We offer theoretical predictions for the values of the resonant frequencies of transport for the hydrodynamic description of bilayer graphene, as well as provide quantification for the relative strength of this signal throughout phase space. Our calculations are based on classical fluid dynamics equations derived from the Boltzmann equation for bilayer graphene, and suggest that while this resonance is accessible to current experimental techniques, the same mechanism which causes the hydrodynamic resonance to differ from the Fermi-liquid value is responsible for a significant broadening of the peak.

Majorana bound states (MBSs) located at the ends of a hybrid superconductor-semiconductor nanowire are only true zero modes if their characteristic localization length is much smaller than the nanowire length, ${\xi }_M\ll L$. Otherwise, their wave function overlap gives rise to a finite energy splitting that shows a characteristic oscillatory pattern $\sim e^{-2L/{\xi }_M}cos\left(k_{F}L\right)$ versus external parameters that modify the Fermi momentum $k_F$. Detecting such “Majorana oscillations,” measurable through low-bias conductance, has been proposed as a strategy for Majorana detection in pristine nanowires. Here we discuss how this detection scheme does not work in full-shell hybrid nanowires, an alternative design to partial-shell nanowires in which a superconductor shell fully wraps the semiconductor core. Using microscopic models, we provide both numerical simulations for Al/InAs hybrids as well as analytical approximations in terms of general nanowire parameters. We find that Majorana oscillations with flux in full-shell nanowires are absent in a wide portion of parameter space. This absence is not a signature of nonoverlapping left- and right-end MBSs, but a consequence of the Majorana oscillation period being systematically larger than the flux window of odd Little-Parks lobes where Majorana zero-energy peaks are predicted to appear. Our results demonstrate that split near-zero modes or individual zero-energy crossings should not be dismissed as trivial even if they are found not to oscillate with flux.

Two-dimensional (2D) van der Waals ferromagnets have potential applications as next-generation spintronic devices and provide a platform to explore the fundamental physics behind 2D magnetism. The dual nature (localized and itinerant) of electrons adds further complexity to the understanding of correlated magnetic materials. Here, we present the temperature evolution of electronic structure in the 2D van der Waals ferromagnet ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ using photoemission spectroscopy in conjunction with density functional theory (DFT) plus dynamical mean field theory (DMFT). With the appearance of a quasiparticle peak and its evolution in the vicinity of the Fermi energy, we unveil empirical evidence of an incoherent-coherent crossover at around 125 K. $\mathrm{DFT}+\mathrm{DMFT}$ results show that the quasiparticle lifetime surpasses thermal energy for temperature below 150 K, confirming incoherent-coherent crossover in the system. The lack of appreciable change in the Fe $2p$ core level, overall valence band spectra across the magnetic transition, and temperature-dependent ferromagnetic $\mathrm{DFT}+\mathrm{DMFT}$ results provide substantial evidence for non-Stoner magnetism in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$. We elucidate the temperature-dependent intimate relation between magnetism and electronic structure in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$. A Sommerfeld coefficient of $\sim 104$ mJ ${\mathrm{mol}}^{-1}{\mathrm{K}}^{-2}$ obtained in the low-temperature limit from $\mathrm{DFT}+\mathrm{DMFT}$ calculations resolves the long-standing issue of a large Sommerfeld coefficient $(\sim 110 \mathrm{mJ} {\mathrm{mol}}^{-1}{\mathrm{K}}^{-2})$ obtained from specific heat measurements.

