Magnetic and topological transitions in three-dimensional topological Kondo insulator

Using an extended slave-boson method,we draw a global phase diagram summarizing both magnetic phases and paramagnetic（PM） topological insulators（TIs） in a three-dimensional topological Kondo insulator（TKI）. By including electron hopping（EH） up to the third neighbors, we identify four strong TI（STI） phases and two weak TI（WTI） phases. Then, the PM phase diagrams characterizing topological transitions between these TIs are depicted as functions of EH,f-electron energy level,and hybridization constant. We also find an insulator-metal transition from an STI phase that has surface Fermi rings and spin textures in qualitative agreement with the TKI candidate SmBs. In the weak hybridization regime, antiferromagnetic（AF） order naturally arises in the phase diagrams. Depending on how the magnetic boundary crosses the PM topological transition lines,AF phases are classified into the AF topological insulator（AFTI） and the non-topological AF insulator, according to their Z2 indices. In two small regions of parameter space, two distinct topological transition processes between AF phases occur, leading to two types of AFTIs showing distinguishable surface dispersions around their Dirac points.

Electronic structures and optical properties of HfO_2–TiO_2 alloys studied by first-principles GGA + U approach

The phase diagram of HfO_2–TiO_2 system shows that when Ti content is less than 33.0 mol%, HfO_2–TiO_2 system is monoclinic; when Ti content increases from 33.0 mol% to 52.0 mol%, it is orthorhombic; when Ti content reaches more than 52.0 mol%, it presents rutile phase. So, we choose the three phases of HfO_2–TiO_2 alloys with different Ti content values. The electronic structures and optical properties of monoclinic, orthorhombic and rutile phases of HfO_2–TiO_2 alloys are obtained by the first-principles generalized gradient approximation（GGA） ＋U approach, and the effects of Ti content and crystal structure on the electronic structures and optical properties of HfO_2–TiO_2 alloys are investigated. By introducing the Coulomb interactions of 5 d orbitals on Hf atom（U_1~d）, those of 3 d orbitals on Ti atom（U_2~d）, and those of 2 p orbitals on O atom（Up） simultaneously, we can improve the calculation values of the band gaps, where U_1~d, U_2~d, and Up values are 8.0 eV, 7.0 eV, and 6.0 eV for both the monoclinic phase and orthorhombic phase, and 8.0 eV, 7.0 eV, and 3.5 eV for the rutile phase. The electronic structures and optical properties of the HfO_2–TiO_2 alloys calculated by GGA ＋U_1~d（U_1~d= 8.0 eV） ＋U_2~d（U_2~d= 7.0 eV） ＋U^p（U^p= 6.0 eV or 3.5 eV） are compared with available experimental results.

Electronic structures and optical properties of monoclinic ZrO2 studied by first-principles local density approximation + U approach

电子结构和单斜晶的 ZrO 2 的光性质(m-ZrO 2) 借助于第一原则的本地密度近似(LDA ) 被调查 + U 途径。没有所在地的库仑相互作用， m-ZrO 2 的乐队差距是 3.60 eV，比试验性的价值(5.8 eV ) 低得多。由在 Zr 原子上介绍 4d orbitals 的库仑相互作用(U d ) 并且 O 原子上的 2p orbitals (U 我们能复制的 p ), 乐队差距的试验性的价值。， m-ZrO 2 的计算绝缘的功能在四角形的 ZrO 2 和它是的立方的 ZrO 2 在它的想象的部分在乐队差距的边展出一个小肩膀不在，它与试验性的观察一致。肩膀的起源在原子价和传导乐队的边附近被归因于电子结构的差别。

Finite temperature physics of ID to pological Kondo insulator: Stable Haldane phase, emergent energy scale and beyond

