${\mathrm{C}}_3{\mathrm{N}}_4$ is a recently discovered phase of carbon nitrides with the tetragonal crystal structure [D. Laniel et al., Adv. Mater. (2023), doi:10.1002/adma.202308030] that is stable at ambient conditions. ${\mathrm{C}}_3{\mathrm{N}}_4$ is a semiconductor exhibiting flat-band anomalies in the valence band, suggesting the emergence of many-body instabilities upon hole doping. Here, using state-of-the-art first-principles calculations we show that hole-doped ${\mathrm{C}}_3{\mathrm{N}}_4$ reveals strong electron-phonon coupling, leading to the formation of a gapped superconducting state. The phase transition temperatures turn out to be strongly dependent on the hole concentration. We propose that holes could be injected into ${\mathrm{C}}_3{\mathrm{N}}_4$ via boron doping which induces, according to our results, a rigid shift of the Fermi energy without significant modification of the electronic structure. Based on the electron-phonon coupling and Coulomb pseudopotential calculated from first principles, we conclude that the boron concentration of 6 atoms per ${\mathrm{nm}}^3$ would be required to reach the critical temperature of $\sim 36$ K at ambient pressure.

We have successfully synthesized four ${\mathrm{Mo}}_3{\mathrm{O}}_8$-type cluster Mott insulators (CMIs) by intercalating lithium into nonmagnetic precursors to regulate the ${\mathrm{Mo}}_3$ cluster valence. The resulting materials are ${\mathrm{Li}}_{1+\mathrm{x}}R{\mathrm{Mo}}_3{\mathrm{O}}_8$ $(R=\mathrm{Sc},\mathrm{Y},\mathrm{Lu})$ and ${\mathrm{Li}}_{\mathrm{x}}{\mathrm{Zn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$. Our magnetic susceptibility measurements revealed that these materials display characteristics akin to a valence-bond glass state and suggest the presence of short-range ordering when the ${\mathrm{Mo}}_3$ cluster valence approximates its ideal value. These findings challenge the prevailing belief that the plaquette charge ordering state is an inherent feature of ${\mathrm{Mo}}_3{\mathrm{O}}_8$-type CMIs. Instead, they underscore the importance of ${\mathrm{Mo}}_3$ cluster valence in determining the physical properties of these systems. These insights furnish a fresh understanding of the ${\mathrm{Mo}}_3{\mathrm{O}}_8$-type CMI and open research opportunities in highly frustrated magnetism.

Superconductivity with spin-polarized Cooper pairs is known to emerge by combining conventional spinless superconductors with materials that have spin-dependent interactions, such as magnetism and spin-orbit coupling. This enables a dissipationless and conserved flow of spin. However, actually utilizing the spin polarization of such supercurrents has proven challenging. Here, we predict an experimental signature of current-carrying triplet Cooper pairs in the form of an induced spin signal. We show that a supercurrent carried only by triplet Cooper pairs induces a nonlocal magnetization that is controlled by the polarization direction of the triplet Cooper pairs. This provides a measurement protocol to directly use the spin polarization of the triplet Cooper pairs in supercurrents to transfer spin information in a dissipationless manner.

The enigma of unconventional superconductivity in doped cuprates presents a formidable challenge in the realm of condensed matter physics. Recent findings of strong near-neighbor attractions in one-dimensional cuprate chains suggest a new avenue for investigating cuprate superconductors. Consequently, we revisited the superconductivity in the extended Hubbard model at the mean-field level. Anticipating a prevalence of antiferromagnetic order due to strong local Coulomb repulsion, our calculations reveal the coexistence of superconducting and antiferromagnetic orders across a wide range of doping at sufficiently low temperatures. The mean-field results capture some key features of cuprate superconductors, including $d$-wave pairing symmetry, a dome-shaped dependence of $T_c$ on doping, and higher superconducting transition temperatures. Additionally, we observe a nearly proportional relationship between $T_c$ and the strength of the nearest-neighbor attraction, reminiscent of experimental findings at the ${\mathrm{FeSe}/\mathrm{SrTiO}}_3$ interface. The mean-field results suggest that the extended Hubbard model could be the appropriate framework for investigating cuprate superconductivity and offer insights for more precise calculations within this model in the future.

