The investigation of the thermal properties of recently emerged two-dimensional materials is a necessary step towards fulfilling their potential applications in nanoelectronics devices. In this study, the thermal conductivities $\mathrm{of}\beta \text{−}\mathrm{N}X\left(X=\mathrm{P},\mathrm{As},\mathrm{Sb}\right)$ monolayers are investigated using a first-principles density-functional theory approach based on the full solution of the linearized Peierls-Boltzmann transport equation. The results show that the room-temperature thermal conductivities of $\beta$-NP, $\beta$-NAs, and $\beta$-NSb are about 1.1, 5.5, and 34.0 times higher than those of their single-element $\beta$-P, $\beta$-As, and $\beta$-Sb monolayers, respectively. The phonon transport analysis reveals that higher phonon group velocities, as well as higher phonon lifetimes, are responsible for such an enhancement in the lattice thermal conductivities of $\beta \text{−}\mathrm{N}X$ binary compounds compared to their single-element group-VA monolayers. We found that $\beta$-NP has the minimum thermal conductivity among $\beta \text{−}\mathrm{N}X$ monolayers, while it has the minimum average atomic mass, which is in contrast with the common assumption that lower-mass systems exhibit higher thermal conductivities. This work demonstrates the tradeoff between harmonic and anharmonic phonon properties in determining the variation of the thermal conductivity among $\beta \text{−}\mathrm{N}X$ monolayers. The higher anharmonicity in $\beta$-NP is found to be responsible for the lower thermal conductivity of this monolayer.

We report the infrared transmission measurement on electrically gated twisted bilayer graphene. The optical absorption spectrum clearly manifests dramatic changes such as the splitting of the interlinear-band absorption step, the shift of the inter-van Hove singularity transition peak, and the emergence of a very strong intravalence (intraconduction) band transition. These anomalous optical behaviors demonstrate consistently a nonrigid band structure modification created by ion-gel gating through layer-dependent Coulomb screening. We propose that this screening-driven band modification is a universal phenomenon that persists to other bilayer crystals in general, establishing electrical gating as a versatile technique to engineer band structures and to create different types of optical absorptions that can be exploited in electro-optical device applications.

The impact of local and nonlocal density-density interactions on the electronic instabilities in the honeycomb lattice is widely investigated. Some early studies proposed the emergence of interaction-induced topologically nontrivial phases, but recently, it was denied in several works including renormalization group calculations with refined momentum resolution. We use the truncated unity functional renormalization group to study the many-body instabilities of electrons on the half-filled honeycomb lattice, focusing on the effect of the exchange interaction. We show that varying the next-nearest-neighbor repulsion and nearest-neighbor exchange integral can lead to diverse ordered phases, namely, the quantum spin Hall, the spin-Kekulé, and some spin- and charge-density-wave phases. The quantum spin Hall phase can be induced by a combination of the ferromagnetic exchange and pair hopping interactions. Another exotic phase, the spin-Kekulé phase, develops in a very small region of the parameter space considered. We encounter the three-sublattice charge-density-wave phase in a large part of the parameter space. It is replaced by the incommensurate charge density wave when increasing the exchange integral. In order to reduce the computational effort, we derive the explicit symmetry relations for the bosonic propagators of the effective interaction and propose a linear-response-based approach for identifying the form factor of order parameter. Their efficiencies are confirmed by numerical calculations in our work.

We study the transport and magnetic properties of hydrated and lithium-intercalated $\alpha \text{−}{\mathrm{RuCl}}_3,{\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}$, to investigate the effect on mobile-carrier doping into candidate materials for a realization of a Kitaev model. From thermogravimetric and one-dimensional electron map analyses, we find two crystal structures of this system, that is, monolayer hydrated ${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}(x\approx 0.56,y\approx 1.3)$ and bilayer hydrated ${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}(x\approx 0.56,y\approx 3.9)$. The temperature dependence of the electrical resistivity shows a temperature hysteresis at 200–270 K, which is considered to relate to the formation of a charge order. The antiferromagnetic order at 7–13 K in pristine $\alpha \text{−}{\mathrm{RuCl}}_3$ is successfully suppressed down to 2 K in bilayer hydrated ${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}$, which is sensitive to not only the electronic state of Ru but also the interlayer distance between Ru-Cl planes.

