Vortex bound states influenced by the Fermi surface anisotropy

The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states.The large-scale calculation of vortex bound states is introduced in the presence of fourfold or twofold Fermi surface by solving the Bogoliubov–de Gennes(BdG)equations.Two kinds of quasiparticles’behaviors can be extracted from the local density of states(LDOS)around a vortex.The angle-dependent quasiparticles will move from high energy to low energy when the angle varies from curvature maxima to minima of the Fermi surface,while the angle-independent quasiparticles tend to stay at a relatively higher energy.In addition,the weight of angle-dependent quasiparticles can be enhanced by the increasing anisotropy degree of Fermi surface.

Evidence for Multiple Underlying Fermi Surface and Isotropic Energy Gap in the Cuprate Parent Compound Ca2CuO2Cl2

The parent compounds of the high-temperature cuprate superconductors are Mott insulators.It has been generally agreed that understanding the physics of the doped Mott insulators is essential to understanding the mechanism of high temperature superconductivity.A natural starting point is to elucidate the basic electronic structure of the parent compound.Here we report comprehensive high resolution angle-resolved photoemission measurements on Ca_2CuO_2Cl_2,a Mott insulator and a prototypical parent compound of the cuprates.Multiple underl.ying Fermi surface sheets are revealed for the first time.The high energy waterfall-like band dispersions exhibit different behaviors near the nodal and antinodal regions.Two distinct energy scales are identified：a d-wave-like low energy peak dispersion and a nearly isotropic lower Hubbard band gap.These observations provide new information of the electronic structure of the cuprate parent compound,which is important for understanding the anomalous physical properties and superconductivity mechanism of the high temperature cuprate superconductors.

Band structure,Fermi surface,elastic,thermodynamic,and optical properties of AlZr3,AlCu3,and AlCu2Zr:First-principles study

The electronic properties（Fermi surface,band structure,and density of states（DOS）） of Al-based alloys AlM3（M=Zr and Cu） and AlCu2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation（GGA）.The structural parameters and elastic constants are evaluated and compared with other available data.Also,the pressure dependences of mechanical properties of the compounds are studied.The temperature dependence of adiabatic bulk modulus,Debye temperature,specific heat,thermal expansion coefficient,entropy,and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T = 0 K-100 K.The parameters of optical properties（dielectric functions,refractive index,extinction coefficient,absorption spectrum,conductivity,energy-loss spectrum,and reflectivity） of the compounds are calculated and discussed for the first time.The reflectivities of the materials are quite high in the IR-visible-UV region up to ~ 15 eV,showing that they promise to be good coating materials to avoid solar heating.Some of the properties are also compared with those of the Al-based Ni3 Al compound.

Fermi surface gapping in the hidden order state of PrFe_(4)P_(12);by point-contact spectroscopy

We have applied point-contact spectroscopy(PCS) to investigate the nonmagnetic hidden order(HO) state of the skutterudite compound PrFe_(4)P_(12) with its transition temperature THO~6.5 K. Its point-contact conductance curves exhibit a reproducible gap structure in the HO state below THOand its temperature dependent gap magnitude follows a BCS-like mean-field behavior.A Fano-like conductance shape is observed to emerge below the coherence temperature of PrFe_(4)P_(12). In a magnetic field, the gap feature is gradually suppressed and evolves into a pronounced Fano peak, signaling the heavy fermion state and vividly demonstrating the competition between HO and the formation of heavy fermion states. Our results strongly suggest the itinerant characteristic of f electrons in PrFe_(4)P_(12), which constrains theoretical models to explain the HO mechanism.

Anomalous Andreev reflection on a torus-shaped Fermi surface

Andreev reflection(AR)refers to the electron-hole conversion at the normal metal-superconductor interface.In a threedimensional metal with a spherical Fermi surface,retro(specular)AR can occur with the sign reversal of all three(a single)components of particle velocity.Here,we predict a novel type of AR with the inversion of two velocity components,dubbed"anomalous Andreev reflection"(AAR),which can be realized in a class of materials with a torus-shaped Fermi surface,such as doped nodal line semimetals.For its toroidal circle perpendicular to the interface,the Fermi torus doubles the AR channels and generates multiple AR processes.In particular,the AAR and retro AR are found to dominate electron transport in the light and heavy doping regimes,respectively.We show that the AAR visibly manifests itself as a ridge structure in the spatially resolved nonlocal conductance,in contrast to the peak structure for the retro AR.Our work opens a new avenue for the AR spectroscopy and offers a clear transport signature of the torus-shaped Fermi surface.