In recent years, mteracting topological insulators have emerged as new frontiers in condensed matter physics, and the hotly studied topological Kondo insulator (TKI) is one of such prototypes. Although its zero-temperature ground-state has been widely investigated, the finite temperature physics on TKI is largely unknown. Here, we explore the finite temperature properties in a simplified model for TKI. namely the one-dimensional p-wave periodic Anderson model, with numerically exact determinant quantum Monte Carlo simulation. It is found that the topological Haldane phase established for groimdstate is still stable against small thermal fluctuation and its characteristic edge magnetization develops at low temperature. Such facts emphasize the robustness of (symmetry-protected) topological order against temperature effect, which always exists at real physical world. Moreover, we use the saturated low-T spin structure factor and the 1/T-law of susceptibility to detect the free edge spin moment, interestingly the low-temperature upturn behaxior of the latter one is similar to experimental finding in SniBg at T < 50 K. It implies that similar physical mechanism may work both for idealized models and realistic correlated electron materials.We have also identified an emergent energy scale Tcr. which signals a crossover into interesting low-T regime and seems to be the expected Ruderman-Kittel- Kasuya Yosida coupling. Finally, the collective Kondo screening effect has been examined and it is heavily reduced at boundary which may give a fruitful playground for novel physics beyond the wellestablished Haldane phase and topological band insulators.

Simulating heavy fermion physics in optical lattice： Periodic Anderson model with harmonic trapping potential

The periodic Anderson model （PAM）, where local electron orbitals interplay with itinerant electronic carriers, plays an essential role in our understanding of heavy fermion materials. Motivated by recent proposals for simulating the Kondo lattice model （KLM） in terms of alkaline-earth metal atoms, we take another step toward the simulation of PAM, which includes the crucial charge/valence fluctuation of local f-electrons beyond purely low-energy spin fluctuation in the KLM. To realize PAM, a transition induced by a suitable laser between the electronic excited and ground state of alkaline-earth metal atoms （^1S0←→^3P0） is introduced. This leads to effective hybridization between local electrons and conduction electrons in PAM. Generally, the SU（N） version of PAM can be realized by our proposal, which gives a unique opportunity to detect large-N physics without complexity in realistic materials. In the present work, high-temperature physical features of standard [SU（2）] PAM with harmonic trapping potential are analyzed by quantum Monte Carlo and dynamic mean-field theory, where the Mott/orbital-selective Mott state was found to coexist with metallic states. Indications for near-future experiments are provided. We expect our theoretical proposal and （hopefully） forthcoming experiments will deepen our understanding of heavy fermion systems. At the same time, we hope these will trigger further studies on related Mott physics, quantum criticality, and non-trivial topology in both the inhomogeneous and nonequilibrium realms.

Superfluid response in heavy fermion superconductors

Motivated by a recent London penetration depth measurement [H. Kim, et al., Phys. Rev. Lett. 114, 027003 （2015）] and novel composite pairing scenario [O. Erten, R. Flint, and P. Coleman, Phys. Rev. Lett. 114, 027002 （2015）] of the Yb-doped heavy fermion superconductor CeCoIns, we revisit the issue of superfluid response in the microscopic heavy fermion lattice model. However, from the literature, an explicit expression for the superfluid response function in heavy fermion superconductors is rare. In this paper, we investigate the superfiuid density response function in the celebrated Kondo- Heisenberg model. To be specific, we derive the corresponding formalism from an effective fermionic large-N mean-field pairing Hamiltonian whose pairing interaction is assumed to originate from the effective local antiferromagnetic exchange interaction. Interestingly, we find that the physically correct, temperature-dependent superfiuid density formula can only be obtained if the external electromagnetic field is directly coupled to the heavy fermion quasi-particle rather than the bare conduction electron or local moment. Such a unique feature emphasizes the key role of the Kondo-screening-renormalized heavy quasi-particle for low-temperature/energy thermodynamics and transport behaviors. As an important application, the theoretical result is compared to an experimental measurement in heavy fermion superconductors CeCoIn5 and Yb-doped Ce1-xYbxCoIn5 with fairly good agreement and the transition of the pairing symmetry in the latter material is explained as a simple doping effect. In addition, the requisite formalism for the commonly encountered nonmagnetic impurity and non-local electrodynamic effect are developed. Inspired by the success in explaining classic 115-series heavy fermion superconductors, we expect the present theory will be applied to understand other heavy fermion superconductors such as CeCu2Si2 and more generic multi-band superconductors.