In this paper, we reveal the intricate interplay between two major nonlinear terahertz (THz) effects: intervalley scattering and impact ionization, generated by an intense few-cycle THz pulse in an undoped (100) indium antimonide semiconductor at room temperature. Our results show an initial transmission enhancement when increasing the peak electric field up to 91 kV/cm, followed by increased absorption for higher fields. Our analytical model explains that the THz strength of 91 kV/cm, is the critical field where the bleaching of absorption (induced by intervalley scattering of electrons in the conduction band) is dominant below this field, whereas above it impact ionization starts to be the dominant energy loss mechanism. The temporal and amplitude change of the total average effective carrier mass and the total carrier density allow us to monitor the THz strength fields where each scattering effect plays a dominant role. We find that the change in the carrier populations is not the only factor that influences the current density, but indeed the average drift velocity of each valley is also a decisive factor, which is derived from the carrier momentum change. The developed theoretical model match very well qualitatively and quantitatively with the experimental results.

Tuning the spectrum of near-field radiative heat transfer is crucial for many potential applications such as near-field thermophotovoltaic and thermophotonic power generation. Mie resonance based metamaterials are promising candidates for tuning the near-field spectra. In this manuscript, we utilize the Fourier modal method to perform nonapproximate simulations of near-field radiative heat flux between Mie resonance based metamaterials. By decomposing the electromagnetic response of the Mie resonators into contributions from various multipoles, we identify the origins of the peaks in the near-field spectra. We study the effect of the refractive index, extinction coefficient, shape, and interspacing of Mie resonators, as well as the separation distance of the metamaterials on the spectrum of near-field heat flux. Our study shows that as the refractive index of the metamaterial increases, the heat flux increases and the spectral locations of the Mie resonances redshift. As the extinction coefficient increases, the near-field heat flux increases and the damping of the Mie resonances eventually results in a broadband spectrum for the heat flux. Resonance splitting is observed when the distance between the Mie resonators approaches the nanometer scale. While the existing studies suggest that Mie resonance based metamaterials increase the near-field heat flux, the near-field heat transfer between these metamaterials is smaller than that between two thin films of the same material and thickness. However, Mie resonance based metamaterials are promising for tuning the spectrum of the near-field heat flux.

Semiconductor moiré superlattices provide a highly tunable platform to study the interplay between electron correlation and band topology. For example, the generalized Kane-Mele-Hubbard model can be simulated by topological moiré flat bands in twisted transition metal dichalcogenide homobilayers. In this system, we obtain the filling factor, twist angle, and electric field-dependent quantum phase diagrams with a plethora of phases, including the quantum spin Hall insulator, the in-plane antiferromagnetic state, the out-of-plane antiferromagnetic Chern insulator, the spin-polarized Chern insulator, the in-plane ferromagnetic state, and the ${120}^{\circ }$ antiferromagnetic state. We predict that a gate-defined junction formed between the quantum spin Hall insulator phase with proximitized superconductivity and the magnetic phases with in-plane magnetization (either ferromagnetism or antiferromagnetism) can realize a one-dimensional topological superconductor with Majorana zero modes. Our proposal introduces semiconductor moiré homobilayers as an electrically tunable Majorana platform with no need for an external magnetic field.

An interface connecting two distinct conformal field theories hosts rich critical behaviors. In this paper, we investigate the entanglement properties of such critical interface theories for probing the underlying universality. As inspired by holographic perspectives, we demonstrate vital features of various entanglement measures regarding such interfaces based on several paradigmatic lattice models. Crucially, for two subsystems adjacent at the interface, the mutual information and the reflected entropy exhibit identical leading logarithmic scaling, giving an effective interface central charge that takes the same value as the smaller central charge of the two conformal field theories. Our paper demonstrates that the entanglement measure offers a powerful tool to explore the rich physics in critical interface theories.

We study a linear rotor in a bosonic bath within the angulon formalism. Our focus is on systems where isotropic or anisotropic impurity-boson interactions support a shallow bound state. To study the fate of the angulon in the vicinity of bound-state formation, we formulate a beyond-linear-coupling angulon Hamiltonian. First, we use it to study attractive, spherically symmetric impurity-boson interactions for which the linear rotor can be mapped onto a static impurity. The well-known polaron formalism provides an adequate description in this limit. Second, we consider anisotropic potentials, and show that the presence of a shallow bound state with pronounced anisotropic character leads to a many-body instability that washes out the angulon dynamics.

