Two-band superconductors exhibit a distinct phase characterized by two correlation lengths, one smaller and the other larger than the magnetic field penetration length. This regime was coined type-1.5 superconductivity, with several unconventional properties, such as vortex clustering. However, a fully microscopic solution for vortex clusters has remained challenging due to computational complexities beyond quasiclassical models. This work presents numerical solutions obtained in a fully self-consistent two-band Bogoliubov–de Gennes model. We show the presence of discrepant correlation lengths leading to vortex clustering in two-band superconductors.

The orthorhombic molybdenum carbide superconductor with $T_c=3.2$ K was investigated by muon-spin rotation and relaxation $\left(\mu \mathrm{SR}\right)$ measurements and by first-principles calculations. The low-temperature superfluid density, determined by transverse-field $\mu \mathrm{SR}$, suggests a fully gapped superconducting state in ${\mathrm{Mo}}_2\mathrm{C}$, with a zero-temperature gap ${\mathrm{\Delta }}_0=0.44$ meV and a magnetic penetration depth ${\lambda }_0=291$ nm. The time-reversal symmetry is preserved in the superconducting state, as confirmed by the absence of an additional muon-spin relaxation in the zero-field $\mu \mathrm{SR}$ spectra. Band-structure calculations indicate that the density of states at the Fermi level is dominated by the $\mathrm{Mo}\text{−}4d$ orbitals, which are marginally hybridized with the $\mathrm{C}\text{−}2p$ orbitals over a wide energy range. The symmetry analysis confirms that, in the absence of spin-orbit coupling (SOC), ${\mathrm{Mo}}_2\mathrm{C}$ hosts twofold-degenerate nodal surfaces and fourfold-degenerate nodal lines. When considering SOC, the fourfold-degenerate nodal lines cross the Fermi level and contribute to the electronic properties. Our results suggest that, similarly to other phases of carbides, also the orthorhombic transition-metal carbides host topological nodal states and may be potential candidates for future studies of topological superconductivity.

We investigate the electronic structure and Seebeck coefficient (SC) of twisted zigzag graphene nanoribbons (TZGNRs) with translational symmetry, considering electron-electron interactions, electric fields, and vacancy defects. Using the mean-field Hubbard model, we find that the semiconducting properties of TZGNRs in the antiferromagnetic ground state are preserved when twisted. However, the energy gap significantly decreases with shorter twist lengths. Unlike GNRs, electric fields, which do not induce spin-polarized features, can reduce the energy gap and SC, and cause a flattening of the band structure around the Fermi energy. The variation in the band energy depends on the twist length and electric field strength. Furthermore, monovacancy defects in TZGNRs induce spin-polarization effects in both the band structure and SC, depending on their spatial position within the nanoribbon structure. These versatile features of TZGNRs indicate their potential in stretchable electronics and thermoelectric applications.

We investigate, for the first time, the thermal signature of a single-stranded helical molecule that is described beyond usual nearest-neighbor electron hopping, by analyzing electronic specific heat. Depending on the hopping of electrons, two different kinds of helical systems are considered. In one case the hopping is confined within a few neighboring lattice sites which is referred to as short-range hopping helix, while in the other case, electrons can hop in all possible sites making the system a long-range hopping one. These two helices accurately emulate the structures of single-stranded DNA and protein molecules, respectively. Each helix geometry is exposed to a transverse electric field applied perpendicular to the helix axis. Due to this field, the system transforms into a correlated disordered one, resembling the well-known Aubry-André-Harper (AAH) model. The interplay among the helicity, higher-order hopping, and the electric field has significant impact on thermal response. Our comprehensive theoretical analysis reveals that, under low-temperature conditions, the short-range hopping helix exhibits greater sensitivity to temperature compared to the long-range hopping helix system. Conversely, the scenario reverses in the high-temperature limit. The thermal response of the helices can be modified selectively by means of the electric field, and the difference between the specific heats of the two helices gradually decreases with increasing the field strength. The molecular handedness, whether left-handed or right-handed, on the other hand does not have any appreciable effect on the thermal signature. In addition, we also explore a significant application of electronic specific heat (ESH). If the helix contains a point defect, then by comparing the results of perfect and defective helices, one can estimate the location of the defect, which might be useful in diagnosing bad cells and different diseases. Finally, we discuss the results of ESH by considering the spin degree of freedom and in the context of real biological helical systems.

