Condensed Matter Physics Research Center

ELECTRONIC, MAGNETIC AND THERMOELECTRIC PROPERTIES OF Pb₂XOsO₆(WHERE X = TRANSITION METALS)

2018

The B-site double perovskites have attractive properties like superconductivity, half-metallicity, ferrimagnetism etc. Pb-based double perovskites have notable dielectric and piezoelectric properties and also hybrid 3d - 4d (5d) double perovskite exhibit high spin polarization for device application at room temperature so these can be used in multi-functional devices. We will study electronic and magnetic properties of Pb-based double perovskite by using WIEN2K based on density functional theory and thermoelectric properties by using BoltzTraP based on Boltzmann transport theory. We expect high value of electrical conductivity and Seebeck coefficient and also low value of thermal conductivity and hence high value of dimensionless figure of merits ZT of Pb-based double perovskite. So we can use Pb-based double perovskite as a good thermoelectric material for the efficient utilization of energy wasted from industrial area and others in the form of heat.

Possible Identification of Magnetic Weyl Semimetal in Double Perovskites

2018

In recent years, scientist are focusing for those materials which are a good example of Weyl semimetals (WSMs). Many materials with the properties of magnetic WSMs have been studied, for instance in magnetic pyrochlore iridates, half- metallic Heusler alloys, antiferromagnetic half Heusler, shandides compounds, etc. However, works on double perovskites are limited despite their interesting properties (like multiferrocity, gaint magnetoresistance, etc) observed so far. Therefore, we are going to focus on complex perovskites. The discovery of WSMs open the door for novel future applications. It could be used to make the electronic or optical devices with novel functionalities. Since, Weyl fermions moves efficiently and in more order way than electrons, the materials containing Weyl fermions will be very useful for high speed computer and transistor with novel functionalities. We are going to use the full potential local-orbital (FPLO) code for our study.

We use the density functional theory approach to investigate structural, electronic and magnetic properties of proposed material. We perform the wannier fitting to find the topological surface Fermi arcs on the surface state. we calculate the chern number to identify how Weyl points behaves as monopole. Finally, we calculate the Berry curvature and anomalous Hall effect.

Possible Investigation of the Properties of Weyl Semimetals in TSn₂ System (T = 3d Transition Metals )

2018

Weyl Semimetals (WSMs) are the crystalline substances and are the sources for massless but charged particle called Weyl fermions. The history of Weyl Physics dates back to 1929 after the formulation of Weyl equation by Herman Weyl. For more than 85 years this concept get restricted to mathematical formulations and theoritical studies. Only after the discovery of Weyl node in TaAs in 2015, the existence of Weyl fermion picture came into the real world. So, very less amount of WSMs has been reported till the today's date, thus our study is focussed to Weyl Physics.

Mainly we will focus upon finding the Weyl point in energy dispersion curve, locating the Fermi arc, calculation of chern number, calculation of Berry curvature and anamolous hall effect calculation in TX2 system through the approach of Density Functional Theory and Full Potential Local Orbital Code (FPLO). The investigated properties of WSMs like as high mobilities can be utilized by high speed electronics and spintronics, the large Berry curvature and high spin hall effect could be used for spin hall effect devices and also this study would be supportive in quantum computing.

Electronic, Magnetic and Thermoelectric Properties of Bi-based Double Perovskite

2018

Double perovskite compounds have been widely investigated due to their diversity in their crystal structure and variety of properties such as high temperature superconductivity, magneto resistance, high dielectric constant, ferroelectric polarization, magnetic media and high thermoelectric power. These perovskite have high elemental abundance, low toxicity and eco-friendliness. Some double-perovskite oxides are called half-metals, a new class of materials, which are neither metals nor insulators; they are not even semi-conductors.

They possess an unusual electronic structure in which electrons with one spin have semiconducting properties and electrons with the opposite spin have metallic properties. We use density functional approach to study structural, electronic and magnetic properties implemented in WIEN2k code and Boltzmann semi-classical theory to study thermal transport properties implemented in BoltzTraP code . Our investigation of properties of this perovskite group (Bi- based double perovskite) should be useful in the development of oxide based electronic device, photo voltaic cell , spintronic and high thermopower materials etc.

Evaluation of Landau Parameters using DFT

2018

Materials with high spin polarization, remarkable spin-orbit coupling, suitable saturation magnetization, high energy product and most preferably cost effective one; which could revolutionize the modern material science with it’s intrinsic magnetic properties is being studied. With the increase in demand; high cost of the materials used to design the magnetic materials is the greatest challenge we are facing. The low cost substitutes are demanding and increasing globally for energy efficient, ecofriendly and renewable resources for green energy revolution. The fundamental parameters which determine the quality of magnetic materials are Magneto-crystalline Anisotropy Energy (MAE), saturation magnetization (Ms), Curie Temperature (Tc), free energy, etc.

These parameters are generally governed by energy product, crystal structure, ability to sustain strain magnetism even in harsh temperature conditions, composition of the system and spin orientations with respect to the crystal. For the wide variety of application of magnetic materials those parameters can be tuned at the Fermi level. First principles calculations using Density Functional Theory (DFT) based Full Potential – Linear Augmented Plane Wave (FP-LAPW) of band structure, electronic and magnetic properties using scalar and full relativistic calculations will be done. In addition to DFT, tight binding calculations and Monte-Carlo simulations are supposed to be done for the nature of the material and Curie temperature and finite temperature domain wall thickness calculation.

Accurate modern electronic structure calculations provide indispensable tool for exploring new materials with desired properties. Various materials ranging from rare-earths to Mott insulators are used as magnetic materials based on the value of MAE including but not limited to industries, transportation, electromagnets, to name a few. With high storage density magnets easy and efficient power generation, non-volatile data storage, safer work place are expected. Our findings on magnetic material would have high curie temperature and experimentally attainable parameters.

