We study new superconductor candidates in functionalized MXenes ${\mathrm{Zr}}_2{\mathrm{NS}}_2$, ${\mathrm{Zr}}_2{\mathrm{NCl}}_2$, and ${\mathrm{Sc}}_2{\mathrm{NCl}}_2$ with ab initio calculations based on density functional theory for superconductors (SCDFT). The superconducting transition temperature $\left(T_c\right)$ at ambient pressure is predicted to reach 9.48 K $\left({\mathrm{Zr}}_2{\mathrm{NS}}_2\right)$, with potential further improvements under applied strain. We note that the changes in the profiles of superconducting gap $\left(\mathrm{\Delta }\right)$ and electron-phonon coupling $\left(\lambda \right)$ across the Fermi surface may be influenced by their modified electronic band-structure components.

In this study, we have investigated the ultrafast photoinduced dynamics of ${\left(\mathrm{EDO}\text{−}\mathrm{TTF}\right)}_2{\mathrm{SbF}}_6$ single crystals under hydrostatic pressure. Our results indicate the occurrence of the charge-ordering phase transition under hydrostatic pressure at room temperature around 2200 bar. This leads to the appearance of oscillatory components into the ultrafast transient photoresponse. This periodic signal is associated with the ultrafast generation of coherent phonons, a clear marker of the insulating charge-ordered phase while photoexcited with ultrashort pulses. The photoinduced dynamics display a strong anisotropic character and an additional slower dynamic involving thermoelastic effects. Furthermore, a peculiar photoresponse at very high pressure (5500 bar) suggests the occurrence of a second phase transition, leading to a possible new charge-ordered state which is absent in the thermally driven case. This finding is supported by the presence of a new coherent phonon mode whose frequency of $\approx 1.7$ THz does not match the ones observed in the two phases present at thermal equilibrium under ambient pressure.

We report a detailed study of the magnetic properties, critical analysis of magnetization, and magnetocaloric effect of a spin-2 kagome lattice ${\mathrm{YCa}}_3{\left(\mathrm{MnO}\right)}_3{\left({\mathrm{BO}}_3\right)}_4$. The experiments are complemented by the density functional band-structure calculations. The magnetic measurements suggest a highly frustrated nature of the compound due to competing ferro- and antiferromagnetic interactions, with the dominant one being ferromagnetic. It undergoes an unconventional ferromagnetic ordering at $T^{*}\simeq 7.8$ K and a field-induced metamagnetic transition in low fields, implying spin canting. A $H\text{−}T$ phase diagram is constructed that features three phase regimes. Indeed, the band-structure calculations reveal dominant ferromagnetic interaction along the chains that are coupled antiferromagnetically, yielding a frustrated kagome geometry. This compound shows a large magnetocaloric effect with isothermal entropy change $\mathrm{\Delta }{S}_m\simeq 12$ J/kg-K, adiabatic temperature change $\mathrm{\Delta }{T}_{\mathrm{ad}}\simeq 8.4$ K, and relative cooling power $\mathrm{RCP}\simeq 349$ J/kg for a field change of 7 T. The critical analysis of magnetization and magnetocaloric parameters suggests that the transition is a second-order phase transition and it is a tricritical mean-field type. Owing to its large magnetocaloric parameters, second-order phase transition, and no thermal hysteresis, ${\mathrm{YCa}}_3{\left(\mathrm{MnO}\right)}_3{\left({\mathrm{BO}}_3\right)}_4$ emerges as a potential rare-earth-free magnetic material for magnetic refrigeration.

