The optical conductivity $\sigma (\omega ,T)$ of CeRhSn was studied by broadband infrared spectroscopy. Temperature-dependent spectral weight transfer occurs over high energy ($0.8\mathrm{eV}$) and temperature ($\sim 500\mathrm{K}$) scales, classifying CeRhSn as a mixed-valent compound. The optical conductivity reveals a substantial anisotropy in the electronic structure. Renormalization of $\sigma (\omega ,T)$ occurs as a function of temperature to a coherent Kondo state with concomitant effective mass generation. Associated spectroscopic signatures were reproduced remarkably well by the combination of density functional theory and dynamical mean-field theory using a momentum-independent self-energy. The theory shows that the anisotropy for energies $>10\mathrm{meV}$ is mainly driven by the bare three-dimensional electronic structure that is renormalized by local electronic correlations. The possible influence of magnetic frustration and quantum criticality is restricted to lower energies.

We show that even with arbitrarily large cyclotron gap, Landau level (LL) mixing can be dominant with scale-free interaction in a fractional quantum Hall system, as long as the filling factor exceeds certain critical values. Such scale-free interaction with kinetic energy can serve as exact model Hamiltonians for certain composite Fermion or parton states (unlike the well-known TK Hamiltonians where the number of LLs needs to be fixed by hand), and they are natural physical Hamiltonians for 2D systems embedded in higher-dimensional space time. Even with LL mixing the null spaces of such Hamiltonians (spanned by the ground state and the quasiholes) can be analytically obtained, and we show these are the generalization of the conformal Hilbert spaces (CHS) to more than one LLs. The effective interaction between the anyons for these topological phases emerges from the kinetic energy of the “elementary particles,” leading to an interesting duality between strongly and weakly interacting systems that can be easily understood via the tuning of parameters in the scale-free interaction. We also propose an experimental platform for approximately realizing such model Hamiltonians with trionlike particles that can potentially lead to very robust (non-Abelian) FQH phases from two-body Coulomb-based interaction.

It has been reported that upon doping a Mott insulator, there can be a crossover to a pseudogapped metallic phase followed by a first-order transition to another thermodynamically stable metallic phase. We call this first-order metal-metal transition the Sordi transition. It was argued that the initial reports of Sordi transitions at finite temperature could be explained by finite size effects and biases related to the model and method used. In this work, we report the Sordi transition on larger clusters at finite temperature on a triangular lattice, where long-range antiferromagnetic fluctuations are frustrated, using a different method, the dynamical cluster approximation instead of the cellular dynamical mean-field theory. This demonstrates that this first-order transition is a directly observable transition in doped Mott insulators and that it is relevant for experiments on candidate spin-liquid organic materials.

We investigate a non-Hermitian Aubry-André-Harper model with short-range as well as long-range $p$-wave pairing. Here, the non-Hermiticity is introduced through the on-site potential. A comprehensive analysis of this system's critical aspects, like eigenspectra, topological properties, localization properties, and the transition from real to complex energies, is conducted. Specifically, we observe the emergence of Majorana zero modes in the case of short-range pairing, whereas the massive Dirac modes emerge in the case of long-range pairing. More importantly, for both cases of pairing, we observe double-phase transitions, that is, simultaneous transitions of topological phases and multifractal to localized phases. Additionally, again, for both the ranges of pairing, we identify another double-phase transition, where delocalized (or metallic) to a critical multifractal state transition is accompanied by an unconventional shift from real to complex energies. Unlike the short-range pairing case, we observe mobility edges in the case of the long-range pairing.

Electric-field control of magnetization is crucial for next-generation spintronic devices with reduced energy consumption and increased integration density. Based on magnetoelectric multiferroics whose Dzyaloshinskii-Moriya interaction (DMI) vectors are coupled to their polarization, we propose the architecture of a DMI transistor which utilizes voltage-controlled DMI torque to reverse the magnetization orientation, enabling current-free magnetization reversal. By leveraging the properties of a CrN monolayer, we demonstrate the feasibility of the DMI transistor through first-principles calculations, micromagnetic simulations, and analytical calculations. We find that the switching time of the DMI transistor (in subnanoseconds) increases with the exchange interaction and decreases with the DMI. We also show how the size of the DMI transistor (in nanometers) depends on the exchange interaction and the DMI and how it can be further tuned by the magnetic anisotropy. In this paper, we pave the way toward highly desired electric-field control and current-free ultrafast spintronic devices, with the potential toward logic-in-memory architecture overcoming the von Neumann bottleneck.

