Quantum phase transitions are a fascinating area of condensed matter physics. The extension through complexification not only broadens the scope of this field but also offers a new framework for understanding criticality and its statistical implications. This mini review provides a concise overview of recent developments in complexification, primarily covering finite temperature and equilibrium quantum phase transitions, as well as their connection with dynamical quantum phase transitions and non-Hermitian physics, with a particular focus on the significance of Fisher zeros. Starting from the newly discovered self-similarity phenomenon associated with complex partition functions, we further discuss research on self-similar systems briefly. Finally, we offer a perspective on these aspects.

Phase transitions and critical phenomena are among the most intriguing phenomena in nature and society. They are classified into first-order phase transitions (FOPTs) and continuous ones. While the latter shows marvelous phenomena of scaling and universality, whether the former behaves similarly is a long-standing controversial issue. Here we definitely demonstrate complete universal scaling in field driven FOPTs for Langevin equations in both zero and two spatial dimensions by rescaling all parameters and subtracting nonuniversal contributions with singular dimensions from an effective temperature and a special field according to an effective theory. This offers a perspective different from the usual nucleation and growth but conforming to continuous phase transitions to study FOPTs.

Motivated by the determination for the spin-parity quantum numbers of the $X(2370)$ meson at BESIII, we extend our dispersive analysis on hadronic ground states to excited states. The idea is to start with the dispersion relation which a correlation function obeys, and subtract the known ground-state contribution from the involved spectral density. Solving the resultant dispersion relation as an inverse problem with available operator-product-expansion inputs, we extract excited-state masses from the subtracted spectral density. This formalism is verified by means of the application to the series of $\rho$ resonances, which establishes the $\rho(770)$, $\rho(1450)$ and $\rho(1700)$ mesons one by one under the sequential subtraction procedure. Our previous study has suggested the admixture of the $f_0(1370)$, $f_0(1500)$ and $f_0(1710)$ mesons (the $\eta(1760)$ meson) to be the lightest scalar (pseudoscalar) glueball. The present work predicts that the $f_0(2200)$ ($X(2370)$) meson is the first excited scalar (pseudoscalar) glueball.

We explore the properties of the bottom-quark on-shell mass ($M_b$) by using its relation to the $\overline{\rm MS}$ mass (${\overline m}_b$). At present, this $\overline{\rm MS}$-on-shell relation has been known up to four-loop QCD corrections, which however still has a $\sim$ $2\%$ scale uncertainty by taking the renormalization scale as ${\overline m}_b({\overline m}_b)$ and varying it within the usual range of $[{\overline m}_b({\overline m}_b)/2,\, 2 {\overline m}_b({\overline m}_b)]$. The principle of maximum conformality (PMC) is adopted to achieve a more precise $\overline{\rm MS}$-on-shell relation by eliminating such scale uncertainty. As a step forward, we also estimate the magnitude of the uncalculated higher-order terms by using the Padé approximation approach. Numerically, by using the $\overline{\rm MS}$ mass ${\overline m}_b({\overline m}_b)=4.183\pm0.007$ GeV as an input, our predicted value for the bottom-quark on-shell mass becomes $M_b\simeq 5.372^{+0.091}_{-0.075}$ GeV, where the uncertainty is the squared average of the ones caused by $\Delta \alpha_s(M_Z)$, $\Delta {\overline m}_b({\overline m}_b)$, and the estimated magnitude of the higher-order terms.

Strong empirical and phenomenological indications exist for large sea-quark admixtures in the low-lying excited baryons. Investigating the low-lying excited baryon $\varSigma^*(1/2^-)$ is important for determining the nature of the low-lying excited baryons. We review the experimental and theoretical progress on the studies of the $\varSigma^*(1/2^-)$. Although several candidates have received intensive discussions, such as $\varSigma(1620)$ and $\varSigma(1480)$, their existence needs further confirmation. Following the prediction of the unquenched quark models for the $\varSigma^*(1/2^-)$, many theoretical works suggested the existence of these states in various processes. Future experimental measurements could shed light on the existence of the low-lying excited $\varSigma^*(1/2^-)$ state.

