Table of contents

Quantum computers have the potential to solve problems that are difficult or impossible to address using classical modes of computation. Laser cooled neutral atoms at ultracold temperatures offer unique possibilities to study interacting many-body quantum systems which is at the heart of various quantum condensed matter phenomena. The first-generation neutral atom quantum computers for performing special purpose quantum computations was realized by trapping ultracold atoms in optical lattices. These tunable and scalable machines provided tremendous opportunities to study various quantum phases of Bose and Fermi Hubbard models, topological phases, and non-equilibrium dynamics, with control over key system parameters enabling insightful explorations within specific quantum models. In a more recent advent, arrays of single neutral atoms trapped in optical tweezers have emerged as dark horse candidate for universal and fault tolerant quantum computing. Here, we review recent advances and achievements obtained with this platform and discuss future perspectives.

The exploration of high-temperature superconductors and the mechanisms underlying superconductivity continues to present significant challenges in condensed matter physics. Identifying new potential superconducting (SC) platforms is critical for advancing our understanding of superconductivity and its interactions with other quantum states. Metal sulfides constitute a diverse family of materials that exhibit unique physical properties, with crystal structures that can be tailored from one-dimensional (1D) to three-dimensional (3D) by varying the metal-to-sulfur ratio. Recent investigations into the superconductivity of metal sulfides have revealed extraordinary quantum phenomena, including chiral superconductivity, two-dimensional (2D) Ising superconductivity, and the competition between charge density waves and superconductivity. Furthermore, pressure tuning—a refined technique for modifying electronic and crystal structures without introducing impurities—has facilitated the emergence of superconductivity in various semiconducting and even insulating metal sulfides. In this review, we summarize and analyze the rich SC properties of metal sulfides, encompassing 3D metal monosulfides, 2D metal disulfides, and quasi-1D transition metal trisulfides. We also discuss additional systems, including hydrogen sulfides, Th₃P₄-type sulfides, and Bi–S systems. Collectively, these findings underscore that metal sulfides not only represent promising SC materials but also serve as excellent platforms for further investigation into the mechanisms of superconductivity.

Ferroelectric materials are considered candidates for functional device application since their discovery in 1920. The functionality is realized by polarization evolution itself or the resulting effects. Studies on ferroelectrics have been going on over a century with a rough journey, because they have the excellent physical properties and also the fatal disadvantages for the device applications, where polarization microstructure and the dynamics are always the core issues. The demand for miniaturization, low energy consumption, and intelligence of devices leads to the advancement of the studies on the polarization microstructure and dynamics towards microscopic and ultrafast scales, as well as precise manipulation. This review mainly focuses on the inherent logic of the development of the theoretical modeling on the polarization dynamics. We would like to discuss the historical background of the development of theoretical models and their limitations, following the historical trajectory how to understand the multiscale nature of polarization microstructure and dynamics and the developing demand of functional devices applications, based on which the prospect and future development direction of theoretical modeling are proposed.

We conducted a detailed experimental investigation of the Ag(977) vicinal surface, a high Miller index surface derived from the (111) surface. The sample surface was prepared using standard methodology and its quality was examined by x-ray photoelectron spectroscopy, low energy electron diffraction (LEED) and scanning tunneling microscopy. I(V)-LEED analysis was used to determine the surface structure focusing the intricate relaxation dynamics expected for this surface. Our LEED analysis revealed an inward relaxation for the step chain (SC) atoms, whereas the corner atoms (CC) relaxed outwards. To gain more information on the obtained relaxations, we also performed density functional theory (DFT) calculations for the constructed structural model. Through charge distribution analysis, we found out that the step atoms interact weakly with their adjacent counterparts, resulting in terrace atoms presenting electronic environment similar to those found on flat surfaces. Furthermore, we conducted angle-resolved photoemission spectroscopy (ARPES) measurements to map the electronic structure of the surface. The DFT calculations and ARPES results have shown that the electronic bands observed arise from the hybridization between bulk and surface electronic states.

