arXiv subjects

Qiangsheng Lu

Publications and source records attributed to Qiangsheng Lu.

22 records · Page 2Linked to original sources

arXiv2019

Electronic and magnetic properties of perovskite selenite and tellurite compounds: CoSeO$_3$, NiSeO$_3$, CoTeO$_3$ and NiTeO$_3$

Selenium and tellurium are among the few elements that form $AB$O$_3$ perovskite structures with a four valent ion in the $A$ site. This leads to highly distorted structures and unusual magnetic behavior. Here we investigate the Co and Ni selenite and tellurite compounds, CoSeO$_3$, CoTeO$_3$, NiSeO$_3$ and NiTeO$_3$ using first principles calculations. We find an interplay of crystal field and Jahn-Teller distortions that underpin the electronic and magnetic properties. While all compounds are predicted to show an insulating G-type antiferromagnetic ground state, there is a considerable difference in the anisotropy of the exchange interactions between the Ni and Co compounds. This is related to the Jahn-Teller distortion. Finally, we observe that these four compounds show characteristics generally associated with Mott insulators, even when described at the level of standard density functional theory. These are then dense bulk band or Slater, Mott-type insulators.

cond-mat.str-el↗

arXiv2019

Realisation of Symmetry Enforced Two-Dimensional Dirac Fermions in Nonsymmorphic $α$-Bismuthene

Two-dimensional (2D) Dirac-like electron gases have attracted tremendous research interest ever since the discovery of free-standing graphene. The linear energy dispersion and non-trivial Berry phase play the pivotal role in the remarkable electronic, optical, mechanical and chemical properties of 2D Dirac materials. The known 2D Dirac materials are gapless only within certain approximations, for example, in the absence of SOC. Here we report a route to establishing robust Dirac cones in 2D materials with nonsymmorphic crystal lattice. The nonsymmorphic symmetry enforces Dirac-like band dispersions around certain high-symmetry momenta in the presence of SOC. Through $μ$-ARPES measurements we observe Dirac-like band dispersions in $α$-bismuthene. The nonsymmorphic lattice symmetry is confirmed by $μ$-LEED and STM. Our first-principles simulations and theoretical topological analysis demonstrate the correspondence between nonsymmorphic symmetry and Dirac states. This mechanism can be straightforwardly generalized to other nonsymmorphic materials. The results open the door for the search of symmetry enforced Dirac fermions in the vast uncharted world of nonsymmorphic 2D materials.

cond-mat.mes-hall↗

arXiv2017

Multiple Topological Electronic Phases in Superconductor MoC

The search for a superconductor with non-s-wave pairing is important not only for understanding unconventional mechanisms of superconductivity but also for finding new types of quasiparticles such as Majorana bound states. Materials with both topological band structure and superconductivity are promising candidates as $p+ip$ superconducting states can be generated through pairing the spin-polarized topological surface states. In this work, the electronic and phonon properties of the superconductor molybdenum carbide (MoC) are studied with first-principles methods. Our calculations show that nontrivial band topology and superconductivity coexist in both structural phases of MoC, namely, the cubic $α$ and hexagonal $γ$ phases. The $α$ phase is a strong topological insulator and the $γ$ phase is a topological nodal line semimetal with drumhead surface states. In addition, hole doping can stabilize the crystal structure of the $α$ phase and elevate the transition temperature in the $γ$ phase. Therefore, MoC in different structural forms can be a practical material platform for studying topological superconductivity and elusive Majorana fermions.

cond-mat.supr-con↗

arXiv2016

Induced robust topological order on an ordinary insulator hetero-structured with a strong topological insulator

Topological states of matter originate from distinct topological electronic structures of materials. As for strong topological insulators (STIs), the topological surface (interface) is a direct consequence of electronic structure transition between materials categorized to different topological genus. Therefore, it is fundamentally interesting if such topological character can be manipulated. Besides tuning the crystal field and the strength of spin-orbital coupling (e.g., by external strain, or chemical doping), there is currently rare report on topological state induced in ordinary insulators (OIs) by the heterostructure of OI/STI. Here we report the observation of a Dirac cone topological surface state (TSS) induced on the Sb2Se3 layer up to 15 nm thick in the OI/STI heterostructure, in sharp contrast with the OI/OI heterostructure where no sign of TSS can be observed. This is evident for an induced topological state in an OI by heterostructure.

cond-mat.mtrl-sci↗