Dirac semimetals, with their protected Dirac points, present an ideal platform for realizing intrinsic topological superconductivity. In this work, we investigate superconductivity in a two-dimensional, square-lattice nonsymmorphic Dirac semimetal. In the normal state near half-filling, the Fermi surface consists of two distinct pockets, each enclosing a Dirac point at a time-reversal invariant momentum $[\mathbf{X}=(\pi ,0)$ and $\mathbf{Y}=(0,\pi )]$. Considering an on-site repulsive and nearest-neighbor attractive interaction, we use self-consistent mean-field theory to determine the ground-state pairing symmetry. We find that an even-parity, spin-singlet $d_{x^2-y^2}$-wave pairing is favored as it gives rise to a fully gapped superconducting state. Since the pairing amplitude has opposite signs on the two Dirac Fermi pockets, the superconducting state is identified as a second-order topological superconductor. The hallmark of this topological phase is the emergence of Majorana zero modes at the system's boundaries. Notably, the positions of these Majorana modes are highly controllable and can be manipulated simply by tailoring the boundary sublattice terminations. Our results highlight the promise of nonsymmorphic Dirac semimetals for realizing and manipulating Majorana modes.

Bound electron–hole pairs in semiconductors known as excitons are the subject of intense research because of their potential for optoelectronic devices and applications, especially in the realm of two-dimensional materials. While the properties of free excitons in these systems are well understood, a general description of the interactions between these quasiparticles is complicated owing to their composite nature, which leads to important exchange processes that can take place between the identical fermions of different excitons. In this work, we employ a variational approach to study interactions between Wannier excitons and obtain an effective interaction potential between two ground-state excitons in a system of spin-degenerate electrons and holes. This potential is in general nonlocal in position space and depends on the combined spin configurations of the electrons and holes. When particularized to the case of hydrogen-like excitons with a heavy hole, this potential becomes local and exactly reproduces the Heitler–London result for two interacting hydrogen atoms. Thus, our result can be interpreted as a generalization of the Heitler–London potential to the case of arbitrary masses. We also show how including corrections arising from excited states into the theory results in a van der Waals potential at large distances, which is expected given the induced dipole–dipole nature of the interactions. Our approach is also applicable to more complicated systems with nonhydrogenic exciton series, such as layered semiconductors with Rytova–Keldysh interactions. Additionally, we use a path-integral formalism to develop a many-body theory for a dilute gas of excitons, resulting in an excitonic action that formally includes many-body interactions between excitons. While in this approach the field representing the excitons is exactly bosonic, we clarify how the internal exchange processes arise in the field-theoretical treatment, and show that the diagrams corresponding to the interactions between excitons align with our variational calculation when evaluated on shell. Our methods and results lay the groundwork for a generalized theory of exciton–exciton interactions and their application to the study of biexciton spectra and correlated excitonic matter.

Deconfined quantum critical points are intriguing transition points not predicted by the Landau-Ginzburg-Wilson symmetry-breaking paradigm which are usually identified by the appearance of a continuous phase transition between locally ordered phases. Here, we reveal the presence of deconfined quantum critical points with unexplored properties. Contrary to previously known examples, we show that the phenomenon of spin-charge separation peculiar to interacting low-dimensional fermions can allow for the appearance of partially gapped deconfined quantum critical points. We first infer this point by performing a field theory analysis of generic one-dimensional fermionic systems in the low energy limit. Subsequently, we derive a microscopic model where phase transitions between different locally ordered phases can take place. Here, by performing a numerical analysis we explicitly derive, among others, the gaps, local order parameters and correlation functions behavior, supporting the presence of partially gapped deconfined quantum critical points. Our results thus provide interesting insights on the widely investigated topic of quantum phase transitions.

Transition metal dichalcogenides, a family of two-dimensional compounds, are of interest for a range of technological applications. ${\mathrm{MoS}}_2$, the most researched member of this family, is hexagonal, from which monolayers may be isolated. Under ambient conditions and during growth/processing, contamination by impurities can occur, of which carbon is significant due to its presence in the common growth techniques. We have performed extensive computational investigations of carbon point defects, examining substitutional and interstitial locations. Previously unreported thermodynamically stable configurations: Fourfold coordinated monocarbon and dicarbon substitutions of Mo, and a complex of carbon substitution of sulfur bound to interstitial sulfur have been identified. We find no evidence to support recent assertions that carbon defects are responsible for electrical doping of ${\mathrm{MoS}}_2$, finding all energetically favorable forms have only deep charge transition levels and would act as carrier traps. To aid in the unambiguous identification of carbon defects, we present electronic and vibrational data for comparison with spectroscopy.

