Faculty Publications
http://hdl.handle.net/10211.2/309
Collection of scholarship submitted by CSUN faculty2018-08-16T10:36:05ZCompeting Spin-Liquid States In The Spin- 1/2 Heisenberg Model On The Triangular Lattice
http://hdl.handle.net/10211.3/205250
Competing Spin-Liquid States In The Spin- 1/2 Heisenberg Model On The Triangular Lattice
Hu, Wen-Jun; Gong, Shou-Shu; Zhu, Wei; Sheng, D. N.
We study the spin-1/2 Heisenberg model on the triangular lattice with antiferromagnetic first- (J1) and second- (J2) nearest-neighbor interactions using density matrix renormalization group. By studying the spin correlation function, we find a 120∘ magnetic order phase for J2≲0.07J1 and a stripe antiferromagnetic phase for J2≳0.15J1. Between these two phases, we identify a spin-liquid region characterized by exponential decaying spin and dimer correlations, as well as large spin singlet and triplet excitation gaps on finite-size systems. We find two near degenerating ground states with distinct properties in two sectors, which indicates more than one spin-liquid candidate in this region. While the sector with spinons is found to respect time reversal symmetry, the even sector without spinons breaks such a symmetry for finite-size systems. Furthermore, we detect the signature of the fractionalization by following the evolution of different ground states with inserting spin flux into the cylinder system. Moreover, by tuning the anisotropic bond coupling, we explore the nature of the spin-liquid phase and find the optimal parameter region for gapped Z2 spin liquids.
2015-01-01T00:00:00ZVariational Monte Carlo Study Of A Gapless Spin Liquid In The Spin- 1/2 XXZ Antiferromagnetic Model On The Kagome Lattice
http://hdl.handle.net/10211.3/205249
Variational Monte Carlo Study Of A Gapless Spin Liquid In The Spin- 1/2 XXZ Antiferromagnetic Model On The Kagome Lattice
Hu, Wen-Jun; Gong, Shou-Shu; Becca, Federico; Sheng, D. N.
By using the variational Monte Carlo technique, we study the spin-12 XXZ antiferromagnetic model (with easy-plane anisotropy) on the kagome lattice. A class of Gutzwiller projected fermionic states with a spin Jastrow factor is considered to describe either spin liquids [with U(1) or Z2 symmetry] or magnetically ordered phases [with q=(0,0) or q=(4π/3,0)]. We find that the magnetic states are not stable in the thermodynamic limit. Moreover, there is no energy gain to break the gauge symmetry from U(1) to Z2 within the spin-liquid states, as previously found in the Heisenberg model. The best variational wave function is therefore the U(1) Dirac state, supplemented by the spin Jastrow factor. Furthermore, a vanishing S=2 spin gap is obtained at the variational level, in the whole regime from the XY to the Heisenberg model.
2015-01-01T00:00:00ZOn Shocks Driven By High-Mass Planets In Radiatively Inefficient Disks. Iii. Observational Signatures In Thermal Emission And Scattered Light
http://hdl.handle.net/10211.3/205248
On Shocks Driven By High-Mass Planets In Radiatively Inefficient Disks. Iii. Observational Signatures In Thermal Emission And Scattered Light
Hord, Blake; Lyra, Wladimir; Flock, Mario; Turner, Neal J.; Mac Low, Mordecai-Mark
Recent observations of the protoplanetary disk around the Herbig Be star HD 100546 show two bright features in infrared (H and bands) at about 50 au,with one so far unexplained. We explore the observational signatures of a high-mass planet causing shock heating in order to determine if it could be the source of the unexplained infrared feature in HD 100546. More fundamentally, we identify and characterize planetary shocks as an extra, hitherto ignored, source of luminosity in transition disks. The RADMC-3D code is used to perform dust radiative transfer calculations on the hydrodynamical disk models, including volumetric heating. A stronger shock heating rate by a factor of 20 would be necessary to qualitatively reproduce the morphology of the second infrared source. Instead, we find that the outer edge of the gap carved by the planet heats up by about 50% relative to the initial reference temperature, which leads to an increase in the scale height. The bulge is illuminated by the central star, producing a lopsided feature in scattered light, as the outer gap edge shows an asymmetry in density and temperature attributable to a secondary spiral arm launched not from the Lindblad resonances but from the 2:1 resonance. We conclude that high-mass planets lead to shocks in disks that may be directly observed, particularly at wavelengths of 10 μm or longer, but that they are more likely to reveal their presence in scattered light by puffing up their outer gap edges and exciting multiple spiral arms.
2017-01-01T00:00:00ZVariational Monte Carlo Study Of A Chiral Spin Liquid In The Extended Heisenberg Model On The Kagome Lattice
http://hdl.handle.net/10211.3/205251
Variational Monte Carlo Study Of A Chiral Spin Liquid In The Extended Heisenberg Model On The Kagome Lattice
Hu, Wen-Jun; Zhu, Wei; Zhang, Yi; Gong, Shoushu; Becca, Federico; Sheng, D. N.
We investigate the extended Heisenberg model on the kagome lattice by using Gutzwiller projected fermionic states and the variational Monte Carlo technique. In particular, when both second- and third-neighbor superexchanges are considered, we find that a gapped spin liquid described by nontrivial magnetic fluxes and long-range chiral-chiral correlations is energetically favored compared to the gapless U(1) Dirac state. Furthermore, the topological Chern number, obtained by integrating the Berry curvature, and the degeneracy of the ground state, by constructing linearly independent states, lead us to identify this flux state as the chiral spin liquid with a C=1/2 fractionalized Chern number.
2015-01-01T00:00:00Z