Chiral superconductors are topological as characterized by a finite Chern number and chiral edge modes. Direct fingerprints of chiral superconductivity are thus often taken to be spontaneous edge currents with associated magnetic signatures. However, a number of recent theoretical studies have shown that the total edge current along semi-infinite edges is greatly reduced or even vanishes in many scenarios for all pairing symmetries except chiral $p$ wave, thus impeding experimental detection. We demonstrate how mesoscopic finite-sized samples can be designed to give rise to a shape- and size-dependent strong enhancement of the chiral edge currents and their generated orbital magnetic moment and magnetic fields. In particular, we find that low rotational symmetry systems, such as pentagons and hexagons, give rise to the largest currents, while circular disks also generate large currents but in the opposite direction. We estimate the resulting magnetic fields to be as large as $0.01–0.5$ mT, with a magnetic moment approaching ${\mu }_{\mathrm{B}}/2$ per Cooper pair, where ${\mu }_{\mathrm{B}}$ is the Bohr magneton. The current and magnetic signatures diverge with shrinking system sizes, eventually cut off by finite-size suppression of chiral superconductivity. We thus also extract the full phase diagram as a function of temperature and system size for different geometries, including competing superconducting orders. In geometries strongly suppressing only one of the $d$-wave components, we find an additional heat capacity jump, as large as $10\%$ of the bulk normal-superconducting transition, marking the transition between a chiral and a nodal $d$-wave state. This further acts as an indirect signature of chiral superconductivity, measurable with nanocalorimetry. Our results are relevant for system sizes on the order of tens to hundreds of coherence lengths, and highlight mesoscopic patterning as a viable route to experimentally identify chiral $d$-wave superconductivity.

The recently synthesized $\eta$-carbide-type superconductors exhibit large critical fields. A notable example is ${\mathrm{Ti}}_4{\mathrm{Ir}}_2\mathrm{O}$, for which the upper critical field strongly violates the Pauli paramagnetic limit, a behavior that is unusual for cubic materials that preserve inversion symmetry. Here, by combining density functional theory (DFT) and analytic modeling, we provide an explanation for this enhanced Pauli limiting field. We show that the nonsymmorphic $\mathrm{Fd}\overline{3}\mathrm{m}$ symmetry implies that the electronic states near the X points exhibit strong spin-orbit coupling (SOC), which leads to a vanishing effective $g$ factor and enables the enhanced Pauli limiting field. Furthermore, our DFT results reveal a Van Hove singularity peak near the X points, accounting for $\sim 65\%$ of the total density of states (DOS), occurring near the chemical potential. We propose that the strong SOC and enhanced DOS in the vicinity of the X points provide the origin of the observed enhancement of the critical field. This leads to a prediction that the magnetic field will lead to a strongly momentum-dependent gap suppression. The gap due to electronic states away from (near to) the X points will be rapidly (slowly) suppressed by fields.

Recently, the signatures of superconductivity with $T_c\approx$ 80 K in pressured ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ has garnered significant attention, which makes it a new candidate of the high-temperature superconductors dominated by $3d$ transition elements after the cuprate and iron-pnictide superconductors. However, due to the high-pressure environment limitation, the electronic structure and magnetic properties of the superconducting system may not be directly measured. Here, we systematically investigate the electronic structure and magnetic order of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ in both its low-pressure and high-pressure phases based on the DFT and DMFT methods. Our results indicate that the Ni-$d_{z^2}$ electrons experience stronger renormalization effect than Ni-$d_{x^2-y^2}$ electrons at both phases, consistent with high-resolution angle-resolved photoemission spectroscopy (ARPES) results. Additionally, we find that electronic correlations effect in the low-pressure phase are stronger than those in the high-pressure phase. Finite temperature DMFT calculations show that the static local spin susceptibility exhibits clear Curie-Weiss behavior at high temperatures. Further analyses of the Fermi surface, self-energy and renormalization factor for both phases show the ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ as the strong correlation metal. We also study the magnetic properties of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ at both phases. For the low-pressure phase, it is shown A-type antiferromagnetic (AFM) state has the lowest energy with the ferromagnetic (FM) order in planar, but the AFM order between different layers when $U\le 4$ eV. But when $U>4$ eV, the FM state is the most stable one, indicating the strong competition between AFM and FM order. For the high-pressure phase, it has a similar result. when $U\le 5$ eV, the A-AFM state has the lowest energy, but when $U>5$ eV, the FM state is the most stable one, which means the spin instabilities in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ at both phases.