The observation of superconductivity (SC) in hole-doped antimonates $\mathrm{B}{\mathrm{a}}_{1-x}{\mathrm{K}}_x\mathrm{Sb}{\mathrm{O}}_3$ (BKSO), isoelectronic compounds to bismuthate $\mathrm{B}{\mathrm{a}}_{1-x}{\mathrm{K}}_x\mathrm{Bi}{\mathrm{O}}_3$ (BKBO) SCs, enables a pathway to clarify the role of hybridizations between electronic states of metals and ligands on the emergence of SC. Herein, using first-principles simulations, the localized electronic structure of antimonates is demonstrated to produce various charge and bond orderings (CBOs) up to $x=0.6$, hence hindering the appearance of a SC state. This is in contrast with bismuthates where the formation of charge orderings is suppressed by doping effects and their native hybridized electronic structure. Although quenched by doping effects, the CBOs mediate the Cooper pair formation, and the resulting electron-phonon coupling reproduces the experimental facts such as a larger $T_c$ in BKSO than in BKBO for $x>0.65$ and a maximal $T_c$ of $\sim 30\mathrm{K}$ observed at $x=0.4-0.5$ for BKBO. The latter point is ascribed to a soft phonon mode at $x=0.5$, while the former observation is ascribed to an intrinsically stronger coupling between lattice distortions and electrons in $\mathrm{BaSb}{\mathrm{O}}_3$. Although materials with a localized electronic structure could warrant larger ${T^{\prime }}_c\mathrm{s}$, the main drawback is the resilience of such compounds to form a metallic state, and hence SC emerges far away of soft phonons possessing a strong coupling with the electronic structure.

Deconfined quantum critical points have attracted lots of attention in the past decades but were mainly restricted to incompressible phases. On the other hand, various experimental puzzles call for a new theory of unconventional quantum criticality between metals at a generic density. Here we explore the possibility of a deconfined transition between two symmetric Fermi liquids (FLs) in a bilayer model tuned by interlayer antiferromagnetic spin-spin coupling $J_{\perp }$. Across the transition the Fermi-surface volume per flavor jumps by $1/2$ of the Brillouin zone, similar to the small to large Fermi-surface transitions in heavy fermion systems and maybe also in the high $T_{\text{c}}$ cuprates. But in the bilayer case the small Fermi-surface phase (dubbed sFL) has neither symmetry breaking nor fractionalization, akin to the symmetric mass generation discussed in high-energy physics. We formulate a deconfined critical theory where the two Fermi liquids correspond to Higgs and/or confined phases of a $\text{U}\left(1\right)\times \text{U}\left(1\right)$ gauge theory. We show that this deconfined FL to FL transition fixed point is unstable to pairing and thus a superconductor dome is expected at low temperature. At finite temperature above the pairing scale, microscopic electron is a composite of three deconfined fractional fermions in the critical theory. We also introduce another parameter which can suppress the pairing instability, leading to a deconfined phase stable to zero temperature. Our work opens a direction to exploring deconfined metallic criticality and pairing mechanism from critical gauge field. The transition may be relevant to the recently found nickelate superconductor ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ and future experiments in bilayer optical lattice.

Light irradiation is a common and flexible method to induce Berry curvature in low-dimensional materials by breaking time-reversal symmetry. The recent Floquet band engineering in black phosphorus (BP) was successfully realized in experiment [S. Zhou et al., Nature (London) 614, 75 (2023)], hereby, we study the anomalous Hall, Nernst, and thermal Hall effects in BP thin films irradiated by an off-resonant circularly polarized light. Using the $k·p$ Hamiltonian and Floquet theory, we derive the effective Hamiltonian and Berry curvature through two-photon processes up to the second order. We find that the light slightly increases the band gap, and the Berry curvature increases with increasing light intensity. Notably, the anomalous Hall conductivity exhibits a negative plateau width equal to the band gap, which is four orders of magnitude larger than that of monolayer BP. On the contrary, the anomalous Nernst conductivity is always zero within the band gap, showing a dip-peak profile. The anomalous thermal Hall conductivity trend mirrors that of the anomalous Hall conductivity, in line with the Wiedemann-Franz law. Our results provide a feasible method to obtain a finite Berry curvature and shed light on possible topological phase in BP thin films.

