The interplay between superconductivity and structural phase transition has attracted enormous interest in recent years. For example, in Fe-pnictide high temperature superconductors, quantum fluctuations in association with structural phase transition have been proposed to lead to many novel physical properties and even the superconductivity itself. Here we report a finding that the quasi-skutterudite superconductors (Sr_1-xCa_x)₃Ir₄Sn₁₃ (x=0, 0.5, 1) and Ca₃Rh₄Sn₁₃ show some unusual properties similar to the Fe-pnictides, through ¹¹⁹Sn nuclear magnetic resonance (NMR) measurements. In (Sr_1-xCa_x)₃Ir₄Sn₁₃, the NMR linewidth increases below a temperature T^* that is higher than the structural phase transition temperature T_s. The spin-lattice relaxation rate (1/T₁) divided by temperature (T), 1/T₁T and the Knight shift K increase with decreasing T down to T^*, but start to decrease below T^*, and followed by more distinct changes at T_s. In contrast, none of the anomalies is observed in Ca₃Rh₄Sn₁₃ that does not undergo a structural phase transition. The precursory phenomenon above the structural phase transition resembles that occurring in Fe-pnictides. In the superconducting state of Ca₃Ir₄Sn₁₃, 1/T₁ decays as exp(-△/k_BT) with a large gap △=2.21 k_BT_c, yet without a Hebel-Slichter coherence peak, which indicates strong-coupling superconductivity. Our results provide new insight into the relationship between superconductivity and the electronic-structure change associated with structural phase transition.

A novel transparent and soft quasi-solid-state electrolyte (QSSE) was proposed and fabricated, which consists of ionic liquid (PYR₁₄TFSI) and nano-fumed silica. The QSSE demonstrates high ionic conductivity of 4.6×10^-4 S/cm at room temperature and wide electrochemical stability window of over 5 V. The Li-O₂ battery using such quasi-solid-state electrolyte exhibits a low charge-discharge overpotential at the first cycle and excellent long-term cyclability over 500 cycles.

The plasmon-enhanced light emission of rutile TiO₂(110) surface has been investigated by a low-temperature scanning tunneling microscope (STM). We found that the photon emission arises from the inelastic electron tunneling between the STM tip and the conduction band or defect states of TiO₂(110). In contrast to the Au(111) surface, the maximum photon energy as a function of the bias voltage clearly deviates from the linear scaling behavior, suggesting the non-negligible effect of the STM tip on the band structure of TiO₂. By performing differential conductance (dI/dV) measurements, it was revealed that such a deviation is not related to the tip-induced band bending, but is attributed to the image charge effect of the metal tip, which significantly shifts the band edges of the TiO₂(110) towards the Femi level (E_F) during the tunneling process. This work not only sheds new lights onto the understanding of plasmon-enhanced light emission of semiconductor surfaces, but also opens up a new avenue for engineering the plasmon-mediated interfacial charge transfer in molecular and semiconducting materials.

The Lieb-Liniger model is a prototypical integrable model and has been turned into the benchmark physics in theoretical and numerical investigations of low-dimensional quantum systems. In this note, we present various methods for calculating local and nonlocal M-particle correlation functions, momentum distribution, and static structure factor. In particular, using the Bethe ansatz wave function of the strong coupling Lieb-Liniger model, we analytically calculate the two-point correlation function, the large moment tail of the momentum distribution, and the static structure factor of the model in terms of the fractional statistical parameter α=1-2/γ, where γ is the dimensionless interaction strength. We also discuss the Tan's adiabatic relation and other universal relations for the strongly repulsive Lieb-Liniger model in terms of the fractional statistical parameter.

We present an experiment of observing the geometric phase in a superconducting circuit where the resonator and the qutrit energy levels are dispersively coupled. The drive applied to the resonator displaces its state components associated with the qutrit's ground state and first-excited state along different circular trajectories in phase space. We identify the resonator's phase-space trajectories by Wigner tomography using an ancilla qubit, following which we observe the difference between the geometric phases associated with these trajectories using Ramsey interferometry. This geometric phase is further used to construct the single-qubit π-phase gate with a process fidelity of 0.851±0.001.

Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on composition design for La(Fe,Si/Al)₁₃-based materials, which are regarded as one of the most promising magnetic refrigerants in practice. Three prediction models are built by using a machine learning algorithm called gradient boosting regression tree (GBRT) to essentially find the correlation between the Curie temperature (T_C), maximum value of magnetic entropy change ((Δ S_M)_max), and chemical composition, all of which yield high accuracy in the prediction of T_C and (Δ S_M)_max. The performance metric coefficient scores of determination (R²) for the three models are 0.96, 0.87, and 0.91. These results suggest that all of the models are well-developed predictive models on the challenging issue of generalization ability for untrained data, which can not only provide us with suggestions for real experiments but also help us gain physical insights to find proper composition for further magnetic refrigeration applications.