Topological phases at quantum criticality have attracted much attention recently. Here we numerically study the interaction-induced phase transitions at around the topological quantum critical points of an extended Su-Schrieffer-Heeger (SSH) chain with next-nearest-neighbor hopping. This extended SSH model shows topological phase transitions between the topologically trivial and nontrivial critical phases when interaction is absent. So long as the interaction terms are turned on, the topologically nontrivial (trivial) critical phases are driven into topologically nontrivial (trivial) insulator phases with finite energy gaps. Particularly, we find the trivial insulator phase is further driven to the nontrivial insulator phase, through interaction-induced topological phase transition, although interaction generally is harmful to nontrivial topology. The stability of the trivial insulator phase against interaction tends to vanish at the multicritical point that separates the trivial and nontrivial critical phases. Our work provides a concrete example for manifesting the impact of interaction on topological quantum criticality.

Recently, the Pr-doped Ruddlesden-Popper (RP) phase of bilayer nickelate $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ has been reported to exhibit a superconducting transition temperature ($T_c$) of 82.5 K and a superconducting volume fraction of about 57% at high pressure. However, the effect of Pr doping on $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ remains unclear. Here, we studied the crystal structures and electronic properties of Pr-doped $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ at 0 and 15 GPa based on the first-principles calculations to explore the doping effect of Pr. Our findings indicate that the praseodymium atoms prefer to occupy the outer La-O layers site. We then investigated the evolution of crystal structures in both the ambient pressure phase and the high-pressure phase of $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ as a function of doping concentration, revealing inconsistent trends in their evolution with increasing doping levels. Finally, by fitting the bilayer two-orbital model, we propose that doping Pr may reduce the required pressure for the superconductivity of $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$. These results not only can help the further experimental search of RP phase nickelate at lower pressure, but also provide a helpful guide for understanding the effect of chemical pressure in an isovalent-doped RP phase nickelate superconductor.

The search for two-dimensional semiconductors with novel physical properties is a key to developing functional nanoelectronic devices. We have succeeded in fabricating a monolayer ${\mathrm{TiS}}_2$ film on bilayer graphene/SiC(0001) by combining the molecular-beam epitaxy and the topotactic chemical reaction, and clarified the electronic states by angle-resolved photoemission spectroscopy and first-principles calculations. We found that monolayer ${\mathrm{TiS}}_2$ takes the octahedral $1T$ structure with an indirect semiconducting band gap of about 1 eV. We also found that monolayer $1T\text{−}{\mathrm{TiS}}_2$ shows no indication of $2\times 2$ charge-density wave (CDW) in contrast to isostructural family compounds, monolayer ${\mathrm{TiSe}}_2$ and ${\mathrm{TiTe}}_2$. By comparing the band structure among monolayer $1T\text{−}\mathrm{Ti}C{h}_2$ series ($Ch=\mathrm{S}$, Se, and Te), we found that the energy level of chalcogen atoms plays an important role for the emergence of CDW. The present results lay a foundation for understanding the electronic properties of atomically thin Ti-based transition metal dichalcogenides and their possible applications toward ultrathin semiconductor devices.

We present a theoretical study of the pump-probe Faraday rotation and ellipticity signals in ensembles of uniaxially anisotropic CdSe nanoplatelets and nanocrystals. We use the Faraday rotation mechanism based on the excitation of negative heavy-hole trions for a magnetic field applied in the Voigt geometry. Three types of ensembles with typical spatial distributions of the orientation of the anisotropy axis with respect to the direction of light propagation are considered. Faraday rotation and ellipticity signals are modeled for excitation by single and repeated pump pulses, taking into account the anisotropy of the electron $g$ factor. We show that spin dephasing caused by the electron $g$-factor anisotropy and the arbitrary orientation of nanoplatelets or nanocrystals result only in partial damping of oscillation amplitude in contrast to the dephasing caused by the dispersion of the electron $g$ factor in the ensemble. We demonstrate that regardless of the $g$-factor anisotropy degree the oscillation frequency of the Faraday rotation and ellipticity signals for a randomly oriented ensemble is determined by the transverse electron $g$-factor component.

Solutions of the wave equations for time-independent disordered media can exhibit Anderson localization where instead of wave propagation we observe their localization around different points in space. Photonic time crystals are spatially homogeneous media in which the refractive index changes periodically in time, leading to the formation of bands in the wave-number domain. By analogy to Anderson localization in space, one might expect that the presence of temporal disorder in photonic time crystals would lead to Anderson localization in the time domain. Here, we show that indeed periodic modulations of the refractive index with the addition of temporal disorder lead to Anderson localization in time, where an electromagnetic field can emerge from the temporally modulated medium at a certain moment in time and then decay exponentially over time. Thus, we are dealing with a situation where, in a fluctuating three-dimensional medium, the birth and death of waves can occur, and the mechanism of this phenomenon corresponds to Anderson localization.