Oxygen vacancies play a critical role in stabilizing the ferroelectric phase of hafnia-zirconia thin films, yet their interplay with zirconium doping is less well understood. In this work, we employ Density Functional Theory to uncover how local cation environments caused by zirconium doping, and charge states ($q=-2$ to $+2$), shape the oxygen vacancy landscape in ferroelectric hafnia-zirconia (${\mathrm{Hf}}_{1-x}{\mathrm{Zr}}_x{\mathrm{O}}_2$; $x=0.25,0.50,0.75$). We reveal the crucial role of the local cation environment in facilitating the formation of oxygen vacancies in ferroelectric hafnia-zirconia compared to hafnia, extending the analysis to nine unique environments. The environment comprised of four zirconium cations was found to have the lowest formation energy out of the set of local cation environments for neutral oxygen vacancy formation. The charge transition to positively charged vacancies ($q=+2$) dramatically increases the number of available sites, suggesting that electric field–induced charge transitions can facilitate vacancy diffusion. We find that the concentration of zirconium doping surprisingly did not impact the formation energies of oxygen vacancies, instead acting as a lever controlling the population of available sites for oxygen vacancy formation. Bonding analysis reveals that zirconium content weakens the cation-oxygen bond by introducing occupied antibonding states, further stabilizing defect formation. These findings reveal how doping and charge state modulate the defect landscape, offering a blueprint for tuning oxygen vacancy behavior and, by extension, the performance of next-generation ferroelectric devices.

We study excited states and finite temperature properties of chains of randomly placed spins with long range interactions. To this end we extend the recently introduced strong disorder renormalization group method in real space, well suited to study bond disordered antiferromagnetic power law coupled quantum spin chains. For bond disordered, short range coupled spin chains, defined by keeping only interactions between adjacent spins, we show that the distribution of the absolute value of the couplings is the infinite randomness fixed point distribution also for the excited states. Moreover, we derive the distribution function of the sign of the couplings and find that the number of negative couplings increases with temperature $T.$ For power law long range interaction with power exponent $\alpha$ we derive and solve the Master equation for the distribution function of couplings for $\alpha >2$. The coupling amplitude is found to have the strong disorder distribution with finite width $2\alpha ,$ with small corrections. We derive resulting finite temperature properties of both short and power law long ranged spin systems for $\alpha >2$. The magnetic susceptibility is dominated by paramagnetic $S=1/2$-spin, resulting in a Curie law susceptibility. The distribution function of pair lengths, and the spin correlation function are found be the same as in the ground state. We find that the entanglement entropy increases logarithmically with the partition length $n$ and has the same functional form as for the ground state of critical quantum spin chains with temperature dependent effective central charge $\overline{c}\left(T\right)$, which converges at high temperature to $\frac{1}{2}ln2$, half the value it has in the ground state. We confirm that the entanglement entropy grows with time $t$ after a quantum quench logarithmically as $S\left(t\right)\sim ln\left(t\right)/\left(2\alpha \right)$.

In quantum magnetic materials it is common to observe both static and dynamic lattice effects on the magnetic excitation spectrum. Less common is to find that the magnetic correlations have a significant impact on the phonon spectrum. Here we study the metal-organic material ${\left({\mathrm{C}}_5{\mathrm{H}}_9{\mathrm{NH}}_3\right)}_2{\mathrm{CuBr}}_4$(Cu-CPA), in which an explanation of the low-lying excitations depends crucially on a full understanding of both the spin and lattice subsystems. We report high-resolution neutron spectroscopy enabled by large, deuterated single crystals that reveal how both sectors are affected by the recently discovered structural phase transition. By measuring over several Brillouin zones, we disentangle the vibrational contribution to the spectrum in order to obtain an accurate estimate of the quasi-one-dimensional magnetic signal. The low-energy magnetic excitations are dominated by two gaps, ${\mathrm{\Delta }}_b=0.41\mathrm{meV}$ and ${\mathrm{\Delta }}_a=0.55\mathrm{meV}$, which contribute with equal intensity ratios, confirming that Cu-CPA realizes a two-ladder spin Hamiltonian, and we deduce the magnetic interaction parameters of both ladders. The phonon spectrum contains highly localized modes at an anomalously low energy around 2 meV. For half of these modes, this characteristic frequency drops by approximately 5% as magnetic correlations become established with decreasing temperature, and we connect this apparent “elastomagnetic” behavior with the location and structure of the cyclopentylammonium rings.