We performed ultra-low temperature thermal conductivity measurements on the single crystal of a new gold-based quasi-two-dimensional superconductor AuTe₂Se_4/3, which has a superconducting transition temperature T_c=2.70 K. A negligible residual linear term κ₀/T in zero magnetic field is observed, which suggests fully gapped superconducting state. Furthermore, the field dependence of κ₀/T is similar to that of the multi-band s-wave superconductor BaFe_1.9Ni_0.1As₂ at low field. These results reveal multiple nodeless superconducting gaps in this interesting quasi-two-dimensional superconductor with Berezinsky-Kosterlitz-Thouless topological transition.

Interactions of magnetic elements with graphene may lead to various electronic states that have potential applications. We report an in-situ experiment in which the quantum transport properties of graphene are measured with increasing cobalt coverage in continuous ultra-high vacuum environment. The results show that e-beam deposited cobalt forms clusters on the surface of graphene, even at low sample temperatures. Scattering of charge carriers by the absorbed cobalt clusters results in the disappearance of the Shubnikov-de Haas (SdH) oscillations and the appearance of negative magnetoresistance (MR) which shows no sign of saturation up to an applied magnetic field of 9 T. We propose that these observations could originate from quantum interference driven by cobalt disorder and can be explained by the weak localization theory.

Hybrid liquid/solid electrolytes (HLSEs) consisting of conventional organic liquid electrolyte (LE), polyacrylonitrile (PAN), and ceramic lithium ion conductor Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) are proposed and investigated. The HLSE has a high ionic conductivity of over 2.25×10^-3 S/cm at 25℃, and an extended electrochemical window of up to 4.8 V versus Li/Li⁺. The Li|HLSE|Li symmetric cells and Li|HLSE|LiFePO₄ cells exhibit small interfacial area specific resistances (ASRs) comparable to that of LE while much smaller than that of ceramic LAGP electrolyte, and excellent performance at room temperature. Bis(trifluoromethane sulfonimide) salt in HLSE significantly affects the properties and electrochemical behaviors. Side reactions can be effectively suppressed by lowering the concentration of Li salt. It is a feasible strategy for pursuing the high energy density batteries with higher safety.

A quantum algorithm provides a new way in solving certain computing problems and usually faster than classical algorithms. Here we report an implementation of a quantum algorithm to determine the parity of permutation in a single three-dimensional (3D) superconducting transmon qutrit system. The experiment shows the capacity to speed up in a qutrit, which can also be extended to a multi-level system for solving high-dimensional permutation parity determination problem.

We report a theoretical study of pumped spin currents in a silicene-based pump device, where two time-dependent staggered potentials are introduced through the perpendicular electric fields and a magnetic insulator is considered in between the two pumping potentials to magnetize the Dirac electrons. It is shown that giant spin currents can be generated in the pump device because the pumping can be optimal for each transport mode, the pumping current is quantized. By controlling the relevant parameters of the device, both pure spin currents and fully spin-polarized currents can be obtained. Our results may shed a new light on the generation of pumped spin currents in Dirac-electron systems.

Using dispersion corrected density functional theory, we systematically examined the pressure effect on crystal structure, cell volume, and band gap of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) to understand its extraordinary chemical stability. Analysis of the Mulliken population and the electron density of states implied a possible charge transfer in TATB with increasing pressure. Raman and infrared spectra of TATB under hydrostatic pressure up to 30 GPa were simulated. The observed strong coupling between NH₂ groups and NO₂ groups with increasing pressure, which is considered to have a tendency of energy transfer with these vibrational modes, was analyzed. The pressure-induced frequency shift of selected vibrational modes indicated minor changes of molecular conformation mainly by the rotation of NH₂ groups. Compression behavior and spectroscopic property studies are expected to shed light on the physical and chemical properties of TATB on an atomistic scale.

Hydration water can even decide the physicochemical properties of hydrated organic molecules. However, by far the most important hydration number for organic molecules, in particular polyethylene glycol which we are concerned with here, usually suffers from a large discrepancy. Here, we provide a scheme for accurate and unambiguous quantification of the hydration number based on the universal water-content dependence of glass transition temperature for aqueous solutions, testified by experimental results for polyethylene glycol molecules of a molar weight ranging from 200 to 20000. Moreover, we also clarify the fundamental misunderstanding lying in the definition and quantification of hydration water for PEG molecules in the literature, therein the hydration number for PEG in water-rich solutions has been determined at a critical concentration, across which the properties of the solution display obviously distinct water-content dependence.