Electrons in closed quantum systems can exhibit Coulomb blockade (CB) oscillations due to charge quantization. Here, we report CB oscillations in aluminum superconducting islands on InAs nanowires in the open regime. The Al island is connected to source/drain leads through two contacts: One is fully transmitting while the other is tuned into the tunneling regime. This device configuration is typical for tunneling spectroscopy where the charging energy is generally considered negligible. The oscillation periods are $2e$ or $1e$, depending on the gate settings. A magnetic field can also induce the $2e$ to $1e$ transition. Our result is reminiscent of the “mesoscopic Coulomb blockade” in open quantum dots caused by electron interference.

Time-resolved microscopy is an established technique for probing the dynamics of laser ablation, thus enabling the exploration of material behavior under extreme conditions produced by laser excitation. Decoding the time-resolved data on the rapid variation of optical properties of a material undergoing nonequilibrium phase decomposition and ejection, however, presents a significant challenge. In this paper, a closely integrated computational and experimental study of laser ablation of FeNi targets is used to establish direct links between the dynamics of laser ablation and the evolution of optical signal in pump-probe experimental measurements. The experiments and large-scale atomistic simulations are performed for a range of fluences covering the onset of material ejection at the threshold for photomechanical spallation and the transition to the phase explosion regime of laser ablation. The connections between the simulations and experiments are established through numerical modeling of the interaction of an electromagnetic wave representing the experimental probe laser pulse with transient states of the ablation plume predicted in the atomistic simulations. The combined modeling and experiments have revealed a complex interplay of processes defining the transient optical properties of the emerging ablation plume, including the oscillations of reflectance due to the interference of parts of the probe pulse reflected from the spalled layer and the newly formed surface of the target in the spallation regime, the disappearance of the interference pattern upon the transition to the regime of phase explosion, nonmonotonous variation of the refractive index of a transient spongy structure of interconnected liquid regions, and the formation of nanoscale hot spots within the expanding spongy structure due to the near-field concentration of electromagnetic field. The results of this study not only provide reliable guidance for the interpretation of optical signals measured in pump-probe experiments but also suggest new ideas for manipulating the ablation plume dynamics to achieve higher efficiency and precision in laser synthesis and processing of materials in the double- or multipulse irradiation regimes.

We investigate the spin Hall conductivity (SHC) of a composition series of a Ta-Re bcc solid solution. At approximately 60 at.% Ta the Ta-Re alloy features a SHC similar to bcc-W, while both endpoints of the compositional series have rather moderate SHC. The intermediate stoichiometries exhibit a substantial enhancement due to Fermi-level tuning through the same band structure feature which gives bcc-W and $\beta$-W its large SHC. We provide experimental evidence for the enhancement of the SHC in the alloy via THz emission upon ultrafast laser excitation of Ta-Re/CoFeB bilayers. We demonstrate that a rigid-band model derived from bcc-W and Fermi-level tuning describes the experimental data with a similar accuracy as the coherent-potential approximation alloy calculations of the SHC.

We theoretically study the supercurrent in antiferromagnet/superconductor (AF/S) Josephson junctions. The AF can become spin-polarized when the parity-time symmetry is broken. In $\mathrm{S}/{\mathrm{AF}}_1/{\mathrm{AF}}_2/\mathrm{S}$ junctions, the supercurrent, carried by spin-singlet Cooper pairs, is highly sensitive to the electrostatic potential $U_2$ in the ${\mathrm{AF}}_2$ layer. At high $U_2$, the supercurrent undergoes a $0-\pi$ transition, similar to the behavior seen in S/F/S junctions. In contrast, at low $U_2$, the supercurrent in the thick fully spin-polarized ${\mathrm{AF}}_2$ layer vanishes, suggesting that a third AF layer (${\mathrm{AF}}_3$) is required to sustain long-range spin-triplet supercurrents. In AF trilayer junctions, the orientations of the Néel vectors in the ${\mathrm{AF}}_1$ and ${\mathrm{AF}}_3$ layers are crucial for determining the supercurrent behavior. Noncollinear configurations of the Néel vectors promote the emergence of long-range spin-triplet supercurrents. At low $U_2$, the current-phase relation (CPR) follows a sinusoidal form, with the $0-\pi$ transition modulated by the Néel vector orientations. Notably, anomalous Josephson current arises when the Néel vectors in the ${\mathrm{AF}}_1$ and ${\mathrm{AF}}_3$ layers lie in the $x-y$ plane. At higher $U_2$, the second harmonic dominates the CPR, leading to a more complex CPR. Furthermore, we propose a simplified physical mechanism to explain the propagation of Cooper pairs, which helps clarify the observed supercurrent behavior.