We consider a one-dimensional system of spinless fermions with single particle and pair hoppings in a potential on-site disorder. The pair hopping term violates integrability of the model and enhances superconducting fluctuations in the bulk of the liquid. By means of the Abelian bosonization and extensive numerical density matrix renormalization group calculations we provide evidence that sufficiently large pair hopping amplitude guarantees the survival of the Tomonaga-Luttinger liquid phase at weak disorder. Large disorder drives the system to the Bose-glass phase, realizing the Giamarchi-Schulz scenario in such a system.

We have found the first instance of a third-order topological Anderson insulator (TOTAI). This disorder-induced topological phase is gapped and characterized by a quantized octupole moment and topologically protected corner states, as revealed by a detailed numerically exact analysis. We also find that the disorder-induced transition into the TOTAI phase can be analytically captured with remarkable accuracy using the self-consistent Born approximation. For a larger disorder strength, the TOTAI undergoes a transition to a trivial diffusive metal that in turn becomes an Anderson insulator at even larger disorder. Our findings show that disorder can induce third-order topological phases in three dimensions, therefore extending the class of known higher-order topological Anderson insulators.

Valence electron concentration (VEC) is a crucial parameter affecting the structure and mechanical properties of materials. Nevertheless, the influence of VEC in multicomponent alloys remains muddy. Here, the correlations between VEC and phase stability, intrinsic mechanical strength, and deformation mechanism are revealed by investigating six equiatomic $\mathrm{CoNi}M$ ($M$ = Ti, V, Cr, Mn, Fe, and Cu) alloys with VEC ranging from 7.7 to 10.0. As VEC increases, the ground-state structure evolves from bcc to hcp and ultimately to fcc. Both elastic moduli and ideal tensile strength increase initially and then decrease with increasing VEC, i.e., an inverted parabolic trend, which arises due to the orbital-filling effect of valence electrons. We highlight that a medium VEC ($\sim 8.3$) has superior intrinsic strength at a full filling of the bonding state but an empty antibonding state. Furthermore, a strong link between intrinsic strength and the energy difference between bcc and fcc ($\mathrm{\Delta }{E}_{\mathrm{fcc}\to \mathrm{bcc}}$) is built. The stacking fault (SF) energy ${\gamma }_{\mathrm{sf}}$ roughly increases with VEC except for in CoNiCr; this correlation is inherited from the energy difference between fcc and hcp. The dependence of intrinsic deformation energy barriers on VEC follows that of $\mathrm{\Delta }{E}_{\mathrm{fcc}\to \mathrm{bcc}}$ since both are linked to the bonding strength. Depending on orientation, dislocation slip (SL) and SF can co-occur in the alloys with low VEC while SL and twinning (TW) coexist in those with high VEC. Both competition between SF or TW and SL and competition between SF and TW are dictated by ${\gamma }_{\mathrm{sf}}$. This work unveils relations between VEC and phase stability, intrinsic strength, and deformation mechanisms and could provide some useful information for designing novel multicomponent alloys.

We study charge transport in voltage-biased single-channel junctions involving helical superconductors with finite Cooper pair momentum. For a Josephson junction, the equilibrium current-phase relation shows a superconducting diode effect: the critical current depends on the propagation direction. We formulate a scattering theory for voltage-biased Josephson diodes and show that multiple Andreev reflection processes cause a rich subharmonic structure in the dc current-voltage curve at low temperatures and small voltages due to Doppler shifts of the spectral gap. In the current-biased case, the diode efficiency has maximal rectification efficiency ${\eta }_0\approx 0.4$ for this model. In the voltage-biased case, however, the rectification efficiency can reach the ideal value $\eta =1$. We also discuss charge transport for normal-superconducting junctions between a normal metal and a helical superconductor and comment on related models with spin-orbit interactions and magnetic Zeeman fields.

Nuclear spin-lattice relaxation signatures in paramagnetic diluted magnetic semiconductors involving magnetic disorder are examined. By utilizing the dynamical mean-field theory for the Kondo lattice model with disorder potential, in the infinite-dimensional limit, we have derived a set of self-consistent equations to enable the numerical evaluation of the single-particle Green's function and its self-energy. The local dynamical spin susceptibility function and then the nuclear spin-lattice relaxation rate is evaluated in terms of the single-particle Green's function. Our numerical results reveal the spin fluctuations, evidenced by the sharp peak appearing at a low frequency in the spin dynamical susceptibility function, become dominant in the case of large magnetic coupling and high magnetic impurity density with temperatures close to the paramagnetic-ferromagnetic transition. In that situation, the nuclear spin-lattice relaxation divided by temperature obeys the Curie law that attributes the formation of the coherent magnetic bound states or the magnons in the paramagnetic state. Sufficiently large intensity of the magnetic disorder or the thermal fluctuations might deplete all of the bound states and then the system would settle in the normal metallic state expressing the Korringa mechanism or the nematic instability. Our observations thus have underlined the significance of the magnetic coupling and the magnetic disorder in determining the spin-lattice relaxation processes in DMSs and highlighted the advantage of the dynamical mean-field theory in studying the spin dynamics in a doped magnetic system.

