Insulator Materials
Synthesis and characterization of new topological insulators
Project 1
Search, preparation and study of novel topological insulators for future spintronics and quantum computing
Topological insulators (TI) are materials insulating in volume, but conducting in surface. The research in this topic has led to the discovery of novel topological states of matter at the surface, enriching our understanding of condensed matter physics and providing new insights into the behavior of quantum materials. These surface states are topologically protected, and therefore robust against impurities and disorder, making them attractive for electronics. The actuality of the project could be approved by the fact that, sustainable development of high technologies always requires design of new materials and development of their synthesis technologies. Target compounds and solid solutions may serve as valuable contribution to the chemistry and materials science of topological insulators (TIs) and magnetic materials, whose working principle is based on change of their spins, rather than on the movement of electrons. Some of them are perspective as basis for the development new magnetic, photovoltaic and thermoelectric materials.
Nowadays, most studied chemical compounds as TIs are tetradymite like layered tellurides and selenides of bismuth and antimony. It was confirmed that ternary layered chalcogenides of Ge, Sn, Pb also demonstrate TI properties. According to the ab-initio calculations, spin-resolved photoemission and scanning tunneling microscopy experiments conducting states can effectively tuned within the homologous series that is formed by the binary chalcogenides (Bi2Te3, Bi2Se3 and Sb2Te3), with the addition of a third element of the group.
Electronic and surface properties of the number of ternary tetradymite-like compounds with the AIVTe·nBV2Te3 (AIV-Ge,Sn,Pb; BV-Sb,Bi, n=1,2,3,4..) general formula including AIVBV2Te4, AIVBV4Te7, AIVBV6Te10, AIVBV2Te7 etc. type compounds, thallous chalcogenides TlBiTe2, TlBiSe2, TlSbTe2, TlSbSe2 , as well as bismuth-tellurohalides BiTeCl, BiTeBr, BiTeI, Bi2TeI etc. were studied theoretically and experimentally.
However, developing these materials requires careful chemical composition refinement and optimization. In addition, cutting-edge techniques and sophisticated equipment are needed for physical characterization. The collaboration therefore must be established between physics and chemistry to guarantee success. In this project, we propose to collaborate with IPCMS physical research team, to develop new TI compounds and optimize their physical properties.
Objectives:
Search, design, and crystal growth of new mixed-layered compounds possessing TI properties, including magnetic TIs.
Preparation of new phases based on known TIs which allow to get an optimal combination of the promising functional properties
Physical characterization of prepared samples
Expected results:
Development of technological conditions of synthesis of discovered new phases, their synthesis as individual phases and identification
Optimization of the functional properties by doping various admixtures and preparation of solid solutions based on them
Growth of high-quality single crystals of obtained novel phases and their crystal structure study
Study of physical properties of prepared phases and identification their possible application fields
Axis Coordinator & Permanent researcher: Dunya Babanly
PhD student: Fuad Safarov
Master student: (to come)
Former master student: Lala Gasimzade
Project 2
Preparation of new series of solid solutions on the basis of pnictides in order to enlarge representatives of the 3D Topological Dirac Semimetals (3D TDS). Thermodynamic study of binary pnictides by the electromotive force measurements (EMF) method
In the transition from insulators to metals, there exists an intermediate state, where the conduction and valence band touch only at discrete points, leading to a narrow or zero bandgap. Graphene is a well-known example for such materials. Narrow or zero gap semiconductors where two (or more) bands get strongly coupled near a level-crossing are called Dirac materials. Prominent examples of Dirac matter are graphene, topological insulators, Dirac semimetals, Weyl semimetals, various high-temperature superconductors etc.
Three-dimensional (3D) topological Dirac semimetals (TDSs) are considered to be a newly proposed state of quantum matter that have attracted immense attention in physics and materials science. Unique electronic structure makes 3D TDSs prominent base materials for unusually high bulk carrier mobility, high-temperature linear quantum magnetoresistance, quantum spin Hall effect and giant diamagnetism. It also helps to realize various applications of graphene in 3D materials. Thus, 3D TDS materials, sometimes noted as the topological bulk Dirac semimetal (BDS) possessing strong spin-orbit coupling and exhibiting many exotic quantum phenomena constitute one of the most active topics in modern materials science. Despite their predicted existence, experimental studies on the BDS phases have been lacking as it has been difficult to realize this phase in real materials, especially in stoichiometric single crystalline non-metastable system with high mobility.
Recently, it was proposed that some binary (Cd3As2, Zn3As2) and ternary pnictides (CaAuAs and its isostructural family, e.g., BaAgAs) are 3D TDSs . Systematical study of the electronic structure of Cd3As2 by the angle-resolved photoemission spectroscopy (ARPES) confirms that Fermi velocity of the 3D Dirac fermions in Cd3As2 is about 3 times higher than that of in the topological surface states of Bi2Se3, 1.5 times higher than in graphene. Observed large Fermi velocity of the 3D Dirac band explains unusually high mobility of Cd3As2 and creates opportunity to the unusual magneto-electrical and quantum Hall transport properties under high-magnetic field of this compound. The distinct electronic structure of this compound gives rise to very promising applied properties, which are important due to potential application in new generation of electronic devices. Cd3As2 exhibits very high mobility charge carrier and large thermoelectric power (S). At 350 K temperature, the value of ZT of this compound has been found to be large ~ 0.16, which is comparable to the well-known thermoelectric material Bi2Te3 .
Thus, a new class of inorganic functional materials – three-dimensional (3D) topological Dirac semimetals based on metal pnictides due to their extraordinary physical properties have extensive
and rational application capabilities, ranging from electronics, spintronics and quantum calculations to medicine and security systems. In this regard, the substantial expansion of the nomenclature of such substances and their modified phases on basis of a complex of information relating to phase diagrams and thermodynamic characteristics of relevant systems is a topical issue.
Considering above-stated facts, proposed research activity is dedicated to the design of new series of Dirac semimetal phases.
In this regard, the project addresses a number of specific issues given below:
Obtaining new solid solution series by replacement of atoms in already known binary and ternary pnictide molecules (Cd3As2, Zn3As2, CaAuAs, BaAgAs etc.) by new similar atoms. For instance, in the Cd3As2 Dirac semimetal, displacement of Cd atoms by Zn, Hg, Sn etc. bivalent elements, as well as displacement of As atoms by P and Sb can help to prepare new materials possessing superior and controllable functional properties while maintaining crystal structure of Cd3As2.
Thermodynamic data are key in the understanding and design of chemical processes, as well as, in enhancement of the synthesis and crystal growth technologies of chemical materials. Since fundamental thermodynamic properties of pnictides are not studied well, it is intended to calculate their thermodynamic properties by the electromotive force (EMF) measurements.
Axis Coordinator & Permanent researcher: Dunya Babanly
PhD student: Fuad Safarov
Master student: (to come)
Former master student: Lala Gasimzade