Topological aspects of the electron wave function—including the Berry curvature and Chern number—play a crucial role in determining the physical properties of materials. In this regard, moire materials has emerged as a promising platform to gain electrical control over the Berry curvature hotspots and the valley Chern numbers of topological flat band. In addition, strain-induced breaking of the threefold rotation symmetry leads to a non-zero first moment of Berry curvature.  We showed that using non-linear Hall effect one can probe the Berry curvature dipole. Sign change in the Berry curvature dipole detects topological transitions in the bands of moire matter. 

see Nature Physics 18, 765 (2022)  Nature Communications 13, 7781 (2022)  Nature Communications, 11, 5548 (2020) Nature Reviews Materials  9, 481 (2024).  Advanced Materials (2025)

Josephson junctions (JJs) and their tunable properties, including their nonlinearities, play an important role in superconducting qubits and amplifiers. JJs together with the circuit quantum electrodynamics architecture form many key components of quantum information processing. In quantum circuits, low-noise amplification of feeble microwave signals is essential, and Josephson parametric amplifiers (JPAs) are the widely used devices. We implemented a quantum-noise-limited JPA using a graphene JJ, that has a linear resonance gate tunability of 3.5 GHz. We observe 24 dB amplification with 10 MHz bandwidth and −130 dBm saturation power, a performance on par with the best single-junction JPAs. Importantly, our gate-tunable JPA works in the quantum-limited noise regime, which makes it an attractive option for highly sensitive signal processing.

see Nature Nanotechnology 17, 1147–1152 (2022). 

Many superconducting systems with broken time-reversal and inversion symmetry show a superconducting diode effect, a non-reciprocal phenomenon analogous to semiconducting p–n-junction diodes. While the superconducting diode effect lays the foundation for realizing ultralow dissipative circuits, Josephson-phenomena-based diode effect (JDE) can enable new quantum circuits. We demonstrated Josephson diode effect persisting up to 77 K using an artificial Josephson junction of twisted layers of Bi2Sr2CaCu2O8+δ. JDE manifests as an asymmetry in the magnitude and distributions of switching currents, attaining the maximum at 45° twist.

see Nature Materials 23, 612 (2024) .  

In the last decade, graphene, a two dimensional sheet of carbons atoms, has received a lot of attention from condensed matter experimentalists as well as theorists. Due to its unique characteristics it is now possible to study, using graphene based experiments, phenomenon that existed only as theoretical concepts. 

In presence of the magnetic field, its unique band structure gives rise to anomalous quantum Hall effect, unique to monolayer.  The role of electronic interactions and topological aspects of bands  can be studied in few layer graphene and twisted bilayers -- this is an aspect that we are focusing on now.

In addition to graphene we have studied spin-orbit interaction in InAs nanowires and other nano-structures.  We demonstrated the use of a series of electrostatic gates to realize 1D tunable superlattice in graphene. 

see  Nano Letters, 13, 3990 (2013).