Strain Tuning Three-state Potts Nematicity in a Correlated Antiferromagnet

Electronic nematicity, a state in which rotational symmetry is spontaneously broken, has become a familiar characteristic of many strongly correlated materials. One widely studied example is the discovered Ising-nematicity and its interplay with superconductivity in tetragonal iron pnictides. Since nematic directors in crystalline solids are restricted by the underlying crystal symmetry, recently identified quantum material systems with three-fold rotational (C3) symmetry offer a new platform to investigate nematic order with three-state Potts character. Here, we report reversible strain tuning of the three-state Potts nematicity in a zigzag antiferromagnetic insulator, FePSe3. Probing the nematicity via optical linear dichroism, we demonstrate either 2{\pi}/3 or {\pi}/2 rotation of nematic director by uniaxial strain. The nature of the nematic phase transition can also be controlled such that it undergoes a smooth crossover transition, a Potts nematic transition, or a Ising nematic flop transition. The ability to tune the nematic order with in-situ strain further enables the extraction of nematic susceptibility, which exhibits a divergent behavior near the magnetic ordering temperature. Our work points to an active control approach to manipulate and explore nematicity in three-state Potts correlated materials.Comment: 20 pages, 4 figures, 6 additional figures. Initial submission on May 30t

Electric-field Control of Magnetism with Emergent Topological Hall Effect in SrRuO3 through Proton Evolution

Ionic substitution forms an essential pathway to manipulate the carrier density and crystalline symmetry of materials via ion-lattice-electron coupling, leading to a rich spectrum of electronic states in strongly correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we demonstrate an efficient and reversible control of both carrier density and crystalline symmetry through the ionic liquid gating induced protonation. The insertion of protons electron-dopes SrRuO3, leading to an exotic ferromagnetic to paramagnetic phase transition along with the increase of proton concentration. Intriguingly, we observe an emergent topological Hall effect at the boundary of the phase transition as the consequence of the newly-established Dzyaloshinskii-Moriya interaction owing to the breaking of inversion symmetry in protonated SrRuO3 with the proton compositional film-depth gradient. We envision that electric-field controlled protonation opens a novel strategy to design material functionalities

Reversible manipulation of the magnetic state in SrRuO3 through electric-field controlled proton evolution

Ionic substitution forms an essential pathway to manipulate the structural phase, carrier density and crystalline symmetry of materials via ion-electron-lattice coupling, leading to a rich spectrum of electronic states in strongly correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we demonstrate an efficient and reversible control of both structural and electronic phase transformations through the electric-field controlled proton evolution with ionic liquid gating. The insertion of protons results in a large structural expansion and increased carrier density, leading to an exotic ferromagnetic to paramagnetic phase transition. Importantly, we reveal a novel protonated compound of HSrRuO3 with paramagnetic metallic as ground state. We observe a topological Hall effect at the boundary of the phase transition due to the proton concentration gradient across the film-depth. We envision that electric-field controlled protonation opens up a pathway to explore novel electronic states and material functionalities in protonated material systems

Optical Study of Symmetry Breaking in Two-dimensional Antiferromagnets

Thesis (Ph.D.)--University of Washington, 2023The advent of two-dimensional (2D) materials has paved the way for the discovery and investigation of unique properties that arise from their low dimensionality. But, it also provided an avenue to study and test traditional, theoretical ideas related to long-range ordering in reduced dimensions. In particular, two-dimensional antiferromagnetism underlies many interesting and pertinent phenomena in modern condensed matter physics. However, the absence of net magnetization in systems exhibiting 2D antiferromagnetic order poses significant experimental challenges for their probing. This thesis delves into the captivating emergent optical behaviors in two-dimensional zigzag antiferromagnetic materials of the transition metal phosphorus trichalcogenide family that can be used to study 2D antiferromagnetic behavior. We first showcase zigzag antiferromagnetic order-induced excitons in NiPS3. The photoluminescence (PL) signal exhibits remarkable characteristics, including an exceptionally narrow linewidth and high linear polarization. Intriguingly, the PL intensity and polarization mirror the behavior of the zigzag antiferromagnetic order, vanishing above the Néel temperature. Our findings reveal a direct link between the exciton properties and the presence of antiferromagnetic order. Expanding our optical investigation, we demonstrate the ubiquitous presence of a linear dichroism response in the MPX3 zigzag antiferromagnets, exemplified by FePS3. The reduction of three-fold rotational symmetry to two-fold, induced by magnetic order, manifests as two-fold anisotropy in the optical response. Lastly, we demonstrate the remarkable ability to reversibly tune the three-state Potts nematicity in FePSe3 using strain. Through in-situ strain measurements, we elucidate the electronic nematic phase as the origin of the linear dichroism response. We also unveil strain-controlled nematic domain populations and the manipulation of the nematic phase transition nature. This strain control of the nematic phase provides a window into the nematic susceptibility near the magnetic ordering temperature, offering deeper insights into the behavior of these correlated materials. Through detailed optical experimental investigations, we provide a comprehensive understanding of the interplay between magnetic order, symmetry breaking, and emergent properties in zigzag antiferromagnets

Reversible manipulation of the magnetic state in SrRuO3 through electric-field controlled proton evolution.

Ionic substitution forms an essential pathway to manipulate the structural phase, carrier density and crystalline symmetry of materials via ion-electron-lattice coupling, leading to a rich spectrum of electronic states in strongly correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we demonstrate an efficient and reversible control of both structural and electronic phase transformations through the electric-field controlled proton evolution with ionic liquid gating. The insertion of protons results in a large structural expansion and increased carrier density, leading to an exotic ferromagnetic to paramagnetic phase transition. Importantly, we reveal a novel protonated compound of HSrRuO3 with paramagnetic metallic as ground state. We observe a topological Hall effect at the boundary of the phase transition due to the proton concentration gradient across the film-depth. We envision that electric-field controlled protonation opens up a pathway to explore novel electronic states and material functionalities in protonated material systems