Based on high-throughput density functional theory calculations, we evaluate the local magnetic moments and Mössbauer properties for Fe-based intermetallic compounds and employ machine learning to map the local crystalline environments to such properties. It is observed that magnetic moments and Mössbauer parameters provide complementary insights into the local crystalline environment, where the statistical features cannot be captured using phenomenological models. Furthermore, we find that the scarcity of the existing data in the Materials Project (MP) poses a significant challenge in developing predictive machine learning models, whereas smooth overlap of atomic positions (SOAP)-based descriptors can be applied for reliable modeling of the enriched datasets with extra structural prototypes. This work advances the mapping of local crystalline structures to magnetic and spectroscopic properties, bridging the gap between empirical observations and theoretical models.

Motivated by recent advances in digital quantum simulation and the overall prospect of solving correlated many-electron problems using quantum algorithms, we design a gate-based quantum circuit that emulates the dynamics of the Kondo impurity model. We numerically determine the impurity magnetization, entanglement between impurity and fermionic sites, and energy as a function of time (i.e., circuit depth) for various initial states and find universal long-time dynamics. We complement the numerical simulations for moderate system size with an asymptotically exact analytical solution that is effective in the limit of large system sizes and for starting states corresponding to a filled Fermi sea. This work opens up the perspective of studying the dynamics of electronic quantum many-body states on quantum chips of the NISQ era.

Majorana bound states (MBSs) have emerged as promising candidates for robust quantum computing due to their non-Abelian statistics and topological protection. In this study, we focus on the dynamical transport of MBSs in the semiconductor-superconductor heterostructure via the piano-key type of setup, wherein each of the keys of the wire can be tuned from topological to trivial phases. We focus on the transport of MBSs under noisy conditions and evaluate the feasibility for realistic scenarios. The central emphasis of our work lies in using both numerical and analytical techniques to understand the effect of noise in inducing diabatic errors during transport and to establish scaling laws that relate these errors to the drive time. To achieve this, we derive an effective model that captures the scaling behavior in both noise-free and noisy scenarios, providing a unified framework for analyzing the transport dynamics. We investigate the optimal number of keys for both noisy and noiseless scenarios. Additionally, we explore the effects of disorder on transport dynamics, highlighting its impact on error scaling and robustness. Our findings provide guiding principles for the design of future MBS-based quantum devices and raise important questions about the interplay between control precision, noise resilience, and scalability in topological quantum architectures.

We describe the evolution of low-temperature thermopower across Fermi-volume-changing quantum phase transitions in Kondo lattice models without translational symmetry breaking. This transition moves from a heavy Fermi liquid with a conventional Luttinger-volume large Fermi surface to a “FL*” state, characterized by a small Fermi surface and a spin liquid with fractionalized excitations. The onset of the large Fermi surface phase is driven by the condensation of a Higgs field that carries a unit gauge charge under an emergent U(1) gauge field. We consider the case with spatially random Kondo exchange, as this leads to strange metal behavior in electrical transport. We find a large asymmetric thermopower in a “skewed” marginal Fermi liquid, with similarities to the skewed non-Fermi liquid of Georges and Mravlje [Phys. Rev. Res. 3, 043132 (2021)]. Our findings are consistent with recent observations in heavy fermion compounds (Z.-Y. Cao et al., arXiv:2408.13604) and describe an enhancement of thermopower on the large Fermi surface side as well as a nonmonotonic behavior on the small Fermi surface side. Our results also apply to single-band Hubbard models and the pseudogap transition in the cuprates. In the ancilla framework, single-band models exhibit an inverted Kondo lattice transition: the small Fermi surface pseudogap state corresponds to the condensed Higgs state. This inversion results in an enhancement of thermopower on the pseudogap side in our theory, consistent with observations in the cuprates [C. Collignon et al., Phys. Rev. B 103, 155102 (2021)); A. Gourgout et al., Phys. Rev. X 12, 011037 (2022)]. We argue that these observations support a non-symmetry-breaking Fermi-volume-changing transition as the underlying description of the onset of the pseudogap in the cuprates.

One-dimensional (1D) systems and models provide a versatile platform for emergent phenomena induced by strong electron correlation. In this work, we extend the newly developed real-space neural network quantum Monte Carlo methods to study the quantum phase transition of electronic and magnetic properties. Hydrogen chains of different interatomic distances are explored systematically with both open and periodic boundary conditions, and the fully correlated ground-state many-body wavefunction is achieved via unsupervised training of neural networks. We demonstrate that neural networks are capable of capturing the quantum critical behavior of Tomonaga-Luttinger liquid (TLL), which is known to dominate 1D quantum systems. Moreover, we reveal the breakdown of the TLL phase and the emergence of a Fermi liquid behavior, evidenced by abrupt changes in the spin structure and the momentum distribution. Such behavior is absent in commonly studied 1D lattice models and is likely due to the involvement of high-energy orbitals of hydrogen atoms. Our work highlights the power of neural networks for representing complex quantum phases.

