arXiv subjects

Jianpeng Liu

Publications and source records attributed to Jianpeng Liu.

93 records · Page 6Linked to original sources

arXiv2014

Weyl semimetals from noncentrosymmetric topological insulators

We study the problem of phase transitions from 3D topological to normal insulators without inversion symmetry. In contrast with the conclusions of some previous work, we show that a Weyl semimetal always exists as an intermediate phase regardless of any constriant from lattice symmetries, although the interval of the critical region is sensitive to the choice of path in the parameter space and can be very narrow. We demonstrate this behavior by carrying out first-principles calculations on the noncentrosymmetric topological insulators LaBiTe$_3$ and LuBiTe$_3$ and the trivial insulator BiTeI. We find that a robust Weyl-semimetal phase exists in the solid solutions LaBi$_{1-x}$Sb$_x$Te$_3$ and LuBi$_{1-x}$Sb$_x$Te$_3$ for $x\!\approx\!38.5-41.9$\% and $x\!\approx\!40.5-45.1$\% respectively. A low-energy effective model is also constructed to describe the critical behavior in these two materials. In BiTeI, a Weyl semimetal also appears with applied pressure, but only within a very small pressure range, which may explain why it has not been experimentally observed.

cond-mat.mes-hall↗

arXiv2014

Spin-orbit spillage as a measure of band inversion in insulators

We propose a straightforward and effective approach for quantifying the band inversion induced by spin-orbit coupling in band insulators. In this approach we define a quantity as a function of wavevector in the Brillouin zone measuring the spillage between the occupied states of a system with and without SOC. Plots of the spillage throughout the BZ provide a ready indication of the number and location of band inversions driven by SOC. To illustrate the method, we apply this approach to the 2D Kane-Mele model, a 2D Bi bilayer with applied Zeeman field, and to first-principles calculations of some 3D materials including both trivial and \Z2\ topological insulators. We argue that the distribution of spillage in the BZ is closely related to the topological indices in these systems. Our approach provides a fresh perspective for understanding topological character in band theory, and should be helpful in searching for new materials with non-trivial band topology.

cond-mat.mes-hall↗

arXiv2013

Topological phase transitions in (Bi$_{1-x}$In$_{x})_2$Se$_3$ and (Bi$_{1-x}$Sb$_{x})_2$Se$_3$

We study the phase transition from a topological to a normal insulator with concentration $x$ in (Bi$_{1-x}$In$_{x})_2$Se$_3$ and (Bi$_{1-x}$Sb$_{x})_2$Se$_3$ in the Bi$_2$Se$_3$ crystal structure. We carry out first-principles calculations on small supercells, using this information to build Wannierized effective Hamiltonians for a more realistic treatment of disorder. Despite the fact that the spin-orbit coupling (SOC) strength is similar in In and Sb, we find that the critical concentration $x_{\rm c}$ is much smaller in (Bi$_{1-x}$In$_{x})_2$Se$_3$ than in (Bi$_{1-x}$Sb$_{x})_2$Se$_3$. For example, the direct supercell calculations suggest that $x_{\rm c}$ is below 12.5% and above 87.5$%$ for the two alloys respectively. More accurate results are obtained from realistic disordered calculations, where the topological properties of the disordered systems are understood from a statistical point of view. Based on these calculations, $x_c$ is around 17% for (Bi$_{1-x}$In$_{x})_2$Se$_3$, but as high as 78%-83% for (Bi$_{1-x}$Sb$_{x})_2$Se$_3$. In (Bi$_{1-x}$Sb$_{x})_2$Se$_3$, we find that the phase transition is dominated by the decrease of SOC, with a crossover or "critical plateau" observed from around 78$%$ to 83$%$. On the other hand, for (Bi$_{1-x}$In$_{x})_2$Se$_3$, the In 5$s$ orbitals suppress the topological band inversion at low impurity concentration, therefore accelerating the phase transition. In (Bi$_{1-x}$In$_{x})_2$Se$_3$ we also find a tendency of In atoms to segregate.

cond-mat.mtrl-sci↗