Competing electronic orders on Kagome lattices at van Hove filling

The electronic orders in Hubbard models on a Kagome lattice at van Hove filling are of intense current interest and debate. We study this issue using the singular-mode functional renormalization group theory. We discover a rich variety of electronic instabilities under short range interactions. With increasing on-site repulsion $U$, the system develops successively ferromagnetism, intra unit-cell antiferromagnetism, and charge bond order. With nearest-neighbor Coulomb interaction $V$ alone (U=0), the system develops intra-unit-cell charge density wave order for small $V$, s-wave superconductivity for moderate $V$, and the charge density wave order appears again for even larger $V$. With both $U$ and $V$, we also find spin bond order and chiral $d_{x^2 - y^2} + i d_{xy}$ superconductivity in some particular regimes of the phase diagram. We find that the s-wave superconductivity is a result of charge density wave fluctuations and the squared logarithmic divergence in the pairing susceptibility. On the other hand, the d-wave superconductivity follows from bond order fluctuations that avoid the matrix element effect. The phase diagram is vastly different from that in honeycomb lattices because of the geometrical frustration in the Kagome lattice.Comment: 8 pages with 9 color figure

A Submillimeter Burst of S255IR~SMA1 - The Rise And Fall Of Its Luminosity

Temporal photometric variations at near infrared to submillimeter wavelengths have been found in low-mass young stellar objects. These phenomena are generally interpreted as accretion events of star-disk systems with varying accretion rates. There is growing evidence suggesting that similar luminosity flaring also occurs in high-mass star/cluster-forming regions. We report in this Letter the rise and fall of the 900 ${\mu}$m continuum emission and the newly found 349.1 GHz methanol maser emission in the massive star forming region S255IR~SMA1 observed with the Submillimeter Array and the Atacama Large Millimeter/submillimeter Array. The level of flux variation at a factor of $\sim$ 2 at the submillimeter band and the relatively short 2-year duration of this burst suggest that the event is probably similar to those milder and more frequent minor bursts seen in 3D numerical simulations.Comment: 8 pages, 4 figures, Accepted for publication in The Astrophysical Journal Lette

Functional renormalization group and variational Monte Carlo studies of the electronic instabilities in graphene near 1/4 doping

We study the electronic instabilities of near 1/4 electron doped graphene using the functional renormalization group (FRG) and variational Monte-Carlo method. A modified FRG implementation is utilized to improve the treatment of the von Hove singularity. At 1/4 doping the system is a chiral spin density wave state exhibiting the anomalous quantized Hall effect, or equivalently a Chern insulator. When the doping deviates from 1/4, the $d_{x^2-y^2}+i d_{xy}$ Cooper pairing becomes the leading instability. Our results suggest near 1/4 electron or hole doped graphene is a fertile playground for the search of Chern insulators and superconductors.Comment: 7 pages, 8 figures, with technical details, published versio

“Waste-free Cities” Construction and Carbon Emission Reduction in China: Based on the Perspective of Circular Economy

Solid waste and carbon dioxide are important elements of environmental governance. Under the background of carbon peaking and carbon neutrality goals, the research on whether and how to promote the construction of “no waste cities” and carbon emission reduction is of great significance in China. The generation of solid waste and greenhouse gases such as carbon dioxide has the same origin, which can be well coordinated to promote environmental governance