A substantial energy gap is essential for quantum spin Hall (QSH) insulators in devices and fundamental research. Monolayer $1T^{\prime }\text{−}{\mathrm{MoTe}}_2$ is recognized as a promising candidate, featuring a potentially large energy gap. However, despite extensive efforts including molecular beam epitaxy growth, mechanical exfoliation, and chemical vapor deposition techniques, achieving stable $1T^{\prime }\text{−}{\mathrm{MoTe}}_2$ with a well-defined energy gap has proven elusive. Here, we successfully open a band gap of approximately 70 meV in bulk $1T^{\prime }\text{−}{\mathrm{MoTe}}_2$ by reducing the interlayer interaction through the intercalation of organic cations ${\mathrm{HMIM}}^{+}$. Both resistivity measurements and infrared spectroscopy confirm distinct semiconducting behaviors. Band structure calculations show that the gap emerges from the absence of interlayer coupling, and that the intercalated $1T^{\prime }\text{−}{\mathrm{MoTe}}_2$ is topologically nontrivial with ${\mathbb{Z}}_2=1$. This work not only demonstrates a bulk $1T^{\prime }\text{−}{\mathrm{MoTe}}_2$ possible QSH insulator with a sizable gap, but also provides a different approach to realizing clean, stable platforms for exploring the QSH effect and designing low-power quantum electronic and spintronic devices.

In this first-principles study, we investigated the thermoelectric properties of the full-Heusler compound ${\mathrm{CsK}}_2\mathrm{Sb}$ at different compressive strains. This material exhibits a valence band structure with significant effective mass anisotropy, forming tubelike energy isosurfaces below the band edge, akin to that of two-dimensional (2D) systems. Such systems can have a large number of high-mobility charge carriers and a beneficial density of states profile. In the calculations, we predicted a maximum p-type figure of merit ($zT$) of 2.6 at 800 K, in line with previous predictions of high $zT$. This high $zT$ arises from the low lattice thermal conductivity of 0.35 ${\mathrm{W}\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ and the beneficial electronic band structure. The high density of states significantly increased the electron-scattering space, but this effect was largely compensated by reduced scattering rates of electrons with large momentum $\mathbf{q}$. We further explored the effect of enhancing the low-dimensionality through compressive strain. This increased the p-type power factor by up to 66%; partly due to more strongly pronounced 2D features of the valence band, but primarily due to increased Fermi velocities. However, compressive strain also increased phonon velocities and hence the lattice thermal conductivity. The maximum p-type $zT$ thus only increased slightly, to 2.7 at 1% compressive strain. In the conduction band, strain aligned the $\mathrm{\Gamma }$- and X-centered valleys, resulting in the optimal n-type $zT$ increasing from 0.9 to 2.3 at 2% compressive strain. Thus highly strained ${\mathrm{CsK}}_2\mathrm{Sb}$ has the potential for both good p- and n-type thermoelectricity.

The efficient detection of the reversal (${180}^{\circ }$ rotation) of the Néel vector is one of the crucial tasks in antiferromagnetic spintronics. Here, we propose a thermal approach to detect the reversal of the Néel vector in the tetragonal $\mathcal{PT}$ antiferromagnetic materials through the unidirectional Seebeck effect (USE). Being different from the previous works in which USE stems from the global Rashba spin-orbit coupling (SOC) or asymmetric magnon scattering, we find that the USE originates from the coupling of the hidden Rashba SOC and the Néel vector in the tetragonal $\mathcal{PT}$ antiferromagnetic materials in the absence of the global Rashba SOC. Using a generic minimal model, we analyze the behaviors of the USE for the two-dimensional tetragonal lattice $\mathcal{PT}$ antiferromagnet. Importantly, it is found that when the Néel vector is reversed, the sign of the USE changes, which can be utilized to detect the reversal of the Néel vector.

Molecular adsorption plays a key role in heterogeneous catalysis, with the $d$-band center theory being extensively utilized for qualitative analysis of adsorption behavior of molecules on transition-metal surfaces. However, adsorption energies predicted by $d$-band center theory can have large errors, especially when a wide range of metals is considered. The physical mechanism responsible for the deviation has been unclear, posing significant challenges of the precise design of catalysts. Here, we have integrated density-functional theory calculations with artificial intelligence approaches to develop a unifying model that quantitatively evaluates the adsorption energy of water on various transition-metal surfaces. Data mining revealed that the large deviations between the $d$-band center theory predictions and first-principles calculations primarily stem from surface relaxation effects. Additionally, we discovered that the synergistic effects of electron donation and back donation, which are mediated by the $d$ and $p$ orbitals in metals, also play a role in these deviations, although their impact is less significant compared to that of the surface relaxation. These findings enhance our understanding of molecular adsorption behavior and are poised to influence research fields such as surface science and heterogeneous catalysis.