Excitonic optical transitions in carbon nanotubes (CNTs) have been extensively studied for at least two decades. However, exploiting these transitions to produce a lasing effect has proven to be unpractical due to the difficulties of achieving an excitonic population inversion in carbon nanotubes. In this work we show that lasing is theoretically possible at a much lower exciton population threshold by taking advantage of phonon stimulated emission. Specifically, the so-called anti-Stokes transitions, where light is generated by the creation of a phonon and the annihilation of an exciton, can be used to sustain the coherent emission of photons. These transitions have been overlooked for long due to their low intensity as a consequence of the low occupancy of the associated phonon branches. We show that the best conditions to achieve the lasing effect are met in CNTs with (i) excitons of nonzero momentum, (ii) a strong exciton-phonon coupling, and (iii) narrow exciton transitions.

Recently, two-dimensional (2D) interlayer-sliding multiferroic materials, consisting of two nonferroelectric monolayer ferromagnetic (FM) layers with specific interlayer stacking and sliding, have garnered significant interest for their potential in expanding the range of 2D multiferroics. However, the low-dimensional nature of 2D multiferroic materials results in relatively weak magnetic and ferroelectric (FE) properties, posing challenges for traditional detection methods in characterizing these two order parameters. In this work, we study the optical fingerprints of 2D interlayer-sliding multiferroic materials. By utilizing an abstract bilayer model, we demonstrate that the four multiferroic states $(P_{\uparrow }{N}_{\uparrow },$ $P_{\uparrow }{N}_{\downarrow },$ $P_{\downarrow }{N}_{\downarrow },$ and $P_{\downarrow }{N}_{\uparrow })$ are interconnected via the horizontal mirror symmetry ${\widehat{M}}_z$, time-reversal symmetry $\widehat{T}$, and their combination symmetries ${\widehat{M}}_z\widehat{T}$. Subsequently, we analyze the tensor elements associated with the optical Kerr effect and second harmonic generation (SHG) effect in multiferroic states, revealing a strong correlation between both the Kerr effect and SHG effect and the multiferroic orders of 2D interlayer-sliding multiferroic materials, as well as the presence of distinct optical characteristics across different multiferroic states. Using ${\mathrm{VSe}}_2$ and ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ as two representative 2D interlayer-sliding multiferroic materials, we further validate the intricate correlations between the symmetries and optical properties. Our research provides theoretical guidance for characterizing 2D interlayer-sliding multiferroic materials by means of optical methods.

The Su-Schrieffer-Heeger chain is a prototype example of a symmetry-protected topological insulator. Coupling it nonperturbatively to local thermal environments, either through the intercell or the intracell fermion tunneling elements, modifies the topological window. To understand this effect, we employ the recently developed reaction-coordinate polaron transform (RCPT) method, which allows treating system-bath interactions at arbitrary strengths. The effective system Hamiltonian, which is obtained via the RCPT, exposes the impact of the baths on the SSH chain through renormalization of tunneling elements and the generation of many-body interaction terms. By performing exact diagonalization and computing the ensemble geometric phase, a topological invariant, which is applicable even to systems at finite temperature, we distinguish the trivial band insulator (BI) from the topological insulator (TI) phases. Furthermore, through the RCPT mapping, we are able to pinpoint the main mechanism behind the extension of the parameter space for the TI or the BI phases (depending on the coupling scheme, intracell or intercell), which is the bath-induced, dimerized, many-body interaction. We also study the effect of on-site staggered potentials on the SSH phase diagram and discuss extensions of our method to higher dimensions.