We report evidence of a finite density of states at the Fermi level at the surface of epitaxial thin films of the narrow bandgap Mott insulator Sr₃Ir₂O₇(001). The Brillouin zone critical points for Sr₃Ir₂O₇(001) thin films have been determined by a comparison of the band mapping from angle-resolved photoemission spectroscopy and low energy electron diffraction. Angle-resolved x-ray photoemission studies reveal the surface termination of Sr₃Ir₂O₇(001) is Sr–O. The absence of dispersion with photon energy, or changing wave vector along the surface normal, indicates the two-dimensional character of the bands contributing to the density of states close to the Fermi level for Sr₃Ir₂O₇(001) thin films. Thus, the finite density of states at the Fermi level is attributed to surface states or surface resonances. The appearance of a finite density of states at the Fermi level is consistent with the increased conductivity with decreasing film thickness for ultrathin Sr₃Ir₂O₇(001) films.

Recent discoveries involving high-temperature superconductivity in H₃S and LaH₁₀ have sparked a renewed interest in exploring the potential for superconductivity within hydrides. These superconductors require extremely high-pressure condition (${\sim} 100\, \textrm{GPa}$), rendering them virtually impractical for industrial applications. In this study, we verify the occurrence of a low pressure superconductivity phase transition in a system containing two graphene layers with sine form corrugations where CeH₉ doped molecules are intercalated between the layers. The lowest-order constrained variational method is applied to calculate the thermodynamic and electrical properties of the valence electrons. We examine 9900 different distributions of CeH₉ molecules separately for finding a second-order phase transition with maximized critical temperature. The novelty of the present work is the prediction of a superconductivity transition at $T_\textrm{c} = 198.61$ K for a specific distribution of CeH₉ molecules with applying no external pressure on the exterior surfaces of the graphene sheets. Notably, this critical temperature is approximately 65 K higher than that observed in cuprate materials (HgBa₂Ca₂Cu₃O$_{8+\delta}$), which are known for their high $T_\textrm{c}$ values at room pressure. It is interesting that in this particular case, the distribution periodicity of CeH₉ molecules bears the closest resemblance to the periodicity of the graphene corrugations among all 9900 examined cases. Computing the energy gap of the valence electrons reveals that this critical behavior corresponds to an unconventional superconductivity phase transition exhibiting a high critical current density on the order of ${\sim} 10^{7}\,\textrm{A cm}^{-2}$.

In this work, we investigate the effect of magnetic disorder on a magnetic topological insulator thin film that supports the semi-magnetic topological insulator, quantum anomalous Hall insulator, and axion insulator phases. Once the magnetic disorder is introduced, we find that the semi-magnetic topological insulator phase exhibits a significant fluctuation in the Hall conductance but its averaged value maintains the half-quantization. The scenario is distinct from that in the quantum anomalous Hall insulator and axion insulator phases, where the Hall conductance is stable and exhibits no fluctuation in the presence of weak magnetic disorder. We propose that the conductance fluctuation in the semi-magnetic topological insulator phase is attributed to the gapless surface state. The fluctuation arises because the system fluctuates between different quantized conductance plateaus, and its origin is different from the conventional conductance fluctuations caused by Anderson disorder.

Accurately modeling nonlinear optical experiments such as second-harmonic scattering and hyper-Raman spectroscopy requires the hyperpolarizability β, a nonlinear response to an applied electric field. The hyperpolarizability tensor is a computationally expensive quantity to calculate, making it a natural target for machine-learning methods. We test a family of recently developed models for the hyperpolarizability of water, trained on small clusters containing up to 8 water molecules. These models are able to predict β for larger clusters, with more complex structures than those observed in the training set. For configurations of bulk water, the agreement is not so straightforward: while the total hyperpolarizability is quite well described, the predicted molecularβ tensors vary wildly between models. This means that while experiments whose outputs depend on total hyperpolarizability can be accurately modeled, those that require molecular quantities will require improved models.

