investigator (2022-2023), and a PECFAR fellow (DST-DFG). AS has set up a cutting-edge optical spectroscopy and material science lab (OUSUMS lab) at IISc. His research explores the synergy between measuring novel physical phenomena and fundamental properties of materials, and synthesizing new materials. AS research is applicable to new high-performance electronics, optical materials, as well as next-generation quantum technologies.
Talk 2: Deterministic Synthesis of High-quality 2D Semiconductors: Controlling Defects, Dopants, and Polytype
by Asst. Prof. Andrew J Mannix from Stanford University
Abstract:
Realizing the full potential of 2D transition metal dichalcogenides (TMDs) in electronic, photonic, and quantum devices requires the growth of films with crystalline quality and defect densities approaching those of mechanically exfoliated flakes. This talk presents a set of synthesis strategies based on deliberate precursor and reactor engineering that improve crystalline quality while enabling systematic control of composition, doping, polytype, and optical response beyond what is accessible through exfoliation alone. For solid-source chemical vapor deposition (CVD) growth of WSe2, oxyselenide contamination drives parasitic nucleation and elevates charged defect densities. A targeted pre-annealing protocol removes these phases and produces a chemically uniform, kinetically favorable precursor. The resulting monolayers exhibit grain sizes of 10 to 30 µm and charged defect densities below 1010 cm-2 (measured via conductive AFM), enabling p-type transistors with on-state currents up to 888 µA/µm. For wafer-scale synthesis and additional chemical tuning, we employ metal-organic CVD (MOCVD). Using MOCVD with solution-processed transition-metal salt precursors, we demonstrate growth of WS2 with repeatable substitutional doping, alloy composition, and polytype, including selective formation of the ferroelectric multilayer 3R phase with nonlinear optical response and excitonic valley physics. Diffusion from locally patterned dopant sources enables control over substitutional doping, resulting in programmed lateral carrier density profiles. These results expand the toolset of materials engineering beyond the capabilities of mechanical exfoliation and open new opportunities for optoelectronic engineering.
About the Speaker:
Andrew (Andy) Mannix is an Assistant Professor of Materials Science and Engineering (MSE) at Stanford University. He earned his B.S. in MSE from the University of Illinois at Urbana-Champaign and his Ph.D. in MSE from Northwestern University as an NSF GRFP Fellow, where he pioneered the growth and atomic-scale characterization of new 2D materials, including borophene. During his postdoctoral fellowship at the University of Chicago, he developed methods for robotic in-vacuum heterostructure assembly. At Stanford, his lab advances the growth, assembly, and atomic-scale control of 2D materials for electronic, optoelectronic, and quantum applications. Andy is a recipient of the US Office of Naval Research’s Young Investigator Award and the US National Science Foundation CAREER Award.
Talk 3: Emerging 2D Lateral Heterostructures for Reconfigurable Quantum Devices
by Asst. Prof. Prasana Kumar Sahoo from Indian Institute of Technology Kharagpur
Abstract:
Two-dimensional (2D) transition metal dichalcogenides (TMDs) have enabled the exploration of exotic quantum phenomena with promising applications. Considerable efforts have been devoted to the van der Waals vertical heterointegration of different 2D layered materials. On the other hand, 2D lateral heterostructures (LHS) offer a unique solid-state platform for engineering the confinement and transport of carriers and excitons across 1D junctions.
We have developed a novel approach for directly fabricating seamless TMD lateral heterostructures (LHS) and superlattices with controlled 1D interfaces, alloying, and spatial modulation using CVD. Electrical transport measurements reveal formation of direct P-N junctions with diode-like rectification and gate-tunable electroluminescence. Temperature-dependent photoluminescence reveals exciton, trion, and quantum emitter dynamics governed by defects and interfacial charge modulation. We further demonstrate multimodal excitonic transistor behavior in bilayer LHS FETs, enabling reconfigurable trion-to-exciton conversion. By tuning bias and excitation energy, we access a regime of polarity-reversible photoconductivity, making these devices ideal for multifunctional optoelectronic systems. Recent moiré-engineering efforts through vertical stacking of LHS (MoS₂–WS₂ and MoSe₂–WSe₂) have unlocked quadruple moiré pockets with twist-angle (θ) control from 0° to 60°, allowing programmable modulation of excitons and phonons. Our findings showcase the promises of 2D LHS as a platform for realizing 1D quantum systems, tunable spectral photodetection, exciton-based logic, and on-chip quantum photonic circuits.
About the Speaker:
Dr. Sahoo is an Assistant Professor at the IIT Kharagpur, where he leads the Quantum Materials and Device Research Laboratory (QMDrL); https://qmdrliitkgp.wixsite.com/qmdrl. His research focuses on 2D quantum materials, van der Waals heterostructures, excitons, and next-generation optoelectronic and quantum devices. He received his PhD in Physics from IGCAR, Homi Bhabha National Institute (HBNI)- a grant-in-aid institute of the Department of Atomic Energy, Govt. of India, India, with a Gold Medal for Outstanding Thesis. He has held research positions at the University of Cambridge (UK), the University of South Florida (USA), and the University of Campinas (Brazil), and has served as a Visiting Professor at EPFL, Switzerland. He has published in leading journals including Nature, Advanced Materials, ACS Nano, and Nano Letters. He currently leads several major projects under India’s National Quantum Mission and DST Nano Mission. His work bridges fundamental science and technology development in quantum and optoelectronic materials.
Talk 4: Probing Atomic Defects in 2D Semiconductors with Light-Coupled STM
by Dr. Laric Bobzien from Empa, Swiss Federal Laboratories for Materials Science and Technology
Abstract:
Two-dimensional (2D) semiconductors offer a powerful platform for engineering atomic quantum systems within a robust, highly tunable solid-state environment. In this talk, we explore the intriguing physics of single point defects in transition metal dichalcogenide (TMD) monolayers using atomically resolved scanning probe microscopy coupled with ultrafast THz pulses.
We demonstrate electrically induced exciton emission from both pristine MoS₂ and individual charged defects using scanning tunnelling microscope luminescence (STML) on ultrathin hBN decoupling layers. Furthermore, I will present our recent advances in time-resolved THz-STM, enabling the investigation of charge and exciton dynamics with atomic spatial, millielectronvolt energy, and picosecond temporal resolution. Together, these results establish a direct correlation between atomic structure, localized electronic states, and dynamic optical responses, providing fundamental design principles for the deterministic engineering of solid-state quantum emitters.
About the Speaker:
Laric Bobzien obtained his PhD in physics from ETH Zürich and the Swiss Federal Laboratories for Materials Science and Technology (Empa) in 2026. His doctoral research specialized in ultrafast scanning tunneling mi-croscopy (THz-STM) and the characterization of single atomic defects in 2D materials. Born in Germany, Laric completed his physics studies at RWTH Aachen University, focusing on condensed matter physics, infrared nano-optics, and metasurfaces. Following a joint project with IBM Research Europe - Zürich on the nanoscale manipulation of phase-change materials, he bridged his expertise in materials science and nano-optics to de-velop techniques for investigating matter at the atomic scale.