arXiv subjects

L. L. Sun

Publications and source records attributed to L. L. Sun.

5 recordsLinked to original sources

arXiv2022

A posteriori error estimates of mixed discontinuous Galerkin method for the Stokes eigenvalue problem

In this paper, for the Stokes eigenvalue problem in $d$-dimensional case $(d=2,3)$, we present an a posteriori error estimate of residual type of the mixed discontinuous Galerkin finite element method using $P_{k}-P_{k-1}$ element $(k\geq 1)$. We give the a posteriori error estimators for approximate eigenpairs, prove their reliability and efficiency for eigenfunctions, and also analyze their reliability for eigenvalues. We implement adaptive calculation, and the numerical results confirm our theoretical predictions and show that our method can achieve the optimal convergence order $O(dof^{-2k/d})$.

math.NA↗

arXiv2020

First order transition in trigonal structure ${\textbf{Ca}}{\textbf{Mn}}_{2}{\textbf{P}}_{2}$

We report structural and physical properties of the single crystalline ${\mathrm{Ca}}{\mathrm{Mn}}_{2}{\mathrm{P}}_{2}$. The X-ray diffraction(XRD) results show that ${\mathrm{Ca}}{\mathrm{Mn}}_{2}{\mathrm{P}}_{2}$ adopts the trigonal ${\mathrm{Ca}}{\mathrm{Al}}_{2}{\mathrm{Si}}_{2}$-type structure. Temperature dependent electrical resistivity $ρ(T)$ measurements indicate an insulating ground state for ${\mathrm{Ca}}{\mathrm{Mn}}_{2}{\mathrm{P}}_{2}$ with activation energies of 40 meV and 0.64 meV for two distinct regions, respectively. Magnetization measurements show no apparent magnetic phase transition under 400 K. Different from other ${\mathrm{A}}{\mathrm{Mn}}_{2}{\mathrm{Pn}}_{2}$ (A = Ca, Sr, and Ba, and Pn = P, As, and Sb) compounds with the same structure, heat capacity $C_{\mathrm{p}}(T)$ and $ρ(T)$ reveal that ${\mathrm{Ca}}{\mathrm{Mn}}_{2}{\mathrm{P}}_{2}$ has a first-order transition at $T$ = 69.5 K and the transition temperature shifts to high temperature upon increasing pressure. The emergence of plenty of new Raman modes below the transition, clearly suggests a change in symmetry accompanying the transition. The combination of the structural, transport, thermal and magnetic measurements, points to an unusual origin of the transition.

cond-mat.mtrl-sci↗

arXiv2017

The extraneous eclipses on binary light curves: KIC 5255552, KIC 10091110, and KIC 11495766

Aims. We aim to find more eclipsing multiple systems and obtain their parameters, thus increasing our understanding of multiple systems. Methods. The extraneous eclipses on the \textit{kepler} binary light curves indicating extraneous bodies were searched. The binary light curves were analyzed using the binary model, and the extraneous eclipses were studied on their periodicity and shape changes. Results. Three binaries with extraneous eclipses on the binary light curves were found and studied based on the \textit{Kepler} observations. The object KIC 5255552 is an eclipsing triple system with a fast changing inner binary and an outer companion uncovered by three groups of extraneous eclipses of $862.1(\pm0.1)$ d period. The KIC 10091110 is suggested to be a double eclipsing binary system with several possible extraordinary coincidences: the two binaries share similar extremely small mass ratios ($0.060(13)$ and $0.0564(18)$), similar mean primary densities ($0.3264(42)\;ρ_\odot$ and $0.3019(28)\;ρ_\odot$), and, most notably, the ratio of the two binaries' periods is very close to integer 2 (8.5303353/4.2185174 = 2.022). The KIC 11495766 is a probable triple system with a $\sim120.73$ d period binary and (at least) one non-eclipse companion. Furthermore, very close to it in the celestial sphere, there is a blended background stellar binary of 8.3404432 d period. A first list of 25 eclipsing multiple candidates is presented, with the hope that it will be beneficial for study of eclipsing multiples.

astro-ph.SR↗

arXiv2016

Identification of prototypical Brinkman-Rice Mott physics in a class of iron chalcogenides superconductors

The 122$^{*}$ series of iron-chalcogenide superconductors, for example K$_x$Fe$_{2-y}$Se$_{2}$, only possesses electron Fermi pockets. Their distinctive electronic structure challenges the picture built upon iron pnictide superconductors, where both electron and hole Fermi pockets coexist. However, partly due to the intrinsic phase separation in this family of compounds, many aspects of their behavior remain elusive. In particular, the evolution of the 122$^{*}$ series of iron-chalcogenides with chemical substitution still lacks a microscopic and unified interpretation. Using angle-resolved photoemission spectroscopy, we studied a major fraction of 122$^{*}$ iron-chalcogenides, including the isovalently `doped' K$_x$Fe$_{2-y}$Se$_{2-z}$S$_z$, Rb$_x$Fe$_{2-y}$Se$_{2-z}$Te$_z$ and (Tl,K)$_x$Fe$_{2-y}$Se$_{2-z}$S$_z$. We found that the bandwidths of the low energy Fe \textit{3d} bands in these materials depend on doping; and more crucially, as the bandwidth decreases, the ground state evolves from a metal to a superconductor, and eventually to an insulator, yet the Fermi surface in the metallic phases is unaffected by the isovalent dopants. Moreover, the correlation-driven insulator found here with small band filling may be a novel insulating phase. Our study shows that almost all the known 122$^{*}$-series iron chalcogenides can be understood {\it via} one unifying phase diagram which implies that moderate correlation strength is beneficial for the superconductivity.

cond-mat.supr-con↗

arXiv2008

Spin-singlet superconductivity with multiple gaps in PrO0.89F0.11FeAs

Since the discovery of high transition-temperature (Tc) superconductivity in copper oxides two decades ago, continuous efforts have been devoted to searching for similar phenomenon in other compounds. With the exception of MgB2 (Tc =39 K), however, Tc is generally far lower than desired. Recently, breakthrough has been made in a new class of oxypnictide compounds. Following the initial discovery of superconductivity in LaO1-x FxFeAs (Tc =26 K), Tc onset has been raised to 55 K in ReO1-xFxFeAs (Re: Ce, Pr, Nd, Sm). Meanwhile, unravelling the nature of the energy associated with the formation of current-carrying pairs (Cooper pairs), referred to as the superconducting energy gap, is the first and vital step towards understanding why the superconductivity occurs at such high temperature and is also important for finding superconductors with still higher Tc. Here we show that, on the basis of the nuclear magnetic resonance (NMR) measurements in PrO0.89F0.11FeAs (Tc =45 K), the Cooper pair is in the spin-singlet state (two spins are anti-paralleled), with two energy gaps opening below Tc. The results strongly suggest the existence of nodes (zeros) in the gap. None of superconductors known to date has such unique gap features, although copper-oxides and MgB2 share part of them.

cond-mat.supr-con↗