Topological insulators have been extended to higher-order versions that possess topological hinge or corner states in lower dimensions. However, their robustness against disorder is still unclear. Here, we theoretically investigate the phase transitions of a three-dimensional chiral second-order topological insulator in the presence of disorder. Our results show that, by increasing disorder strength, the nonzero densities of states of the side surface and bulk emerge at disorder strengths of $W_S$ and $W_B$, respectively. The spectral function indicates that the bulk gap is only closed at one of the $R_{4z}\mathcal{T}$-invariant points, i.e., ${\mathrm{\Gamma }}_3$. The closing of the side surface gap or bulk gap is ascribed to a significant decrease of the elastic mean free time of quasiparticles. Based on the scaling theory of localization length, we obtain two fixed points as two critical disorder strengths for any given Fermi energy, indicating that the three-dimensional chiral second-order topological insulator gradually enters the diffusive metallic phase and Anderson insulating phase, respectively. In the end, a global phase diagram is provided to clearly demonstrate the evolution of different phases.

We study the nonlocal magnetotransport through a strongly correlated quantum dot, connected to multiple terminals consisting of two normal and one superconducting (SC) leads. Specifically, we present a comprehensive view on the interplay between the crossed Andreev reflection (CAR), the Kondo effect, and the Zeeman splitting at zero temperature in the large SC gap limit. The ground state of this network shows an interesting variety, which varies continuously with the system parameters, such as the coupling strength ${\mathrm{\Gamma }}_S^{}$ between the SC lead and the quantum dot, the Coulomb repulsion $U$, the impurity level ${\varepsilon }_d^{}$, and the magnetic field $b$. We show, using the many-body optical theorem which is derived from the Fermi-liquid theory, that the nonlocal conductance is determined by the transmission rate of the Cooper pairs ${\mathcal{T}}_{\mathrm{CP}}^{}=\frac{1}{4}{sin}^2\mathrm{\Theta }{sin}^2({\delta }_{\uparrow }+{\delta }_{\downarrow })$ and that of the Bogoliubov particles ${\mathcal{T}}_{\mathrm{BG}}^{}=\frac{1}{2}{\sum }_{\sigma }{sin}^2{\delta }_{\sigma }^{}$. Here, ${\delta }_{\sigma }^{}$ is the phase shift of the renormalized Bogoliubov particles, and $\mathrm{\Theta }\equiv {cot}^{-1}({\xi }_d^{}/{\mathrm{\Gamma }}_S^{})$ is the Bogoliubov-rotation angle in the Nambu pseudospin space, with ${\xi }_d^{}={\varepsilon }_d^{}+U/2$. It is also demonstrated, using Wilson's numerical renormalization group approach, that the CAR is enhanced in the crossover region between the Kondo regime and the SC-proximity-dominated regime at zero magnetic field. The magnetic fields induce another crossover between the Zeeman-dominated regime and the SC-dominated regime, which occurs when the renormalized Andreev resonance level of majority spin crosses the Fermi level. We find that the CAR is enhanced and becomes less sensitive to magnetic fields in the SC-dominated regime close to the crossover region spreading over the angular range of $\pi /4\lesssim \mathrm{\Theta }\lesssim 3\pi /4$. At the level crossing point, a spin-polarized current flows between the two normal leads, and it is significantly enhanced in the directions of $\mathrm{\Theta }\simeq 0$ and $\mathrm{\Theta }\simeq \pi$ where the SC proximity effect is suppressed.

The density fluctuation spectrum captures many fundamental properties of strange metals. Using momentum-resolved electron energy loss spectroscopy (M-EELS), we recently showed that the density response of the strange metal ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+x}$ (Bi-2212) at large momentum, $q$, exhibits a constant-in-frequency continuum [M. Mitrano et al., Proc. Natl. Acad. Sci. USA 115, 5392 (2018); A. A. Husain et al., Phys. Rev. X 9, 041062 (2019)] reminiscent of the marginal Fermi liquid (MFL) hypothesis of the late 1980s [C. M. Varma et al., Phys. Rev. Lett. 63, 1996 (1989)]. However, reconciling this observation with infrared (IR) optics experiments, which show a well-defined plasmon excitation at $q\sim 0$, has been challenging. Here we report M-EELS measurements of Bi-2212 using $4\times$ improved momentum resolution, allowing us to reach the optical limit. For momenta $q<0.04$ reciprocal lattice unites (r.l.u.), the M-EELS data show a plasmon feature that is quantitatively consistent with IR optics. For $q>0.04$ r.l.u., the spectra become incoherent with an MFL-like, constant-in-frequency form. We speculate that, at finite frequency, $\omega$, and nonzero $q$, some attribute of this Planckian metal randomizes the probe electron, causing it to lose information about its own momentum.

