Interfaces significantly modulate the thermal properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), especially in molybdenum disulfide $\left({\mathrm{MoS}}_2\right)$. In this work, we have studied the thermal transport of CVD-grown monolayer ${\mathrm{MoS}}_2$ interfaced with amorphous silicon dioxide/silicon $({\mathrm{SiO}}_2/\mathrm{Si})$ and crystalline sapphire $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ using Raman opto-thermal technique along with finite element simulations. Raman and photoluminescence studies reveal that the relative effects of other factors, like defects, strain, and charge transfer, are comparable and low in both systems, making the case for comparison of interfacial effects. We observed a four-fold enhancement in the thermal conductivity for ${\mathrm{MoS}}_2$ on ${\mathrm{Al}}_2{\mathrm{O}}_3$ $(\kappa \sim 78 \mathrm{W}/\mathrm{mK})$ in comparison with ${\mathrm{SiO}}_2/\mathrm{Si}$ $(\kappa \sim 21 \mathrm{W}/\mathrm{mK})$, in agreement with recent theoretical predictions. This enhancement emphasizes the importance of substrate vibrational properties and interfacial interactions in controlling thermal transport in ${\mathrm{MoS}}_2$. A concomitant reduction in the interface thermal conductance from $\sim 13$ to $\sim 3$ $\mathrm{MW}/{\mathrm{m}}^2\mathrm{K}$ is also seen. This study provides valuable insights for thermal engineering at the nanoscale and integration of ${\mathrm{MoS}}_2$ in nano-electronic devices.

We demonstrate the reverse circulation mode (RCM) based on optical antiresonance in a single microring resonator (MRR) with parity-time ($PT$) structure. Unlike the situation in typical MRRs, the direction of the outgoing light in RCM mode opposes that of the incident light. We numerically determine the origin of the RCM in the $PT$-MRR coupled to a two-port waveguide through directional coupling analysis using the transfer matrix method. The RCM arises from coupling between clockwise and counterclockwise resonances in the MRR, which occurs at a unique wavelength within a broad spectral range.

Using a combination of unbiased quantum Monte Carlo simulations and a decoupled dimer mean-field theory, we investigate the thermal and quantum phase transitions of the spin-$\frac{1}{2}$ Heisenberg model on the dimerized diamond lattice. We find that at sufficiently strong dimerization the system exhibits a quantum disordered ground state, in contrast to the antiferromagnetic phase stabilized at weak dimerization. We determine the quantum critical point and examine the thermodynamic responses in both regimes. The ratio for the critical interdimer $\left(J_c\right)$ to intradimer $\left(J_D\right)$ coupling is obtained as $J_c/J_D=0.3615\left(5\right)$. Our results show that the decoupled dimer mean-field theory well captures the competition between the local singlet formation and the antiferromagnetic ordering tendency, and thus provides an appropriate qualitative description of this three-dimensional quantum magnet, in contrast to the conventional mean-field decoupling. We also examine the differences in the ordering temperatures between the antiferromagnetic and the ferromagnetic spin-$\frac{1}{2}$ Heisenberg model on the diamond lattice based on quantum Monte Carlo simulations.

Topologically protected corner states serve as a key indicator for two-dimensional higher-order topological insulators, yet they have not been experimentally identified in realistic materials. Here, by utilizing the effective tight-binding model and symmetry arguments, we establish a connection between higher-order topological insulators and twisted bilayer kagome lattices. We find that the topologically nontrivial bulk band gap arises in the twisted bilayer kagome lattice system due to twist-induced intervalley scattering, leading to the emergence of higher-order topological insulators with a range of commensurate twist angles, and the higher-order band topology is verified by the second Stiefel-Whitney number and fractionally quantized corner charges. Moreover, we investigate the influence of disorder and charge density wave order on the stability of higher-order topological insulator phases. The results show that the corner states of twisted bilayer kagome lattice systems are robust with respect to disorder and charge density wave. Our paper not only provides a feasible approach to realize the readily controllable higher-order topological insulator phases by employing a simple twist technique but also demonstrates that the twisted bilayer kagome lattice systems exhibit the robustness of higher-order band topology, making it feasible to check above prediction in experiments.