We investigate the ultrafast magnetization dynamics of an interlayer-exchange-coupled Co/Mn/Co trilayer system after excitation with an ultrafast optical pump. We probe element- and time-resolved ferromagnetic order by x-ray magnetic circular dichroism in resonant reflectivity. We observe an accelerated Co demagnetization time in the case of weak total parallel interlayer coupling at 9.5 ML Mn thickness for antiparallel alignment of both Co layers compared to parallel alignment as well as for parallel alignment in the case of strong parallel interlayer coupling at 11 ML of Mn. From ab initio time-dependent density functional theory calculations, we conclude that optically induced intersite spin transfer of spin-polarized electrons from Co into Mn acts as a decay channel to enhance and accelerate ultrafast demagnetization. This spin transfer can only take place in case of a collinear Mn spin structure. We argue that this is the case for antiparallel alignment of both Co layers at 9.5 ML Mn thickness and parallel alignment in case of 11 ML of Mn. Our results point out that an antiferromagnetic spacer layer and its spin structure have a significant effect on the magnetization dynamics of adjacent ferromagnetic layers. Our findings provide further insight into fundamental mechanisms of ultrafast demagnetization and may lead to improve dynamics in multilayered systems for faster optical switching of magnetic order.

We present a general mechanism for large charge and spin Josephson diode effects in strongly spin-polarized superconductor-ferromagnet hybrid structures with a noncoplanar spin texture, formulated in terms of quantum-geometric phases. We present necessary conditions for this effect to occur, and show numerical results for disordered materials relevant to applications. We calculate Josephson diode efficiencies for both charge and spin diodes and show that a spin-diode efficiency of 100% can be reached. Finally, we present a SQUID device that can switch between nearly pure spin-up and spin-down equal-spin supercurrents across the ferromagnet by reversing the flux. These findings establish functionalities that are absent in coplanar spin textures.

We present a systematic study of the spin-resolved Josephson diode effect (JDE) in strongly spin-polarized ferromagnets (sFM) coupled to singlet superconductors (SC) via ferromagnetic insulating interfaces (FI). All metallic parts are described in the framework of the quasiclassical Usadel Green's function theory applicable to diffusive systems. The interfaces are characterized by an S-matrix obtained for a model potential with exchange vectors pointing in an arbitrary direction with respect to the magnetization in the sFM. Our theory predicts a large charge Josephson diode effect with an efficiency exceeding $33\%$ and a perfect spin diode effect with $100\%$ efficiency. To achieve these, the following conditions are necessary: (i) a noncoplanar profile of the three magnetization vectors in the system and (ii) different densities of states of spin-$\uparrow$ and spin-$\downarrow$ bands in the sFM achieved by a strong spin polarization. The former gives rise to the quantum-geometric phase $\mathrm{\Delta }\phi$ that enters the theory in a very similar manner to the superconducting phase difference across the junction $\mathrm{\Delta }\chi$. We perform a harmonic analysis of the Josephson current in both variables and find symmetries between Fourier coefficients, allowing an interpretation in terms of transfer processes of multiple equal-spin pairs across the two ferromagnetic spin bands. We point out the importance of crossed-pair transmission processes. Finally, we study a spin-switching effect of an equal-spin supercurrent by reversing the magnetic flux in a SQUID device incorporating the mentioned junction and propose a way to measure it.

The interactions between conduction electrons and magnetism can significantly enhance the Hall signal, a phenomenon known as the anomalous Hall effect (AHE). While the AHE is generally not expected in antiferromagnets, a large AHE is observed in certain antiferromagnets with noncollinear spin textures and nonvanishing Berry curvature. In this work, we present a rich temperature and magnetic phase diagram with eight distinct magnetic phases for the antiferromagnetic kagome compound ${\mathrm{LuMn}}_6{\mathrm{Sn}}_6$. The Hall effect analysis in ${\mathrm{LuMn}}_6{\mathrm{Sn}}_6$ reveals both intriguing physical phenomena and methodological challenges. In the coplanar canted antiferromagnetic phase, we observe an AHE, which likely originates from the intrinsic effects. At low temperatures, upon entering the ferromagnetic phase, the AHE sharply increases and exceeds the conventional limits expected from intrinsic mechanisms. We also demonstrate the limitations of standard experimental methods in extracting the topological contribution to the Hall effect data. In particular, we show that accounting for magnetoresistance anisotropy helps reduce spurious contribution that can mimic topological Hall signals, although it does not fully resolve it. These shortcomings in current approaches in partitioning the Hall response necessitate new tools to interpret transport results in complex magnetic materials such as ${\mathrm{LuMn}}_6{\mathrm{Sn}}_6$.