We report the magnetic and electrical properties of a kagome magnet $\mathrm{ZrM}{\mathrm{n}}_6\mathrm{S}{\mathrm{n}}_6$, which undergoes a collinear antiferromagnetic to a noncollinear antiferromagnetic transition at $T_{\mathrm{t}}=89\mathrm{K}$. The magnetoresistances are negative and unsaturated until 14 T for both the in-plane and out-of-plane magnetic fields. An anomalous Hall effect was observed, with the anomalous Hall conductivity ${\sigma }_{xy}^{\mathrm{A}}$ and ${\sigma }_{zx}^{\mathrm{A}}$ being independent of ${\sigma }_{xx}^{}$, suggesting that the intrinsic Berry curvature mechanism is dominant. The nonvanishing Berry curvature arises from the noncollinear antiferromagnetic structure. In addition, the topological Hall effect was also observed in the noncollinear antiferromagnetic phase, attributed to the nonzero spin chirality induced by the external field. The scalar spin chirality originates from a canting moment along the $c$ axis, generated by both in-plane and out-of-plane fields.

Non-Abelian braiding is a key property of Majorana zero modes (MZMs) that can be utilized for topological quantum computation. However, the presence of trivial Andreev bound states (ABSs) in topological superconductors can hinder the non-Abelian braiding of MZMs. We systematically investigate the braiding properties of ABSs induced by various inhomogeneous potentials in nanowires and quantify the main obstacles to non-Abelian braiding. We find that if a trivial ABS is present at zero energy with a tiny energy fluctuation, the non-Abelian braiding property can be sustained for a larger braiding time cost since the undesired dynamic phase is suppressed. Under certain conditions, the non-Abelian braiding of ABSs can even surpass that of MZMs in realistic systems, suggesting that nearly zero energy ABSs with a tiny energy fluctuation might also be suitable for quantum computation.

Quantum dots (QDs) are pivotal for the development of quantum technologies, with applications ranging from single-photon sources for secure communication to quantum computing infrastructures. Understanding the electron dynamics within these QDs is essential for characterizing their properties and functionality. Here, we show how by virtue of the recently introduced quantum polyspectral analysis of transport measurements, the complex transport measurements of multi-electron QD systems can be analyzed. This method directly relates higher-order temporal correlations of a raw quantum point contact (QPC) current measurement to the Liouvillian of the measured quantum system. By applying this method to the two-level switching dynamics of a double QD system, we reveal a hidden third state, without relying on the identification of quantum jumps or prior assumptions about the number of involved quantum states. We show that the statistics of the QPC current measurement can identically be described by different three-state Markov models, each with significantly different transition rates. Furthermore, we compare our method to a traditional analysis via waiting-time distributions for which we prove that the statistics of a three-state Markov model is fully described without multitime waiting-time distributions even in the case of two-level switching dynamics. Both methods yield the same parameters with a similar accuracy. The quantum polyspectra method, however, stays applicable in scenarios with low signal-to-noise, where the traditional full counting statistics falters. Our approach challenges previous assumptions and models, offering a more nuanced understanding of QD dynamics and paving the way for the optimization of quantum devices.

For the nanoscale structures, disorder scattering plays a vital role in the carriers' transport, including electrons and high-frequency phonons. The capability for effectively treating the disorders, including both diagonal and off-diagonal disorders, is indispensable for quantum transport simulation of realistic device materials. In this work, we report a self-consistent nonequilibrium mean-field quantum transport approach, by combining the auxiliary coherent potential approximation (ACPA) and nonequilibrium Green's function method, for calculating the phonon transport through disordered material structures with the force-constant disorders (including the Anderson-type disorder). The nonequilibrium vertex correction (NVC) is derived in an extended local degree of freedom to account for both the multiple disorder scattering by force-constant disorder and the nonequilibrium quantum statistics. We have tested the ACPA-NVC method with the fluctuation-dissipation theorem at the equilibrium and obtained very good agreement with supercell calculations for the phonon transmission. To demonstrate the applicability, we apply ACPA-NVC to calculate the thermal conductance for the disordered Ni/Pt interface, and important effects of force-constant disorder are revealed. ACPA-NVC method provides an effective quantum transport approach for simulating disordered nanoscale devices, and the generalization to simulate disordered nanoelectronic device is straightforward.