This study examines the ultrafast carrier dynamics of topological semimetals ${\mathrm{NiTe}}_2$ and ${\mathrm{PdTe}}_2$, highlighting the influence of their distinct electronic structures. Transient absorption spectroscopy in reflectance mode reveals that ${\mathrm{NiTe}}_2$ exhibits a sharp feature at 2.03 eV, linked to Dirac states near the Fermi level, while ${\mathrm{PdTe}}_2$ shows a broader, featureless response due to its Dirac states lying 0.5 eV below the Fermi level. In the near-infrared region, ${\mathrm{NiTe}}_2$ demonstrates rapid state filling and short-lived dynamics, whereas ${\mathrm{PdTe}}_2$ supports prolonged absorption due to accessible Dirac states. Temperature-dependent studies reveal a nonmonotonic relaxation in ${\mathrm{NiTe}}_2$, attributed to a Lifshitz transition around T*≈ 50 K, altering the Fermi surface topology. In contrast, ${\mathrm{PdTe}}_2$ exhibits conventional relaxation dynamics across temperatures. These findings underscore the role of Dirac states and topological transitions in shaping carrier dynamics, offering insights for advancing optoelectronic and thermal management technologies.

Two-dimensional (2D) topological superconductors not only provide a platform for exploring novel quantum physical phenomena but also play a significant role in the field of quantum computing. However, reports on 2D topological superconductors are quite scarce. Here, based on first-principles calculations, we study the superconductivity of a class of monolayer ${TM}_m{X}_n$ ($TM=\text{V}$, Nb, Ta; $X=\text{C}$, N; $m=2$, 3; $n=2$, 3; $m\ne n$) with $P\overline{6}m2$ (No. 187) and $P\overline{3}m1$ (No. 164) symmetries, referred to as $h\text{−}{TM}_m{X}_n$ (No. 187) and $t\text{−}{TM}_m{X}_n$ (No. 164), respectively. Among them, monolayer $h\text{−}{\mathrm{V}}_2{\mathrm{N}}_3$ is predicted to have the highest critical temperature $T_c$ as high as 38.4 K and a superconducting gap of about 9 meV. The superconductivity of monolayer $h\text{−}{\mathrm{V}}_2{\mathrm{N}}_3$ mainly originates from the strong coupling between conduction electrons from the V $3d$ and N $2p$ orbitals near the Fermi level and the low-frequency V- and N-related phonons. Moreover, nontrivial $Z_2$ band topology further demonstrates that monolayer $h\text{−}{\mathrm{V}}_2{\mathrm{N}}_3$ is a promising candidate for realizing 2D topological superconductivity. Our findings provide a robust platform to study the emergent phenomena in 2D topological superconductors.

Controlling valley physics of carriers is crucially important for valleytronics. Current studies are mainly based on spin orientation reversal driven by magnetic means, which is less favored in terms of efficiency. Here, through first-principles calculations and effective model analysis, we demonstrate the control of valley physics and anomalous valley Hall effect (AVHE) via electric means in ferroelectric ferrimagnetic single-layer $\mathrm{C}{\mathrm{e}}_2\mathrm{C}{\mathrm{O}}_2$. This system exhibits intrinsic ferro-valleytricity, arising from the synergistic effect of symmetry breakings and spin-orbit coupling. Notably, its ferroelectric transition is associated with unconventional lattice breathing of Ce atomic trigons, which facilitates the realization of electrically switchable valley physics and AVHE, generating the long-sought ferroelectrovalley phenomenon. Through effective model analysis, we elucidate the fundamental mechanisms underlying these phenomena, highlighting the crucial role of ferroelectricity-driven staggered trigonal breathing modes. Our findings not only provide a paradigm for valley reversal manipulation but also significantly advance the frontier of valleytronic research.

