Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a po- larization of 80%) and protons (with a polarization of 70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2–3)×10³³ cm−2•s−1. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC.

The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies.

This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.

Initial State Radiation (ISR) plays an important role in e⁺e⁻ collision experiments such as the BESIII. To correct the ISR effects in measurements of hadronic cross-sections of e⁺e⁻ annihilation, an iterative method that weights simulated ISR events is proposed here to assess the efficiency of event selection and the ISR correction factor for the observed cross-section. The simulated ISR events were generated only once, and the obtained cross-sectional line shape was used iteratively to weigh the same simulated ISR events to evaluate the efficiency and corrections until the results converge. Compared with the method of generating ISR events iteratively, the proposed weighting method provides consistent results, and reduces the computational time and disk space required by a factor of five or more, thus speeding-up e⁺e⁻ hadronic cross-section measurements.

In this paper, we systematically investigated the structural and magnetic properties of CrTe by combining particle swarm optimization algorithm and first-principles calculations. By considering the electronic correlation effect, we predicted the ground-state structure of CrTe to be NiAs-type (space group P6₃/mmc) structure at ambient pressure, consistent with the experimental observation. Moreover, we found two extra meta-stable Cmcaand R\overline{3}m structures which have negative formation enthalpy and stable phonon dispersion at ambient pressure. The Cmcastructure is a layered antiferromagnetic metal. The cleaved energy of a single layer is 0.464 J/m² , indicating the possible synthesis of CrTe monolayer. The R\overline{3}m structure is a ferromagnetic half-metal. When external pressure is applied, the ground-state structure of CrTe transitions from P63/mmc structure to R\overline{3}m structure at a pressure of 34 GPa, then to R\overline{3}m structure at 42 GPa. We thought these results help to motivate experimental studies of the CrTe compounds in the application of spintronics.

We developed a systematic non-perturbative method base on Dyson–Schwinger theory and the Φ-derivable theory for Ising model at broken phase. Based on these methods, we obtain critical temperature and spin spin correlation beyond mean field theory. The spectrum of Green function obtained from our methods become gapless at critical point, so the susceptibility become divergent at Tc. The critical temperature of Ising model obtained from this method is fairly good in comparison with other non-cluster methods. It is straightforward to extend this method to more complicate spin models for example with continue symmetry.

Three-dimensional (3D) topological insulators (TIs) have been studied for approximately fifteen years, but those made from group-IV elements, especially Ge and Sn, seem particularly attractive owing to their nontoxicity, sizable intrinsic spin–orbit coupling (SOC) strength and natural compatibility with the current semiconductor industry. However, group-IV elemental TIs have rarely been reported, except for the low temperature phase of α-Sn under strain. Here, based on first-principles calculations, we propose new allotropes of Ge and Sn, named T5-Ge/Sn, as desirable TIs. These new allotropes are also highly anisotropic Dirac semimetals if the SOC is turned off. To the best of our knowledge, T5-Ge/Sn are the first 3D allotropes of Ge/Sn that possess topological states in their equilibrium states at room temperature. Additionally, their isostructures of C and Si are metastable indirect and direct semiconductors. Our work not only reveals two promising TIs, but more profoundly, we justify the advantages of group-IV elements as topological quantum materials (TQMs) for fundamental research and potential practical applications, and thus reveal a new direction in the search for desirable TQMs.

We investigated the coexistence of superconductivity and antiferromagnetic order in the compound Er₂O₂Bi with anti-ThCr₂Si₂-type structure through resistivity, magnetization, specific heat measurements and first-principle calculations. The superconducting transition temperature T_c of 1.23 K and antiferromagnetic transition temperature TN of 3 K are observed in the sample with the best nominal composition. The superconducting upper critical field H_c2(0) and electron-phonon coupling constant λ_e−ph in Er₂O₂Bi are similar to those in the previously reported non-magnetic superconductor Y2O2Bi with the same structure, indicating that the superconductivity in Er₂O₂Bi may have the same origin as in Y₂O₂Bi. The first-principle calculations of Er₂O₂Bi show that the Fermi surface is mainly composed of the Bi 6p orbitals both in the paramagnetic and antiferromagnetic state, implying minor effect of the 4f electrons on the Fermi surface. Besides, upon increasing the oxygen incorporation in Er₂O_xBi, Tc increases from 1 to 1.23 K and T_N decreases slightly from 3 K to 2.96 K, revealing that superconductivity and antiferromagnetic order may compete with each other. The Hall effect measurements indicate that hole-type carrier density indeed increases with increasing oxygen content, which may account for the variations of T_c and T_N with different oxygen content.

Electrocatalytic CO₂ reduction reaction (CO2RR) to obtain C₂ products has drawn widespread attentions. Copper-based materials are the most reported catalysts for CO₂ reduction to C₂ products. Design of high-efficiency pseudo-copper catalysts according to the key characteristics of copper (Cu) is an important strategy to understand the reaction mechanism of C₂ products. In this work, density function theory (DFT) calculations are used to predict nickel–zinc (NiZn) alloy catalysts with the criteria similar structure and intermediate adsorption property to Cu catalyst. The calculated tops of 3d states of NiZn3(001) catalysts are the same as Cu(100), which is the key parameter affecting the adsorption of intermediate products. As a result, NiZn3(001) exhibits similar adsorption properties with Cu(100) on the crucial intermediates *CO₂, *CO and *H. Moreover, we further studied CO formation, CO hydrogenation and C–C coupling process on Ni–Zn alloys. The free energy profile of C₂ products formation shows that the energy barrier of C₂ products formation on NiZn3(001) is even lower than Cu(100). These results indicate that NiZn3 alloy as pseudo-copper catalyst can exhibit a higher catalytic activity and selectivity of C₂ products during CO₂RR. This work proposes a feasible pseudo-copper catalyst and provides guidance to design high-efficiency catalysts for CO₂RR to C₂ or multi-carbon products.

We present a way to transfer maximally- or partially-entangled states of n single-photon-state (SPS) qubits onto ncoherent-state (CS) qubits, by employing 2nmicrowave cavities coupled to a superconducting flux qutrit. The two logic states of a SPS qubit here are represented by the vacuum state and the single-photon state of a cavity, while the two logic states of a CS qubit are encoded with two coherent states of a cavity. Because of using only one superconducting qutrit as the coupler, the circuit architecture is significantly simplified. The operation time for the state transfer does not increase with the increasing of the number of qubits. When the dissipation of the system is negligible, the quantum state can be transferred in a deterministic way since no measurement is required. Furthermore, the higher-energy intermediate level of the coupler qutrit is not excited during the entire operation and thus decoherence from the qutrit is greatly suppressed. As a specific example, we numerically demonstrate that the high-fidelity transfer of a Bell state of two SPS qubits onto two CS qubits is achievable within the present-day circuit QED technology. Finally, it is worthy to note that when the dissipation is negligible, entangled states of n CS qubits can be transferred back onto n SPS qubits by performing reverse operations. This proposal is quite general and can be extended to accomplish the same task, by employing a natural or artificial atom to couple 2nmicrowave or optical cavities.