Effects of carrier density and interactions on pairing symmetry in a t_(2g) model

By utilizing the fluctuation exchange approximation method,we perform a study on the superconducting pairing symmetry in a t_(2g) three-orbital model on the square lattice.Although the tight-binding parameters of the model are based on Sr_(2)RuO_(4),we have systematically studied the evolution of superconducting pairing symmetry with the carrier density and interactions,making our findings relevant to a broader range of material systems.Under a moderate Hund’s coupling,we find that spin fluctuations dominate the superconducting pairing,leading to a prevalent spin-singlet pairing with a d_(x^(2)-y^(2))-wave symmetry for the carrier density within the range of n=1.5-4 per site.By reducing the Hund’s coupling,the charge fluctuations are enhanced and play a crucial role in determining the pairing symmetry,leading to a transition of the pairing symmetry from the spin-singlet d_(x^(2)-y^(2))-wave to the spin-triplet p-wave.Furthermore,we find that the superconducting pairings are orbital dependent.As the carrier density changes from n=4 to n=1.5,the active orbitals for superconducting pairing shift from the quasi-two-dimensional orbital dxy to the quasi-one-dimensional orbitals d_(xz) and d_(yz).

The de Haas-van Alphen quantum oscillations in the kagome metal RbTi_(3)Bi_(5)

The kagome system has attracted great interest in condensed matter physics due to its unique structure that canhost various exotic states such as superconductivity(SC),charge density waves(CDWs)and nontrivial topological states.The topological semimetal RbTi_(3)Bi_(5)consisting of a Ti kagome layer shares a similar crystal structure to the topologicalcorrelated materials AV_(3)Sb_(5)(A=K,Rb,Cs)but without the absence of CDW and SC.Systematic de Haas-van Alphenoscillation measurements are performed on single crystals of RbTi_(3)Bi_(5)to pursue nontrivial topological physics and exoticstates.Combining this with theoretical calculations,the detailed Fermi surface topology and band structure are investigated.A two-dimensional Fermi pocket b is revealed with a light effective mass,consistent with the semimetal predictions.TheLandau fan diagram of RbTi_(3)Bi_(5)reveals a zero Berry phase for the b oscillation in contrast to that of CsTi_(3)Bi_(5).Theseresults suggest that kagome RbTi_(3)Bi_(5)is a good candidate for exploring nontrivial topological exotic states and topologicalcorrelated physics.

Some corrections to the Thomas-Fermi theory

In the presented model the wave function describing the electron is a superposition of contributions from individual components of the system, in the case of metals -- lattice ions and in this sense refers not to a single electron, but rather to the system as a whole. An unconventional approach to the Schrtdinger equation can provide a simple analytical relationship between the total energy of the electron and the wave number. This expression can directly determine the basic parameters such as Fermi radius, the screening radius or work function and also produce a graphical interpretation of the Fermi surface.

Superconductivity in octagraphene

This article reviews the basic theoretical aspects of octagraphene, an one-atom-thick allotrope of carbon, with unusual two-dimensional(2 D) Fermi nesting, hoping to contribute to the new family of quantum materials. Octagraphene has an almost strongest sp^(2)hybrid bond similar to graphene, and has the similar electronic band structure as iron-based superconductors, which makes it possible to realize high-temperature superconductivity. We have compared various possible mechanisms of superconductivity, including the unconventional s;superconductivity driven by spin fluctuation and conventional superconductivity based on electron–phonon coupling. Theoretical studies have shown that octagraphene has relatively high structural stability. Although many 2 D carbon materials with C;carbon ring and C;carbon ring structures have been reported, it is still challenging to realize the octagraphene with pure square-octagon structure experimentally.This material holds hope to realize new 2 D high-temperature superconductivity.

A possible mechanism for magnetar soft X-ray/γ-ray emission

Once the energies of electrons near the Fermi surface obviously exceed the threshold energy of the inverse β decay,electron capture（EC） dominates inside the magnetar.Since the maximal binding energy of the 3 P 2 neutron Cooper pair is only about 0.048 MeV,the outgoing high-energy neutrons（E k（n） 60 MeV） created by the EC can easily destroy the 3 P 2 neutron Cooper pairs through the interaction of nuclear force.In the anisotropic neutron superfluid,each 3 P 2 neutron Cooper pair has magnetic energy 2μ n B in the applied magnetic field B,where μ n = 0.966 × 10 23 erg.G 1 is the absolute value of the neutron abnormal magnetic moment.While being destroyed by the high-energy EC neutrons,the magnetic moments of the 3 P 2 Cooper pairs are no longer arranged in the paramagnetic direction,and the magnetic energy is released.This released energy can be transformed into thermal energy.Only a small fraction of the generated thermal energy is transported from the interior to the surface by conduction,and then it is radiated in the form of thermal photons from the surface.After highly efficient modulation within the star＇s magnetosphere,the thermal surface emission is shaped into a spectrum of soft X-rays/γ-rays with the observed characteristics of magnetars.By introducing related parameters,we calculate the theoretical luminosities of magnetars.The calculation results agree well with the observed parameters of magnetars.

Crossover from a pseudogap state to a superconducting state

This paper deduces that the particular electronic structure of cuprate superconductors confines Cooper pairs to be first formed in the antinodal region which is far from the Fermi surface, and these pairs are incoherent and result in the pseudogap state. With the change of doping or temperature, some pairs are formed in the nodal region which locates the Fermi surface, and these pairs are coherent and lead to superconductivity. Thus the coexistence of the pseudogap and the superconducting gap is explained when the two kinds of gaps are not all on the Fermi surface. It also shows that the symmetry of the pseudogap and the superconducting gap are determined by the electronic structure, and non-s wave symmetry gap favours the high-temperature superconductivity. Why the high-temperature superconductivity occurs in the metal region near the Mott metal-insulator transition is also explained.