Preparing realistic atom-scale models of amorphous silicon (a-Si) is a decades-old condensed-matter physics challenge. Herein, we combine the activation relaxation technique nouveau (ARTn) to a moment tensor potential (MTP) to generate seven a-Si models containing between 216 and 4096 atoms. A thorough analysis of their short-range and medium-range structural properties is performed, alongside assessments of excess energy and mechanical properties. The seven ARTn-MTP models are compared with available experimental data and other high-quality a-Si models present in the literature. The seven ARTn-MTP a-Si models are in excellent agreement with available experimental data. Notably, several of our models, including the 216-atom, 512-atom, and 1000-atom a-Si models, exhibit low coordination defects without any traces of crystalline grains. Historically overlooked in previous research, our study underlines the need to assess the validity of the continuous random-network hypothesis for the description of perfect amorphous model by characterizing local crystalline environment and to explore the crystallization process of a-Si through modeling.

Recently, ${\mathrm{RuO}}_2$ has gained significant attention as a promising altermagnetic candidate. However, the presence of magnetism in ${\mathrm{RuO}}_2$ has been a topic of ongoing debate, with stoichiometry identified as a key factor by Smolyanyuk et al. [Phys. Rev. B 109, 134424 (2024)]. To explore the stoichiometric effects in ${\mathrm{RuO}}_2$, we oxidized pure single-element Ru at several temperatures. The band structure modulation near Fermi level by stoichiometric variation was clearly observed by in situ angle-resolved photoemission spectroscopy. First-principles calculations revealed that this evolution was relevant to surface reconstruction induced by excessive O rather than altermagnetism. Additionally, our results indicate that the experimentally measured band structure of ${\mathrm{RuO}}_2$(100)/Ru($10\overline{1}0$) aligns well with the nonmagnetic band calculations. Our findings not only provide a clue to resolve the current experimental discrepancy but also support the nonmagnetic ground state of ${\mathrm{RuO}}_2$ films grown on Ru metal.

Significant progress has been made for the emerging concept of a magnon frequency comb (MFC), but mainly in the classical region. The quantum property of the comb structure is yet to be explored. Here we theoretically investigate the quantum fluctuations of frequency combs and demonstrate the continuous-variable quantum entanglement and Einstein-Podolsky-Rosen steering between different teeth of the MFC. Without loss of generality, we address this issue in a hybrid magnon-skyrmion system. We observe a strong two-mode squeezed entanglement and asymmetric steering between the sum- and difference-frequency magnon teeth mediated by the skyrmion that acts as an effective reservoir to cool the Bogoliubov mode delocalized over the first-order magnon pair in the MFC. The larger skyrmion dissipation induces stronger entanglement and the direction of quantum steering can be flexibly controlled by magnon dissipation, which means that the dissipation, which is generally regarded as a negative effect in the magnetic system, becomes a favorable way to enhance and manipulate quantum correlation. Moreover, the physical mechanism of quantum correlation could be extended to high-order magnon modes. Our findings show the prominent quantum nature of the MFC, which has the potential to be utilized in ultrafast quantum metrology and multitask quantum information processing.

We have reinvestigated the crystal structure of a spinel-type ${\mathrm{CuIr}}_2{\mathrm{S}}_4$ at low temperatures using a single crystal in a synchrotron radiation x-ray diffraction experiment. The crystal structure of the low-temperature phase of ${\mathrm{CuIr}}_2{\mathrm{S}}_4$ has been already studied by diffraction experiments using a powder sample, and it has been reported that the formation of dimer molecules accompanied by charge ordering of Ir has been achieved. The crystal structure of the low-temperature phase obtained in our reanalysis was the same as the previously reported structure in that it showed the formation of Ir dimers accompanied by charge ordering, but the charge-ordering pattern and arrangement of the dimers in the unit cell were different. We will discuss the validity of the structure obtained in this study and provide the structural parameters revealed in the reanalysis. The results of this study should provide a basis for further studies of the physical properties of ${\mathrm{CuIr}}_2{\mathrm{S}}_4$, which are still being actively investigated.