Photonic nanoparticle arrays present a unique platform for exploring optical topological phenomena. In this study, we incorporate the concept of synthetic dimensions into the plasmonic system, which allows us to investigate Weyl physics within a chain of metallic nanoparticles. By introducing two extra periodic positional parameters into the chain, we construct a synthetic three-dimensional space that gives rise to synthetic Weyl points (WPs). Our findings reveal that the chain maintains topologically protected edge modes even when the inversion symmetry of the chain is broken. The topological properties of these edge modes are intrinsically linked to the WPs within the synthetic three-dimensional space. However, degenerate edge modes emerge exclusively in chains possessing inversion symmetry. Furthermore, we uncover the bulk-edge correspondence in the chains, yielding a deeper understanding of the topological nature of edge modes in systems without symmetry. Our research not only clarifies the topological origin of a class of edge states within asymmetric nanoparticle chains but also provides perspectives for realizing higher-dimensional topological effects in nanoparticle arrays.

Transduction of quantum information between distinct quantum systems is an essential step in various applications, including quantum communications and quantum computing. However, mediating photons of vastly different frequencies and designing high-performance transducers are highly nontrivial, due to multifaceted and sometimes conflicting requirements. In this work, we first discuss some general principles for quantum transducer design, and then propose solid-state antiferromagnetic topological insulators to serve as particularly effective transducers. First, the antiferromagnetic order can minimize detrimental magnetic influences on nearby quantum systems. Second, topological insulators exhibit band inversion, which can greatly enhance their optical responses. This property, coupled with robust spin-orbit coupling and high spin density, results in strong nonlinear interaction in magnetic topological insulators, thereby substantially improving transduction efficiency. Using $\mathrm{MnB}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ as an example, we discuss potential experimental realizations of quantum transduction based on magnetic topological materials. Particularly, we showcase that quantum transduction efficiency exceeding 90% can be achieved with modest experimental requirements, while the transduction bandwidth can reach the gigahertz range. The strong nonlinear photonic interactions in magnetic topological insulators can find diverse applications besides quantum transduction, such as quantum squeezing.

The higher-order topological insulator is an extended concept of the conventional topological insulator, which obeys the generalization of the standard bulk-boundary correspondence. In our paper, we predict the monolayer d1T-phase transition metal dichalcogenide ${\mathrm{MoS}}_2$ to be a higher-order topological insulator, while also possessing intriguing ferroelectric characteristics. We explicitly demonstrate the nontrivial topological index and reveal the hallmark corner states with quantized fractional charge within the bulk band gap. Second, we show the existence of a nonzero orbital Hall conductivity plateau within the energy gap which is a signature to identify higher-order topology system. Additionally, we investigate the relationship between the ferroelectricity and the orbital Hall conductivity of d1T ${\mathrm{MoS}}_2$ and find that the direction of ferroelectric polarization can modulate the positive and negative values of the orbital Hall conductivity ${\sigma }_{\mathrm{OH}}^x$. Our findings provide the theory and material candidate for ferroelectricity tunable orbital Hall effect which is promising to realize the external electric field controllable orbitronics.