We demonstrate the realization and interplay of two ferromagnetic resonances in one SFS ${\phi }_0$ Josephson junction. The first resonance, which is realized under microwave radiation, is the famous Kittel resonance. The other is the Buzdin one, appearing as a result of the interaction of a superconducting current and ferromagnetic interlayer magnetization. Transformations of one type of resonance to another under variation of external electromagnetic radiation and the ${\phi }_0$ junction parameters open an interesting way to manipulate both of them. The combined ferromagnetic resonance that exhibits the features of both resonances is also demonstrated. The coupling of the Josephson phase with the magnetization of the ferromagnetic layer, caused by the spin-orbit interaction, leads to double synchronization, namely, synchronization of both magnetic precession and Josephson oscillations by external radiation. The obtained results demonstrate rich physics and unique opportunities for various applications.

Recently, electrides have received great attention because of their unique electronic, structural, and electron-phonon coupling behaviors, which are mainly attributed to the localizations of nonbound electrons at crystalline interstitial regions. Here, we propose several stable exotic Li-In compounds under pressures based on the crystal structure predictions and first-principles calculations. We identify a ${\mathrm{Li}}_7\mathrm{In}$ compound with electride characters, which transitions from a metallic state into an insulating state with increasing pressure due to the orbital overlapping and electron localization. ${\mathrm{Li}}_7\mathrm{In}$ is also calculated to have a superconducting transition temperature of 7.33 K at 60 GPa. Moreover, superionic states are found in ${\mathrm{Li}}_4\mathrm{In}$ and ${\mathrm{Li}}_7\mathrm{In}$ at high temperatures with diffused lithium atoms. It is remarkable to observe the coexistence behavior of superconducting, insulating, and superionic states within a single electride system. Our results enrich the high-pressure phase diagram of Li-In alloys and provide theoretical support for subsequent experiments.

We examine excitation suppression in the transverse-field Ising model (TFIM), where finite-time drive across a quantum critical point is assisted by the presence of a time-dependent coupling parameter. While conventional counterdiabatic protocols are designed to eliminate excitations, they often require complex many-body terms that are difficult to realize experimentally. In contrast, our approach employs a local, time-dependent modulation of an existing coupling term in the Hamiltonian. Within the framework of quantum optimal control, we find that under a linear ramp of the transverse field, the optimal evolution of the second parameter follows a nonmonotonic trajectory. For the TFIM, this protocol yields higher fidelity and improved robustness against noise compared to several orders of approximate counterdiabatic driving. Furthermore, we provide an analytical demonstration of anti-Kibble-Zurek scaling in the presence of noise acting on either the transverse field or the longitudinal coupling. These results highlight the potential of this approach for developing simple, noise-resilient protocols for finite-time quantum state preparation.

We investigate thermalization and the quantum-classical correspondence in the collective Bose-Hubbard model, focusing on the four-site case. Our analysis of the classical phase-space structure and its excited-state quantum phase transitions leads us to three dynamical regimes: symmetry-breaking low-energy states, an intermediate region where quantum and classical equilibrium states markedly disagree, and a high-energy regime with restored correspondence. The observed classical intermittency above the first excited-state quantum phase transition contrasts with quantum dynamics, which remains trapped in symmetry-breaking sectors despite the existence of a classically connected phase. This mismatch originates from the population of imbalance-carrying eigenstates and persists even for a relatively large number of particles. Our results reveal unexpectedly slow convergence to the classical limit, signaling robust finite-size effects in collective many-body dynamics.

In a Galilean superfluid, the depletion of superfluid density with rising temperature can be attributed to thermally excited noninteracting phonons. For systems without Galilean symmetry, it has been shown [Berger et al., Phys. Rev. Lett. 136, 166001 (2026)] that “phonon wind” is no longer responsible for the depletion of superfluid density. In this work, we develop the theory of superfluid density at low temperature ($T$) and provide detailed derivations of all results announced by Berger et al. [Phys. Rev. Lett., submitted]. Using Popov's hydrodynamic action, we show that the theory of low-temperature depletion in a $d$-dimensional quantum superfluid maps onto the problem of finite-size ($L$) corrections in a $(d+1)$-dimensional anisotropic (pseudo-)classical-field system with $U$(1)-symmetric complex-valued action. In addition to generalizing Landau's (canonical) formula, we develop the grand canonical theory, which in a broader context reveals a universal scaling, $T^{d+1}$ and $1/L^{d+1}$, for finite-$T$ and finite-$L$ effects of many thermodynamic quantities. We validate our theory with numeric simulations of interacting lattice bosons and the $J$-current model.

