We propose a practical, all-electrical setup to generate valley polarization in graphene using only conventional metal contacts. Our approach exploits transverse momentum matching between graphene and metallic electrodes to selectively inject electrons into specific valleys of graphene’s band structure. The configuration involves a graphene sheet connected to four metallic terminals—two on each side—with a bias applied at one terminal while the other three are grounded, enabling directional injection of electrons. We identify the key geometric and electronic conditions that enable high valley polarization and demonstrate its robustness against disorder, interface roughness, and edge imperfections. The mechanism relies on a minimal, physically meaningful model that captures the essential features of metal–graphene junctions. This work paves the way for valley-based information encoding and control in graphene, offering a promising direction for low-power, quantum-capable nanoelectronic devices.

Link to the paper: https://doi.org/10.1103/x8yx-vwng 

Our research explores a new way to enhance a quantum phenomenon known as crossed Andreev reflection (CAR) using a class of newly discovered magnetic materials called altermagnets. CAR is important because it can help develop advanced quantum devices by splitting electron pairs, known as Cooper pairs, from superconductors, which are materials that conduct electricity without resistance.  In traditional setups using ferromagnets, external magnetic fields are needed to enhance CAR, which can complicate device design due to undesired effects of applied fields. However, altermagnets do not require such fields, making them more practical. We discovered that by orienting two altermagnets at specific angles relative to each other, CAR can be significantly increased, even completely dominating other competing processes under the right conditions. This finding has the potential to improve the efficiency and versatility of quantum computing components and other superconducting technologies.

Link to the paper: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.109.245424

Talk delivered at ICTS-TIFR in a conference

Talk delivered at ICTS-TIFR in a conference

We propose a multiterminal Josephson junction enabling simultaneous measurement of transverse and longitudinal Josephson currents under a phase bias. The system features a central spin–orbit coupled (SOC) region with an in-plane Zeeman field, connected to four superconducting terminals and modelled using a tight-binding approach on a square lattice. Due to momentum symmetry breaking in the SOC region, the system exhibits both the anomalous Josephson effect (AJE) and the Josephson diode effect (JDE): breaking the symmetry between momentum modes in longitudinal direction induces AJE and JDE in the longitudinal Josephson current, while breaking symmetry between momentum modes in transverse direction generates a finite transverse Josephson current which exhibits diode effect. Remarkably, the transverse diode coefficient can reach up to 500%, and for a certain choice of parameters, the transverse Josephson current becomes unidirectional, demonstrating significant potential for superconducting device applications.
Link to paper: https://doi.org/10.1088/1361-648X/adf1d0