Existing schemes for semiconductor spin qubit readout involve either spin-to-charge conversion or electric dipole coupling to a superconducting resonator. The former requires destructive readout while the latter suffers from enhanced qubit dephasing, limiting the potential performance of quantum measurement: an open challenge in semiconductor quantum computing. Here we propose a coupling to a superconducting resonator based on qubit energy curvature versus gate voltage, which enables quantum nondemolition (QND) readout while the qubit resides in its full sweet spot and with zero dipole coupling (offering resilience to charge noise). Readout strengths of tens to hundred megahertz (MHz) can be reached, at least ten times larger than in the previously proposed schemes. We show how this curvature interaction generates two strictly QND readout approaches: (i) via a “dispersive-like” (quantum capacitance) spin-dependent resonator energy shift, similar in implementation to circuit-QED dispersive readout, but avoiding the Purcell effect; and (ii) with the addition of qubit gate voltage modulation, a longitudinal readout which can be selectively switched on, for a chosen n-qubit subsystem. Neither scheme requires the qubit and resonator to be close in frequency.

In dynamical and acoustical systems, breaking reciprocity is achievable by employing external biases, spatial temporal variations of material properties, or nonlinearities. In this present work, we propose, theoretically analyze, and experimentally demonstrate the first passive broad-band mechanical diode, by adding an asymmetric local nonlinear interface to an otherwise linear waveguide. It is shown that for a broad range of input energies and frequencies, three different types of nonreciprocal behavior are obtained, (i) different transmitted energies depending on the direction of wave propagation, (ii) transmission of acoustic waves allowed in one direction but not in the reverse direction, and (iii) arrest of propagating waves at the nonlinear interface only in one (preferred) direction. A unique feature of the proposed acoustic device compared with previous designs is its capability to achieve passive nonreciprocity without altering or distorting the frequency content of the sending signal. The proposed system can pave the way for designing passive acoustic or thermal diodes, and adaptable nonreciprocal wave transmission devices of enhanced robustness that are tunable with, and passively adaptive to energy.

Polar lacunar spinels, such as $\mathrm{Ga}{\mathrm{V}}_4{\mathrm{S}}_8$ and $\mathrm{Ga}{\mathrm{V}}_4\mathrm{S}{\mathrm{e}}_8$, were proposed to host skyrmion phases under magnetic field. In this work, we put forward, as a candidate for Néel-type skyrmion lattice, the isostructural $\mathrm{GaM}{\mathrm{o}}_4{\mathrm{S}}_8$, which is systematically studied via both first-principles calculations and Monte Carlo simulations of a model Hamiltonian. Electric polarization, driven by the Jahn-Teller distortion, is predicted to arise in $\mathrm{GaM}{\mathrm{o}}_4{\mathrm{S}}_8$, showing a comparable size but an opposite sign with respect to that evaluated in V-based counterparts and explained in terms of different electron counting arguments and resulting distortions. Interestingly, a larger spin-orbit coupling of $4d$ orbitals with respect to $3d$ orbitals in vanadium spinels leads to stronger Dzyaloshinskii-Moriya interactions, which are beneficial to stabilize a cycloidal spin texture, as well as smaller-sized skyrmions $\left(\mathrm{radius}<10\mathrm{nm}\right)$. Furthermore, the possibly large exchange anisotropy of $\mathrm{GaM}{\mathrm{o}}_4{\mathrm{S}}_8$ may lead to a ferroelectric-ferromagnetic ground state as an alternative to the ferroelectric-skyrmionic one, thus calling for further experimental verification.

Recent research discovered that charge-transfer processes in chiral molecules can be spin-selective, and the effect was named chiral-induced spin selectivity (CISS). Follow-up work studied hybrid spintronic devices with conventional electronic materials and chiral (bio)molecules. However, a theoretical foundation for the CISS effect is still in development, and the spintronic signals were not evaluated quantitatively. We present a circuit-model approach that can provide quantitative evaluations. Our analysis assumes the scheme of a recent experiment that used photosystem I (PSI) as spin injectors, for which we find that the experimentally observed signals are, under any reasonable assumptions on relevant PSI timescales, too high to be fully due to the CISS effect. We also show that the CISS effect can in principle be detected using the same type of solid-state device, and by replacing silver with graphene, the signals due to spin generation can be enlarged four orders of magnitude. Our approach thus provides a generic framework for analyzing these types of experiments and advancing the understanding of the CISS effect.