We study the transport properties of a tight-binding model of noninteracting fermions with random hopping on the honeycomb lattice. At the particle-hole-symmetric chemical potential, the absence of diagonal disorder (random on-site potentials) places the system in the well-studied chiral orthogonal universality class of disordered fermion problems, which are known to exhibit both a critical metallic phase and a dimerization-induced localized phase. Here, our focus is the behavior of the two-terminal conductance and the Lyapunov spectrum in quasi-one-dimensional geometry near the dimerization-driven transition from the metallic to the localized phase. For a staggered dimerization pattern on the square and honeycomb lattices, we find that the renormalized localization length $\xi /M$ ($M$ denotes the width of the sample) and the typical conductance display scaling behavior controlled by a crossover length scale that diverges with exponent $\nu \approx 1.05\left(5\right)$ as the critical point is approached. However, for the plaquette dimerization pattern, we observe a relatively large exponent $\nu \approx 1.55\left(5\right)$, revealing an apparent nonuniversality of the delocalization-localization transition in the BDI symmetry class.

Motivated by recent experiments on a compound displaying Ising-type short-range correlations on the triangular lattice, we study the anisotropic easy-axis spin-$\frac{1}{2}$ Heisenberg model on the triangular and kagome lattices by performing numerical calculations of finite-temperature properties, in particular of static spin structure factor and of thermodynamic quantities, on systems with up to 36 sites. On the triangular lattice, the low-temperature spin structure factor exhibits long-range spin correlations in the whole range of anisotropies, whereas thermodynamic quantities reveal a crossover upon increasing the anisotropy, most pronounced in the vanishing generalized Wilson ratio in the easy-axis regime. In contrast, on the kagome lattice, the spin structure factor is short range, and thermodynamic quantities evolve steadily between the easy-axis and the isotropic cases, consistent with the interpretation in terms of a spin liquid.

In the equilibrium thermodynamics framework, expressions were obtained that determine the dependences of the specific surface energy $\sigma$ and surface pressure $P_{Sf}$ on the size ($N$) and shape of a freestanding nanocrystal at different pressure $P$ and temperature $T$. Based on these expressions, the behavior of the $\sigma (P,T,N)$ and $P_{Sf}(P,T,N)$ functions for fcc Au have been studied. The calculations performed for the macrocrystal showed good agreement with the experimental data. Calculations for a nanocrystal have shown that at $P=0$, the $P_{Sf}\left(N\right)$ function lies in the negative region, i.e., the nanocrystal is stretched by surface pressure the more the higher of temperature, or the more the nanocrystal shape is deviated from an energy-optimal shape. With a decrease in $N$ at $P=0$, the function $\sigma \left(N\right)$ decreases more noticeably the higher of temperature, or the more the nanocrystal shape deviates from an energy-optimal shape. Based on these results, it was shown that the increase in the $\sigma \left(N\right)$ function obtained in some articles with an isomorphic-isothermal decrease in $N$ does not correspond to the physical properties of nanoparticles. In these articles, the nanoparticle was compressed by surface pressure, which increased with an isomorphic-isothermal decrease of the $N$ value. This compression led to the corresponding growth of the $\sigma \left(N\right)$ function both with an isomorphic-isothermal decrease in size and with an isomeric (i.e., at $N=\mathrm{const}$) increase in the nanoparticle temperature.

Photonic bound states in the continuum (BIC) promise a versatile platform for construction of optical resonators with highly confined electromagnetic fields and ultralong radiative lifetime. Merging multiple BIC can enable suppression of out-of-plane radiative losses and further boost the quality (Q) factor of the resonance state. However, current studies on merging BIC (M-BIC) are primarily restricted to the elementary BIC with topological charge $\pm 1$, which hinders further improvement of the performance of optical resonators. Here, an all-silicon terahertz metasurface (THz-MS) is investigated that supports the symmetry-protected BIC (SP-BIC) with topological charge $-2$ and accidental BIC (A-BIC) with topological charge $\pm 1$ simultaneously. Empowered by the topological nature of BIC, we merge twelve A-BIC with a higher-order SP-BIC at the $\mathrm{\Gamma }$ point. By tailoring in-plane mirror symmetry of the THz-MS, we achieve M-BIC at almost arbitrary position in the momentum space. Unlike original isolated BIC, M-BIC manifests the dramatic enhancement of the Q factors of nearby resonances and are robust against radiation losses introduced by fabrication imperfections. Our work presents a paradigm for realizing higher-order at-$\mathrm{\Gamma }$ M-BIC and momentum-steerable M-BIC that can substantially enhance light-matter interaction and further improve the performance of terahertz optoelectronic devices.

