Evidence for the presence of high-energy magnetic excitations in overdoped ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (LSCO) has raised questions regarding the role of spin fluctuations in the pairing mechanism. If they remain present in overdoped LSCO, why does $T_c$ decrease in this doping regime? Here, using results for the dynamic spin susceptibility $\mathrm{Im}\chi (\mathit{q},\omega )$ obtained from a determinantal quantum Monte Carlo calculation for the Hubbard model, we address this question. We find that while high-energy magnetic excitations persist in the overdoped regime, they lack the momentum to scatter pairs between the antinodal regions. It is the decrease in the spectral weight at large momentum transfer, not observed by resonant inelastic x-ray scattering, which leads to a reduction in the $d$-wave spin-fluctuation pairing strength.

We report on the discovery and transport study of the superconducting ground state present at the (111)${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ (LAO/STO) interface. The superconducting transition is consistent with a Berezinskii-Kosterlitz-Thouless transition and its two-dimensional nature is further corroborated by the anisotropy of the critical magnetic field, as calculated by Tinkham. The estimated superconducting layer thickness and coherence length are 10 and $60\mathrm{nm}$, respectively. The results of this work provide insight to clarify the microscopic details of superconductivity in LAO/STO interfaces, in particular in what concerns the link with orbital symmetry.

To clarify the nature of the transformation in liquid iodine, which is reported to occur at around 4 GPa, we have conducted x-ray absorption fine structure (XAFS) and x-ray diffraction (XRD) measurements up to 9 GPa. In the XAFS spectra, the oscillation attributable to the molecular bond persisted to 9 GPa but showed a significant decay above 4–5 GPa. Similarly, in the pair-distribution function obtained from XRD profiles, the peak assigned to the molecular bond persisted to 9 GPa but showed a significant broadening above 4–5 GPa. While the volume contracts significantly (more than $30\%$), the molecular bond expands by about $5\%$ with increasing pressure between 1 and 9 GPa. Detailed analyses, with the aid of Reverse Monte Carlo modeling techniques, clarify that the transformation may be characterized by the onset (or drastic increase in the probability) of rebonding among adjacent molecules and the change in electronic state (possibly metallization) without molecular dissociation.

We examine the thermodynamic stability of compounds and alloys in the ternary B-As-P system theoretically using first-principles calculations. We demonstrate that the icosahedral ${\mathrm{B}}_{12}{\mathrm{As}}_2$ is the only stable compound in the binary B-As system, while the zinc-blende BAs is thermodynamically unstable with respect to ${\mathrm{B}}_{12}{\mathrm{As}}_2$ and the pure arsenic phase at 0 K, and increasingly so at higher temperature, suggesting that BAs may merely exist as a metastable phase. On the contrary, in the binary B-P system, both zinc-blende BP and icosahedral ${\mathrm{B}}_{12}{\mathrm{P}}_2$ are predicted to be stable. As for the binary As-P system, ${\mathrm{As}}_{1-x}{\mathrm{P}}_x$ disordered alloys are predicted at elevated temperature—for example, a disordered solid solution of up to $\sim 75$ at.% As in black phosphorus as well as a small solubility of $\sim 1$ at.% P in gray arsenic at $T=750$ K, together with the presence of miscibility gaps. The calculated large solubility of As in black phosphorus explains the experimental syntheses of black-phosphorus-type ${\mathrm{As}}_{1-x}{\mathrm{P}}_x$ alloys with tunable compositions, recently reported in the literature. We investigate the phase stabilities in the ternary B-As-P system and demonstrate a high tendency for a formation of alloys in the icosahedral ${\mathrm{B}}_{12}$(${\mathrm{As}}_{1-x}{\mathrm{P}}_x$)${}_2$ structure by intermixing of As and P atoms at the diatomic chain sites. The phase diagram displays noticeable mutual solubility of the icosahedral subpnictides in each other even at room temperature as well as a closure of a pseudobinary miscibility gap around 900 K. As for pseudobinary ${\mathrm{BAs}}_{1-x}{\mathrm{P}}_x$ alloys, only a tiny amount of BAs is predicted to be able to dissolve in BP to form the ${\mathrm{BAs}}_{1-x}{\mathrm{P}}_x$ disordered alloys at elevated temperature. For example, less than 5% of BAs can dissolve in BP at $T=1000$ K. The small solubility limit of BAs in BP is attributed to the thermodynamic instability of BAs with respect to ${\mathrm{B}}_{12}{\mathrm{As}}_2$ and As.

We image the remnant magnetization configurations of CoFeB and permalloy nanotubes (NTs) using x-ray magnetic circular dichroism photoemission electron microscopy. The images provide direct evidence for flux-closure configurations, including a global vortex state, in which magnetization points circumferentially around the NT axis. Furthermore, micromagnetic simulations predict and measurements confirm that vortex states can be programmed as the equilibrium remnant magnetization configurations by reducing the ratio of the NT's length and diameter.