We perform a comprehensive study of charge excitations in a bilayer electron system in the presence of the long-range Coulomb interaction (LRC). Our major point is to derive formulas of the LRC that fully respect the bilayer lattice structure. This is an extension of the LRC obtained by Fetter in the electron-gas model 50 years ago and can now be applicable to any electron density. We then provide general formulas of the charge susceptibility in the random phase approximation and study them numerically. The charge ordering tendency is not found and instead we find two plasmon modes: ${\omega }_{+}$ and ${\omega }_{-}$ modes. Our second major point is to elucidate their spectral weight distribution and the effect of electron tunneling between the layers. The spectral weight of the ${\omega }_{\pm }$ modes does not have $2\pi$ periodicity along the $q_{z}c$ direction; $q_z$ and $c$ are momentum and the lattice constant along the $z$ direction, respectively. The ${\omega }_{+}$ mode loses spectral weight at in-plane momentum ${\mathbf{q}}_{\parallel }=(0,0)$ at $q_{z}c=2n\pi$ with $n$ being integer whereas the ${\omega }_{-}$ mode has no spectral weight at $q_{z}c=0$ for any ${\mathbf{q}}_{\parallel }$ but acquires sizable spectral weight at $q_{z}c=2n\pi$ with $n\ne 0$. Both ${\omega }_{\pm }$ modes are gapped at ${\mathbf{q}}_{\parallel }=(0,0)$. When $q_{z}c$ is away from $2n\pi$, the ${\omega }_{\pm }$ modes show striking behavior. When the intrabilayer hopping $t_z$ is relatively small (large), the ${\omega }_{-}$ (${\omega }_{+}$) mode becomes gapless at ${\mathbf{q}}_{\parallel }=(0,0)$ whereas the ${\omega }_{+}$ (${\omega }_{-}$) mode retains the gap. However, when the interbilayer hopping integral $t_z^{\prime }$ is taken into account, the gapless mode acquires a gap at ${\mathbf{q}}_{\parallel }=(0,0)$ and both ${\omega }_{\pm }$ modes are gapped at any $q_{z}c$. To highlight the special feature of the LRC, we also clarify a difference to the case of a short-range interaction. While the strong electron correlation effects are not included, the present theory captures available data of the charge excitations observed by resonant inelastic x-ray scattering for Y-based cuprate superconductors.

We present minimal toy models for topological skyrmion phases of matter, which generically realize type-II topological phase transitions in effectively noninteracting systems, those which occur without closing of the minimum direct bulk energy gap. We study the bulk-boundary correspondence in detail to show that a nontrivial skyrmion number yields a rich bulk-boundary correspondence. We observe gapless edge states, which are robust against disorder, due to nontrivial skyrmion number. Edge states corresponds to bands, which do not traverse the bulk gap, instead yielding gaplessness due to their overlap in energy and exponential localization on opposite edges of the system. These gapless boundary modes can occur for total Chern number zero, and furthermore correspond to rich real-space spin textures with strong polarization of spin along the real-space edge. By introducing toy models generically exhibiting type-II topological phase transitions and characterizing the bulk-boundary correspondence due to nontrivial skyrmion number in these models, we lay the groundwork for understanding consequences of the quantum skyrmion Hall effect.

Monolayer ${\mathrm{NbSe}}_2$, as an Ising superconductor, has attracted considerable attention. Experimentally, its samples inevitably contain defects, yet the effects of these defects on superconductivity remain largely unexplored. Here, we demonstrate that selenium (Se) monovacancies, the most common defects in monolayer ${\mathrm{NbSe}}_2$, critically affect superconductivity. Specifically, Se monovacancies disrupt both the out-of-plane mirror symmetry and the $C_{3z}$ rotational symmetry in pristine monolayer ${\mathrm{NbSe}}_2$, resulting in an asymmetric spin-orbit coupling (SOC). While pristine monolayer ${\mathrm{NbSe}}_2$, which possesses Ising SOC, exhibits an isotropic in-plane upper critical field $\left(B_{c2}\right)$, the asymmetric SOC induced by Se monovacancies leads the in-plane $B_{c2}$ to display an anisotropic twofold symmetry in response to the direction of the in-plane magnetic field. Furthermore, Se monovacancies significantly reduce the in-plane spin susceptibility of the superconducting state, causing $B_{c2}$ to exceed the Pauli limit only moderately, consistent with experimental observations. These findings provide valuable insights into the role of defects in tuning superconductivity of two-dimensional materials.

We study multifractal thermovoltage fluctuations in a Sb-doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ nanowire, previously reported in Kwon et al. [iScience 26, 105691 (2023)], revealing an unexplored regime of thermoelectric behavior in topological insulators under mesoscopic conditions. Through multifractal detrended fluctuation analysis, we show that thermovoltage fluctuations display a robust multifractal structure under varying gate voltages and low temperatures, while transitioning to monofractality at higher temperatures due to dephasing. By establishing multifractality as a fundamental property of mesoscopic thermoelectric observables, our results open avenues for studying quantum interference in thermoelectric systems, with potential applications for topological insulators in quantum technology.