In this study, we have investigated the temperature dependence of atomic ordering at multiple length scales in a lead-free sodium niobate-based relaxor, i.e., 0.75 ${\mathrm{NaNbO}}_3$-0.25 ${\mathrm{Ba}}_{0.9}{\mathrm{Ca}}_{0.1}{\mathrm{TiO}}_3$ (NN-25BCT) via synchrotron x-ray diffraction, Raman spectroscopy, and pair distribution function analysis. High-resolution synchrotron x-ray powder diffraction (SXRD) measurements reveal a ferroelectric phase transition in the relaxor ferroelectric NN-25BCT below the Vogel-Fulcher freezing temperature ($T_{\text{VF}}\approx 270$ K). In addition, SXRD analysis demonstrates the competition between in-phase octahedral tilting and ferroelectric order at the long-range scale using mode crystallography. On the other hand, Raman spectroscopic analysis provides evidence of polar ordering for $T>T_{\text{VF}}$ (with tetragonal symmetry) persisting up to the Burns temperature ($T_{\text{B}}$). Furthermore, pair distribution function (PDF) analysis reveals the presence of a polar antiferrodistortive tetragonal phase with $P4\mathit{bm}$ space group at short ranges throughout the studied temperatures (i.e., $110\text{K}\le T\le 500$ K), irrespective of nonpolar long-range ordering above $T_{\text{VF}}$. Therefore, our measurements provide direct evidence for the presence of polar ordering at short ranges and their gradual transformation into long-range polar ordering using an integrated multiscale structural analysis. As a result of a transition from relaxor to a ferroelectric phase in the vicinity of room temperature, NN-25BCT can be exploited for applications in pyroelectric detectors, electrocaloric devices, and multilayered ceramic capacitors.

Magnetic materials are promising for the ultrafast and Joule-loss free data storage and processing devices, where the information is encoded by a spin state. Femtosecond pulses are known as an efficient method of spin control with such advantages as ultrafast subpicosecond timescales, submicron spatial localization, and tunability as well. At the same time, quite low amplitude of optically launched spin dynamics is a stumbling block for optomagnetic applications. We propose a way to increase efficiency of photon-spin interaction and to launch large-amplitude spin precession nonthermally by optical pulses in the special types of the ferrimagnets. The key point is to use a soft mode excited in a low damping ferrimagnetic film near the spin-reorientation phase transition between the collinear and noncollinear phases. The physical mechanism of the enhanced spin dynamics is in a dramatic growth of the spin susceptibility to the nonthermal impact of the circularly polarized femtosecond laser pulses which takes place at the phase transition. The observed dynamic deviation of spins from their equilibrium position reaches 9 ° for an optical pump fluence of $30\mathrm{mJ}/{\mathrm{cm}}^2$ which is significantly higher than typical values of optically induced precession reported before.

The inertial magnetization diffusion of magnetic nanoparticles in a strong external dc magnetic field in the presence of thermal noise is studied. A method of calculation of the transient response of a magnetization due to a sudden change in the external field is presented. The method is based on the simplification of the inertial Fokker-Planck equation by using the Fourier transformation with respect to the angular velocities, and then representing the resultant equation in operator form using angular momentum operators. The infinite hierarchy of differential-recurrence relations for the decay functions describing the relaxation of the system is derived. The solution of this hierarchy is obtained in terms of matrix continued fractions. The longitudinal dynamic magnetic susceptibility of the system is obtained as a particular case of the general method and analyzed for typical values of the model parameters. The high-frequency part of the longitudinal susceptibility spectrum in the region of nutation resonance can be approximated by a single Lorentzian. Comparison of the exact solution with the predictions of the analytical Lorentz formula demonstrates very good agreement. The effect of inertia on the magnetic properties of magnetic nanoparticles subjected to a strong external field in the presence of thermal noise is discussed.

Quantumness imposes a fundamental limit on measurement accuracy. The paradigmatic cases are Heisenberg's uncertainty relation in the original formulation, Robertson's formulation, and improved uncertainty relations. However, the more universal measures are given in terms of quantum entropies. Uncertainties of measurements done on one quantum system correlated with another quantum system constitute a more intriguing question. Quantum correlations can influence the lower bound of uncertainties, and the reason for this is the quantum memory. In this article, we study uncertainties of measurements performed on one quantum dot correlated with the second one through the superconductor, hosting the Majorana boundary modes. We prove that the Majorana quasiparticles allow the uncertainties to reach the minimal possible lower bound. By rigorous theoretical considerations, we obtain the result of experimental relevance expressed in terms of only two parameters: the overlap between Majorana modes and their coupling strength with the quantum dots. We show that the overlap between Majorana modes reduces quantum uncertainties, which is a general result of fundamental importance. We also propose the protocol to measure spins in both quantum dots, consecutively, and demonstrate that the result of the second measurement would depend on the presence of Majorana quasiparticles. This could serve as an indirect tool for their empirical observation, which is of importance for the ongoing discussions concerning unambiguous detection of the Majorana quasiparticles in nanoscopic hybrid structures.

