Quantum Materials Modelling

1. Magnetic and electronic properties of transition metal oxides

The field of transition metal oxides (TMO), mainly perovskite and double-perovskite posed major challenges in their understanding that they cannot follow the common wisdom in terms of magnetic and electronic  behaviors; specially for 4d and 5d systems where electronic correlation and spin-orbit coupling (SOC) play a significant role. Therefore it will be very important and interesting to address these challenging issues at the electronic structure level using state of art first principles DFT based method. In particular my interest is on the 4d-Ru and 5d-Os/Ir based TMO, for their unusual electronic and magnetic ground state such as spin-orbit Mott phases, topological quantum spin liquid, magnetic frustration, unconventional incommensurate magnetism, half-metallicity, unconventional orbital ordering etc.

 

2. Low dimensional quantum magnetism:

Quantum spin systems are important as they provide prototypical and conceptually simple models of quantum magnetic insulators. While crystallographically these materials are three dimensional, the effective low dimensionality arises due to interplay between the geometry and directional nature of the chemical bonding that can give rise to highly anisotropic electronic interactions. Magnetic systems of low dimensionality where the anisotropic electronic interaction translates into anisotropic magnetic interaction are of particular interest, specially for systems with small spins like S=½ or S=1, due to the additional complexity arises due to the interplay of thermal and quantum fluctuations of smaller electronic spins, which can give rise to fascinating phenomenon like formation of spin gap states, spin charge separation, quantum criticality etc. Actually crystal structure like Kagome, Pyrochlores have been at main focus of this direction of research in the field of geometrical frustrated system.

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3. Designing novel topological phase of matters

Till now research on topological states of matter mainly restricted within the s-p band derived weakly correlated type. Contrary the effect of strong correlation on the topological properties yet not understood at material specific level. Hence an investigation of the formation of topological phases in the correlated oxides in the presence of strong spin orbit coupling in bulk and heterostructures oxides would be worth studying. For that 5d oxides in bulk and their heterostructures or thin film form grown in [111] and [001] directions is most suited. The main advantages of heterostructures is that, it offer variety of option to chose suitable elements from the periodic table to tune band structure, strength of correlation and SOC. Most of the 5d oxides possess intrinsic magnetic moments, which help us to design quantum anomalous Hall (QAH) states in 2D layer of heterostructure or in thin film geometry, Chern insulator etc. It is highly interesting to explore to explore the influence of external pressure on the transition from trivial to nontrivial band topology.

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4. Spin-orbit coupling driven novel electronic phases

In most of the 5d oxides the SOC is very strong and in most cases it would be dominating terms compared to other energy scales in the system. However, it's an over simplified prescription that all unusual and counter-intuitive recent emergent phenomena in Iridates are driven by SOC. In strong SOC limit orbital (L) and spin (S) angular momentum are no longer good quantum number and the electronic states would be best described in terms of total angular momentum (Jeff) picture instead of S and L. Very recently there are few experimental and theoretical studies have been performed to explore the exception of this common notion. However, this is not very clear the mechanism of breakdown of strong SOC limit in different compounds. Therefore, it would be interesting to explore this aspect for 5d oxides to understand the interplay of Jahn-Teller distortion, electronic correlation, in these classes of material, which can lead to unconventional orbital ordering due to the intermediate coupling (neither complete L-S nor J-J) regime.

 

5. Multifunctional Metal-Organic framework

In recent years, crystalline hybrid materials (metal-organic framework) containing transition metal magnetic centres, connected with organic ligands are in frontier in research with a goal to achieve improved and tunable materials properties compared to conventional inorganic materials. For example, the  switchable spin crossover (SCO) from low-spin state (LS) to high-spin state (HS) under the influence of external stimulus such as pressure, temperature, illumination of light etc. In spite of its technological importance, the SCO phenomenon is not yet well understood, especially on the atomistic level, due to the limitation of in-situ experimentation. In this context, to understand the exotic behavior at the atomistic level and to help screen candidate materials, the quantum-chemical calculations, take into account the structural and chemical complexity is most important. Among the different external stimuli, the effect of pressure, temperature and chemical doping on the SCO phenomena.

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