In this work, we propose a family of piezoelectrics whose sign of piezoelectric response can be either positive or negative under different synthesis conditions in thin films. These novel piezoelectrics are “double-path” ferroelectrics, characterized by two competing polarization switching paths for which the change in polarization is of opposite sign. Depending on which polarization switching path is favorable under given conditions, the identification of up- and down-polarized states is different. Since the sign of piezoelectric response depends on the assignment of up- or down-polarized state for a specific structure, a “double-path” ferroelectric can exhibit different signs of the piezoelectric response. ${\mathrm{HfO}}_2$ is a natural candidate since previous work has shown that ${\mathrm{HfO}}_2$ has two competing switching paths. Our first-principles calculations further confirm that the two paths are approximately equally favorable, and also predict how to favor one path over another by changes in synthesis conditions and compositional tuning. These results provide a natural explanation for the recently observed discrepancy in the signs of piezoelectric responses in ${\mathrm{HfO}}_2$ between theoretical first-principles calculations and experimental observation. This family of materials with electromechanical properties also includes other candidates, such as ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ and some charge-ordering induced ferroelectrics.

The quest for non-Abelian anyons is attracting tremendous attention. A Majorana quasiparticle has attracted great interest since the non-Abelian anyon is a key particle for topological quantum computation. Much effort has been made toward the quest of the Majorana state in solids, and some candidate material platforms have been reported. Among various materials that can host the Majorana state, a chiral $p$-wave superconductor is one of the suitable materials, and the iron-based layered superconductor FeTeSe is one of the promising material platforms because its surface can host an effective $p$-wave superconducting state that is analogous to the chiral $p$-wave superconducting state thanks to its topological surface state. Given that a chiral $p$-wave superconductor possesses spin polarization, detecting the spin polarization can be evidence for the chiral $p$-wave trait, which results in the existence of Majorana excitation. Here, we show successful detection of the spin polarization at the surface of ${\mathrm{FeTe}}_{0.6}{\mathrm{Se}}_{0.4}$ in its superconducting state, where the spin polarization is detected via a potentiometric method. Amplitudes of the spin signal exhibit characteristic dependence for temperature and bias current, suggesting detection of spin polarization of the Bogoliubov quasiparticles. Our achievement opens an avenue to exploration of topological superconductivity for fault-tolerant quantum computation.

Non-Hermitian Hamiltonians, as effective models, capture phenomena such as energy dissipation and nonunitary evolution in open quantum systems. New phases and phenomena appear that are not present in their Hermitian counterparts. Such a Hamiltonian, the non-Hermitian Kondo model, has been used to describe inelastic scattering between mobile and confined atoms in an optical lattice [M. Nakagawa, N. Kawakami, and M. Ueda, Phys. Rev. Lett. 121, 203001 (2018)]. Using a combination of Bethe ansatz and perturbative calculation, the authors argued that this model has two distinct phases: the Kondo and the non-Kondo phases, where the impurity is screened and unscreened, respectively. We show, however, that a novel phase termed $\widetilde{YSR}$ emerges between the Kondo and unscreened phases. Characterized by two RG invariants: a generalized Kondo temperature ($T_K$) and a loss strength parameter ($\alpha$), the system exhibits three distinct phases. In the increasing order of losses, they are: the Kondo phase ($0<\alpha <\pi /2$), the $\widetilde{YSR}$ phase ($\pi /2<\alpha <3\pi /2$), and the local moment phase ($\alpha >3\pi /2$). Notably, phase transition driven by dissipation occurs across $\alpha =\pi /2$, where both energetics and different timescales associated with loss play roles.

The localization of thermal phonons is a well-represented phenomenon in disordered atomic systems. Traditional disorder entities, such as random defects and aperiodicity, impede mid- and high-frequency phonons more than low-frequency modes, thus increasing the relative contributions of low-frequency phonon to thermal conductivity. Recognizing the constraints that this drawback imposes on the design of thermal functional materials, our research proposes a disordered structure for Si/Ge nanowires utilizing a checkerboard pattern. By combining molecular dynamics simulations with machine learning techniques, we identified an optimal configuration that minimizes thermal conductivity. This structure incorporates a distinctive design that achieves both strong phonon Anderson localization and enhanced interface scattering. This dual effect significantly hinders phonon transport across the broadband frequency spectrum, reducing the contribution of low-frequency phonons to thermal conductivity to a mere 9%. Our study deepens insights into phonon behavior in disordered structures and introduces a practical method for precise thermal conductivity control.