Nonreciprocity of spin-wave propagation is a well-known consequence of antisymmetric exchange contributions in magnetic spin systems that lack inversion symmetry. In this case, the energy of a state depends on the sign of its momentum as $ħ\omega \left(k\right)\ne ħ\omega \left(-k\right)$. We discuss here the consequences of this nonreciprocity on counterpropagating traveling spin-wave states. In a confined geometry we find states with well-defined nodes which are inherently phase modulated such that space-inversion symmetry of the mode profile is lost. This entails that additional spectral features become visible in ferromagnetic resonance studies of microelements with Dzyaloshinskii-Moriya interaction (DMI), allowing a quantification of the amplitude and direction of the DMI. Moreover, this interference between nonreciprocal modes forms the basis for a generalized concept of mode confinement.

We have combined high sensitivity, extra-low differential temperature scanning rate calorimetry, and acoustic emission (AE) measurements to study avalanches during the cubic ↔ 18R martensitic transition of a Cu-Al-Be single crystalline shape memory alloy. Both AE and calorimetry corroborate a good power-law behavior for cooling with an exponent $\varepsilon \simeq 1.6$. For heating, a slope is observed in the maximum likelihood curves, which confirms that our data are affected by an exponential cutoff. An effective energy exponent, $\varepsilon \sim 1.85$, and a cutoff, ${\lambda }^{-1}=0.115\left(38\right)\times {10}^{-3}\mathrm{aJ}$, were determined by fits of power-laws with exponential damping. The long tail observed in the low-temperature region by calorimetric measurements suggests the existence of significant elastic effects that constrain the progress of the transformation at low temperatures. While thermodynamic features such as transformation enthalpy and entropy are those expected for Cu-based shape-memory alloys undergoing a cubic ↔ 18R transition, the critical behavior deviates from the corresponding behavior expected from this symmetry change. These deviations are a consequence of the elastic hardening induced by the interplay of the transformation with dislocation jamming, which has the effect of effectively reducing the number of pathways connecting the parent and martensitic phase.

Single-crystal elastic moduli $C_{ij}$, shear modulus $G$, and Zener anisotropic ratio $A$ of solid argon having the face-centered cubic (fcc) structure were determined at high pressures between 12 and 64 GPa using a combination of experimental and theoretical approaches. The experimental data, namely, the maximal and minimal values of the product of the longitudinal sound velocity and refractive index $n·V_L$, were obtained from the 3D scanning of elastic inhomogeneities in compressed samples of argon using the technique of time-domain Brillouin scattering. These inhomogeneities, caused by elastic anisotropy of solid argon, were revealed to be about twice as strong as those reported in the earlier experiments using classical Brillouin light scattering (BLS). To derive the $V_L$ values, we used the refractive index obtained here from ab initio calculations which also permitted us to rule out any contribution to the amplitude of the observed elastic inhomogeneities of the hexagonal close-packed phase of argon, proposed to coexist with the fcc phase at high pressures. From the measured $C_{ij}\left(P\right)$, we derived pressure dependence of shear modulus of the fcc argon $G_H\left(P\right)$ using the Voigt-Reuss-Hill approximation and found a very good agreement with the earlier $G\left(P\right)$ obtained from shear sound velocities in the classical BLS measurements. Our results agree very well with the earlier predictions based on a relatively simple many-body model employing the Buckingham pair potential. Finally, our measurements show a much weaker change of the Cauchy discrepancy $(C_{12}-C_{44}-2P)$ of the fcc argon with pressure than reported in all earlier experimental and theoretical works.

We introduce microscopic polarization and magnetization fields at each site of an extended system, as well as free charge and current density fields associated with charge movement from site to site, by employing a lattice gauge approach based on a set of orthogonal orbitals associated with each site. These microscopic fields are defined using a single-particle electron Green function, and the equations governing its evolution under excitation by an electromagnetic field at arbitrary frequency involve the electric and magnetic fields rather than the scalar and vector potentials. If the sites are taken to be far from each other, we recover the limit of isolated atoms. For an infinite crystal, we choose the orbitals to be maximally localized Wannier functions, and in the long-wavelength limit we recover the expected linear response of an insulator, including the zero frequency transverse conductivity of a topologically nontrivial insulator. For a topologically trivial insulator, we recover the expected expressions for the macroscopic polarization and magnetization in the ground state and find that the linear response to excitation at arbitrary frequency is described solely by the microscopic polarization and magnetization fields. For very general optical response calculations, the microscopic fields necessarily satisfy charge conservation, even under basis truncation, and do not suffer from the false divergences at zero frequency that can plague response calculations using other approaches.