Motivated by the important role of next-nearest-neighbor hopping $t^{\prime }$ in the Hubbard model, we perform a systematic quantum Monte Carlo study of the superconducting pairing correlation in the heavily doped Hubbard model. By combining the determinant quantum Monte Carlo with constrained-path quantum Monte Carlo simulations, we discover that the dominant $d_{xy}$-wave pairing symmetry is sharply enhanced by positive $t^{\prime }$ both at finite and zero temperatures, highlighting the critical role of $t^{\prime }$ in manipulating superconducting pairing symmetry. Accompanied by the occurrence of $d_{xy}$-wave pairing symmetry, the antiferromagnetic fluctuations disappear but the spiral magnetic order can be enhanced by increasing $U$ or $t^{\prime }$. Moreover, when the pairing correlation of $d_{xy}$-wave pairing symmetry is sharply increased by $t^{\prime }$, the sign problem also shows a sharp decrease, indicating an interesting relationship between superconductivity and the sign problem. Generally, our unbiased simulations provide an important insight into the superconducting pairing mechanism in the heavily doped Hubbard model and also might offer useful information to understand the superconducting pairing symmetry of unconventional superconductors.

Extremely large magnetoresistance (XMR) observed in topological materials holds significant promise for spintronic applications. In this work, we systematically investigate the magnetotransport properties and quantum oscillations in high-quality single crystals of the magnetic nodal-line semimetal ${\mathrm{FeGe}}_2$. Synthesized via chemical vapor transport, the ${\mathrm{FeGe}}_2$ crystals exhibit an exceptional residual resistivity ratio of 533 and achieve a nonsaturating XMR of $\mathrm{23 000}\%$ at 1.8 K and 14 T, accompanied by ultrahigh carrier mobility ($1\times {10}^5{\text{cm}}^2{\text{V}}^{-1}{\text{s}}^{-1}$). Shubnikov-de Haas oscillations reveal a $\pi$-Berry phase, suggesting a possible nontrivial topological nature of ${\mathrm{FeGe}}_2$. The remarkably high ratio of transport-to-quantum lifetimes (${\tau }_{\text{tr}}/{\tau }_Q\approx 1571$) further confirms suppression of backscattering, possibly related to topological protection. Combined with Hall effect measurements and extended Kohler scaling analysis, we establish that the origin of XMR in ${\mathrm{FeGe}}_2$ arises from the synergistic interplay between topological protection and high carrier mobility, rather than conventional electron-hole compensation. These findings not only provide critical experimental insights into the XMR mechanism of magnetic nodal-line semimetals but also highlight ${\mathrm{FeGe}}_2$ as a promising candidate for designing next-generation topological spintronic devices.

Recent studies have highlighted the combination of tensor-network methods and the stabilizer formalism as a very effective framework for simulating quantum many-body systems, encompassing areas from ground-state to time-evolution simulations. In these approaches, the entanglement associated with stabilizers is transferred to Clifford circuits, which can be efficiently managed due to the Gottesman-Knill theorem. Consequently, only the nonstabilizerness entanglement needs to be handled, thereby reducing the computational resources required for accurate simulations of quantum many-body systems in tensor-network-related methods. In this work, we adapt this paradigm for finite-temperature simulations in the framework of the time-dependent variational principle, in which imaginary-time evolution is performed using the purification scheme. Our numerical results on the one-dimensional Heisenberg model and the two-dimensional $J_1-J_2$ Heisenberg model demonstrate that Clifford circuits can significantly improve the efficiency and accuracy of finite-temperature simulations for quantum many-body systems. This improvement not only provides a useful tool for calculating finite-temperature properties of quantum many-body systems, but also paves the way for further advancements in boosting the finite-temperature tensor-network calculations with Clifford circuits and other quantum circuits.