Magnetic Doping on Layered Bi_xTeI (x = 1-3)

2018

Doping the Topological Insulators (TIs) with transition metals forms the magnetic topological insulators (MTIs) displacing the element, anamolous hall effect (AHE) arises due to spin-orbit coupling in Bloch bands between current and magnetic moment in absence of external magnetic field give rise to quantized AHE. The magnetic properties depend on the parent compounds and the dopants. When applied magnetic field and electron spins on the surface states couple, mass becomes non-zero and opening gap for Dirac cones. Quantum anamolous hall (QAH) state also adds new dimension for future experiments to verify other properties directly linked to Time Reversal Symmetry at the surface of topological insulators and also other topological properties. QAH effect also has potential applications in future electronic devices, for which chiral edge stage is the signature and can carry electrical current without dissipation and because of spin polarization in spintronics too. With the application of electric field and due to electric polarization TI behaves like multiferroits mostly used in electromagnets and optoelectronics.

The electronic structure of bulk and surface of BixTeI (x = 1-3) and identification of band crossing in scalar relativistic and gap opening in relativistic band structure will be done by DFT using WEIN2k for former and Quantum ESPRESSO for later Z2 Topological invariant will also be reported. While completing the calculations weak/strong TI will be reported with formation of Dirac cone at the fermi level without SOC, band gap opening with SOC before and after doping leading to observation of QAHE. By means magnetic doping of TI, QAHE is supposed to be observed without applying external field.

Investigation on Evaluation of Coupling Constants in Multiferroic Double Perovskite

2018

Recently there are many researches being conducted on the development and device applications of multiferroics. This study is about evaluation of coupling constant in multiferrroic double perovskite. The coupling constant gives the measure of the strength of any interactions and these constants can justify the properties, behaviors and possible areas of device applications. For instance, the exchange coupling describes the magnetic properties of the material and the magneto-electric coupling provides vision of possible applications of multiferroics.

I will be using the Full Potential Linearized Augmented Plane Wave (FPLAPW) + local orbital (lo) methods with the help of WIEN2k code within density functional theory (DFT) to study ground state properties. There will be some approximations in use, like local density approximation (LDA) and generalized gradient approximation (GGA) for calculations and also to study the electric and magnetic properties of the material within DFT. The double perovskite being stable material with high working temperature and high coupling is the good choice for this study. The study of the multiferroic and their use in market had been quite challenging depending on the facts of them being found few in numbers and having low coupling along with difficulty in developing the devices. The multiferroic can be used in developing spintronics, multi-state memories, non-volatile memories, transducers, multiferroic RAM, sensors, etc. and many more devices to be used.

Investigation of thermolelectric and optical properties of trirutile oxides

2018

Thermoelectric generators (TEG) generate electric voltage from temperature gradients. So TEG can be used to convert waste heat into usable electrical energy. The suitability of materials for such applications is measured by a dimensionless parameter called the figure of merit (ZT) given by the relation, ZT = S^2 Tκ/σ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and κ is the thermal conductivity. The higher the value of ZT the more suitable is the material for thermoelectric applications. One strategy to increase the ZT value is to decrease the lattice thermal conductivity without affecting electrical thermal conductivity. For this, materials with complex crystal structures and with heavy ions in their crystal lattice are preferred. Trirutile oxides (TRO) of type AB2O6 (A and B can be transitions metals or alkaline metals or the lanthanides) satisfies both of these requirements.

These oxides have space group P42/mnm. Further, some TRO have shown promising properties for applications in novel electronics, photonic devices, solar cells, as transparent conductor, and low-temperature refrigeration. So we want to study the thermoelectric and optical properties of TRO. We intend to use density functional theory as implemented in WIEN2k code to study the electronic, optical, and magnetic properties of the compound and use the BoltzTraP code to calculate the thermoelectric parameters. We expect to increase the ZT values of TRO by doping with suitable metal.

Identification of Topological Insulators on BISb-SbBi based Layered Material

2018

Topological insulators (TI) are new classes of quantum materials that have a bulk band gap like an ordinary insulator, but have protected conducting states on their edge or surface. This highly unusual characteristics of the material inspired me to choose this title as my research work. This topic is one of the most concerned research topic in the context of 21st century. Identification of TI on Bismuth based layered material can bring a huge development in the field of Quantum materials as well as Electronics. Such topological Insulators may provide new routes to generating novel phases and particles, possibly finding uses in technological applications in spintronics and quantum computing research work on TI could lead to new architecture of quantum bits which ultimately lead helpful in quantum computer and operate them exponentially faster than digital computers.

This class of materials is a unique platform for exploring exotic physics and significant advances in technology especially in electronics by replacing the use of transistors by topological field effect transistors. We use density functional approach with different approximation such as Kohn-sham theory, Local density approximation ( LDA) and Generalized Gradient approximation (GGA) to study the structural properties, band Structures, phase stability and other more information of Bismuth based materials. Density functional approach enable us to find the ground state properties without dealing directly with the many electron state. This research work mostly involves computational calculations. For these calculations we need different computer software. First Principle band calculation were performed with an augmented plane wave method using WIEN2k. The electronic structure calculations and material modeling based on DFT is performed by Quantum Espresso. In this research work we are intended to study the material based on Bismuth. We are intended to identify band crossing in scalar relativistic and gap opening in relativistic band calculations. We will calculate Z2 Topological Invariant of materials to determine Indices (𝞾0; 𝞾1, 𝞾2, 𝞾3). The expected novel properties are to identify the types of TI either weak IT or strong TI and expected to find Dirac cone with clear formation of valance band and conduction band. Also we are expected to calculate the band gap of given Bismuth based material.