A conventional superconductor with spin-orbit coupling turns into a topological superconductor beyond a critical strength of the Zeeman energy. The spin-expectation values $\mathit{S}\left(\mathit{k}\right)$ in momentum space trace this transition via a characteristic change in the topological character of the spin texture within the Brillouin zone. At the transition the skyrmion counting number switches from 0 to 1/2 identifying the topological superconductor via its meron-like spin texture. The change in the skyrmion counting number is crucially controlled by singular points of the map $\mathit{S}\left(\mathit{k}\right)/\left|\mathit{S}\right(\mathit{k}\left)\right|$ from the Brillouin zone, i.e., a torus, to the unit sphere. The complexity of this spin map is discussed at zero temperature as well as for the extension to finite temperatures.

One-dimensional (1D) conductors such as Bechgaard and Fabre salts are a prototypal example of correlated systems where the phase diagram is controlled by sizable electron-electron repulsions. In deuterated ${\left(\mathrm{TMTTF}\right)}_2\mathrm{P}{\mathrm{F}}_6$, where this interaction achieves charge localization at ambient pressure on donor stacks, magnetostructural coupling plays a decisive role to stabilize a spin-Peierls (SPs) ground state at $T_{\mathrm{SP}}=13\mathrm{K}$. In this paper, we present the first inelastic neutron scattering investigation of SP magnetic excitations in organics. Our paper reveals the presence above $T_{\mathrm{SP}}$ of sizable critical fluctuations leading to the formation of a pseudogap in the 1D antiferromagnetic (AF) $S=1/2$ magnetic excitation spectrum of the donor stack, concomitant with the local formation of singlet of paired spins into dimers below $T_{\mathrm{SP}}^{\mathrm{MF}}\approx 40\mathrm{K}$. In addition, the inelastic neutron scattering investigation allows us also to probe the SP critical lattice dynamics and to show that at ambient pressure these dynamics are of relaxation or order-disorder type. Below $T_{\mathrm{SP}}$, our paper reveals the emergence of a two gap SP magnetic excitation spectrum towards a well-defined $S=1$ magnon mode and a continuum of two excitations, as theoretically predicted. Our measurements allow us to locate the ambient pressure SP phase of ${\left(\mathrm{TMTTF}\right)}_2\mathrm{P}{\mathrm{F}}_6$ in the classical (adiabatic) limit close to the classical/quantum crossover line. Then we provide arguments suggesting that pressurized ${\left(\mathrm{TMTTF}\right)}_2\mathrm{P}{\mathrm{F}}_6$ shifts to the quantum (antiadiabatic) SP gapped phase, which ends in a quantum critical point allowing the stabilization of an AF phase that competes with superconductivity at higher pressure. Finally, we propose that the magnetostructural coupling mechanism in the Fabre salts is caused by dimer charge/spin fluctuations driven by the coupling of donors with anions.

We study interacting Majorana fermions in two dimensions as a low-energy effective model of a vortex lattice in two-dimensional time-reversal-invariant topological superconductors. For that purpose, we implement ab initio quantum Monte Carlo simulation to the Majorana fermion system in which the path-integral measure is given by a semipositive Pfaffian. We discuss spontaneous breaking of time-reversal symmetry at finite temperatures.

An analytical theory, based on the perturbative treatment of the disorder and extended into a self-consistent set of equations for the dynamical density correlations, is developed and applied to the prototype one-dimensional model of many-body localization. Results show a qualitative agreement with the numerically obtained dynamical structure factor in the whole range of frequencies and wave vectors, as well as across the transition to nonergodic behavior. The theory reveals the singular nature of the one-dimensional problem, whereby on the ergodic side the dynamics is subdiffusive with dynamical conductivity $\sigma \left(\omega \right)\propto {\left|\omega \right|}^{\alpha }$, i.e., with vanishing dc limit ${\sigma }_0=0$ and $\alpha <1$ varying with disorder, while we get $\alpha >1$ in the localized phase.

The electronic and structural properties of excitons and trions in monolayer transition metal dichalcogenides are investigated using both a multiband and a single-band model. In the multiband model we construct the excitonic Hamiltonian in the product base of the single-particle states at the conduction and valence band edges. We decouple the corresponding energy eigenvalue equation and solve the resulting differential equation self-consistently, using the finite element method (FEM), to determine the energy eigenvalues and the wave functions. As a comparison, we also consider the simple single-band model which is often used in numerical studies. We solve the energy eigenvalue equation using the FEM as well as with the stochastic variational method (SVM) in which a variational wave function is expanded in a basis of a large number of correlated Gaussians. We find good agreement between the results of both methods, as well as with other theoretical works for excitons, and we also compare with available experimental data. For trions the agreement between both methods is not as good due to our neglect of angular correlations when using the FEM. Finally, when comparing the two models, we see that the presence of the valence bands in the mutiband model leads to differences with the single-band model when (interband) interactions are strong.