We use a classical, microscopic model of pointlike dipolarizable entities (a model that is standard in the case of positive polarizability) and investigate its behavior for simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc) crystals with one entity per primitive cell when the static polarizability of the entities is negative and the mutual electrostatic interaction between the entities is taken into account. We find that the static electric susceptibility is bounded below due to an instability towards self-polarization but negative values are possible in each case. The usual Clausius-Mossotti relation between the static polarizability and the static electric susceptibility remains valid in the case of negative parameters but is truncated at the lower bound; the value of the bound depends on the crystal structure and is always unrelated to the asymptote of the Clausius-Mossotti curve. The lower bounds of the static electric susceptibility are found to be $-0.906$ for sc and $-1.00$ for bcc and fcc. These results confirm that, although the magnitude of the static electric susceptibility does not diverge in the negative case (as it can in the positive case), the magnitudes attainable in the negative case for condensed media may, nevertheless, be many orders of magnitude greater than those predicted previously for inverted vapors and gases. This is a promising result in relation to the development of potential new technologies that exploit the phenomenon.

Magnetic excitations in the spin chain candidate ${\mathrm{Sr}}_2{\mathrm{V}}_3{\mathrm{O}}_9$ have been investigated by inelastic neutron scattering on a single crystal sample. A spinon continuum with a bandwidth of $\sim 22$ meV is observed along the chain formed by alternating magnetic ${\mathrm{V}}^{4+}$ and nonmagnetic ${\mathrm{V}}^{5+}$ ions, which reveals the importance of the orbital degree of freedom in determining the chain axis as identified by prior electronic structure calculations. Incipient magnetic Bragg peaks due to weak ferromagnetic interchain couplings emerge when approaching the magnetic transition at $T_N\sim 5.3$ K, while the excitations remain gapless within the instrumental resolution. Comparisons to the Bethe ansatz, density matrix renormalization group calculations, and effective field theories confirm ${\mathrm{Sr}}_2{\mathrm{V}}_3{\mathrm{O}}_9$ as a host of weakly coupled $S=1/2$ chains dominated by antiferromagnetic intrachain interactions of $\sim 7.1$(1) meV.

We present a theoretical approach to incorporate electronic interactions in the study of two-dimensional topological insulators. By exploiting the correspondence between edge-state physics and entanglement spectrum in gapped topological systems, we deconstruct the system into one-dimensional channels. This framework enables a simple and elegant inclusion of fermionic interactions into the discussion of topological insulators. We apply this approach to the Kane-Mele model with interactions and magnetic impurities.

The effect of pressure on the crystal structure of ${\mathrm{Ni}}_2\mathrm{MnGa}$ was investigated up to 41 GPa using in situ angle-dispersive x-ray diffraction with synchrotron radiation, an imaging plate detector, and a diamond anvil cell. A pressure-induced transition from a cubic $L{2}_1$ structure (space group $\mathit{Fm}\overline{3} m$) to a 10-layer modulated monoclinic structure ($C2/m$) with a distortion of $\beta \sim {92}^{\circ }$ occurred at a pressure of 19.1 GPa or lower. The volume change at the martensitic transition is a minute value of about $-0.1\%$. The bulk modulus for the low-pressure phase is 147(2) GPa, consistent with previous studies. In contrast, the bulk modulus for the high-pressure phase is 229(4) GPa, significantly higher than the former bulk modulus. Initial permeability measurements of the ${\mathrm{Ni}}_2\mathrm{MnGa}$ were also conducted at various pressures up to 1 GPa. The pressure dependencies of the Curie temperature, premartensitic, and martensitic transition temperatures are discussed in detail.

Hyperuniformity is a property of certain heterogeneous media in which density fluctuations in the long-wavelength range decay to zero. In reciprocal space this behavior translates into a decay of Fourier intensities in the range near small wave numbers. In this paper, quasiperiodic tilings constructed by word concatenation are under study. The lattice is generated from a parameter given by its continued fraction so that quasiperiodicity emerges for infinity when irrational generators are taken into consideration. Numerical simulations show a quite regular quadratic decay of Fourier intensities, regardless of the number considered for the generator parameter, which leads us to formulate the hypothesis that this type of media is strongly hyperuniform of order 3. Theoretical derivations show that the density fluctuations scale in the same proportion as the wave numbers. Furthermore, it is rigorously proved that the structure factor decays around the origin according to the pattern $S\left(k\right)\sim k^4$. This result is validated with several numerical examples with different generating continued fractions.

