Towards ideal topological materials: Comprehensive database searches using symmetry indicators (1807.09744v3)

Abstract: Topological materials (TMs) showcase intriguing physical properties defying expectations based on conventional materials, and hold promise for the development of devices with new functionalities. While several theoretically proposed TMs have been experimentally confirmed, extensive experimental exploration of topological properties as well as applications in realistic devices have been held back due to the lack of excellent TMs in which interference from trivial Fermi surface states is minimized. We tackle this problem in the present work by applying our recently developed method of symmetry indicators to all non-magnetic compounds in the 230 space groups. An exhaustive database search reveals thousands of TM candidates. Of these, we highlight the excellent TMs, the 258 topological insulators and 165 topological crystalline insulators which have either noticeable full band gap or a considerable direct gap together with small trivial Fermi pockets. We also give a list of 489 topological semimetals with the band crossing points located near the Fermi level. All predictions obtained through standard generalized gradient approximation (GGA) calculations were cross-checked with the modified Becke-Johnson (MBJ) potential calculations, appropriate for narrow gap materials. With the electronic and optical behavior around the Fermi level dominated by the topologically non-trivial bands, these newly found TMs candidates open wide possibilities for realizing the promise of TMs in next-generation electronic devices.

• The paper introduces a comprehensive symmetry indicator-based method to identify topological materials across 17,258 non-magnetic compounds.
• It highlights key findings including 258 topological insulators, 165 TCIs, and 489 topological semimetals with clean electronic structures.
• The systematic database search accelerates experimental validation and paves the way for deploying advanced electronic and spintronic materials.

An Analysis of Topological Material Discovery through Symmetry Indicators

The paper "Towards ideal topological materials: Comprehensive database searches using symmetry indicators" presents significant advancements in the systematic identification of topological materials (TMs) by leveraging symmetry indicators applied across a vast range of known non-magnetic compounds. This work aims to address the existing gap between theoretical predictions and experimental realizations of TMs due to the interference from trivial Fermi surface states, which has historically hindered the deployment of TMs in practical devices.

Methodology

The authors utilize the recent developments in the theory of topology, particularly symmetry-based indicators (SIs), integrated with first-principles calculations. This methodology is applied to a comprehensive set of about 17,258 materials across all 230 crystallographic space groups, focusing on stoichiometric and non-radioactive compounds devoid of typical magnetic ions. The predictions of topological properties stem from calculations performed using the generalized gradient approximation (GGA), verified by the modified Becke-Johnson (MBJ) potential for greater accuracy, particularly in terms of band gap estimations.

Key Findings

The research identifies thousands of candidate TMs, with a distinguished subset featuring particularly favorable characteristics for potential experimental validation and application:

1. Topological Insulators (TIs): The paper identifies 258 topological insulators with substantial full band gaps or direct gaps alongside minimal trivial Fermi pockets, exemplified by materials like Ag₂Zr and Ba₁₁Bi₁₄Cd₈, which show promise for applications due to their favorable band structures.
2. Topological Crystalline Insulators (TCIs): This search highlights 165 TCIs with minimal interference from trivial states, such as BaGe and Bi₂Se₂. These materials demonstrate non-trivial topology protected by crystalline symmetries.
3. Topological Semimetals (TSMs): The paper identifies 489 topological semimetals with band crossing points in proximity to the Fermi level, critical for realizing Dirac or Weyl fermionic behavior in such materials. PdO is presented as a representative Dirac semimetal with its Dirac points located near the Fermi level, being protected by the $C_{4v}$ symmetry.

Implications and Future Directions

The authors' exhaustive search and the resulting database of nearly 8% identified ideal TMs candidates offer a novel resource that could accelerate experimental investigations, potentially transforming the landscape of advanced electronic and spintronic materials. These materials are prime candidates for further experimental validation due to their clean electronic structures devoid of confounding trivial Fermi surface states.

Moreover, the work encourages the exploration of existing materials databases with a refined lens of topological theories, thereby potentially revealing previously unnoticed materials for technological implementations. This paper not only paves the way for practical uses of TMs but also advances theoretical understanding by aligning computational predictions with experimental feasibilities.

Future research could explore the implementation of these findings in real-world applications and the synthesis of high-quality TM samples. Furthermore, expanding the methodology to include magnetic materials could unlock additional phenomena associated with symmetry-protected topological phases.

This comprehensive paper effectively demonstrates a pathway towards identifying and realizing materials with robust topological properties, underscoring the power of symmetry indicators in modern condensed matter physics research. The integration of computational tools with a systematic theoretical framework exemplifies a vital approach in the ongoing pursuit of novel materials with unprecedented functionalities.