We investigate the problem of quantum heat transport, based on the quadratic fermionic systems with the help of the Peschel trick of single-particle correlation functions. The efficient numerical method is applied to the particular case of a single mode heat valve and the results are compared to analytical formulas. Comparing several configurations and parameters we perform the systematic analysis of the method to most efficiently and accurately describe the simple quantum heat valve system.

Efficient $p$-type doping in wide-band-gap (WBG) oxides is fundamentally hindered by their low-lying and localized valence-band maximum (VBM). One promising approach to overcome this limitation is to elevate the VBM through alloy formation. Although the tuning of electronic structures in semiconductor alloys has been widely explored, the defect behavior in such systems remains poorly understood. Here, using first-principles calculations, we investigate the electronic structure and acceptor behavior of dilute α-$\mathrm{G}{\mathrm{a}}_2{\left({\mathrm{S}}_x{\mathrm{O}}_{1-x}\right)}_3$ anion alloys. We show that S incorporation significantly raises the VBM of $\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$, thereby creating favorable conditions for $p$-type doping. Among eight candidate acceptors, $\mathrm{B}{\mathrm{e}}_{\mathrm{Ga}}, \mathrm{M}{\mathrm{g}}_{\mathrm{Ga}}, \mathrm{C}{\mathrm{a}}_{\mathrm{Ga}}, \mathrm{S}{\mathrm{r}}_{\mathrm{Ga}}, \mathrm{Z}{\mathrm{n}}_{\mathrm{Ga}}$, and $\mathrm{C}{\mathrm{d}}_{\mathrm{Ga}}$ remain deep acceptors in the alloy, whereas the very deep $\mathrm{A}{\mathrm{g}}_{\mathrm{Ga}}$ and, notably, $\mathrm{C}{\mathrm{u}}_{\mathrm{Ga}}$ levels in α-$\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ become much shallower upon alloying. Charge-density analysis reveals that the former six defects form hole-polaron states strongly coupled to the VBM, while $\mathrm{A}{\mathrm{g}}_{\mathrm{Ga}}$ and $\mathrm{C}{\mathrm{u}}_{\mathrm{Ga}}$ are decoupled from the VBM.

We propose and analyze an all-mechanical route to coherent control and quantum-state reconstruction of the fundamental flexural mode of a suspended carbon nanotube (CNT) operated in the anharmonic (Duffing/Kerr) regime. A nearby atomic force microscope (AFM) tip provides a single, localized actuator that applies calibrated, time-dependent forces to the CNT. In the presence of mechanical anharmonicity, this enables spectrally selective control of the lowest vibrational transition and thus supports effective two-level protocols such as Rabi oscillations and Ramsey interferometry. The same actuator also implements the controlled phase-space displacements required for Wigner function tomography via displaced-parity sampling, thereby unifying control and tomography without optical heating and without dedicated on-chip microwave drive lines at the CNT resonator. We develop explicit pulse sequences and a master equation framework that connect experimentally accessible signals to energy relaxation and phase coherence times and to parity-based quantum signatures, including negative regions of the Wigner function. The approach is compatible with multiple readout modalities, including direct AFM-based detection and dispersive coupling to superconducting circuitry such as a Cooper-pair box and/or a microwave cavity. Together, these techniques provide complete access to populations, coherence, and parity within a single device architecture. This minimal scheme provides a practical route to all-mechanical quantum control and state-resolved characterization of decoherence in mesoscopic mechanical systems.

Atomically thin two-dimensional (2D) metals, termed metallenes, represent an ideal platform for exploring exotic superconducting states. However, their limited dynamical stability at atomic thickness makes the realization of superconductivity challenging. Through comprehensive high-throughput screening and first-principles calculations, we systematically investigate the energetics, dynamic and thermodynamic stability, and electronic and superconducting properties of elemental metallenes across 14 main-group elements in 8 different lattice configurations (i.e., hc, hex, sq, bhc, bhex, bsq, 1H, and 1T). Among the 112 metallenes screened, 31 are identified as dynamically stable, of which 19 exhibit superconductivity. Notably, the $1\mathrm{T}\text{−}\mathrm{Mo}{\mathrm{S}}_2$-like gallenene (1T-gallenene) exhibits the highest $T_{\mathrm{c}}$ of 6.90–9.79 K among all predicted 2D metallenes. Detailed analysis reveals that the strong electron-phonon coupling dynamically stabilizes out-of-plane phonon vibrations of Ga atoms, while simultaneously mediating surface Ga-$p$ Cooper pairing and driving superconductivity. This mechanism is generalizable to other superconducting metallenes, as exemplified by isostructural configurations including Li, Na, Mg, Be, and Al. These results substantially expand the family of metallenes and pave a promising avenue for realizing exotic superconducting states in 2D elemental metals.