The thermal conductivity of mantle materials, viz., oxides, perovskites, and silicates, controls the heat balance and thermal evolution of the Earth. We report the pressure $\left(P\right)$ and temperature $\left(T\right)$ dependence of lattice thermal conductivity of quicklime, an important insulating oxide in the deepest mantle, by employing the phonon anharmonicity added and density functional theory assisted Debye-Callaway (DC) model. The previous [Vyas et al., Phys. Rev. B 107, 014107 (2023) and Physica B 645, 414250 (2022)] first-principles calculations that included the anharmonic contribution to the vibrational response were utilized to deduce the input parameters of the DC model, such as the characteristic temperature, the average phonon velocity, and the thermal Grüneisen parameter. In this paper, instead of the conventional Debye temperature, we used a different characteristic temperature $\left(\theta \right)$ to derive the resistive umklapp phonon scattering rate. The equilibrium value of $\theta$ is derived from the second-order volume $\left(V\right)$ derivative of the self-consistent plane-wave total energy, whereas the $V$ and $T$ variation of $\theta$ is governed by the explicit $V,T$-dependent Grüneisen parameter. We employed the lowest-order thermodynamic perturbation theory to find an explicit $T$-dependent thermal gamma and thereby $\theta \left(V,T\right)$. The high-$P,T$ lattice thermal conductivity ($K_{\mathrm{lat}}$) results for the B2 phase (CsCl structure) of CaO were also computed and compared with those derived using the Boltzmann transport equation (BTE) approach. While the DC model relies on the equation of states and average phonon group velocity, the discrepancy in high-$P$ data suggests that the effect of inflection of the phonon-phonon scattering mechanism with volume is critical. However, the DC model remains successful for the high-$T$ and low-$P$ evaluation of $K_{\mathrm{lat}}$, and the calculated results for high-$T$ but zero-pressure $\left(K_{\mathrm{lat}}\right)$ coincides with results based on the BTE approach. Further, we also obtained the radiative part of the thermal conductivity ($K_{\mathrm{rad}}$) from the absorption coefficient that was derived within the independent particle approximation and using the Planck function for the blackbody radiation. The computed results at $P$ and $T$ relevant to the Earth's lower mantle and outer core regions suggest that (i) the radiative component $K_{\mathrm{rad}}$ remains two to three orders of magnitude smaller compared to the lattice part, and it is negligible; (ii) the B2 phase of CaO is important at the examined $P,T$ plane, and decisively contributes to the heat transport; and (iii) the estimated value $(\sim 4.9\text{–}8\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1})$ of $K_{\mathrm{lat}}$ at the core-mantle boundary is of the same order of magnitude as that of cubic $\mathrm{CaSi}{\mathrm{O}}_3$ perovskite, and $\mathrm{MgSi}{\mathrm{O}}_3$ perovskite and bridgmanite along the geotherm.

Origami-inspired approaches have presented exciting possibilities for engineering and manipulating two-dimensional (2D) materials in three-dimensional space. By introducing curvature through folding and bending, curved 2D materials offer unique opportunities to explore exotic magnetic phenomena that are absent in their planar counterparts. Here we demonstrate the existence of origami-driven Dzyaloshinskii-Moriya interaction (DMI) in centrosymmetric 2D magnets by means of symmetry analysis and noncollinear spin-polarized density functional theory. By taking $\mathrm{Cr}{\mathrm{I}}_3$ as an example, we show the decisive effect of spin-orbit interaction on the DMI of folded structures, which corresponds to the three-site Fert-Lévy model. Furthermore, the geometry-governed anisotropy and the DMI contribute to the magnetic energy, resulting in chiral domain walls as the ground state. Our results present a general method for creating topological spin textures in centrosymmetric 2D magnets, providing insights into the formation of magnetochirality in origami 2D magnets, which will be beneficial to both the fundamental study of curvilinear magnetism and the application of chiral spin textures in spintronic devices.