Experimental demonstration of substantially large and negative spin Hall angle in CuBi alloys, in which diluted Bi atoms are doped into Cu, sheds light on a novel aspect of spin-charge interconversion physics using Bi, where much effort has been paid to explore large spin-charge interconversion efficiency expected from the gigantic spin-orbit interaction of Bi. Since the spin Hall effect allows concomitant spin-orbit torque (SOT) that is a significant trait in spintronic phenomena for applications, an investigation of the spin-orbit torque efficiency in CuBi, that has not been thoroughly studied, is an important challenge. In this study, we estimate the SOT efficiency of CuBi by suppressing unwanted spin backflow. Surprisingly, the sign of the SOT efficiency is positive, unlike that in previous work. The amplitude of the SOT efficiency decreases monotonically as a function of the Bi composition of the CuBi alloy, which is attributed to the interplay of the orbital Hall effect of Cu and the interfacial Rashba effect in the SOT devices.

The $\alpha \text{−}\mathrm{Mn}$ phase exhibits a large anomalous Hall effect (AHE) in its pressure-induced weak ferromagnetic (WFM) state, despite its relatively small spontaneous magnetization of $\sim 0.02{\mu }_{\mathrm{B}}/\mathrm{Mn}$. To understand the underlying mechanism behind this AHE, we performed single crystal neutron diffraction measurements at 2.0 GPa to determine the magnetic structure of the WFM phase. Our investigation reveals a ferrimagnetic structure characterized by nearly collinear magnetic moments aligned along the [001] direction at sites I, II, III-1, and IV-1. In contrast, the small moments at sites III-2 and IV-2 lie within the (001) plane. The calculated net magnetization of this magnetic structure, $(-0.08\pm 0.10){\mu }_{\mathrm{B}}/\mathrm{Mn}$ atom, is in agreement with the experimentally determined spontaneous magnetization. The observation of a magnetic reflection at $\mathit{q}=(0,0,0)$ satisfies a key condition for the emergence of the AHE.

The behavior of muons in water and ice is investigated by measuring spin rotation and relaxation of positive muons in water at 140–300 K, where we successfully observe oscillation in the zero-field spectra of muons in ice. The oscillation is attributed to the spin–dipole interactions between the muon in $Mu\mathrm{OH}$ and neighboring protons and to hyperfine transitions of triplet states of axially symmetric anisotropic muonium in ice. The $Mu–\mathrm{H}$ distance in $Mu\mathrm{OH}$ exceeds the H–H distance in ${\mathrm{H}}_2\mathrm{O}$ by 5% in ice.

Manifested as the accumulation of bulk eigenstates at open boundaries, non-Hermitian skin effects have been studied extensively in various wave systems with either nonreciprocal couplings or on-site gain/loss effects. Here, by unraveling the space-time duality between the elastostatics of two-dimensional continua and the one-dimensional wave mechanics, we show a non-Hermitian topology inherent in the static deformation response of orthotropic, lossless elastic continua with geometry incompatibility between the fiber alignment and sample construction. The eigenstates of the open boundary system are spatially biased towards the boundary, whose degeneracy and chirality are governed by a spectral winding number unique to continuous systems. The directional accumulation of strain energy within a spatial trajectory excited by a quasistatic load emulates a dynamic skin effect, which can be exploited to program the material deformation response. Our study discloses an underlying non-Hermitian topology in static elastic continua with purely passive modulations, and it sheds light on the exploration of the skin effect in other continuous waveguides.

${\mathrm{NbSe}}_2$ is expected to host a rich variety of quantum phenomena such as Ising superconductivity and the orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. So far, these intriguing states have been accessed only in discrete samples with a fixed set of parameters regarding the spin-orbit coupling strength, lattice symmetry, and dimensionality. Here, we invoke a lithium ion backgate to continuously tune those parameters and reveal a systematic evolution of superconductivity in both ultrathin and bulklike ${\mathrm{NbSe}}_2$ samples. The ultrathin ${\mathrm{NbSe}}_2$ after lithium intercalation possesses a further enhanced upper critical magnetic field over the Pauli limit, confirming the doping dependence of Ising superconductivity. Moreover, we successfully tune the bulklike ${\mathrm{NbSe}}_2$ to a two-dimensional Ising superconductor at high doping. Additionally, at intermediate doping, we observe behaviors akin to the emergent orbital FFLO state.