Quantum oscillation measurements in high magnetic field and ultra-low temperature

The physical properties of a solid are determined by the electrons near the Fermi energy and their low-lying excitations. Thus, it is crucially important to obtain the band structure near the Fermi energy of a material to understand many novel phenomena that occur, such as high-To superconductivity, density waves, and Dirac-type excitations. One important way to determine the Fermi surface topology of a material is from its quantum oscillations in an external magnetic field. In this article, we provide a brief introduction to the substation at the Synergetic Extreme Condition User Facility （SECUF）, with a focus on quantum oscillation measurements, including our motivation, the structure of and the challenges in building the substation, and perspectives.

A semiclassical approach to surface Fermi arcs in Weyl semimetals

We present a semiclassical explanation for the morphology of the surface Fermi arcs of Weyl semimetals.Viewing the surface states as a two-dimensional Fermi gas subject to band bending and Berry curvatures,we show that it is the non-parallelism between the velocity and the momentum that gives rise to the spiral structure of Fermi arcs.We map out the Fermi arcs from the velocity field for a single Weyl point and a lattice with two Weyl points.We also investigate the surface magnetoplasma of Dirac semimetals in a magnetic field,and find that the drift motion,the chiral magnetic effect and the Imbert-Fedorov shift are all involved in the formation of surface Fermi arcs.Our work not only provides an insightful perspective on the surface Fermi arcs and a practical way to find the surface dispersion,but also paves the way for the study of other physical properties of the surface states of topological semimetals,such as transport properties and orbital magnetization,using semiclassical methods.

Wobbling motion for a triaxial rotor plus a single quasiparticle

Wobbling motion in a system comprising a triaxial rotor and a single quasiparticle is studied employing the particle-rotor model.The energy spectra,wobbling frequencies,electromagnetic transition probabilities,g-factors,angular momentum components,spin coherent state maps,and static quadrupole moments are investigated.These investigations were conducted with regard to the Fermi surface transitioning from the lowest h_(11/2) orbit to the highest one.As the Fermi surface increases,notable transformations occur in the wobbling mode.Initially,the mode exhibits a transverse revolution around the short axis of the nucleus.However,as the Fermi surface continues to increase,the mode gradually shifts to a longitudinal revolution around the intermediate axis.Eventually,it transitions to a transverse revolution around the long axis.Notably,the stability of the long axis transverse mode diminishes relative to its counterpart along the short axis as the total angular momentum increases atγ=20∘.

In situ carrier tuning in high temperature superconductor Bi2Sr2CaCu2O(8+δ)by potassium deposition

We report a successful tuning of the hole doping level over a wide range in high temperature superconductor Bi2Sr2CaCu2O8＋δ （Bi2212） through successive in situ potassium （K） deposition. By taking high resolution angleresolved photoemission measurements on the Fermi surface and band structure of an overdoped Bi2212 （To = 76 K） at different stages of K deposition, we found that the area of the hole-like Fermi surface around the Brillouin zone corner （n,n） shrinks with increasing K deposition. This indicates a continuous hole concentration change from initial - 0.26 to eventual 0.09 after extensive K deposition, a net doping level change of 0.17 that makes it possible to bring Bi2212 from being originally overdoped, to optimally-doped, and even- tually becoming heavily underdoped. The electronic behaviors with K deposition are consistent with those of Bi2212 samples with different hole doping levels. These results demonstrate that K deposition is an effective way of in situ controlling the hole concentration in Bi2212. This work opens a good way of studying the doping evolution of electronic structure and establishing the electronic phase diagram in Bi2212 that can be extended to other cuprate superconductors.

Inter-valley spiral order in the Mott insulating state of a heterostructure of trilayer graphene-boron nitride

Recent experiment has shown that the ABC-stacked trilayer graphene-boron nitride Moire super-lattice at half-filling is a Mort insulator. Based on symmetry analysis and effective band structure calculation, we propose a valley-contrasting chiral tight-binding model with local Coulomb interaction to describe this Moire super-lattice system. By matching the positions of van Hove points in the low-energy effective bands, the valley-contrasting staggered flux per triangle is determined around π/2. When the valence band is half-filled, the Fermi surfaces are found to be perfectly nested between the two valleys. Such an effect can induce an inter-valley spiral order with a gap in the charge excitations, indicating that the Mott insulating behavior observed in the trilayer graphene-boron nitride Moire super-lattice results predominantly from the inter-valley scattering,

Properties of the ν7/2^-[503](f_(7/2)) band in ^(185)Pt

High-spin states in 185Pt have been reinvestigated via the reaction 173Yb（16O, 4n） at a beam energy of 90 MeV. The previously known band based on the ν7/2-[503]（f7/2） Nilsson orbital has been extended to higher spin states. Properties of the ν7/2-[503]（f7/2） band have been discussed with an emphasis on the evolution of configuration while increasing the spin