The large lattice dynamics of lithium, driven by its low atomic mass, results in energetically similar structures and significant isotope effects under pressure, posing challenges to current theoretical models. Above 20 GPa and at low temperatures, lithium's electronic properties deviate from simple metallic behavior, with superconductivity emerging in a complex, pressure-dependent manner, alongside an unusual isotope effect. The structural phases of ${}^7\mathrm{Li}$ reported under these conditions are inconsistent across studies, and the structures of ${}^6\mathrm{Li}$ remain unexamined. These gaps limit our understanding of the effects of pressure on lithium's electronic properties and the role of quantum lattice effects on its structural behavior under pressure. Here, we integrate experimental and theoretical approaches to investigate the low-temperature structural phase boundaries in lithium isotopes. We map the structural phase diagram of ${}^7\mathrm{Li}$ from 5 to 55 GPa and 15–75 K, identifying the sequence $\mathrm{fcc}\to hR1\to cI16$. A pronounced isotope effect is observed, with ${}^6\mathrm{Li}$ shifting the $\mathrm{fcc}\to hR1$ phase boundary to lower pressures at 15 K. Density functional theory calculations further clarify how these structural changes affect superconducting properties, particularly emphasizing the role of the $\mathrm{fcc}\to hR1$ transition in lithium's superconductivity. Our findings offer insights into the unique behavior of lithium isotopes under pressure.

In non-Hermitian systems, the energy spectra and eigenstates exhibit high sensitivity to boundary conditions, lattice geometries, and local impurities. In this paper, we study the effect of long-range impurity coupling, located far from the boundaries, on the paradigmatic non-Hermitian Hatano-Nelson model. Through exact analytical treatment, we reveal the intriguing tentaclelike spectral structures that emerge from the otherwise Bloch or non-Bloch spectra under periodic or open boundary conditions, respectively. We show that these spectral tentacles are associated with emergent bound states near the impurity, with their number determined by the coupling range. We further determine the localization length of these tentacled states using the transfer matrix. Our work indicates that the long-range impurity coupling cannot be treated as a mere perturbative effect and holds promise for state manipulations in non-Hermitian systems.

We introduce “holographic shadows,” a new class of randomized measurement schemes for classical shadow tomography that achieves the optimal scaling of sample complexity for learning geometrically local Pauli operators at any lengthscale, without the need for fine-tuning protocol parameters such as circuit depth or measurement rate. Our approach utilizes hierarchical quantum circuits, such as tree quantum circuits or holographic random tensor networks. Measurements within the holographic bulk correspond to measurements at different scales on the boundary (i.e., the physical system of interests), facilitating efficient quantum state estimation across observable at all scales. Considering the task of estimating stringlike Pauli observables supported on contiguous intervals of $k$ sites in a one-dimensional system, our method achieves an optimal sample complexity scaling of $\sim d^k\mathrm{poly}\left(k\right)$, with $d$ the local Hilbert space dimension. We present a holographic minimal cut framework to demonstrate the universality of this sample complexity scaling and validate it with numerical simulations, illustrating the efficacy of holographic shadows in enhancing quantum state learning capabilities.

An inelastic neutron scattering technique is employed to investigate the paramagnetic spin dynamics in a single-crystalline sample of the magnetocaloric compound ${\mathrm{MnFe}}_4{\mathrm{Si}}_3$. In the investigated temperature range, $1.033\times T_C$ to $1.5\times T_C$, where $T_C$ is the Curie temperature, the spin fluctuations are well described by the ferromagnetic Heisenberg model predictions. Apart from the Heisenberg exchange, additional pseudodipolar interactions manifest through a finite long-wavelength relaxation rate that vanishes at the transition temperature ($T_C=305$ K). Based on the characteristic extent of spin fluctuations in wave-vector and energy space, we determine that the nature of magnetism in ${\mathrm{MnFe}}_4{\mathrm{Si}}_3$ is localized above room temperature. This contrasts with the most celebrated Mn- and Fe-based magnetocaloric materials that are considered as itinerant magnets. The field dependence of the paramagnetic spectra shows a strong suppression of the quasielastic excitations, while a field-induced spin-wave mode appears at finite-energy transfers for a magnetic field of 2 T. This modification of the spectra suggests a decrease of magnetic entropy with applied magnetic field that finds echo in the magnetocaloric properties of the system.