The geometry of quantum states could offer indispensable insights for characterizing the topological properties, phase transitions, and entanglement nature of many-body systems. In this work, we reveal the quantum geometry and the associated entanglement entropy (EE) of Floquet topological states in one-dimensional periodically driven systems. The quantum metric tensors of Floquet states are found to show nonanalytic signatures at topological phase transition points. Away from the transition points, the bipartite geometric EE of Floquet states exhibits an area-law scaling vs the system size, which holds for a Floquet band at any filling fractions. For a uniformly filled Floquet band, the EE further becomes purely quantum geometric. At phase transition points, the geometric EE scales logarithmically with the system size and displays cusps in the nearby parameter ranges. These discoveries are demonstrated by investigating typical Floquet models including periodically driven spin chains, Floquet topological insulators, and superconductors. Our findings uncover the rich quantum geometries of Floquet states, unveiling the geometric origin of EE for gapped Floquet topological phases, and introducing information-theoretic means of depicting topological transitions in Floquet systems.

Recent theoretical work suggests that a pair-density wave superconducting state can be realized by doping a one-dimensional spin-1 chain. Here, we report the physical properties of single crystals of ${\mathrm{Mg}}_x{\mathrm{Ag}}_{1-x}{\mathrm{VP}}_2{\mathrm{S}}_6$ $[x=0,$ $x=0.017\left(6\right),$ $x=0.067\left(8\right), \text{and} 0.098\left(11\right)]$ prepared by solid-state synthesis. Single-crystal x-ray-diffraction measurements confirm that $\mathrm{M}{\mathrm{g}}^{2+}$ is substituting for $\mathrm{A}{\mathrm{g}}^{+}$ to electron dope the ${\mathrm{V}}^{3+}$ zigzag chains. Magnetization measurements reveal that electron doping breaks up the ${\mathrm{V}}^{3+}$ chains, resulting in unpaired spins at the chain ends. The ${\mathrm{Mg}}_x{\mathrm{Ag}}_{1-x}{\mathrm{VP}}_2{\mathrm{S}}_6$ series is consistent with random-exchange Heisenberg antiferromagnetic chain behavior and can be well described by the exchange-coupled pair model at low temperatures. Transport measurements show ${\mathrm{Mg}}_x{\mathrm{Ag}}_{1-x}{\mathrm{VP}}_2{\mathrm{S}}_6$ remains insulating in the range 0 $\le$ $x$ $\le 0.098\left(11\right)$, with the band gap decreasing to $\sim 0.2\mathrm{eV}$ at $x=0.098\left(11\right)$.

Electric field control of magnetism in solids, i.e., the converse magnetoelectricity, is highly desired for applications of scalable energy-efficient logic devices. However, it is not only a technical challenge but also a scientific paradox, since in principle the electric and magnetic degrees of freedom obey distinct rules of symmetries. Despite the great progress obtained in the community of multiferroics during the past decades, the success of magnetoelectricity remains on its way and more alternative approaches with conceptual revolution are urgently needed. Here, by introducing the concept of topology into multiferroics, an exotic magnetoelectric double-leaf Riemann surface is unveiled based on the mechanism of spin-dependent $d-p$ hybridization in a two-dimensional magnet: ${\mathrm{GdI}}_2$ monolayer. Protected by the topology, a ${180}^{\circ }$ spin reversal can be precisely achieved by an electric cycle, leading to a robust and dissipationless converse magnetoelectric function. Such a topological magnetoelectricity allows the nontrivial manipulation of magnetization by ac electric field. In this category, more candidate materials with better performance are designed targetedly, which paves the road to the potential applications with topological magnetoelectrics.

We explore the impact of optical excitation using two interfering ultrashort optical pulses on ultrafast magnetization dynamics. Our investigation focuses on Pt/Co/Pt multilayers and TbCo alloy samples, employing a dual pump approach. We observe significant variations in the dynamics of magnetization suppression and subsequent recovery when triggered with two optical pulses of the same polarization—essentially meeting conditions for interference. Conversely, dynamics triggered with cross-polarized pump beams exhibit expected similarity to that triggered with a single pulse. Delving into the underlying physical processes contributing to laser-induced demagnetization and recovery dynamics, we find that our current understanding cannot elucidate the observed trends. Consequently, we propose that optical excitation with interfering light possesses the capacity to induce long-lasting alterations in the dynamics of angular momentum.

