arXiv subjects

X. P. Wang

Publications and source records attributed to X. P. Wang.

10 recordsLinked to original sources

arXiv2024

Ground-state mass of $^{22}$Al and test of state-of-the-art \textit{ab initio} calculations

The ground-state mass excess of the $T_{z}=-2$ drip-line nucleus $^{22}$Al is measured for the first time to be $18103(10)$ keV using the newly-developed B$ρ$-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou. The new mass excess value allowed us to determine the excitation energies of the two low-lying $1^+$ states in $^{22}$Al with significantly reduced uncertainties of 51 keV. Comparing to the analogue states in its mirror nucleus $^{22}$F, the mirror energy differences of the two $1^+$ states in the $^{22}$Al-$^{22}$F mirror pair are determined to be $-625(51)$ keV and $-330(51)$ keV, respectively. The excitation energies and the mirror energy differences are used to test the state-of-the-art \textit{ab initio} valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory. The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of the $πs_{1/2}$ orbital.

nucl-ex↗

arXiv2016

Improving quantum-transition temperatures in BaFe2As2-based crystals by removing local-lattice strain & electronic-structure disorder

Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFe2As2-based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Neel-ordering temperature in BaFe2As2 crystal (TN=132 K to 136 K) by removing in-plane electronic defects and overall reduction of a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFe2As2 crystal (Tc=23 to 25 K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. Although annealing promotes local chemical and electronic uniformity resulting in higher TN in the parent, it results in nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystalline regions, which lead to both higher overall Tc and critical-current-density, Jc.

cond-mat.supr-con↗

arXiv2016

Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/yz orbital yield quasi-particles with dxy} orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital differentiation is debated between the Hund's coupling induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasi-particle (QP) anomaly in LiFeAs. The excellent agreement between our photoemission measurements and first-principles many-body theory calculations shows that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.

cond-mat.str-el↗

arXiv2015

On the Chemistry and Physical Properties of Flux and Floating Zone Grown SmB6 Single Crystals

Recent theoretical and experimental findings suggest that the long-known but not well understood low temperature resistance plateau of SmB6 may originate from protected surface states arising from a topologically non-trivial bulk band structure having strong Kondo hybridization. Yet other studies have ascribed this feature to impurity phases, sample vacancies, and surface reconstructions. Given the typical methods used to prepare SmB6 single crystals, the flux and floating zone procedures, these ascriptions should not be taken lightly. Here, we demonstrate how compositional variations and observable amounts of impurity phases in SmB6 crystals grown by floating zone and flux affect the physical properties. From neutron diffraction and X-ray computed tomography experiments, we observe that a 154Sm11B6 crystal prepared using aluminum flux contains co-crystallized, epitaxial aluminum. A large, nearly stoichiometric crystal of SmB6 was successfully grown using the float-zone technique; upon continuing the zone melting, samarium vacancies are introduced. These samarium vacancies drastically alter the resistance and plateauing magnitude of the low temperature resistance compared to stoichiometric SmB6. These results highlight that small presences of impurity phases and compositional variations must be considered when collecting and analyzing physical property data of SmB6. Finally, a more accurate samarium-154 coherent neutron scattering length value, 8.9(1) fm, is reported.

cond-mat.str-el↗

arXiv2015

Experimental discovery of Weyl semimetal TaAs

Weyl semimetals are a class of materials that can be regarded as three-dimensional analogs of graphene breaking time reversal or inversion symmetry. Electrons in a Weyl semimetal behave as Weyl fermions, which have many exotic properties, such as chiral anomaly and magnetic monopoles in the crystal momentum space. The surface state of a Weyl semimetal displays pairs of entangled Fermi arcs at two opposite surfaces. However, the existence of Weyl semimetals has not yet been proved experimentally. Here we report the experimental realization of a Weyl semimetal in TaAs by observing Fermi arcs formed by its surface states using angle-resolved photoemission spectroscopy. Our first-principles calculations, matching remarkably well with the experimental results, further confirm that TaAs is a Weyl semimetal.

cond-mat.mtrl-sci↗

arXiv2015

Observation of two distinct $d_{xz}/d_{yz}$ band splittings in FeSe

We report the temperature evolution of the detailed electronic band structure in FeSe single-crystals measured by angle-resolved photoemission spectroscopy (ARPES), including the degeneracy removal of the $d_{xz}$ and $d_{yz}$ orbitals at the $Γ$/Z and M points, and the orbital-selective hybridization between the $d_{xy}$ and $d_{xz/yz}$ orbitals. The temperature dependences of the splittings at the $Γ$/Z and M points are different, indicating that they are controlled by different order parameters. The splitting at the M point is closely related to the structural transition and is attributed to orbital ordering defined on Fe-Fe bonds with a $d$-wave form in the reciprocal space that breaks the rotational symmetry. In contrast, the band splitting at the $Γ$ points remains at temperature far above the structural transition. Although the origin of this latter splitting remains unclear, our experimental results exclude the previously proposed ferro-orbital ordering scenario.

cond-mat.supr-con↗

arXiv2014

Carathéodory theorems for Slice Regular Functions

In this paper a quaternionic sharp version of the Carathéodory theorem is established for slice regular functions with positive real part, which strengthes a weaken version recently established by D. Alpay et. al. using the Herglotz integral formula. Moreover, the restriction of positive real part can be relaxed so that the theorem becomes the quaternionic version of the Borel-Carathéodory theorem. It turns out that the two theorems are equivalent.

math.CV↗

arXiv2014

Slice regular composition operators

In the article the class of slice regular functions is shown to be closed under a new regular composition. The new regular composition turns out to be globally defined in contrast to the locally defined version by Vlacci. Its advantage over Vlacci's is demonstrated by its associated theory of composition operators and dynamical systems for slice regular functions. Especially, the corresponding Littlewood subordination principle and the Denjoy-Wolff type theorem can be established.

math.CV↗

arXiv2011

Vacancy Induced Splitting of Dirac Nodal Point in Graphene

We investigate the vacancy effects on quasiparticle band structure of graphene near the Dirac point. It is found that each Dirac nodal point splits into two new nodal points due to the coherent scattering among vacancies. The splitting energy between the two nodal points is proportional to the square root of vacancy concentration. In addition, an extra dispersionless impurity band of zero energy due to particle-hole symmetry is found. Our theory offers an excellent explanation to the recent experiments.

cond-mat.quant-gas↗

arXiv2010

Accurate evaluation of the Green's function of disordered graphenes

An accurate simulation of Green's function and self-energy function of non-interacting electrons in disordered graphenes are performed. Fundamental physical quantities such as the elastic relaxation time τe, the phase velocity vp, and the group velocity vg are evaluated. New features around the Dirac point are revealed, showing hints that multi-scattering induced hybridization of Bloch states plays an important role in the vicinity of the Dirac point.

cond-mat.mes-hall↗