Carbon nanotubes (CNTs) have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potential for the interactions between cations and CNTs plays a crucial role in understanding the transport behaviors of ions near and inside the CNT, which is key to these expectations. Here, using density functional theory calculations, we provide classical force field potentials for the interactions of Na⁺/hydrated Na⁺ with (7,7), (8,8), (9,9), and (10,10)-type CNTs. These potentials can be directly used in current popular classical software such as nanoscale molecular dynamics (NAMD) by employing the tclBC interface. By incorporating the potential of hydrated cation-π interactions to classical all-atom force fields, we show that the ions will move inside the CNT and accumulate, which will block the water flow in wide CNTs. This blockage of water flow in wide CNTs is consistent with recent experimental observations. These results will be helpful for the understanding and design of desalination membranes, new types of nanofluidic channels, nanosensors, and nanoreactors based on CNT platforms.

The Andreev-like levels and the free energy of the spin superconductor/insulator/spin superconductor junction are obtained by using the Bogoliubov-de Gennes equation. The phase dependence of the spin supercurrents exhibits a 0-π transition by changing the barrier strength. The dependences of the critical current on the barrier strength and the temperature are also presented.

Absorption and carrier transport behavior plays an important role in the light-to-electricity conversion process, which is difficult to characterize. Here we develop a method to visualize such a conversion process in the InGaN/GaN multi-quantum wells embedded in a p-n junction. Under non-resonant absorption conditions, a photocurrent was generated and the photoluminescence intensity decayed by more than 70% when the p-n junction out-circuit was switched from open to short. However, when the excitation photon energy decreased to the resonant absorption edge, the photocurrent dropped drastically and the photoluminescence under open and short circuit conditions showed similar intensity. These results indicate that the escaping of the photo-generated carriers from the quantum wells is closely related to the excitation photon energy.

Kondo semimetal CeRu₄Sn₆ is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single-and poly-crystalline samples. The electrical resistivity ρ(T) is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high-and low-temperature windows are found to increase with pressure. A flat ρ(T) observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.

We discuss the concept of typicality of quantum states at quantum-critical points, using projector Monte Carlo simulations of an S=1/2 bilayer Heisenberg antiferromagnet as an illustration. With the projection (imaginary) time τ scaled as τ=aL^z, L being the system length and z the dynamic critical exponent (which takes the value z=1 in the bilayer model studied here), a critical point can be identified which asymptotically flows to the correct location and universality class with increasing L, independently of the prefactor a and the initial state. Varying the proportionality factor a and the initial state only changes the cross-over behavior into the asymptotic large-L behavior. In some cases, choosing an optimal factor a may also lead to the vanishing of the leading finite-size corrections. The observation of typicality can be used to speed up simulations of quantum criticality, not only within the Monte Carlo approach but also with other numerical methods where imaginary-time evolution is employed, e.g., tensor network states, as it is not necessary to evolve fully to the ground state but only for sufficiently long times to reach the typicality regime.

Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr_1-xBa_xFe_1.97Ni_0.03As₂, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Sr_1-xBa_xFe₂As₂ is determined by the strength of the magnetic-elastic coupling.

PdTe₂, a member of layered transition metal dichalcogenides (TMDs), has aroused significant research interest due to the coexistence of superconductivity and type-Ⅱ Dirac fermions. It provides a promising platform to explore the interplay between superconducting quasiparticles and Dirac fermions. Moreover, PdTe₂ has also been used as a substrate for monolayer antimonene growth. Here in this paper, we report the epitaxial growth of high quality PdTe₂ films on bilayer graphene/SiC(0001) by molecular beam epitaxy (MBE). Atomically thin films are characterized by scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and Raman spectroscopy. The band structure of 6-layer PdTe₂ film is measured by angle-resolved photoemission spectroscopy (ARPES). Moreover, our air exposure experiments show excellent chemical stability of epitaxial PdTe₂ film. High-quality PdTe₂ films provide opportunities to build antimonene/PdTe₂ heterostructure in ultrahigh vacuum for future applications in electronic and optoelectronic nanodevices.

Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increasing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional (2D) systems, few-layer h-BN and indium iodide (InI). We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the competition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.

By exactly solving the effective two-body interaction for a two-dimensional electron system with layer thickness and an in-plane magnetic field, we recently found that the effective interaction can be described by the generalized pseudopotentials (PPs) without the rotational symmetry. With this pseudopotential description, we numerically investigate the behavior of the fractional quantum Hall (FQH) states both in the lowest Landau level (LLL) and first excited Landau level (1LL). The enhancements of the 7/3 FQH state on the 1LL for a small tilted magnetic field are observed when layer thickness is larger than some critical values, while the gap of the 1/3 state in the LLL monotonically reduced with increasing the in-plane field. From the static structure factor calculation, we find that the systems are strongly anisotropic and finally enter into a stripe phase with a large tilting. With considering the Landau level mixing correction on the two-body interaction, we find the strong LL mixing cancels the enhancements of the FQH states in the 1LL.

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.