Trial wave functions such as the Moore-Read and Read-Rezayi states, which minimize short-range multibody interactions, are candidate states for describing the fractional quantum Hall effects at filling factors $\nu =1/2$ and $2/5$ in the second Landau level. These trial wave functions are unique zero-energy states of three-body and four-body interaction Hamiltonians, respectively, but they are not close to the ground states of the Coulomb interaction. Previous studies using extensive parameter scans have found optimal two-body interactions on the sphere that produce states close to these. Here we focus on short-ranged four-body interaction and study two mean-field approximations that reduce the four-body interactions to two-body interactions on the sphere by replacing composite operators with their incompressible ground-state expectation values. We present the results for pseudopotentials of these approximate interactions. A comparison of finite system spectra on the sphere of the four-body and the approximate interactions at filling fraction $\nu =3/5$ shows that these approximations produce good effective descriptions of the low-energy structure of the four-body interaction Hamiltonian. The approach also independently reproduces the optimal two-body interaction inferred from parameter scans. We also show that for $n=3$, but not for $n=4$, the mean-field approximations of the $n$-body interaction are equivalent to particle-hole symmetrization of the interaction. Within the system sizes accessible, analysis of the spectrum of the mean-field two-body Hamiltonian on the torus was inconclusive, and indicates a competing anisotropic state in the system.

In the study of strongly correlated, many-electron systems, the Hubbard-Kanamori (HK) model has emerged as one of the prototypes for transition metal oxide physics. The model is multiband in nature and contains Hund's coupling terms, which have pronounced effects on metal-insulator transitions, high-temperature superconductivity, and other physical properties. In the following, we present a complete theoretical framework for treating the HK model using the ground-state auxiliary field quantum Monte Carlo (AFQMC) method and analyze its performance on few-band models whose parameters approximate those observed in ruthenates, rhodates, and other materials exhibiting Hund's physics. Unlike previous studies, the constrained path and phaseless approximations are used to respectively control the sign and phase problems, which enables high-accuracy modeling of the HK model's ground-state properties within parameter regimes of experimental interest. We demonstrate that, after careful consideration of the Hubbard-Stratonovich transformations and trial wave functions employed, relative errors in the energy of less than $1\%$ can routinely be achieved for moderate to large values of the Hund's coupling constant. Crucially, our methodology also accurately predicts magnetic ordering and phase transitions. The results presented open the door to more predictive modeling of Hund's physics within a wide range of strongly correlated materials using AFQMC.

We study the heat conductance of hybrid superconducting junctions. Our analysis involves single-channel junctions with arbitrary transmission as well as diffusive connectors and shows the influence of the superconducting gaps and phases of the contacts on the heat conductance. If the junction is diffusive, these effects are completely quenched on average, however, we find that their influence persists in weak-localization corrections and conductance fluctuations. While these statistical properties strongly deviate from the well-known analogs for the charge conductance, we demonstrate that the heat conductance fluctuations maintain a close to universal behavior. We find a generalized Wiedemann-Franz law for Josephson junctions with equal gaps and vanishing phase difference.

The recent development in topological photonics has revealed a variety of exotic phenomena such as Weyl degeneracy. However, a Weyl nodal surface, a two-dimensional topological degeneracy, has not been reported in Hermitian photonics. In this paper, topologically nontrivial photonic nodal surface in a helix structure possessing twofold screw symmetry and time-reversal symmetry is demonstrated. In contrast to nodal surfaces in other wave systems in which topological phase depends on the system parameters such as coupling strength, nontrivial topological properties of nodal surface in our work are guaranteed by effective photonic properties. Calculated Chern number, Berry curvature, and photonic Fermi arcs support the existence of nontrivial topological phase of the nodal surface. This work suggests the possibilities of many intriguing photonic topological features with nonzero dimensions.

In time-resolved photoemission experiments, more than one electron can be emitted from the solid by a single ultrashort pulse. We theoretically demonstrate how correlations between the momenta of outgoing electrons relate to time-dependent two-particle correlations in the solid. This can extend the scope of time- and angle-resolved photoemission spectroscopy to probe superconducting and charge density fluctuations in systems without long-range order, and to reveal their dynamics independent of the electronic gap and thus unrestricted by the energy-time uncertainty. The proposal is illustrated for superconductivity in a BCS model. An impulsive perturbation can quench the gap on ultrafast timescales, while nonequilibrium pairing correlations persist much longer, even when electron-electron scattering beyond mean-field theory is taken into account. There is thus a clear distinction between a dephasing of the Cooper pairs and the thermalization into the normal state. While a measurement of the gap would be blind to such pairing correlations, they can be revealed by the angular correlations in photoemission.