The bulk ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Co}}_2{\mathrm{O}}_8$ crystal is an insulator at low temperature and experiences an insulator-metal transition at $T_C\approx 60\mathrm{K}$. The new experiment showed that $T_C$ increases to 140 K for a mechanically exfoliated nanosheet of four blocks and is beyond room temperature for nanosheets thinner than four blocks. We show that the thickness-dependent insulator-metal transition observed in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Co}}_2{\mathrm{O}}_8$ nanosheets can naturally be explained by the strongly correlated low-spin-state insulator (LS state) and intermediate-spin-low-spin-state metal (IS-LS state). In particular, the energy difference between the LS state and IS-LS state qualitatively reproduces the trend of the transition temperature with the nanosheet thickness. The predicted transition temperature of a nanosheet with three blocks is only slightly above room temperature, a result that can be used to check our proposed mechanism. Further experiments on the distinct magnetotransport properties and spin-fluctuation behaviors of the LS state and IS-LS state are also very helpful to resolve the issue. The weak interblock binding is also consistent with the layer-resolved partial densities of states.

We study the sticking rate of atomic hydrogen to suspended graphene using four different methods that include contributions from processes with multiphonon emission. We compare the numerical results of the sticking rate obtained by: (i) the loop expansion of the atom self-energy; (ii) the noncrossing approximation (NCA); (iii) the independent boson model approximation (IBMA); and (iv) a leading-order soft-phonon resummation method (SPR). The loop expansion reveals an infrared problem, analogous to the infamous infrared problem in QED. The two-loop contribution to the sticking rate gives a result that tends to diverge for large membranes. The latter three methods remedy this infrared problem and give results that are finite in the limit of an infinite membrane. We find that for micromembranes (sizes ranging 100 nm to $10\mu \mathrm{m})$, the latter three methods give results that are in good agreement with each other and yield sticking rates that are mildly suppressed relative to the lowest-order golden rule rate. Lastly, we find that the SPR sticking rate decreases slowly to zero with increasing membrane size, while both the NCA and IBMA rates tend to a nonzero constant in this limit. Thus, approximations to the sticking rate can be sensitive to the effects of soft-phonon emission for large membranes.

We develop a microscopic formulation of dynamical spin injection in heterostructure comprising nonmagnetic metals in contact with ferromagnets. The spin pumping current is expressed in terms of Green's functions of the nonmagnetic metal attached to the ferromagnet where a precessing magnetization is induced. The formulation allows for the inclusion of spin-orbit coupling and disorder. The Green's functions involved in the expression for the current are expressed in real-space lattice coordinates and can thus be efficiently computed using recursive methods.

A quantum phase transition is an unequivocal signature of strongly correlated many-body physics. Signatures of such phenomena are yet to be observed in ballistic transport through quantum wires. Recent developments in quantum wires have made it possible to enhance the interaction between the electrons. Here we show that hitherto unexplained anticrossing between conduction energy subbands, observed in such experiments, can be explained through a simple yet effective discretized model which undergoes a second-order quantum phase transition within the Ising universality class. Accordingly, we observe how the charge distribution, transverse to the direction of the wire, will vary across the phase transition. We show that data coming from three different samples with differing electron densities and gate voltages show a remarkable universal scaling behavior, determined by the relevant critical exponent, which is only possible near a quantum phase transition.

The repulsion between free electrons inside a metal makes its optical response spatially dispersive, so that it is not described by Drude's model but by a hydrodynamic model. We give here fully analytic results for a metallic slab in this framework, thanks to a two-mode cavity formalism leading to a Fabry-Perot formula, and show that a simplification can be made that preserves the accuracy of the results while allowing much simpler analytic expressions. For metallic layers thicker than 2.7 nm modified Fresnel coefficients can actually be used to accurately predict the response of any multilayer with spatially dispersive metals (for reflection, transmission, or the guided modes). Finally, this explains why adding a small dielectric layer [Y. Luo et al., Phys. Rev. Lett. 111, 093901 (2013)] allows one to reproduce the effects of nonlocality in many cases, and especially for multilayers.

By using a state-of-the-art tensor network state method, we study the ground-state phase diagram of an extended Bose-Hubbard model on the square lattice with frustrated next-nearest-neighbor tunneling. In the hard-core limit, tunneling frustration stabilizes a peculiar half-supersolid phase with one sublattice being superfluid and the other sublattice being Mott insulator away from half filling. In the soft-core case, the model shows very rich phase diagrams above half filling, including three different types of supersolid phases depending on the interaction parameters. The considered model provides a promising route to experimentally search for a novel stable supersolid state induced by frustrated tunneling in the region below half filling with dipolar atoms or molecules.

We study the temperature dependence of the optical conductivity of rare-earth nickelate films of varying composition and strain close to the antiferromagnetic ordering temperature, $T_N$. Two prominent peaks at 0.6 and 1.3 eV, which are characteristic of the insulating phase, display a small but significant increase in intensity when the material passes from para- to antiferromagnetic. This observation indicates the presence of a positive feedback between antiferromagnetic (AF) and bond disproportionation (BD) order. By analyzing the temperature dependence near $T_N$, and using a Landau-type free-energy expression for BD and AF order, we infer that BD order is a necessary condition for the AF phase to appear, and that the antiferromagnetism contributes to stabilization of the bond disproportionation. This model also explains why hysteresis is particularly strong when the transition into the insulating state occurs simultaneously with antiferromagnetic order.