We explore topological electronic structure of magnetic phases in a multiorbital Hubbard model with spin-orbit interactions. To account for more general antiferromagnetic orders that go beyond the collinear Néel order, two different spin-orbit interactions, Dresselhaus and Rashba spin-orbit interactions, are considered. By performing the canonical transformation, we derive the corresponding generalized $t\text{−}J$ model. At half-filling, employing self-consistent magnetic order calculations, we find distinctive spin arrangements under Dresselhaus or Rashba spin-orbit interactions. For the Dresselhaus spin-orbit interaction, the spin configuration exhibits collinear antiferromagnetic order. On the other hand, the Rashba interaction results in spins antiferromagnetically aligning in the $xy$ plane and a small interaction controlled by hopping parameter induces spin tilting, causing antiferromagnetic alignment in the $xy$ plane but ferromagnetic alignment in the $z$ direction. We categorize topological properties of these phases for low doping in the generalized $t\text{−}J$ model: for three-dimensional collinear antiferromagnetic order, the system possesses a modified time-reversal symmetry, characterized by the $Z_2$ index. In contrast, for systems with tilted antiferromagnetic orders, it is protected by inversion symmetry and characterized by the $Z_4$ index. We further examine the bulk-edge correspondence for noncollinear magnetic phases, revealing that the glide-symmetry-protected gapless surface state emerges when the surface is parallel to the ferromagnetic component of tilted antiferromagnetic order; otherwise, the surface state exhibits a gap. Our findings offer a comprehensive topological characterization for doped and canted antiferromagnetic insulators with spin-orbit interactions, providing valuable insights into the interplay between spin arrangements, symmetries, and topological properties in systems governed by the multiorbital Hubbard model.

We propose a unified mechanism to understand the remarkable stability of the body-centered cubic (bcc) phase in compressed solids, rooted in the orbital character of the electronic structure. In our previous study [Phys. Rev. B 108, 094112 (2023)], we showed that the contrasting high-pressure behavior of phosphorus (P), arsenic (As), and antimony (Sb)—where As and Sb adopt a stable bcc phase, but P does not—can be explained by whether a bonding-antibonding state composed purely of $p$ orbitals is preserved or not. In this paper, we extend this framework to the chalcogen elements and to the $d$-electron system titanium (Ti). First-principles calculations reveal that sulfur (S) exhibits a similar $p$-orbital-driven stabilization of the bcc phase, while heavier chalcogens are destabilized due to the occupation of antibonding $p$ states. In Ti, we identify a pressure-induced $s-d$ transition accompanied by the orbital-symmetry-resolved formation of a bonding-antibonding state within the $d$ manifold. Under high pressure, the electronic occupations of the $t_{2g}$ and $e_g$ orbitals approach an ideal 2:1 ratio, reinforcing the bonding framework and enhancing the stability of the bcc phase up to at least 1000 GPa. These results support a general criterion for the bcc phase stability in compressed elements based on orbital purity and symmetry, providing a unifying perspective across disparate chemical families.

Despite the tremendous interest raised by the recent realization of magnetic Weyl semimetals and the observation of giant anomalous Hall signals, most of the theories used to interpret experimental data overlook the influence of magnetic fluctuations, which are ubiquitous in such materials and can massively impact topological and transport properties. In this work, we predict that in such magnetic topological systems, the interaction between electrons and magnons substantially destabilizes the Weyl nodes, leading to a topological phase transition below the Curie temperature. Remarkably, the sensitivity of the Weyl nodes to electron-magnon interaction depends on their spin chirality. We find that Weyl nodes with a trivial chirality are more sensitive to electron-magnon interactions than Weyl nodes presenting an inverted chirality, demonstrating the resilience of the latter compared to the former. Our results open perspectives for the interpretation of the transport signatures of Weyl semimetals, especially close to the Curie temperature.