Non-Hermitian quantum systems exhibit fascinating characteristics such as non-Hermitian topological phenomena and skin effects, yet their studies are limited by the intrinsic difficulties associated with their eigenvalue problems, especially in larger systems and higher dimensions. In Hermitian systems, the semiclassical theory has played an active role in analyzing spectrum, eigenstate, phase, transport properties, etc. Here we establish a complex semiclassical theory applicable to non-Hermitian quantum systems by an analytical continuation of the physical variables such as momentum, position, time, and energy in the equations of motion and quantization condition to the complex domain. Further, we propose a closed-orbit scheme and physical meaning under such complex variables. We demonstrate that such a framework straightforwardly yields complex energy spectra and quantum states, topological phases and transitions, and even the skin effect in non-Hermitian quantum systems, presenting an unprecedented perspective toward nontrivial non-Hermitian physics, even with larger systems and higher dimensions.

We study a one-band Hubbard model for a twisted cuprate bilayer with a twist angle of $43.6^{\circ }$ and a moiré cell containing 58 sites. We use the variational cluster approximation (VCA), which treats short-range correlations exactly and leads, in single layers, to a dome of $d$-wave superconductivity away from half filling from strong on-site repulsion alone. We find a time-reversal-symmetry (TRS) breaking phase in a small doping interval in the overdoped region when interlayer tunneling is strong enough. Contrary to expectations, being closer to the ${45}^{\circ }$ twist angle does not expand this TRS region compared to a previous study [Lu and Sénéchal, Phys. Rev. B 105, 245127 (2022)] on a ${53}^{\circ }$ twist angle. This is attributed to the fact that the two superconducting states in competition have almost identical nodal structures.

The microscopic pairing mechanism for superconductivity in magic-angle twisted bilayer graphene remains an open question. Recent experimental studies seem to rule out a purely electronic mechanism due to the insensitivity of the critical superconducting temperature to either a highly doped screening layer or the proximity to a metallic screening gate. In this theoretical work, we explore the role of external screening layers on the superconducting properties of twisted bilayer graphene within a purely electronic mechanism. Consistent with the experimental observations, we find that the critical temperature is unaffected by screening unless the screening layer is closer than 3 nm from the superconductor. Thus, the available transport data are not in contradiction with a plasmon-mediated mechanism. We also investigate other properties of this plasmon-mediated superconductivity, including signatures in the tunneling density of states as probed in spectroscopy experiments.

Time modulation provides an important degree of freedom for classical wave steering in topological manners. Rather than using the spatial dimension to mimic time, here we design and implement an acoustic temporal lattice with time-varying couplings to demonstrate a unique type of strongly localized Floquet π modes that are gauge independent and can be robustly excited at the frequency in the nontrivial band gap. We observe the topological phase transitions by changing modulation frequency, consistent with the calculated quasienergy spectra. Our work paves the way for investigating intrinsic characteristics of various temporal systems and may inspire other intriguing discoveries in topological systems, such as higher-order temporal Floquet topological insulators.

Degeneracy points in non-Hermitian systems are of great interest. While a homotopic framework exists for understanding their behavior in the absence of symmetry, it does not apply to symmetry-protected degeneracy points with reduced codimension. In this work, utilizing algebraic topology, we provide a systematic classification of these symmetry-protected degenerate points and investigate the braid conservation rule followed by them. Using a model Hamiltonian and circuit simulation, we discover that, contrary to simple annihilation, pairwise-created symmetry-protected degeneracy points merge into a higher-order degeneracy point, which goes beyond the abelian picture. Our findings empower researchers across diverse fields to uncover new phenomena and applications harnessing symmetry-protected non-Hermitian degeneracy points.

Measurement-induced phase transitions (MIPTs) are known to be described by nonunitary conformal field theories (CFTs) whose precise nature remains unknown. Most physical quantities of interest, such as the entanglement features of quantum trajectories, are described by boundary observables in this CFT. We introduce a transfer matrix approach to study the boundary spectrum of this field theory, and consider a variety of boundary conditions. We apply this approach numerically to monitored Haar and Clifford circuits, and to the measurement-only Ising model where the boundary scaling dimensions can be derived analytically. Our transfer matrix approach provides a systematic numerical tool to study the spectrum of MIPTs.