A flat band is a significant platform for investigating a series of novel quantum phase in the condensed matter physics. However, its realization highlights the fundamental challenge and it has only been discovered in a small number of systems. In this work, we propose a bend-sliding atomic model to design the flat bands by mechanical bending in two-dimensional materials. We reveal that the bending can cause intersublayer sliding within a monolayer, thereby inducing changes in the interatomic distances and bonding. Especially, atomic reconstruction and changes in orbital occupation can significantly weaken the electron hopping, leading to the emergence of flat bands. Through the first-principles calculations, we use the two-dimensional materials $\mathrm{CuIn}{\mathrm{P}}_2{\mathrm{S}}_6$ and ${\mathrm{CuCrP}}_2{\mathrm{S}}_6$ as examples to verify the feasibility of the bend-sliding model. We find that when the degree of bending exceeds a critical value, the local atomic reconstruction occurs with the formation of new Cu-S chemical bonds. This changes the orbital occupation of top valence bands from the $P_y$ to $P_z$ orbital of S atoms and thus significantly weakens electron hopping between adjacent Cu-S configuration units, accompanied by the emergence of flat bands. Furthermore, according to Stoner's theory, we successfully induce magnetism in nonmagnetic $\mathrm{CuIn}{\mathrm{P}}_2{\mathrm{S}}_6$ through hole doping in flat bands. Our study indicates that the bend-sliding model offers a different perspective for the design of flat bands in two-dimensional flexible materials.

We investigate Floquet-engineered topological phases in two-dimensional $d_{x^2-y^2}$-wave altermagnets irradiated by circularly polarized light in the off-resonant regime. These materials exhibit large momentum-dependent spin splitting governed by distinctive magnetic symmetries. Using a lattice model combined with Floquet theory, we demonstrate that irradiation induces light-tunable quantum anomalous Hall phases with Chern numbers up to $\pm 3$. The resultant phase diagram is verified by calculating the anomalous Hall conductivity and also the edge modes inside the band gap of a nanoribbon version of the altermagnet. Our findings establish $d$-wave altermagnets as promising platforms for realizing nonequilibrium topological states of matter. The low-energy continuum limit of the lattice-based Floquet Hamiltonian results in linear and higher-order-in-momentum spin-orbit couplings, and also a Zeeman-like magnetization, all arising from light-induced virtual photon processes. The resulting higher-order spin-orbit coupling generates additional gapless Dirac points which, together with high-symmetry gap closings, yield enhanced Berry curvature and high Chern numbers. The light irradiation effectively breaks the static $d_{x^2-y^2}$-wave magnetic symmetry mixing in an isotropic photoinduced $s$-wave correction.

The impacts of the mass imbalance and Coulomb interaction on the complex phase structures of the polaritonic condensates and their Bardeen-Cooper-Schrieffer (BCS)–Bose-Einstein condensation (BEC) crossover in semiconductor and semimetal microcavities are investigated. In the framework of the unrestricted Hartree-Fock approximation, a two-band electron-hole model involving photon mode is analyzed by treating Coulomb attraction and light-matter coupling on equal footing. The single-particle spectral functions and the luminescence properties are then examined. In the semiconducting regime, a positive band gap stabilizes tightly bound excitons and yields predominantly BEC-type excitoniclike polaritonic condensates at low density, while increasing excitation density and reducing mass imbalance drives a continuous crossover toward BCS-type pairing with intermediate and photoniclike polaritonic character. In contrast, the semimetallic regime favors itinerant electron-hole pairing, with BCS-type condensates dominating and BEC excitoniclike coherence emerging only at sufficiently strong Coulomb interaction and large mass imbalance situations. The evolution of luminescence spectra provides clear spectroscopic signatures of these crossover phenomena, offering a unified framework for understanding and controlling polaritonic condensates in microcavity systems.