We investigate magnetoresistivity and the Hall effect in a 6.3-nm gapless HgTe quantum well—a two-dimensional hybrid band system featuring coexisting linear (Dirac-like) and parabolic hole energy bands at low energies. Using a classical two-subband model that includes intervalley scattering, we reveal a striking tenfold enhancement of the Hall resistance, mainly driven by the dominant transport contribution of Dirac holes. A comprehensive magnetotransport analysis allows us to extract key parameters, such as the mobilities of both carrier types, providing insight into their complex interplay. These results establish the HgTe quantum well as a distinctive platform for investigating novel transport phenomena in hybrid band systems, enhancing our understanding of mixed-carrier magnetotransport.

While free/excited electron-phonon coupling has been extensively investigated, crucial physical processes—such as ultrafast thermal transport and many phase transitions—are mainly governed by nonequilibrium intrinsic phonons, which remain challenging to observe. Here, the relaxation dynamics of nonequilibrium intrinsic phonons in a high-quality hBN flake is studied based on the advanced femtosecond mid-infrared (MIR) transient absorption micro-spectroscopy. We observe a near-unity degree of polarization in the transient absorption after the resonant phonon excitation. Nonequilibrium intrinsic phonons exhibit nonmonotonic relaxation dynamics. Based on time-dependent density functional theory simulations, this behavior is attributed to the cascaded anharmonic interactions that redistribute energy and momentum among phonons and bound electrons. Our work sheds new light on the ultrafast dynamics of collective excitations, which provides critical insights into atomic-scale ultrafast thermal transport and offers a novel strategy for active ultrafast mid-infrared light modulation.

We construct a model of a three-dimensional chiral second-order topological insulator (SOTI) from an array of weakly coupled nanowires. We show that, in a suitable parameter regime, the interplay between rotating magnetic fields and spatially modulated interwire tunnelings leads to the opening of gaps in the bulk and surface spectrum of the system, while one or more chiral hinge states propagating along a closed path of one-dimensional hinges are left gapless. The exact path of these hinge states is determined by the hierarchy of interwire couplings and the boundary termination of the sample. Depending on the ratio between the period of the rotating magnetic field and the Fermi wavelength, our model can realize both integer and fractional chiral SOTIs. The fractional regime emerges in the presence of strong electron-electron interactions and features hinge states carrying only a fraction $e/p$ of the electronic charge $e$ for a positive odd integer $p$.

Material inhomogeneities in a superconductor generically lead to broadening of the density of states and to subgap states. The latter are associated with spatial fluctuations of the gap in which quasiparticles can be trapped. Recombination between such localized quasiparticles is hindered by their spatial separation and hence their density could be higher than expectations based on the recombination between mobile quasiparticles. We show here that the recombination between localized and mobile excitations can be efficient at limiting the quasiparticle density. We comment on the significance of our findings for devices such as superconducting resonators and qubits. We find that for typical aluminum devices, the subgap states do not significantly influence the quasiparticle density.

In this Letter, we introduce a next generation of Andreev spin qubits—three-terminal Andreev spin qubits. These qubits outperform two-terminal devices in the speed of two-qubit gates, benefiting from enhanced spin splitting. Our theoretical analysis reveals increased tunability and interqubit coupling mediated by the supercurrent. Furthermore, it provides a comprehensive explanation for the results of a recent experiment on a three-terminal device [M. Coraiola et al., Phys. Rev. X 14, 031024 (2024)]. We identify the optimal operational regime for single- and two-qubit gates. Moreover, our concise theoretical framework for the equilibrium multiterminal Josephson effect offers significant potential for exploring nontrivial physics in the artificial dimensions of superconducting phase differences–—a rapidly growing field of research.