Driven-dissipative light-matter systems can exhibit collective nonequilibrium phenomena due to loss and gain processes on the one hand and effective photon-photon interactions on the other hand. As a generic example we study a bosonic lattice system implemented via an array of driven-dissipative coupled nonlinear resonators with linearly increasing resonance frequencies across the lattice. The model also describes a driven-dissipative Bose-Hubbard model in a tilted potential without a particle-conservation constraint. We numerically predict a diverse range of stationary and nonstationary states resulting from the interplay of the tilt, tunneling, on-site interactions, and loss and gain processes. Our key finding is that, under weak on-site interactions, the bosons mostly condense into a selected, single-particle Wannier-Stark state without exhibiting the expected Bloch oscillations. As the strength of the on-site interactions increase, a nonstationary regime emerges which, surprisingly, exhibits periodic Bloch-type oscillations. As a direct consequence of the driven-dissipative nature of the system we predict a highly nontrivial phase diagram including regular oscillating as well as chaotic dynamical regimes. While a straightforward photonic implementation using microwave or optical modes is possible, such dynamics might also be observable for an ultracold gas in a vertical lattice with gravity or a tilted external potential.

Inspired by recent experimental discoveries of superconductivity in multilayer graphene, we study models of $f$-wave superconductivity on the honeycomb lattice with arbitrary numbers of layers. For odd numbers of layers, these systems are topologically nontrivial, characterized by a mirror-projected winding number ${\nu }_{\pm }=\pm 1$. Along each mirror-preserving edge in armchair nanoribbons, there are two protected Majorana zero modes. These modes are present even if the sample is finite in both directions, such as in rectangular and hexagonal flakes. Crucially, zero modes can also be confined to vortex cores. Finally, we apply these models to twisted bilayer and trilayer systems, which also feature boundary-projected and vortex-confined zero modes. Since vortices are experimentally accessible by local scanning probes, our study suggests that superconducting multilayer graphene systems are promising platforms to create and manipulate Majorana zero modes.

We show from many-body quantum mechanical calculations that there occur structurally distinct triplet-pair eigenstates in the intramolecular singlet fission (iSF) compound pentacene-tetracene-pentacene. Triplet excitons occupy neighboring pentacene and tetracene monomers in the higher energy doubly degenerate triplet-triplet multiexcitons, and terminal pentacene chromophores in the lower energy multiexciton. The lowest energy multiexciton is reached by ultrafast triplet migration within the triplet-triplet manifold, a result with profound implication for the design of superior iSF compounds.

The observation of the Sagnac effect for massive material particles offers a significant enhancement in sensitivity when compared to optical interferometers with equal area and angular rotation velocity. For this reason, there have been suggestions to employ solid-state interferometers that rely on semiconductors and graphene. We investigate the Sagnac effect in Dirac materials governed by the relativisticlike quasiparticle dispersion law and show that the fringe shift is still determined by the mass of a free electron. This confirms that graphene is indeed a promising material for creating solid-state Sagnac interferometers. Considering monolayer graphene with its linear dispersion law and comparing it with light provides a deeper understanding of the Sagnac effect.

The origin of the charge density wave (CDW) instabilities in the isostructural but not isoelectronic octahedral layers of the three-dimensional solids $\gamma \text{−}{\mathrm{Mo}}_4{\mathrm{O}}_{11}$ and ${\mathrm{P}}_4{\mathrm{W}}_{12}{\mathrm{O}}_{44}$ is discussed on the basis of first-principles density functional theory calculations. These layers contain three different and superposed one-dimensional (1D) systems (two diagonal and one horizontal) associated with the three $t_{2g}$ orbitals of the transition metal in octahedral coordination. Because of the special topology of the layers the three 1D systems are practically independent (hidden nesting) and the Lindhard function contains three different lines of intensity maxima associated with each of them. Clear cusps (six for ${\mathrm{P}}_4{\mathrm{W}}_{12}{\mathrm{O}}_{44}$ and four for $\gamma \text{−}{\mathrm{Mo}}_4{\mathrm{O}}_{11}$) occur at the intersections of these intensity lines. The wave vector of the structural modulations associated with some of these cusps from our calculations is in good agreement with the observed CDW wave vectors. The nature of the different modulations is analyzed on the basis of the calculated thermal dependence of intrachain and interchain coherence lengths of the diffuse lines associated with the diagonal and horizontal chains. Modulation in the diagonal chains is found to be more favorable than in the horizontal chain. The same type of wave vector is selected for $\gamma \text{−}{\mathrm{Mo}}_4{\mathrm{O}}_{11}$ and ${\mathrm{P}}_4{\mathrm{W}}_{12}{\mathrm{O}}_{44}$ despite having a different band filling. The coupling of the electronic instability to the phonon spectra and the relationship between the nature of the high-temperature modulation with the width of the octahedral layers is discussed. Among the two Magnéli phases the interlayer coupling is found to be somewhat stronger in $\eta \text{−}{\mathrm{Mo}}_4{\mathrm{O}}_{11}$. The relationship with other hidden-nesting series of materials as the rare-earth tellurides is commented.

