Research Projects

Combining disparate physical phenomena within a single material is a potent strategy for developing functional materials to enable new technologies. For example, the co-existence and coupling of ferroelectricity and magnetism in multiferroic materials, despite their individual preferences for empty versus partially filled d shells, holds the promise of electric-field controlled magnetization switching. Similarly, materials combining high electrical conductivity with low thermal conductivity are crucial for developing efficient thermoelectric energy conversion devices. Another intriguing example is polar metals, characterized by broken inversion symmetry and a well-defined Fermi surface. The very existence of a polar metallic phase fundamentally contradicts the classical electrodynamic principle of Gauss's Law, which mandates a zero net electric field within a metal. While free electrons are expected to screen internal dipoles, Anderson and Blount in 1965 theoretically predicted the possibility of a polar metal phase. They proposed that a weak interaction between itinerant electrons and transverse optical (TO) phonons, which drive the polar distortion, could stabilize such a phase. Given the profound implications of polar metals across various fields, including topology, superconductivity, spintronics, and magnetoelectricity, their realization in engineered materials has garnered significant research interest in recent years, especially since only a few intrinsic polar metals [LiOsO3, WTe2, Ca3Ru2O7, Ca3Co3O8] have been discovered to date. Since perovskite oxides (ABO3) exhibit a plethora of collective electronic and magnetic phenomena and they can be also combined to form heterostructures, significant effort has been dedicated over the last decade to stabilize a polar metal phase in these materials. Two main routes for realizing artificial polar metals: doping a ferrolectric material to introduce itinerant carriers or stabilizing polar distortions within a metal through interface engineering. However, the existing perovskite oxide systems that demonstrate a polar metal phase lack simultaneous tunability of carrier concentration and polarity, demanding alternative design principles and new materials platforms. Another long-standing issue for both fundamental research and potential applications (e.g., in nanoscale electronic and thermoelectric devices ) concerns the ability to control polarity via an appropriate external field. While an applied electric field is the most apparent method for switching polarity in ferroelectrics, it's often ineffective due to the presence of free carriers in the bulk. Recent theoretical studies suggest flexoelectricity could provide a solution, which is yet to be experimentally demonstrated. Another proposition is changing the spin structure by magnetic field in spin-spiral driven polar metal. This project focuses on demonstrating a tunable, switchable polar metal phase. This will be achieved through a tightly integrated approach encompassing computational material prediction, pulsed laser deposition for material growth, and characterization of polar behavior using several complementary techniques. Our investigation will explore two distinct material platforms: incipient ferroelectrics and high-entropy oxides. The experimental realization of polar metals has unlocked the potential to explore numerous exotic quantum phenomena, including the Rashba interaction and its spintronic applications, the nonlinear Hall effect, the kinetic magnetoelectric effect, and ferroelectric superconductivity, all of which will be thoroughly investigated. In the project's final phase, one major goal will be to demonstrate room-temperature switchability, which will be the foundation for the second stage of this project [4th-5th year].