Thermal quantities, including the entropy density and gluon spectrum, of quark matter within a box that is finite in the longitudinal direction are calculated using a bag model. Under the assumption of entropy conservation, the corresponding gluon dissociation rate of $J/\psi$ is studied. It reaches a maximum at a certain longitudinal size $L_{\rm m}$, below which the suppression is weak even if the temperature becomes higher than that without the finite size effect, and above which the dissociation rate approaches to the thermodynamic limit gradually with increasing longitudinal size of the fireball.

Second harmonic generation (SHG) in optical materials serves as important techniques for laser source generations in awkward spectral ranges, physical identities of materials in crystalline symmetry and interfacial configuration. Here, we present a comprehensive review on SHGs in nanowires (NWs), which have been recognized as an important element in constructing photonic and optoelectronic devices with compact footprint and high quantum yield. Relying on NW's one-dimensional geometry, its SHG could be employed as a sophisticated spectroscopy to determine the crystal phase and orientation, as well as the internal strain. The enhancements of SHG efficiency in NWs are discussed then, which were realized by hybrid integrating them with two-dimensional materials, nanophotonic and plasmonic structures. Finally, the potential applications of NW SHGs are concluded, including the areas of optical correlators and constructions of on-chip nano-laser sources.

Site disorder exists in some practical semiconductors and can significantly impact their intrinsic properties both beneficially and detrimentally. However, the uncertain local order and structure pose a challenge for experimental and theoretical research. Especially, it hinders the investigation of the effects of the diverse local atomic environments resulting from the site disorder. We employ the special quasi-random structure method to perform first-principles research on connection between local site disorder and electronic/optical properties, using cation-disordered AgBiS$_2$ (rock salt phase) as an example. We predict that cation-disordered AgBiS$_2$ has a bandgap ranging from 0.6 to 0.8 eV without spin-orbit coupling and that spin-orbit coupling reduces this by approximately 0.3 eV. We observe the effects of local structural features in the disordered lattice, such as the one-dimensional chain-like aggregation of cations that results in formation of doping energy bands near the band edges, formation and broadening of band-tail states, and the disturbance in the local electrostatic potential, which significantly reduces the bandgap and stability. The influence of these ordered features on the optical properties is confined to alterations in the bandgap and does not markedly affect the joint density of states or optical absorption. Our study provides a research roadmap for exploring the electronic structure of site-disordered semiconductor materials, suggests that the ordered chain-like aggregation of cations is an effective way to regulate the bandgap of AgBiS$_2$, and provides insight into how variations in local order associated with processing can affect properties.

With the rapid increase in power density of electronic devices, thermal management has become urgent for the electronics industry. Controlling temperature in the back-end-of-line is crucial for maintaining the reliability of integrated circuits, where many atomic-scale interfaces exist. The theoretical models of interface thermal conductance not only accurately predict the values but also help to analyze the underlying mechanism. This review picks up and introduces some representative theoretical models considering interfacial roughness, elastic and inelastic processes, and electron–phonon couplings, etc. Moreover, the limitations and problems of these models are also discussed.

In the quasi-free electron model, the Fermi surface spreads into a sphere in the Brillouin zone, i.e., the Fermi sphere. The Fermi sphere exists widely in metal systems, no matter whether the crystal is in a body-center cubic, face-center cubic, or hexagonal close-packed lattice. Here, we report a class of compounds stabilized at high pressure with Rubik's cubic Fermi surface, in which the representative example is $Pm\bar{3}n$-CaCl$_{3}$. Our quantum-mechanical variable-composition evolutionary simulations predict the thermal stabilities of CaCl$_{3}$, and the tight-binding model reveals that its unique Fermi surface originates from the quasi-one-dimensional interaction, structural symmetric protection, and particle-hole symmetry breaking. Furthermore, by its flat and steep band structure, CaCl$_{3}$ has a huge span of effective mass from $9.08\times 10^{3} m_{\rm e}$ (super-heavy) to $5.13\times 10^{-4} m_{\rm e}$ on the Fermi level, which supplies an interesting platform for quasiparticle research.

Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors. However, accurately characterizing anisotropic strain can be challenging and complex. Here, we utilize a cryogenic optical system equipped with a high-spatial-resolution microscope to characterize surface strains in iron-based superconductors using the digital image correlation method. Compared with other methods such as high-resolution x-ray diffraction, strain gauge, and capacitive sensor, digital image correlation offers a non-contact full-field measurement approach, acting as an optical virtual strain gauge that provides high spatial resolution. The results measured on detwinned BaFe$_2$As$_2$ are quantitatively consistent with the distortion measured by x-ray diffraction and neutron Larmor diffraction. These findings highlight the potential of cryogenic digital image correlation as an effective and accessible tool for probing the isotropic and anisotropic strains, facilitating applications of uniaxial strain tuning in research of quantum materials.

SrIrO$_{3}$, a Dirac material with a strong spin-orbit coupling (SOC), is a platform for studying topological properties in strongly correlated systems, where its band structure can be modulated by multiple factors, such as crystal symmetry, elements doping, oxygen vacancies, magnetic field, and temperature. Here, we find that the engineered carrier density plays a critical role on the magnetoelectric transport properties of the topological semimetal SrIrO$_{3}$. The decrease of carrier density subdues the weak localization and the associated negative magnetoresistance, while enhancing the SOC-induced weak anti-localization. Notably, the sample with the lowest carrier density exhibits high-field positive magnetoresistance, suggesting the presence of a Dirac cone. In addition, the anisotropic magnetoresistance indicates the anisotropy of the electronic structure near the Fermi level. The engineering of carrier density provides a general strategy to control the Fermi surface and electronic structure in topological materials.

Topological phonon is a new frontier in the field of topological materials. Different from electronic structures, phonons are bosons and most topological phonons are metallic form. Previous studies about topological phonon states were focused on three-dimensional (3D) materials. Owing to the lack of material candidates, two-dimensional (2D) and van der Waals $f$-electron-related topological phonons were rarely reported. Based on first-principles calculations, we investigate the topological phononic state in the heavy fermion material CeSiI with a layered structure. Both 3D bulk and 2D monolayers have topological nontrivial states in the rarely seen $f$ electron dominated van der Waals metal. Owing to the $PT$ and $C_{3z}$ symmetries, Weyl nodal lines with nonzero Chern numbers exist on the hinge of the Brillouin zone. Protected by $C_{3z}$ rotation symmetry, three pairs of Weyl points with $\pm \pi$ Berry phase exist at point $K$ near the frequency of 8 and 10 THz. In addition to the bulk topological charges, corresponding surface/edge states are also systematically analyzed, which gives a consistent understanding. Our results propose another interesting point in the newly discovered rear earth heavy fermion material CeSiI and are helpful for future experimental research of CeSiI topological phonons.

Chemical doping is a critical factor in the development of new superconductors or optimizing the superconducting transition temperature ($T_{\rm c}$) of the parent superconducting materials. Here, a new simple urea approach is developed to synthesize the N-doped $\alpha$-Mo$_{2}$C. Benefiting from the simple urea method, a broad superconducting dome is found in the Mo$_{2}$C$_{1-x}$N$_{x}$ ($0\leqslant x \leqslant 0.49$) compositions. X-ray diffraction results show that the structure of $\alpha$-Mo$_{2}$C remains unchanged and there is a variation of lattice parameters with nitrogen doping. Resistivity, magnetic susceptibility, and heat capacity measurement results confirm that $T_{\rm c}$ was strongly increased from 2.68 K ($x=0$) to 7.05 K ($x=0.49$). First-principles calculations and our analysis indicate that increasing nitrogen doping leads to a rise in the density of states at the Fermi level and doping-induced phonon softening, which enhances electron–phonon coupling. This results in an increase in $T_{\rm c}$ and a sharp rise in the upper critical field. Our findings provide a promising strategy for fabricating transition metal carbonitrides and provide a material platform for further study of the superconductivity of transition metal carbides.