Recent observations of a contradictory impurity effect in the heavy-fermion superconductor ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ at ambient pressure have hindered the identification of its pairing symmetry. Here, we perform theoretical analyses with both intraband and interband impurity scatterings for the nodeless $s^{\pm }$-wave pairing, and report an anomalous nonmonotonic variation of its $T_c$ suppression with the scattering strength. Our results reproduce the prominent reduction of $T_c$ in good agreement with earlier experiments by atomic substitution and explains as well its robustness against electron irradiation. We ascribe the latter to the screening of the interband impurity potential in the strong scattering or unitary region. This resolves the seeming contradiction in different experimental probes and provides an important support to the nodeless $s^{\pm }$-wave scenario in ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ at ambient pressure. Our theory may be extended to other narrow-band systems such as twisted bilayer graphene and the recently discovered bilayer or trilayer nickelate superconductors, and provide a useful way to distinguish different pairing candidates thereof.

We use vibrational dynamical mean-field theory (VDMFT) to study the vibrational structure of type-I clathrate solids, specifically $X_8{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$, where $X=\text{Ba,}\text{Sr}$. These materials are cagelike chemical structures hosting loosely bound guest atoms, resulting in strong anharmonicity, short phonon lifetimes, and ultralow thermal conductivities. Presenting the methodological developments necessary for application to three-dimensional, atomistic materials, we validate our approach through comparison to molecular dynamics simulations and show that VDMFT is extremely accurate at a fraction of the cost. Through the use of nonperturbative methods, we find that anharmonicity is dominated by four-phonon and higher-order scattering processes, and it causes rattler modes to shift up in frequency by 50% $(10 {\mathrm{cm}}^{-1})$ and to have lifetimes of less than 1 ps; this behavior is not captured by traditional perturbation theory. Furthermore, we analyze the phonon self-energy and find that anharmonicity mixes guest rattling modes and cage acoustic modes, significantly changing the character of the harmonic phonons.

In a recent work [Sharma and Bhosale, Phys. Rev. B 109, 014412 (2024)], an $N$-spin Floquet model with infinite-range Ising interaction was introduced. In this paper, we generalize the strength of interaction to $J$, such that the $J=1$ case reduces to the aforementioned work. We show that for $J=1/2$ the model still exhibits integrability only for an even number of qubits. We analytically solve the cases of 6, 8, 10, and 12 qubits, finding the eigensystem, the dynamics of the entanglement for various initial states, and the unitary evolution operator. These quantities exhibit the signature of quantum integrability (QI). For the general case of even $N>12$ qubits, we conjuncture the presence of QI using numerical evidence such as spectrum degeneracy and the exact periodic nature of both the entanglement dynamics and the time-evolved unitary operator. We numerically show the absence of QI for odd $N$ by observing a violation of the signatures of QI. We analytically and numerically find that the maximum value of time-evolved concurrence $\left(C_{\max }\right)$ decreases with $N$, indicating the multipartite nature of entanglement. Possible experiments to verify our results are discussed.

In this work, we report that electrically controlled ferroic properties and multistate storage can be achieved in dual-metal trihalide ${\mathrm{WRuCl}}_6$ monolayer from the perspectives of first-principles calculations. We confirm that it is a rare two-dimensional (2D) triferroics, and, particularly, ferromagnetism and ferroelasticity are coupled strongly to the ferroelectricity of 120 ° rotation symmetry. It therefore can enable the flexible and reversible switching of ferroic orders via electric field. In addition, ${\mathrm{WRuCl}}_6$ monolayer is an intrinsic bipolar magnetic semiconductor; thus, the switchable spin-polarized carrier can be obtained by applying an electric gate voltage. Therefore, it provides an extra parameter to further improve the storage density. Our work not only offers a paradigm for the multiferroic coupling physics, but also provides a promising platform for multistate storage and multifunctional nanodevices.