We study an exactly solvable spin-orbital model that can be regarded as a classical analog of the celebrated Kitaev honeycomb model and describes interactions between Rydberg atoms on the ruby lattice. We leverage its local and nonlocal symmetries to determine the exact partition function and the static structure factor. A mapping between $S=3/2$ models on the honeycomb lattice and kagome spin Hamiltonians allows us to interpret the thermodynamic properties in terms of a classical kagome spin ice. Partially lifting the symmetries associated with line operators, we obtain a model characterized by immobile excitations, called classical fractons, and a ground-state degeneracy that increases exponentially with the length of the system. We formulate a continuum theory that reveals the underlying gauge structure and conserved charges. Extensions of our theory to other lattices and higher-spin systems are suggested.

It has always been a difficult issue to experimentally identify topological materials, though we can theoretically define and calculate various topological indices, such as the ${\mathbb{Z}}_2$ index. In this paper, we conduct first-principles calculations to investigate the spin Hall effect for topological insulators with $\mathcal{PT}$ symmetry and find that the gating dependence of the static SHC exhibits a five-stage evolution with band inversion and a three-stage evolution without band inversion, while the dynamical SHC features a reverse resonance peak in the frequency-dependent curve. We demonstrate the spin Hall conductivity with these signatures for three typical topological materials, for example, nonmagnetic topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, magnetic static axion insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, and magnetic dynamical axion insulator ${\mathrm{Mn}}_2{\mathrm{Bi}}_2{\mathrm{Te}}_5$. Our finding provides another perspective from the transportation signal to reveal the topological materials in experiments.

We present Ir $4f$ core-level hard-x-ray photoemission spectroscopy (HAXPES) experiments conducted across the antiferromagnetic (AFM) ordering transition in Ruddlesden-Popper iridates ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ and ${\mathrm{Sr}}_3{\mathrm{Ir}}_2{\mathrm{O}}_7$. The Ir $4f$ spectra exhibit distinct changes between the AFM and paramagnetic (PM) phases, with the spectral difference $I_{\text{PM}}-I_{\text{AFM}}$ showing a contrasting behavior in the two compounds. By employing computational simulations using the local density approximation combined with the dynamical mean-field theory method, we elucidate that $I_{\text{PM}}-I_{\text{AFM}}$ primarily reflects the Slater or Mott-Hubbard character of the AFM insulating state rather than material-specific details, such as crystal and/or band structures. This sensitivity to fine low-energy electronic structure arises from the dependence of charge-transfer responses to the sudden creation of a localized core hole on both metal-insulator transitions and long-range AFM ordering. Our result broadens the applications of core-level HAXPES as a tool for characterization of electronic structure in $5d$ transition-metal compounds.

We present a detailed study of the magnetotransport properties and electronic band structure of the Zintl single crystal $\mathrm{CaZn}{}_2\mathrm{Sb}{}_2$. The resistivity upturn at low temperatures under perpendicular magnetic fields associated with observed high magnetoresistance is observed. Magnetoresistance (MR) exhibits cusplike features, a characteristic of weak antilocalization (WAL) effect. The -$ln(B$) dependence of the magnetoconductivity curves suggests two-dimensional (2D) WAL behavior, signifying the presence of nodal line fermions. Nonlinear Hall resistivity is analyzed using a two-band model, confirming uncompensated carrier concentrations. Temperature-dependent resistivity reveals Mott interband scattering below 70 K and electron-phonon scattering above 70 K. The MR follows extended Kohler's rule, indicating multiple scattering origins and temperature-dependent carrier densities, with maximum MR of 110% at 2 K and 9 T. The Bloch-Gruneisen-Mott fitting of the temperature-dependent resistivity also supports the presence of multiple scattering mechanisms. First-principles calculations reveal that three bands cross the Fermi level ($E_F$) without spin-orbit coupling (SOC) and nontrivial drumheadlike surface states merge into bulk states at the Dirac point, further corroborating nodal line semimetallic features. With the inclusion of SOC, the band touching point around the $\mathrm{\Gamma }\text{−}A$ direction becomes fourfold degenerate and band inversion is observed at the Dirac point. Additionally, a four-band effective Hamiltonian based on the $k.p$ model is proposed around the crossing point.