We present an ab initio computational analysis of the topological Hall effect arising from stable magnetic skyrmions in the Pd/Fe/Ir(111) film using noncollinear spin density functional calculations within the Korringa-Kohn-Rostoker Green function method. The semiclassical Boltzmann transport equation is employed for the resistivity and the Hall angle of the system. We explore the influence of the skyrmion size and the impact of disorder on the topological Hall angle.

In this work, we have systematically investigated the structural, vibrational, and electrical transport properties of topological semimetal $\mathrm{Zr}{\mathrm{P}}_2$ under pressure using synchrotron x-ray diffraction (XRD), Raman spectroscopy, electrical resistance, and Hall-effect measurements, in combination with theoretical calculations. The XRD data show that while no evident structural transitions occur with pressures up to 43.1 GPa, the lattice-parameter ratio ($a/b$) reveals a diplike anomaly at $P_{\mathrm{C}}\sim 25$ GPa. Concomitantly, one Raman-active phonon mode (∼113.3 $\mathrm{c}{\mathrm{m}}^{-1}$) becomes increasingly softening with pressure and then beyond $P_{\mathrm{C}}$ shows a hardening behavior, at various fixed temperatures from 300 K down to 10 K. This soft mode can be assigned to the $A^1{}_{\mathrm{g}}$ mode and refers to $ac$-plane vibrations of Zr and P atoms with “vortexlike” eigenvectors. Strikingly, superconductivity (SC) was observed to emerge around $P_{\mathrm{C}}$, with the onset critical temperature of ∼0.6 K increasing gradually to ∼1.3 K at the highest measured pressure of 49.5 GPa. In addition, a hole- to electron-dominated carrier-type crossover takes place again around $P_{\mathrm{c}}$, involving the Fermi-level crossing of higher-energy electron-like pockets along the Γ-$Y$ path. Analysis suggests that the emergence of SC may be triggered by the phonon-softening related enhancement of ionic polarizability. The present system thus can serve as an ideal platform to study the interplay of phonon softening and SC.

Multiferroic materials combine multiple ferroic orders that may enable cross functionalities, e.g., control of one ferroic order by the field conjugate to the other one. ${\mathrm{BaCoSiO}}_4$ shows peculiar triangular vortices, unit cell-tripling modes, structural chirality, and ferroelectric polarization. We derive the Landau free-energy expression describing interacting trimerization, electric polarization, and structural chirality and find the model parameters from first-principles calculations. The model simulations rationalize recent experimental results on domain walls and vortices.

We present a scaling theory of the many-body localization transition in terms of emergent, characteristic energy scales. The analysis is based on the decomposition of the eigenstates in the basis of trivially localized states, resolved in the energies of the latter, which we refer to as the spectral decomposition of the eigenstates. The characteristic energy scales emerge when the multifractal properties, or lack thereof, of the spectral decomposition are studied at different scales. These characteristic scales correspond to the ones, above which the spectral decompositions exhibit their global behavior, namely full ergodicity in the ergodic phase and multifractality in the many-body localized phase. On the other hand, at scales below the characteristic ones, the decomposition in the ergodic phase shows finer (multi)fractal structures whereas in the localized phase, the decomposition picks out well-separated, localized resonant peaks. The scaling of these characteristic energy scales across the many-body localization transition admits a scaling theory consistent with a Kosterlitz-Thouless-type scenario and bears striking resemblances to that of inverse participation ratios of eigenstates.

We conduct a theoretical investigation into the explosive growth of bistability in a cavity magnonic system incorporating magnetic nonlinearity. In this system, the coupling between the magnon and photon generates the cavity magnon polaritons. When driving the photon-like polariton mode, the bistability can undergo a sudden transition with the increase of the driving power, resulting in an explosive growth of the bistable region by several times. Conversely, driving the magnon-like polariton mode only gives rise to normal bistability. This depends on whether the minimum driving power required to generate the bistability is nonmonotonic with respect to the driving frequency. In addition, despite driving only the photon-like polariton mode, the photon- and magnon-like polariton modes can show simultaneous explosive growth of the bistability in microwave transmission, owing to the light-matter interaction. Our research sheds light on the hidden side of the nonlinear cavity magnonic system and provides a potential application for cavity spintronic devices founded on this novel feature.