Areas of Research
- Prediction of 2-dimensional ferroelectricity (which is contraindicative) emerging at a metal-semiconductor phase transition in MoS2.
- Demonstrating how anomalously large dielectric response of ferroelectric oxides arises from the inhomogeneously ordered states, for example, states with domain structure.
- Development of a technique to derive Ginzburg-Landau theory of fluctuation-driven 1st order ferroelectric phase transition from first-principles, and pointing out corrections to the conventional Landau theory.
- Determination of epitaxial strain-temperature phase diagrams of nano-thin films of ferroelectric BaTiO3 and PbTiO3, which guide experimentalists in design of devices based on ultra-thin ferroelectric films.
- Prediction of lead-free ferroelectrics, BiAlO3 and BiGaO3, which was later verified experimentally in Japan.
- Demonstrating how short-range chemical ordering gives rise to nano-polar regions that are responsible for diffuse phase transition and giant dielectric response of relaxor ferroelectrics.
Electronic Topological Materials
- Demonstration of broken adiabaticity at the Dirac semi-metallic state at a transition from normal to topological insulating states, and developing a model to explain the observed Raman anomalies serving as bulk signature of the transition.
- Prediction of strain-induced topological insulating state of As2Te3, and proposing its application as a charge pump.
- Demonstration of surface multiferroic behavior in elemental Se as a consequence of its electronic topology and chirality.
- Proposed symmetry dependent renormalization of phonons to explain the observed Raman spectra of MoS2 as a function of doping, useful in characterization of field effect transistors based on MoS2.
- Determination of the structure of point and line defects in graphene and 2-dimensional BN, and providing phenomenological explanation of how they lead to buckling (line defects seen later in experiments).
- Calculation of dynamical effects of e-phonon coupling to explain the observed Raman spectra of graphene as a function of doping, useful in characterization of graphene-based field effect transistors.
- Provided theoretical basis to substitutional, molecular and electrochemical doping in graphene identifying their spectroscopic signatures.
- Explained experiments on how few-layers or bilayers of graphene (rather than graphene) are effective in storage of hydrogen as a green fuel.
Mechanical Deformation of Materials
- Introduced the idea of multi-scale hyperelasticity as a mechanism for size-dependent plasticity in nano-scale hcp metals. This has relevance to a number of light-weight (Mg, Ti) alloys used in a automobile and aerospace technologies.
- Demonstrating how soft phonon modes are responsible for the observed mechanical failure in SiC to be used in power electronic devices.
- Analyzed interfacial strength of nano-precipitates in Ni-Al superalloys used in making of blades of jet engines.
Multiferroics and Dilute Magnetic Semiconductors
- Identified specific phonons that couple strongly with spins in multiferroic perovskite oxides.
- Contributed to theoretical explanation of anomalous disparity in ferroelectric polarization observed in the bulk form and thin films of BiFeO3.
- Showed how cationic disorder and spin-phonon coupling are responsible for magnetoelectric effects, interpreting the observed Raman spectra of AlFeO3.
- Theory of magnetoelectric coupling observed in nano-particles of BaTiO3 in terms of coupling between magnetic ordering due to O vacancies at the surface and ferroelectricity at the core.
- Provided evidence for a strong spin-phonon coupling in a double perovskite La2NiMnO6, establishing it to be the mechanism of its observed magnetocapacitance.
- First-principles prediction of room temperature ferromagnetism in Co-Li co-doped ZnO, which was verified experimentally.
Materials for Energy and Environment
- Uncovering mechanisms of high performance thermoelectrics based on metal-semiconductor superlattices and chalcogenides.
- Identified a number of oxides and 2-dimensional materials suitable as photo-catalysts for splitting of water using solar energy.
- Uncovered the mechanism of charge transfer in cathodes of Li ion batteries during charging and discharging operation.
- Identified the rate limiting step in use of metal hydrides to store Hydrogen.
- Determined the structural origin of activation of oxygen and enhanced catalytic activity of CeO2 with cation substitution, with applications to oxidation of CO and hydrocarbons.
Development of Formalism and Methods
- Showed how Wannier functions of electrons in 1-dimensional crystal are eigenfunctions of non-Abelian Berry phase matrices.
- Developed the formalism of phonon Wannier functions for construction of model Hamiltonian of structural phase transitions in crystals.
- Developed a “polarization-stat” which can be used within molecular dynamics and thermodynamic integration to obtain free energies and Landau theory of ferroelectrics.
- Contributed to generalization of the technique to model site occupancy disorder in crystals to grand-canonical ensembles.
- Developed mixed-space molecular dynamics for efficient simulations of model hamiltonians of ferroelectrics (contributed to release of free software FERAM).
- Established the relevance of magnetic frustration and spin-phonon coupling to superconducting transition in Iron pnictides using theory and the observed Raman spectra.
Select Recent Papers
Shashwat Anand, Krishnamohan Thekkepat, Umesh V Waghmare, Two-Dimensional Rectangular and Honeycomb Lattices of NbN: Emergence of Piezoelectric and Photocatalytic Properties at Nanoscale, Nano Letters 16, 126 (2016).
K Pal, S Anand, UV Waghmare, Thermoelectric properties of materials with nontrivial electronic topology, Journal of Materials Chemistry C 3 (46), 12130-12139 (2015).
Anjali Singh, Sharmila N Shirodkar, Umesh V Waghmare, 1H and 1T polymorphs, structural transitions and anomalous properties of (Mo, W)(S, Se) 2 monolayers: first-principles analysis, 2D Materials 2, 035013 (2015).
Bhogra Meha, Ramamurty U, Waghmare UV, “Smaller is Plastic: Polymorphic Structures and Mechanism of Deformation in Nanoscale hcp Metals”, Nano Letters, 15 , 6, 3697-3702, 2015.
Kandagal VS, Mridula Dixit B, Waghmare, UV, “Theoretical prediction of a highly conducting solid electrolyte for sodium batteries: Na10GeP2S12”, Journal Of Materials Chemistry A, 3, 24, 12992-12999, 2015.
UV Waghmare, “First-Principles Theory, Coarse-Grained Models, and Simulations of Ferroelectrics”, Accounts of chemical research 47, 11, 3242–3249 (2014).
S N Shirodkar and U V Waghmare, “Emergence of ferroelectricity at a metal-semiconductor transition in 1T monolayer of MoS2”, Phys Rev. Lett. 112,15, 157601 (2014).
Koushik Pal, Umesh V Waghmare, “Strain induced Z2 topological insulating state of β-As2Te3”, Applied Physics Letters 105, 062105 (2014).