In this work, we discuss the origin of several anomalies present in the point-contact Andreev reflection spectra of (Li_1-xFe_x)OHFeSe, LiTi₂O₄, and La_2-xCe_xCuO₄. While these features are similar to those stemming from intrinsic superconducting properties, such as Andreev reflection, electron-boson coupling, multigap superconductivity, d-wave and p-wave pairing symmetry, they cannot be accounted for by the modified Blonder-Tinkham-Klapwijk (BTK) model, but require to consider critical current effects arising from the junction geometry. Our results point to the importance of tracking the evolution of the dips and peaks in the differential conductance as a function of the bias voltage, in order to correctly deduce the properties of the superconducting state.

Monolayer transition-metal dichalcogenides (TMDs) have attracted a lot of attention for their applications in optics and optoelectronics. Molybdenum disulfide (MoS₂), as one of those important materials, has been widely investigated due to its direct band gap and photoluminescence (PL) in visible range. Owing to the fact that the monolayer MoS₂ suffers low light absorption and emission, surface plasmon polaritons (SPPs) are used to enhance both the excitation and emission efficiencies. Here, we demonstrate that the PL of MoS₂ sandwiched between 200-nm-diameter gold nanoparticle (AuNP) and 150-nm-thick gold film is improved by more than 4 times compared with bare MoS₂ sample. This study shows that gap plasmons can possess more optical and optoelectronic applications incorporating with many other emerging two-dimensional materials.

Based on the first-principles density functional theory electronic structure calculation, we investigate the possible phonon-mediated superconductivity in arsenene, a two-dimensional buckled arsenic atomic sheet, under electron doping. We find that the strong superconducting pairing interaction results mainly from the p_z-like electrons of arsenic atoms and the A₁ phonon mode around the K point, and the superconducting transition temperature can be as high as 30.8 K in the arsenene with 0.2 doped electrons per unit cell and 12%-applied biaxial tensile strain. This transition temperature is about ten times higher than that in the bulk arsenic under high pressure. It is also the highest transition temperature that is predicted for electron-doped two-dimensional elemental superconductors, including graphene, silicene, phosphorene, and borophene.

A new oxide CaCr_0.5Fe_0.5O₃ was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr⁵⁺/Fe³⁺ with the presence of unusual Cr⁵⁺ state in octahedral coordination, although Cr⁴⁺ and Fe⁴⁺ occur in the related perovskites CaCrO₃ and CaFeO₃. The randomly distributed Cr⁵⁺ and Fe³⁺ spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe³⁺-O-Fe³⁺ interaction. In spite of the B-site Cr⁵⁺/Fe³⁺ disorder, the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of CaCr_0.5⁵⁺Fe_0.5³⁺O₃ charge combination, and the electron correlation effect of Fe³⁺ plays an important role for the insulting ground state. CaCr_0.5Fe_0.5O₃ provides the first Cr⁵⁺ perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states.

We report combined magnetic susceptibility, dielectric constant, nuclear quadruple resonance (NQR), and zero-field nuclear magnetic resonance (NMR) measurements on single crystals of multiferroics CuBr₂. High quality of the sample is demonstrated by the sharp magnetic and magnetic-driven ferroelectric transition at T_N=T_C≈ 74 K. The zero-field ⁷⁹Br and ⁸¹Br NMR are resolved below T_N. The spin-lattice relaxation rates reveal charge fluctuations when cooled below 60 K. Evidences of an increase of NMR linewidth, a reduction of dielectric constant, and an increase of magnetic susceptibility are also seen at low temperatures. These data suggest an emergent instability which competes with the spiral magnetic ordering and the ferroelectricity. Candidate mechanisms are discussed based on the quasi-one-dimensional nature of the magnetic system.

Periodic Anderson model is one of the most important models in the field of strongly correlated electrons. With the recent developed numerical method density matrix embedding theory, we study the ground state properties of the periodic Anderson model on a two-dimensional square lattice. We systematically investigate the phase diagram away from half filling. We find three different phases in this region, which are distinguished by the local moment and the spin-spin correlation functions. The phase transition between the two antiferromagnetic phases is of first order. It is the so-called Lifshitz transition accompanied by a reconstruction of the Fermi surface. As the filling is close to half filling, there is no difference between the two antiferromagnetic phases. From the results of the spin-spin correlation, we find that the Kondo singlet is formed even in the antiferromagnetic phase.

We demonstrate a high performance GaAs/AlGaAs-based quantum-well photodetector (QWP) device with a peak response frequency of 4.3 THz. The negative differential resistance (NDR) phenomenon is found in the dark current-voltage (I-V) curve in the current sweeping measurement mode, from which the breakdown voltage is determined. The photocurrent spectra and blackbody current responsivities at different voltages are measured. Based on the experimental data, the peak responsivity of 0.3 A/W (at 0.15 V, 8 K) is derived, and the detection sensitivity is higher than 10¹¹ Jones, which is in the similar level as that of the commercialized liquid-helium-cooled silicon bolometers. We attribute the high detection performance of the device to the small ohmic contact resistance of ~2Ω and the big breakdown bias.