Current Projects
Currently I am working on correlations between magnetic systems and Superconductivity. I take superconductivity for granted (somebody has to!), trying to figure out if we can use the superconducting order parameter to manipulate magnetic domain walls and other magnetic solitons. Check our latest work on Majorana modes here!!! I am always open to collaborations so if anything on this page seems to your fancy, do drop a mail!
Magnetic systems:
The mysterious Hall: In this multi everything (author, teams, unis) collaboration we show that the order parameter controlling the Anomalous Hall Effect in Mn3X is independent of the magnetization. We control this order parameter through strains and switch the Hall effect using very modest strains. The details are in Nat Phys, the gloss was covered in a Phys Org article. I worked out some more details and how to do this switching with no external magnetic fields in a separate artice in Phys. Rev. B.
Ground state of Mn3Sn: This project was done in collaboration with the neutron scattering group of Collin Broholm. On the theory end, we constructed a field theory for the spin wave modes for the stacked kagome systems. This was then matched with data from inelastic neutron scattering to determine the exchange constants and anisotropy coefficients. The paper was chosen to be an Editor's Suggestions at PRB.
Quantum statistics in the XY ferromagnet: This was a yearlong effort to understand the nature of the XY ferromagnet field theory. It is well known that a dual map exists between this system and electrostatics. The spin waves play the role of the photon, and the vortices act as charges. This fact was used in the Nobel(y) famous work of Kosterlitz. We take this theory and extend it to electrodynamics in 2+1 d. One of the crucial points that emerged was that because of their cores, at which point spins have to leave the xy plane, magnetic vortices are charge-flux composites. Such objects have non-traditional quantum statistics.
Ordering in tripod Kagome (order fragmentation): The standard lore with antiferromagnetic interactions on a pyrochlore lattice is that it orders into an all-in-all-out state (AIAO). Then there are cases where the spins are rotated such that only a part of the spin length participates in the AIAO behaviour, while the other bit exists in a state of disorder. This weird admixture leads to a neutron scattering signature of a diffuse background (Coulomb Spin Liquid?) with distinct Bragg peaks. We (with Collin and Allen Scheie) studied one of these compounds: Nd3Sb3Mg2O14 . Unfortuantely for us, it seems that even though there might be a disordered state, it is gapped and not the photon we are looking for.
Spintronics (micromagnetism)
Creating a Zeeman term for the Neel field using DMI: This was a nice collaborative project with Ji Zou from UCLA. Here we explored what combinations of perturbations could give rise to a Zeeman like coupling for the Neel field. This allows us to drive Neel solitons directly.
Theory of the triangular symmetric antiferromagnet: This was my magnum opus for the Ph.D. We characterised the field theory for a three sub lattice antiferromagnet. This work has garnered some attention, including the portentiously viral PRB hashtag of #PRBtopdownloads. The theory has some fairly non-trivial implications for kagome systems like Mn3X, where we can use the magnetic order parameter to leverage conduction band electron effects.
Energy-momentum tensor in micromagnetics: We took a lens to the Noether currents that rise from spin conservation in the ferromagnetic Lagrangian. The naive formulations are gauge dependent. These we modified through the introduction of an integration dimension. In this schematic, the kinetic term of the Lagrangian is a Wess-Zumino connection.
Gauge fields and forces in antiferromagnet solitons: Here we investigate how to induce gauge fields in antiferromagnets. In particular, we devise a way of generating a Magnus for antiferromagnetic vortices. This was till now firmly in the realm of ferro and ferrimagnets.
Quantum Dynamics
Trapping a Majorna with a magnetic vortex: In this I teamed up with Marcel and Vedangi to design an effective system for generating, and stabilising a Majorna Zero mode at the core of trivial superconducting vortex (s-wave). The technique used to break the time reversal symmetry necessary for the process is unique, we use an emergent gauge field created from magnetization of an underlying magnetic vortex. This is not a Zeeman field as usual but maps to one with a radial dependence.
Tuning Hall without a magnetic field: In this collaboration with Oleg Tretiakov from UNSW we investigated the response of the Mn3X system to spin transfer torques. We show how one can combine strain and spin torques to completely switch the Hall signal with no external magnetic field. This is crucial for device engineering. In addition, to aid our colleagues in optics, we analyzed the system under oscillating magnetic fields, detailing how strain can be used to tune these oscillations.
Parity anomaly search in topological insulators: This was done in collaboration with the Hopkins ThZ group led by Peter Armitage. We show that a robust magneto-electric effect exists in the 3D Topological Insulator at very low carrier densities. The switching of the Faraday angle, with doping across the half filling point, signals a Parity Anomaly for the TI surface state. This work got a nod for the Editor's Suggestions as a PRB Letter.
The pulsed Kitaev model (hexagonal): We coupled the hexagonal model to a drive through a magneto-electric term. The driving protocol then allows us to interpolate between the gapped topological and the gapless states of the Kitaev model.
The pulsed Dicke model: We take our driving enthusiasm and protocols to one of the most popular models of Quantum Optics. We dynamically control the entry into the super-radiant phase. Our protocol, a square wave drive, also fragments the energy space. This indicates the creation of metastable regions intermediate to the super-radiant minima.
Loschmidt echo as a probe of quantum chaos in the Dicke model: We used a ground state overlap operator (the Loschmidt echo) as a probe of the onset of quantum chaos in the Dicke model. This incidentally is my first publication !