The low thermal conductivity of some semiconducting cubic spinel chalcogenides makes them promising for thermoelectric applications. A key challenge is understanding mechanisms for low thermal conductivity in this class of materials. Here, we theoretically investigated two spinel semiconductors ${\mathrm{CdBi}}_2{\mathrm{Se}}_4$ and ${\mathrm{PbBi}}_2{\mathrm{Se}}_4$. We find that these show intrinsic ultra-low lattice thermal conductivities (${\kappa }_l$) of 0.52–1.24 W ${\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 300 K. We investigated the origin of such low ${\kappa }_l$ by analyzing the nature of the chemical bonding in relation to the crystal structure. The interaction between $\mathrm{Pb}\text{−}6s/\mathrm{Bi}\text{−}6s$ and $\mathrm{Se}\text{−}4p$ orbitals was found to generate antibonding states below the Fermi level in the electronic band structures resulting in softening of the lattice of these compounds. The lattice dynamics of these compounds exhibit strong acoustic-optical coupling and avoided-crossing features. The presence of additional anticrossing in ${\mathrm{PbBi}}_2{\mathrm{Se}}_4$ is attributed to strong anharmonic vibrations of the Se atoms as a result of the formation of antibonding states by ${\mathrm{Pb}}^{2+}{s}^2$ active lone pairs with Se. Further, bridging Se atoms between tetrahedra and octahedra have asymmetric, anisotropic potential energy surfaces along the $x, y$, and $z$ directions with strong lattice anharmonicity. The electronic band structure exhibits complex degenerate conduction bands, leading to multiple anisotropic carrier pockets with small transport effective masses. This nontrivial band structure leads to both high Seebeck coefficient and high conductivity. The estimated maximum thermoelectric figure of merit is approximately 1.32 at 500 K in ${\mathrm{PbBi}}_2{\mathrm{Se}}_4$. These findings offer valuable insights for the future design and exploration of thermoelectric materials with low lattice thermal conductivity.

Microwave transmission line spectroscopy is used to observe the integer quantum Hall effect in two samples of monolayer graphene with different geometries that are resistively coupled to a coplanar waveguide. We find plateaus in transmitted power that do not vary significantly with microwave frequency but are significantly different for two samples due to their shape. With each drop in transmitted power corresponding to an additional quantum Hall edge mode that shorts the transmission line to ground, these well-known quanta of conductance allow us to calibrate the sensitivity of the devices. One sample with short contact regions matched the sensitivity expected when considering only the quantum Hall conductance of $\nu e^2/h$; another sample with long contact regions demonstrated a nearly threefold enhancement in sensitivity. We model this result with a purely resistive circuit that introduces an additional resistance to explain the increased sensitivity.

The topological properties of multiband systems have recently garnered significant attention due to their potential non-Abelian characteristics, which are absent in single-band or band-gap systems. However, the complex electronic structures inherent in these systems pose challenges for the direct observation of non-Abelian topological phenomena in condensed matter. In this study, we propose a plasmonic system constructed by arranging metal nanoparticles into a T-graphene lattice. This configuration facilitates the realization of non-Abelian topological phase transitions within the resulting photonic multiwave bands, effectively simulating a multiband electronic system. Furthermore, the topological plasmonic states exhibit a diverse array of phases that can be easily controlled by varying the polarization of the external light field, allowing for straightforward observation through measurements of the light field distribution. The results obtained using the eigenequation method are validated through an independent approach, specifically by analytically solving for the electric field distribution; both methods yield consistent findings. This platform, which synergizes the advantages of non-Abelian topological theory with a controllable plasmonic system, holds promise for advancing the field of topological physics and enhancing its applications in plasmonics in the future.

Polar metals are an intriguing class of materials that feature a polar crystal structure while also exhibiting metallic conductivity. The unique properties of polar metals challenge expectations, making way for the exploration of exotic phenomena such as unconventional magnetism, hyperferroelectric multiferroicity, and the development of multifunctional devices that can leverage both the material's polar structure and its asymmetry in the spin conductivity, that arises due to the Rashba effect. Here, via a high-pressure single-crystal diffraction study, we report the pressure-induced enhancement of polar distortions in such a metal, ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$. Our density functional theory calculations highlight that naive assumptions about the linear dependency between polar distortion amplitudes and the magnitude of the Rashba spin splitting may not be generally valid.