The bulk and surface electronic structures of Sn-doped $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ thin films have been studied by soft and hard x-ray photoemission spectroscopy (soft PES at 1486.6 eV and HAXPES at 5920 eV). The experimental spectra are compared with density functional theory calculated density of states in the valence band and conduction band. Excellent agreement was found between experimental spectra and calculated density of states by taking into account the photoionization cross section of different orbitals involved in the valence and conduction bands. The electronic states derived from Ga $4s$ character are selectively enhanced by HAXPES. This allows us to infer that the states at the conduction band and bottom of the valence band contain pronounced Ga $4s$ character. The occupation of the lower conduction band in degenerately Sn-doped ${\mathrm{Ga}}_2{\mathrm{O}}_3$ is clearly observed by HAXPES, which allows for direct measurement of Burstein-Moss shift and band-gap renormalization as a function of Sn doping. A comparison of the valence band spectra of Sn-doped ${\mathrm{Ga}}_2{\mathrm{O}}_3$ films with Si-doped samples suggests that Sn doping has different effects on the electronic structure than Si doping. An in-gap electronic state is observed for Sn-doped ${\mathrm{Ga}}_2{\mathrm{O}}_3$, which is attributed to self-compensating $\mathrm{S}{\mathrm{n}}^{2+}$ related defects. Furthermore, a larger band-gap renormalization is found in Sn-doped samples, because the Sn $5s$ dopant orbital mixes strongly with the host Ga $4s$ derived conduction band. Finally, a comparison of the valence band and core-level spectra excited with soft and hard x rays allows us to identify an upward band bending at the surface region of Sn-doped ${\mathrm{Ga}}_2{\mathrm{O}}_3$ films.

A fully analytical approach based on the equation of motion technique to investigate the spectral properties and orbital occupations in an interacting double quantum dot in equilibrium is presented. By solving a linear system for the density correlators analytically, an explicit expression for the one-body Green's function in terms of local occupations, intra- and interdot Coulomb interactions, and the model parameters is derived. In the uncontacted limit, the results coincide with those obtained from the grand canonical ensemble. The analytical results compare favorably with numerical results obtained with the noncrossing approximation and the hierarchical equation of motion methods accurately reproducing peak positions and spectral weight distributions in the Coulomb blockade regime.

Layered complex nitrides have emerged as a novel class of thermoelectric materials due to their unique geometrical and electronic structures. In this work, we employ density functional theory calculations combined with Boltzmann transport equation and thermal transport unified theory to explore the electrical and thermal transport properties and thermoelectric performance of layered nitrides ${AM\mathrm{N}}_2$ $(A=\mathrm{Sr}, \mathrm{Ba}; M=\mathrm{Ti}, \mathrm{Zr}, \mathrm{Hf})$. It is found that the ${AM\mathrm{N}}_2$ family exhibits a large Seebeck coefficient and high power factor, ascribed to its multiband degeneracy and the presence of unique two-dimensional (2D) electronic structure. As the atomic mass of M increases, the lattice thermal conductivity ${\kappa }_L$ decreases significantly. In particular, ${\mathrm{BaHfN}}_2$ demonstrates ultralow lattice thermal conductivity of 0.18 W/mK at room temperature. Even after accounting for both the particlelike propagation and wavelike phonon tunneling transport, ultralow ${\kappa }_L$ is found across a wide temperature range. The ultralow ${\kappa }_L$ is mainly attributed to the strong anharmonicity in ${\mathrm{BaHfN}}_2$ as reflected by the high phonon-phonon scattering rate and short phonon lifetime. Importantly, we find that $p$-type ${\mathrm{BaHfN}}_2$ exhibits a high figure of merit (ZT), achieving values of 2.19 at 300 K and 7.29 at 900 K, respectively. Additionally, through strain engineering, applying a moderate tensile stress of 0.5% remarkably increases the ZT of $p$-type increases to 2.58 at 300 K and reaches a maximum of 9.02 at 900 K, respectively. The present work unveils the importance of unique 2D electronic structures and strong anharmonicity induced by the weak-bonded heavy element on the thermoelectric performance, suggesting that the layered ${AM\mathrm{N}}_2$ family is a promising candidate for the development of high-performance thermoelectric devices.

