The CP-PACS Project and Lattice QCD Results

The aim of the CP-PACS project was to develop a massively parallel computer for performing numerical research in computational physics with primary emphasis on lattice QCD. The CP-PACS computer with a peak speed of 614 GFLOPS with 2048 processors was completed in September 1996, and has been in full operation since October 1996. We present an overview of the CP-PACS project and describe characteristics of the CP-PACS computer. The CP-PACS has been mainly used for hadron spectroscopy studies in lattice QCD. Main results in lattice QCD simulations are given.Comment: 10 pages, 5 figures, Talk at the 5th International Conference on Computational Physics (ICCP5), 11-13 October, 1999, Kanazawa, to appear in Prog. Theor. Phys. (Suppl.) No. 138 (2000

Co-existence of Weyl Fermion and Massless Triply Degenerate Nodal Points

By using first-principles calculations, we propose that WC-type ZrTe is a new type of topological semimetal (TSM). It has six pairs of chiral Weyl nodes in its first Brillouin zone, but it is distinguished from other existing TSMs by having additional two paris of massless fermions with triply degenerate nodal points as proposed in the isostructural compounds TaN and NbN. The mirror symmetry, three-fold rotational symmetry and time-reversal symmetry require all of the Weyl nodes to have the same velocity vectors and locate at the same energy level. The Fermi arcs on different surfaces are shown, which may be measured by future experiments. It demonstrates that the "material universe" can support more intriguing particles simultaneously.Comment: 16 pages and 9 figure

Hamiltonian lattice quantum chromodynamics at finite density with Wilson fermions

Quantum chromodynamics (QCD) at sufficiently high density is expected to undergo a chiral phase transition. Understanding such a transition is of particular importance for neutron star or quark star physics. In Lagrangian SU(3) lattice gauge theory, the standard approach breaks down at large chemical potential $\mu$, due to the complex action problem. The Hamiltonian formulation of lattice QCD doesn't encounter such a problem. In a previous work, we developed a Hamiltonian approach at finite chemical potential $\mu$ and obtained reasonable results in the strong coupling regime. In this paper, we extend the previous work to Wilson fermions. We study the chiral behavior and calculate the vacuum energy, chiral condensate and quark number density, as well as the masses of light hadrons. There is a first order chiral phase transition at zero temperature.Comment: 23 pages. Version accepted for publication in Physical Review

Topological Semimetals with Triply Degenerate Nodal Points in \theta-phase Tantalum Nitride

Using first-principles calculation and symmetry analysis, we propose that \theta-TaN is a topological semimetal having a new type of point nodes, i.e., triply degenerate nodal points. Each node is a band crossing between degenerate and non-degenerate bands along the high-symmetry line in the Brillouin zone, and is protected by crystalline symmetries. Such new type of nodes will always generate singular touching points between different Fermi surfaces and 3D spin texture around them. Breaking the crystalline symmetry by external magnetic field or strain leads to various of topological phases. By studying the Landau levels under a small field along $c$-axis, we demonstrate that the system has a new quantum anomaly that we call "helical anomaly".Comment: 21 pages, 5 figures with supplemental material

Pseudo-Spin, Real-Spin and Spin Polarization of Photo-emitted Electrons

In this work, we discuss the connections between pseudo spin, real spin of electrons in material and spin polarization of photo-emitted electrons out of material. By investigating these three spin textures for Bi$_2$Se$_3$ and SmB$_6$ compounds, we find that the spin orientation of photo-electrons for SmB$_6$ has different correspondence to pseudo spin and real spin compare to Bi$_2$Se$_3$, due to the different symmetry properties of the photo-emission matrix between initial and final states. We calculate the spin polarization and circular dichroism spectra of photo-emitted electrons for both compounds, which can be detected by spin-resolved and circular dichroism angle resolved photo-emission spectroscopy experiment.Comment: 9 pages, 11 figure

Interaction-induced quantum anomalous Hall phase in (111) bilayer of LaCoO3_3

In the present paper, the Gutzwiller density functional theory (LDA+G) has been applied to study a bilayer system of LaCoO$_3$ grown along the $(111)$ direction on SrTiO$_3$. The LDA calculations show that there are two nearly flat bands located at the top and bottom of $e_{g}$ bands of Co atoms with the Fermi level crossing the lower one, which is almost half-filled. After including both the spin-orbit coupling and the Coulomb interaction in the LDA+G method, we find that the interplay between spin-orbit coupling and Coulomb interaction stabilizes a very robust ferromagnetic insulator phase with non-zero Chern number, which indicates the possibility to realize quantum anomalous Hall effect in this system.Comment: 8 pages, 8 figure