arXiv subjects

Chao Lian

Publications and source records attributed to Chao Lian.

24 records · Page 2Linked to original sources

arXiv2018

Momentum-resolved TDDFT algorithm in atomic basis for real time tracking of electronic excitation

Ultrafast electronic dynamics in solids lies at the core of modern condensed matter and materials physics. To build up a practical ab initio method for studying solids under photoexcitation, we develop a momentum-resolved real-time time dependent density functional theory (rt-TDDFT)algorithm using numerical atomic basis, together with the implementation of both the length and vector gauge of the electromagnetic field. When applied to simulate elementary excitations in two-dimensional materials such as graphene, different excitation modes, only distinguishable in momentum space, are observed. The momentum-resolved rt-TDDFT is important and computationally efficient for the study of ultrafast dynamics in extended systems.

cond-mat.mtrl-sci↗

arXiv2018

Photoexcitation Induced Quantum Dynamics of Charge Density Wave and Emergence of a Collective Mode in 1T-TaS$_2$

Photoexcitation is a powerful means in distinguishing different interactions and manipulating the states of matter, especially in complex quantum systems. As a well-known charge density wave (CDW) material, 1T-TaS2 has been widely studied experimentally thanks to its intriguing photoexcited responses. However, the microscopic atomic dynamics and underlying mechanism are still under debate. Here, we demonstrate photoexcitation induced ultrafast dynamics in 1T-TaS2 using time-dependent density functional theory molecular dynamics. We discover a novel collective mode induced by photodoping, which is significantly different from thermally-induced phonon mode in TaS2. In addition, our finding validates nonthermal melting of CDW induced at low light intensities, supporting that conventional hot electron model is inadequate to explain photoinduced dynamics. Our results provide a deep insight on coherent electron and lattice quantum dynamics during the formation and excitation of CDW in 1T-TaS2.

cond-mat.str-el↗

arXiv2017

Dirac Cone Pairs in Silicene Induced by Interface Si-Ag Hybridization: A First Principles Effective Band Study

Using density functional theory combined with orbital-selective band unfolding techniques, we study the effective band structure of silicene($3\times3$)/Ag(111)($4\times4$) structure. Consistent with the ARPES spectra recently obtained by Feng et al. [Proc. Natl. Acad. Sci. 113, 14656 (2016)], we observe six pairs of Dirac cones near the boundary of the Brillouin zone (BZ) of Ag($1\times1$), while no Dirac cone is observed inside the BZ. Furthermore, we find that these Dirac cones are induced by the interfacial Si-Ag hybridization, mainly composed of Si p$_z$ orbitals and Ag sp bands, which is intrinsically different from the Dirac cones in freestanding silicene.

cond-mat.mes-hall↗

arXiv2016

$\textit{Ab initio}$ evidence for nonthermal characteristics in ultrafast laser melting

Laser melting of semiconductors has been observed for almost 40 years; surprisingly, it is not well understood where most theoretical simulations show a laser-induced thermal process. $\textit{Ab initio}$ nonadiabatic simulations based on real-time time-dependent density functional theory reveal intrinsic nonthermal melting of silicon, at a temperature far below the thermal melting temperature of 1680 K. Both excitation threshold and time evolution of diffraction intensity agree well with experiment. Nonthermal melting is attributed to excitation-induced drastic changes in bonding electron density, and the subsequent decrease in the melting barrier, rather than lattice heating as previously assumed in the two-temperature models.

cond-mat.mtrl-sci↗

arXiv2016

Direct Evidence of Metallic Bands in a Monolayer Boron Sheet

The search for metallic boron allotropes has attracted great attention in the past decades and recent theoretical works predict the existence of metallicity in monolayer boron. Here, we synthesize the \b{eta}12-sheet monolayer boron on a Ag(111) surface and confirm the presence of metallic boron-derived bands using angle-resolved photoemission spectroscopy. The Fermi surface is composed of one electron pocket at the S point and a pair of hole pockets near the X point, which is supported by the first-principles calculations. The metallic boron allotrope in \b{eta}12 sheet opens the way to novel physics and chemistry in material science.

cond-mat.mtrl-sci↗

arXiv2016

Magnetic Dirac Fermions and Chern Insulator Supported on Pristine Silicon Surface

Emergence of ferromagnetism in non-magnetic semiconductors is strongly desirable, especially in topological materials thanks to the possibility to achieve quantum anomalous Hall effect. Based on first-principles calculations, we propose that for Si thin film grown on metal substrate, the pristine Si(111)-root3xroot3 surface with a spontaneous weak reconstruction has a strong tendency of ferromagnetism and nontrivial topological properties, characterized by spin polarized Dirac-fermion surface states. In contrast to conventional routes relying on introduction of alien charge carriers or specially patterned substrates, the spontaneous magnetic order and spin-orbit coupling on the pristine silicon surface together gives rise to quantized anomalous Hall effect with a finite Chern number C=-1. This work suggests exciting opportunities in silicon-based spintronics and quantum computing free from alien dopants or proximity effects.

cond-mat.mes-hall↗