Large exciton-polariton optical nonlinearities present a key mechanism for photonics-based communication, ultimately in the quantum regime. Enhanced nonlinear response from various materials hosting excitons and allowing for their strong coupling with light is therefore the topic of intense studies, both in theoretical and experimental domains. Reports on the scattering rates arising due to various system's nonlinearities, such as the exciton-exciton Coulomb interaction and the Pauli blocking that leads to the saturation of the exciton oscillator strength, however, are contradictory. In this work, we develop a formalism allowing to track the exciton nonlinearities appearing in the regime of strong coupling with photons, that includes finite temperatures, mixing of the exciton excited states, and the dark exciton contributions to saturation self-consistently. The equilibrium path integration approach employed here to address the polariton composite nature leads to a transparent hierarchy of various contributions to nonlinearity. At the same time, by taking the simplest limit of zero temperature and so-called “rigid” excitons, through our framework we retrieve the expressions derived in conventional approaches for exciton interaction constants. In particular, our theory allows to clearly show that such interaction constants cannot be used as fitting parameters tunable in a wide range of values, as they are strictly defined by the material properties, and that other explanations are due for large optical nonlinearities recently reported.

The excitonic effects play an important role in the optical response of two-dimensional (2D) magnetic semiconductors, which are crucial for identifying magnetic properties. Although diverse magnetic orders and corresponding appealing physical properties are reported in the emerging layered ${\text{Ni}X}_2$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$, the influence of magnetic order on excitonic effects remains unrevealed. Here, we employ the many-body GW plus Bethe-Salpeter equation method to conduct a comparative investigation of the electronic structure and optical properties of monolayer ${\mathrm{NiBr}}_2$ in ferromagnetic (FM) and antiferromagnetic (AFM) phases, focusing particularly on the excitons. For both FM and AFM phases, strong self-energy effects on the quasiparticle band structures are found, which are spin dependent owing to the localized nature of the $3d$ orbitals. Compared to the FM monolayer, the AFM spin configuration significantly changes the optical spectra and excitonic effects, affecting aspects such as the anisotropic response, intensity and location of absorption peaks, excitonic binding energy, spatial distribution of excitonic wave functions, as well as the dark excitons. Our work provides a theoretical understanding of the optical response in different magnetic phases, which is essential for developing magneto-optical and optoelectronic devices based on 2D magnetic semiconductors.

Topological optical states are promising in waveguiding, sensing, and information processing which are localized over the boundaries and robustly protected by the band topology. Topological phonon polaritons (TPhPs), as a special type of topological optical states, have been shown to play a vital role in modulating radiative heat transfer in many-particle systems. In this paper, we propose subwavelength lattices composed of identical SiC nanoparticles (NPs) which support phonon polaritons to mimic the 2D Su-Schrieffer-Heeger (SSH) model. By using the coupled-dipole model and taking all the near- and far-field dipole-dipole interactions into account, we numerically calculate the band structures of the NP arrays under periodic boundary conditions (PBCs) and study the topological properties of the NP arrays characterized by their 2D Zak phases. Subsequently, we confirm the existence of edge states and high-order corner states in the topologically nontrivial 2D SSH lattices under open boundary conditions (OBCs), which are protected by the nonzero 2D Zak phases and consistent with the bulk-edge-corner correspondence. The radiative heat transfer between certain NPs is calculated based on many-body radiative heat transfer theory. We demonstrate that these high-order TPhPs can considerably modulate long-range radiative heat transport by constructing the topological “heat guiding” systems made of NP arrays with different boundary conditions. Moreover, by decomposing the radiative heat flux into two parts according to the polarization directions of dipoles, we find that the high-order TPhPs play different roles in the in-plane and out-of-plane components. We further show the modulation effect can robustly exist in the topologically nontrivial lattice by introducing defects and disorders. Our study provides an in-depth understanding on the near-field radiative heat transfer in many-particle systems with high-order topological properties.