The two-dimensional magnetic van der Waals heterojunctions have opened unprecedented opportunities to explore new physics due to their potential for spintronic applications. Here, combing density functional theory with non-equilibrium Green's function technique, we systematically investigate the spin-polarized transport properties of Cu/FeX$_{2}$/h-BN/FeX$_{2}$/Cu (X = Cl, Br, I) magnetic tunnel junctions (MTJs). It is found that the maximum tunneling magnetoresistance of Cu/FeCl$_{2}$/h-BN/FeCl$_{2}$/Cu, Cu/FeBr$_{2}$/h-BN/FeBr$_{2}$/Cu, and Cu/FeI$_{2}$/h-BN/FeI$_{2}$/Cu MTJs can reach 3443%, 3069%, and 1676%, respectively. In the parallel state, the resistance area products at zero bias for Cu/FeCl$_{2}$/h-BN/FeCl$_{2}$/Cu, Cu/FeBr$_{2}$/h-BN/FeBr$_{2}$/Cu, and Cu/FeI$_{2}$/h-BN/FeI$_{2}$/Cu MTJs are 0.92, 0.47, and 0.32 $\Omega$$\cdot$µm$^{2}$, respectively. More interestingly, our results indicate that Cu/FeX$_{2}$/h-BN/FeX$_{2}$/Cu (X = Cl, Br, I) MTJs can realize spin filtering effect, while Cu/FeCl$_{2}$/h-BN/FeCl$_{2}$/Cu and Cu/FeI$_{2}$/h-BN/FeI$_{2}$/Cu MTJs exhibit negative differential resistance. Our results demonstrate that large tunneling magnetoresistance, negative differential resistance effect, low resistance area product as well as excellent spin filtering effect coexist in Cu/FeCl$_{2}$/h-BN/FeCl$_{2}$/Cu and Cu/FeI$_{2}$/h-BN/FeI$_{2}$/Cu MTJs, and that the feasible tunability of such a kind of van der Waals magnetic tunnel junctions is beneficial to designing next-generation logic devices.

Fe$_{3}$GaTe$_{2}$, as a layered ferromagnetic material, has a Curie temperature ($T_{\rm c}$) higher than room temperature, making it the key material in next-generation spintronic devices. To be used in practical devices, large-sized high-quality Fe$_{3}$GaTe$_{2}$ thin films need to be prepared. Here, the centimeter-scale thin film samples with high crystal quality and above-room-temperature ferromagnetism with strong perpendicular magnetic anisotropy were prepared by molecular beam epitaxy technology. Furthermore, the $T_{\rm c}$ of the samples raises as the film thickness increases, and reaches 367 K when the film thickness is 60 nm. This study provides material foundations for the new generation of van der Waals spintronic devices and paves the way for the commercial application of Fe$_{3}$GaTe$_{2}$.

Recent experimental and theoretical work has focused on two-dimensional van der Waals (2D vdW) magnets due to their potential applications in sensing and spintronics devises. In measurements of these emerging materials, conventional magnetometry often encounters challenges in characterizing the magnetic properties of small-sized vdW materials, especially for antiferromagnets with nearly compensated magnetic moments. Here, we investigate the magnetism of 2D antiferromagnet CrPS$_{4}$ with a thickness of 8 nm by using dynamic cantilever magnetometry (DCM). Through a combination of DCM experiment and the calculation based on a Stoner–Wohlfarth-type model, we unravel the magnetization states in 2D CrPS$_{4}$ antiferromagnet. In the case of $H\parallel c$, a two-stage phase transition is observed. For $H\perp c$, a hump in the effective magnetic restoring force is noted, which implies the presence of spin reorientation as temperature increases. These results demonstrate the benefits of DCM for studying magnetism of 2D magnets.

We explore the structural evolutions of stoichiometric LiMO$_{2}$ using the first-principles calculations combined with the cluster expansion method. We automatically obtain the ground state structures of the stoichiometric LiMO$_{2}$ by just considering the cation orderings in the quasi rock-salt structures and the following structural relaxations due to both the atomic size mismatches and the Jahn–Teller distortions. We point out that, on the one hand, the cation orderings are mainly determined by the nearest, the second nearest, and the third nearest cation interactions and can be obtained from the ‘phase diagram’ we have built using the relative strengths of effective cluster interaction (ECI). On the other hand, the structural relaxations are dominated by the crystal field splitting (CFS) energies, i.e., structures with larger CFS energies are more stable. By calculating the ECIs and CFS energies for various structures of LiMO$_{2}$, we clearly show how ECI and CFS play roles in determining the structural evolution mechanism of these systems.