Spin torque oscillators generate a periodic output signal from a nonperiodic input, making them promising candidates for applications like microwave communications and neuromorphic computing. However, traditional spin torque oscillators suffer from a limited precessional cone angle and thermal stability, as well as a need for an applied bias magnetic field. Here, we use micromagnetic simulations to demonstrate a spin torque oscillator that relies on spin-orbit effects in ferromagnets to overcome these limitations. The key mechanism behind this oscillator is the generation of an out-of-plane spin current, in which both the spin flow and the spin orientation are out of plane. The torque from this spin current enables easy-plane coherent magnetic precession with a large cone angle and high thermal stability over a micron-scale lateral area. Moreover, the precession occurs about an internal field in the free layer, thereby eliminating the need for an external bias field. We find that the ratio of the unconventional out-of-plane spin current to the conventional spin-Hall spin current can be as low as $4\%$ and still result in bias-field-free, room-temperature, self-sustained oscillations. Our results are fundamentally important in demonstrating that a small ratio of unconventional to conventional spin currents critically affects magnetization dynamics. Our findings also provide a theoretical proof of concept of a spintronic device with promising applications.

Due to the unique properties of compensated ferrimagnets, such as long spin coherence length, fast domain wall motion, and large spin-orbit torque, to manipulate ferrimagnetic order is crucial in spintronics. Here, we investigate the proximity effect of the two-dimensional van der Waals material ${\mathrm{WS}}_2$ on the interfacial ferrimagnetic order of CoTb. By increasing the thickness of ${\mathrm{WS}}_2$ from one to three layers, a dramatic increase of ferrimagnetic compensation temperature by 75 K is observed in CoTb. Based on a two-sublattice mean-field approximation, the increased compensation temperature is ascribed to the ${\mathrm{WS}}_2$-mediated tuning of the magnetic moments of the sublattices Tb and Co, rather than from the changed exchange interactions $J_{\text{Co-Co}}$ and $J_{\text{Co-Tb}}$. First-principles calculations reveal that the tuned magnetic moments of the sublattices Tb and Co are realized through the proximity effect, where the charge transfer occurs between the interface of CoTb and ${\mathrm{WS}}_2$. Our study proposes a viable approach to manipulate the interfacial ferrimagnetic order through the proximity effect, which has potential applications for spintronic devices.

The hexagonal polymorph of ${\mathrm{Ba}}_3\mathrm{Tb}{\left({\mathrm{BO}}_3\right)}_3$ contains ${\mathrm{Tb}}^{3+}$ ions on a quasi-2D triangular lattice, resulting in geometric magnetic frustration. Powder samples of ${\mathrm{Ba}}_3\mathrm{Tb}{\left({\mathrm{BO}}_3\right)}_3$ have been investigated using specific heat, powder neutron diffraction (PND), inelastic neutron scattering (INS), and muon-spin relaxation spectroscopy ($\mu \mathrm{SR}$). No long-range magnetic ordering is observed down to the lowest measured temperatures of 75 mK in PND and specific heat data and 1.5 K in the $\mu \mathrm{SR}$ data. Modeling the INS spectrum using a point charge model suggests that the ground state is a singlet with a low-lying doublet on each of the two crystallographically independent ${\mathrm{Tb}}^{3+}$ sites and that both the Tb ions display weak $\mathit{XY}$ single-ion anisotropy.

We theoretically propose a universal superconducting diode device based on double magnetic impurities which are coupled to the connection region of the Josephson junction. The positive and negative currents flowing across the junction can generate opposite magnetic fields, flipping the magnetic moment of the side magnetic impurity to the opposite directions, and in turn, the two impurities will have different impacts on the opposite currents. This results in the phenomenon that the positive and negative critical currents are unequal, referred to as the superconducting diode effect (SDE). Using the nonequilibrium Green's function method (NEGF), we obtain the direction-dependent critical currents. We confirm the emergency of the SDE and demonstrate the dependence of the superconducting diode efficiency on a range of parameters including the magnitude, the direction, and the position of the magnetic moment. In addition, we systematically analyze the symmetry relations of the nonreciprocity in our system. Our proposal has high practicability by avoiding the demand on the external magnetic field, the Cooper pair momentum, and the spin-orbit coupling. Our approach opens up new possibilities for the development of nonreciprocal electronic circuits and provides an alternate perspective on the advancement of superconducting devices.