The infinite layered ($T^{\prime }$) nickelates have recently garnered significant attention due to the discovery of superconductivity in hole-doped ${R\text{NiO}}_2$ ($R=\mathrm{La},\mathrm{Pr},\text{or}\mathrm{Nd}$), which is the $n=\infty$ member of the series $R_{n+1}{\mathrm{Ni}}_n{\mathrm{O}}_{2n+2}$. Here, we investigate the $n=3$ member, namely $R_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ ($R=\mathrm{La},\mathrm{Pr},\text{or}\mathrm{Nd}$), of this family. The compound ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ exhibits simultaneous charge/spin-stripe ordering at $T_N^{*}$ = 105 K, which occurs concomitantly with the onset of the metal-to-insulator (MIT) transition below $T_N^{*}$. We investigate the conspicuous absence of this transition in the Pr and Nd analogs of ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$. For this purpose, we synthesized solid solutions of the form $(\mathrm{La},{\mathrm{Pr})}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ and $(\mathrm{La},{\mathrm{Nd})}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$, and examined the behavior of $T_N^{*}$ as a function of the average $R$-site ionic radius ($r_{\overline{R}}$). We show that after an initial quasilinear decrease with decreasing $r_{\overline{R}}, T_N^{*}$ suddenly vanishes in the narrow range $1.134\le r_{\overline{R}}\le 1.143\text{Å}$. In the same range, we observed the emergence of a weak anomaly in the specific heat, whose onset temperature ($T^{*}$) increases as $r_{\overline{R}}$ further decreases reaching a maximum of 13 K for ${\mathrm{Nd}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$. We suggest, therefore, that the sudden vanishing of charge/spin-stripe/MIT ordering upon decreasing $r_{\overline{R}}$ is related to the appearance of this new electronic phase for $r_{\overline{R}}<r_c$. The nature of this phase or the weak anomaly and the point $r_{\overline{R}}\approx r_c$, where $T_N^{*}$ vanishes and $T^{*}$ appears, should be investigated further. In this regard, ${\mathrm{Pr}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ and Pr-rich samples should be useful due to the weak magnetization response associated with the Pr sublattice, as shown here.

Spin-orbit torque (SOT) has been widely recognized and applied as the most promising approach for magnetic memory, primarily due to its lower energy consumption and longer device lifetime. However, the mechanism of SOT remains controversial in ferrimagnets, particularly regarding the role of fieldlike torque (FLT). This uncertainty arises from the presence of different gyromagnetic ratios of the sublattices, which generates significant variations particularly in the vicinity of the angular momentum compensation point. In this paper, we demonstrate that, in the vicinity of the angular momentum compensation point, FLT can act as a main driving term for magnetization switching in ferrimagnets through rigorous mathematical analysis and ferrimagnetic macrospin simulation. We also provide clear indications about the materials damping factor on how to tailor the magnetic layer where a charge current is injected. These findings shed light on the intricate behavior of SOT in ferrimagnetic systems and pave a way for further advancements in high-performance magnetic memory devices.