Self-assembly of bacteria in electric fields is a promising route to fabricate biomaterials with reversible and specific structures. However, due to relatively less studies, our understanding of the self-assembly of bacteria in electric fields is still incomplete. Particularly, how different bacterial species behave differently in their field-mediated self-assembly behavior remains to be disclosed. In this study, we choose four bacterial species, including Shewanella oneidensis, Pseudomonas aeruginosa, Bacillus subtilis and Lactococcus lactis as model systems, and investigate their self-assembly behavior in alternating-current (AC) electric fields for both diluted and concentrated suspensions. The phase diagrams in the plane of applied field strength vs frequency are obtained. The results show that in diluted suspensions, a transition sequence of isotropic–paranematic–string–columnar phases is observed in all strains as the field strength increases. Details of the assembled structures are quantitatively differentiated among different strains. In concentrated suspensions, besides the isotropic and paranematic phases, a higher ordered phase with interdigitating rectangular crystal domains (OIR) and an ordered phase with smectic A liquid crystal domains are observed for S. oneidensis and P. aeruginosa, respectively. Our findings shed new light on fabricating potential biomaterials by assembling cells of appropriately chosen bacterial species that have desired surface properties under AC electric fields.

Fast radio bursts (FRBs) are short-duration radio transients with mysterious origins. Since their uncertainty, there are very few FRBs observed by different instruments simultaneously. This study presents a detailed analysis of a burst from FRB 20190520B observed by FAST and Parkes at the same time. The spectrum of this individual burst ended at the upper limit of the FAST frequency band and was simultaneously detected by the Parkes telescope in the 1.5–1.8 GHz range. By employing spectral energy distribution (SED) and spectral sharpness methods, we confirmed the presence of narrow-band radiation in FRB 20190520B, which is crucial for understanding its radiation mechanisms. Our findings support the narrow-band characteristics that most repeaters exhibit. This work also highlights the necessity of continued multiband observations to explore its periodicity and frequency-dependent properties, contributing to an in-depth understanding of FRB phenomena.

As a major interstellar medium, the atomic neutral hydrogen (H ${\scriptstyle{\rm I}}$) HI plays an important role in the galaxy evolution. It provides the ingredient for star formation, and sensitively traces the internal processes and external perturbations influencing the galaxy. With the beginning of many new radio telescopes and surveys, H ${\scriptscriptstyle{\rm I}}$ may make a more significant contribution to the understanding of galaxies in the near future. This review discusses the major development of the 21 cm emission-line H ${\scriptscriptstyle{\rm I}}$ observations and studies in the past few years, including its scaling relations with other galaxy properties, its kinematics and structures, its role in environmental studies, and its constraints on hydrodynamical simulations. The local-Universe H ${\scriptscriptstyle{\rm I}}$ scaling relations of stellar-mass-selected samples extend smoothly to 10$^{9}M_\odot$ stellar mass, with a tentative evolution to the redshift of $\sim$ 0.1. The development of measurement techniques enables better estimations of H ${\scriptscriptstyle{\rm I}}$ non-circular motion, dispersion, and thickness, and new observations revealed extended or extra-planar H ${\scriptscriptstyle{\rm I}}$ structures, both helpfully constraining the gas accretion, stellar feedback, and star formation processes of galaxy evolution models. H ${\scriptscriptstyle{\rm I}}$ is very useful for tracing the satellite evolution in dense environments, the studies of which would benefit from ongoing blind H ${\scriptscriptstyle{\rm I}}$ surveys. Though simulations still cannot fully reproduce H ${\scriptscriptstyle{\rm I}}$ gas properties, they help to understand the role of possible factors in regulating H ${\scriptscriptstyle{\rm I}}$ properties.