We present ground-state phase diagrams for the antiferromagnetic long-range Ising model under a linear coupling to a single bosonic mode on the square and triangular lattice. In the limit of zero coupling, the ground-state magnetization forms a devil's staircase structure of magnetization plateaux as a function of an applied longitudinal field in Ising direction. Apart from a paramagnetic superradiant phase with a finite photon density at strong linear coupling to a single bosonic mode, the long-range interactions lead to a plethora of intermediate phases that break the translational symmetry of the lattice and have a finite photon density at the same time. To qualitatively study the ground-state phase diagrams, we apply an adaption of the unit-cell-based mean-field calculations, which capture all possible magnetic unit cells up to a chosen extent. Further, we exploit an exact mapping of the nonsuperradiant phases to an effective pure Dicke model in order to calculate upper bounds for phase transitions towards superradiant phases. Finally, to treat quantum fluctuations in a quantitative fashion, we extend a wormhole quantum Monte Carlo algorithm for Dicke-spin systems to long-range spin-spin interactions. We discuss how these three methods are used in a cooperative fashion. In the calculated phase diagrams we see several features arising from the long-range interactions: the devil's staircases of distinct magnetically ordered normal phases and nontrivial magnetically ordered superradiant phases beyond the findings for nearest-neighbor interactions. Examples are a superradiant phase with a three-sublattice magnetic order on the square lattice and the superradiant Wigner crystal with four sites per unit cell on the triangular lattice. Further, we classify the nature of the quantum phase transitions between different phases. Concretely, between normal and superradiant phases with the same (different) magnetic order, the transition is of second order with Dicke universality (first order). Further, between superradiant phases we find first-order phase transitions, besides specially highlighted regimes for which we find indications of continuous second-order behavior.

$\mathrm{MgT}{\mathrm{i}}_2{\mathrm{O}}_4$ is a spinel superconductor with an optimal $T_{\mathrm{c}}\approx 5$ K recently discovered by employing superlattice engineering. Here, we study the pressure effect on the superconducting properties of $\mathrm{MgT}{\mathrm{i}}_2{\mathrm{O}}_4$ thin films deposited on the ($00l$)-oriented $\mathrm{MgA}{\mathrm{l}}_2{\mathrm{O}}_4$ substrate via measurements of resistance under various pressures up to 12 GPa. We find that the superconducting $T_{\mathrm{c}}$($P$) displays a nonmonotonic evolution, i.e., it first shows a gradual decrease and then exhibits an enhancement above $P_{\mathrm{c}}\sim 3$ GPa, resulting in a V-shaped double dome with two maxima. In addition, our results reveal an interesting correlation between $T_{\mathrm{c}}$ and the normal-state resistance, which exhibits an opposite trend with respect to $T_{\mathrm{c}}$($P$). Moreover, the extracted ${\mu }_0{H}_{c2}$(0) that exceeds the Pauli limit and the obtained large Maki parameter α suggest that the dominant pair-breaking effect is a spin-paramagnetic channel in the measured pressure range. In this work, we not only demonstrate the potential to further raise $T_{\mathrm{c}}$ of the Ti-based spinel superconductors but also offer more insight into the rich physics related to the superconducting mechanism of this family.

Electride superconductors with unique interstitial anionic electrons (IAEs) have recently attracted considerable attention. Lithium-based electride superconductors are of particular interest because of their striking electride states and superconductivity. Electrides containing Li and Bi are not yet known despite the previously reported Li-Bi binary compounds. In this study, we systematically simulated Li-rich bismuthides under compression using a state-of-the-art structure search approach combined with first-principles calculations. Strikingly, several unforeseen stable electride phases with high lithium coordination, diverse distributions of IAEs, and metallic characteristics were identified, that is, ${\mathrm{Li}}_5\mathrm{Bi}, {\mathrm{Li}}_7\mathrm{Bi}, {\mathrm{Li}}_8\mathrm{Bi}, {\mathrm{Li}}_9\mathrm{Bi}$, and ${\mathrm{Li}}_{10}\mathrm{Bi}$, where continuous phase transitions from orthorhombic Pmmn to Cmcm were observed in ${\mathrm{Li}}_5\mathrm{Bi}$, accompanied by a transformation from two-dimensional to zero-dimensional IAEs. Furthermore, superconducting property calculations revealed that ${\mathrm{Li}}_{10}\mathrm{Bi}$, featuring one-dimensional zigzag-like IAEs, had a superconducting transition temperature ($T_c$) of 4.5 K at a moderate pressure of 50 GPa, making it the highest lithium concentration electride superconductor consisting of Li and nitrogen group elements. The strong coupling between the electron states of Li $2p$ and the IAEs and Li-associated phonon modes dominates the remarkable superconductivity of ${\mathrm{Li}}_{10}\mathrm{Bi}$. This study offers valuable insights into emerging lithium-bearing electride superconductors.