We investigate chiral quantum dot (QD)-based Josephson junction and show the correlation-induced Josephson diode effect (JDE) in it. The presence of electron-electron interaction spontaneously creates an imbalance between up- and down-spin electrons during the non-equilibrium transport making the QD effectively magnetic. The simultaneous presence of the chirality and the interaction eventually results in the field-free JDE in our chiral QD junction. We employ the Keldysh non-equilibrium Green's function technique to study the behavior of the Josephson current and the rectification coefficient (RC) of our Josephson diode (JD). We show a sign-changing behavior of the RC with the Coulomb correlation and the lead-to-dot coupling strength and find the maximum magnitude of the RC $\sim 72\%$ for moderate interaction strength. Our proposed field-free JD based on interacting chiral QD may be a potential switching component in superconductor based devices.

In this work, we explore the structural, mechanical, and electronic properties of 2D-B9, a borophene allotrope with a unique bonding structure and promising potential for strain engineering. Through first-principles calculations, we investigate the material's stability, revealing a robust phonon spectrum and favorable mechanical flexibility, including isotropic behavior and a moderate Young's modulus. The electronic structure of 2D-B9 features key characteristics such as a van Hove singularity (vHS) and a Dirac point, which can be dynamically tuned via strain. Under tensile strain, the vHS shifts downward, while compressive strain causes it to rise, with the vHS aligning with the Fermi level at 10% compression. This strain-induced tuning of the electronic structure is further confirmed by examining changes in Fermi velocity, which is found to be similar to that of graphene at 9 × 10⁵ m s⁻¹, indicating high electronic mobility. These results highlight the potential of 2D-B9 for applications in flexible electronics, quantum devices, and other technologies where strain-sensitive electronic properties are essential.

Ferro-rotational magnet RbFe(SO₄)₂ has attracted attention for its stable ferro-rotational phase and electric-field-controlled magnetic chirality. This work presents the multiferroic properties and H–T phase diagram of RbFe(SO₄)₂, which have been underexplored. Our measurements of magnetic susceptibility, ferroelectric polarization, and dielectric constant under various magnetic fields reveal four distinct phases: (I) a ferroelectric and helical magnetic phase below 4 K and 6 T, (II) a paraelectric and collinear magnetic phase below 4 K and above 6 T, (III) a paraelectric and non-collinear magnetic phase below 4 K and above 9 T, and (IV) a paraelectric and paramagnetic above 4 K. This study clarifies the multiferroic behavior and H–T phase diagram of RbFe(SO₄)₂, providing valuable insights into ferro-rotational magnets.

The paper theoretically studies thin ferromagnetic films obtained by successive deposition of layers of easy-axis and easy-plane materials. It is shown that in films of this type, under certain conditions, effective anisotropy can arise, leading to the appearance of new directions of easy magnetization, set of which is divided into two independent orbits. The structure of domain walls (DWs) arising as a result of the transition of the magnetization vector from one orbit to another was studied. It has been proven that in the presence of perforations in the films under consideration, topologically protected inhomogeneities can arise, which are localized in the vicinity of two closely spaced holes and can be in one of six nonequivalent states, as a result of which paired perforations can be considered as memory cells for recording data in a base 6 number system. A numerical experiment has demonstrated that two adjacent cells can actually independently encode two digits in the specified number system due to the possibility of forming thin DWs between the cells.

MAX phases are a family of atomically laminated materials with various potential applications. Mn₂GaC is a prototype magnetic MAX phase, where complex magnetic behaviour arises due to competing interactions. We have resolved the room temperature magnetic structure of Mn₂GaC by neutron diffraction from single-crystal thin films and we propose a magnetic model for the low temperature phase. It orders in a helical structure, with a rotation angle that changes gradually between 120° and 90° depending on temperature.