Transition metal dihalides have recently garnered interest in the context of two-dimensional van der Waals magnets as their underlying geometrically frustrated triangular lattice leads to interesting competing exchange interactions. In particular, ${\mathrm{NiI}}_2$ is a magnetic semiconductor that has been long known for its exotic helimagnetism in the bulk. Recent experiments have shown that the helimagnetic state survives down to the monolayer limit with a layer-dependent magnetic transition temperature that suggests a relevant role of the interlayer coupling. Here, we explore the effects of hydrostatic pressure as a means to enhance this interlayer exchange and ultimately tune the electronic and magnetic response of ${\mathrm{NiI}}_2$. We study first the evolution of the structural parameters as a function of external pressure using first-principles calculations combined with x-ray diffraction measurements. We then examine the evolution of the electronic structure and magnetic exchange interactions via first-principles calculations and Monte Carlo simulations. We find that the leading interlayer coupling is an antiferromagnetic second-nearest-neighbor interaction that increases monotonically with pressure. The ratio between isotropic third- and first-nearest-neighbor intralayer exchanges, which controls the magnetic frustration and determines the magnetic propagation vector $\mathbf{q}$ of the helimagnetic ground state, is also enhanced by pressure. As a consequence, our Monte Carlo simulations show a monotonic increase in the magnetic transition temperature, indicating that pressure is an effective means to tune the magnetic response of ${\mathrm{NiI}}_2$.

Hydrogen-rich superconductors are promising candidates to achieve room-temperature superconductivity. However, the extreme pressures needed to stabilize these structures significantly limit their practical applications. An effective strategy to reduce the external pressure is to add a light element M that binds with H to form ${\mathrm{MH}}_x$ units, acting as a chemical precompressor. We exemplify this idea by performing ab initio calculations of the Ac–Be–H phase diagram, proving that the metallization pressure of Ac–H binaries, for which critical temperatures as high as 200 K were predicted at 200 GPa, can be significantly reduced via beryllium incorporation. We identify three thermodynamically stable (${\mathrm{AcBe}}_2{\mathrm{H}}_{10}, {\mathrm{AcBeH}}_8$, and ${\mathrm{AcBe}}_2{\mathrm{H}}_{14}$) and four metastable compounds (fcc ${\mathrm{AcBeH}}_8, {\mathrm{AcBeH}}_{10}, {\mathrm{AcBeH}}_{12}$ and ${\mathrm{AcBe}}_2{\mathrm{H}}_{16}$). All of them are superconductors. In particular, fcc ${\mathrm{AcBeH}}_8$ remains dynamically stable down to 10 GPa, where it exhibits a superconducting-transition temperature $T_{\text{c}}$ of 181 K. The Be–H bonds are responsible for the exceptional properties of these ternary compounds and allow them to remain dynamically stable close to ambient pressure. Our results suggest that high-$T_{\text{c}}$ superconductivity in hydrides is achievable at low pressure and may stimulate experimental synthesis of ternary hydrides.

Competing measurements alone can give rise to distinct phases characterized by entanglement entropy—such as the volume-law phase, symmetry-breaking (SB) phase, and symmetry-protected topological (SPT) phase—that can only be discerned through quantum trajectories, making them challenging to observe experimentally. In another burgeoning area of research, recent studies have demonstrated that steering can give rise to additional phases within quantum circuits. In this work we show that new phases can appear in measurement-only quantum circuits with steering. Unlike conventional steering methods that rely solely on local information, the steering scheme we introduce requires the structure of the circuit as an additional input. These steering-induced phases are termed “informative” phases. They are distinguished by the intrinsic dimension of the bitstrings measured in each circuit run, making them substantially easier to detect in experimental setups. We explicitly show this phase transition by numerical simulation in three circuit models that were previously studied: the projective transverse-field Ising model, the lattice gauge-Higgs model, and the XZZX model. When the informative phase coincides with the SB phase, our steering mechanism effectively serves as a “preselection” routine, making the SB phase more experimentally accessible. Additionally, an intermediate phase may manifest, characterized by a discrepancy that arises between the quantum information captured by entanglement entropy and the classical information conveyed by bitstrings. Our findings demonstrate that steering not only adds theoretical richness but also offers practical advantages in the study of measurement-only quantum circuits.

The low-energy electronic spin precession is measured in the molecular field of a CoAl thin film. Designed to have a low Curie temperature, the variation of the CoAl molecular field results in an electronic spin precession angle that varies with temperature. The behavior is observed for injection energies between 0.9 and 1.2 eV and the results are explained on the basis of an exchange field varying with temperature.