Recent quantum-gas microscopy of ultracold atoms and scanning tunneling microscopy of the cuprates reveal new detailed information about doped Mott antiferromagnets, which can be compared with calculations. Using cellular dynamical mean-field theory, we map out the antiferromagnetic (AF) phase of the two-dimensional Hubbard model as a function of interaction strength $U$, hole doping $\delta$, and temperature $T$. The Néel phase boundary is nonmonotonic as a function of $U$ and $\delta$. Frustration induced by second-neighbor hopping reduces Néel order more effectively at small $U$. The doped AF is stabilized at large $U$ by kinetic energy and at small $U$ by potential energy. The transition between the AF insulator and the doped metallic AF is continuous. At large $U$, we find in-gap states similar to those observed in scanning tunneling microscopy. We predict that, contrary to the Hubbard bands, these states are only slightly spin polarized.

In typical conditions of the observation of multiple paramagnetic Raman resonance in model heterostructures containing manganese ions, we observed a never-reported series of Raman peaks, showing up in a narrow range of applied magnetic fields. These weak “fractional” peaks are located close to the middle between the strong “integer” Mn spin-flip peaks, and they reveal a remarkably weak dependence of the intensity on the peak number, in a pronounced contrast with the “integer” series. We discuss conditions to observe the “fractional” series as well as pathways for further exploration of the effect.

The success of polynomial-time tensor network methods for computing ground states of certain quantum local Hamiltonians has recently been given a sound theoretical basis by Arad et al. [Math. Phys. 356, 65 (2017)]. The convergence proof, however, relies on “rigorous renormalization group” (RRG) techniques which differ fundamentally from existing algorithms. We introduce a practical adaptation of the RRG procedure which, while no longer theoretically guaranteed to converge, finds matrix product state ansatz approximations to the ground spaces and low-lying excited spectra of local Hamiltonians in realistic situations. In contrast to other schemes, RRG does not utilize variational methods on tensor networks. Rather, it operates on subsets of the system Hilbert space by constructing approximations to the global ground space in a treelike manner. We evaluate the algorithm numerically, finding similar performance to density matrix renormalization group (DMRG) in the case of a gapped nondegenerate Hamiltonian. Even in challenging situations of criticality, large ground-state degeneracy, or long-range entanglement, RRG remains able to identify candidate states having large overlap with ground and low-energy eigenstates, outperforming DMRG in some cases.

Using density functional theory calculations, we have found an enhanced magneto-optical Kerr effect in Fe/insulator interfaces. The results of our study indicate that interfacial Fe atoms in the Fe films have a low-dimensional nature, which causes the following two effects: (i) The diagonal component ${\sigma }_{xx}$ of the optical conductivity decreases dramatically because the hopping integral for electrons between Fe atoms is suppressed by the low dimensionality. (ii) The off-diagonal component ${\sigma }_{xy}$ of the optical conductivity does not change at low photon energies, but it is enhanced at photon energies around 2 eV, where we obtain enhanced orbital magnetic moments and spin-orbit correlations for the interfacial Fe atoms. A large Kerr angle develops in proportion to the ratio ${\sigma }_{xy}/{\sigma }_{xx}$. Our findings indicate an efficient way to enhance the effect of spin-orbit coupling at metal/insulator interfaces without using heavy elements.

In the framework of Keldysh-Usadel kinetic theory, we study the temperature dependence of flux-flow conductivity (FFC) in diffusive superconductors. By using self-consistent vortex solutions we find the exact values of dimensionless parameters that determine the diffusion-controlled FFC both in the limit of the low temperatures and close to the critical one. Taking into account the electron-phonon scattering, we study the transition between flux-flow regimes controlled by either the diffusion or the inelastic relaxation of nonequilibrium quasiparticles. We demonstrate that the inelastic electron-phonon relaxation leads to the strong suppression of FFC compared to the previous estimates, making it possible to obtain numerical agreement with experimental results.

We report an unambiguous phonon resonance effect originating from germanium nanoparticles embedded in silicon matrix. Our approach features the combination of the phonon wave-packet method with atomistic dynamics and the finite element method rooted in continuum theory. We find that multimodal phonon resonance, caused by destructive interference of coherent lattice waves propagating through and around the nanoparticle, gives rise to sharp and significant transmittance dips, blocking the lower-end frequency range of phonon transport that is hardly diminished by other nanostructures. The resonance is sensitive to the phonon coherent length, where the finiteness of the wave-packet width weakens the transmittance dip even when coherent length is longer than the particle diameter. Further strengthening of transmittance dips is possible by arraying multiple nanoparticles, which gives rise to the collective vibrational mode. Finally, it is demonstrated that these resonance effects can significantly reduce thermal conductance in the lower-end frequency range.

We derive a dynamical equation that describes the exact time evolution in generic (inhomogeneous) noninteracting spin-chain models. Assuming quasistationarity, we develop a (generalized) hydrodynamic theory. The question at hand is whether some large-time corrections are captured by higher-order hydrodynamics. We consider in particular the dynamics after two chains, prepared in different conditions, are joined together. In these situations, a light cone, separating regions with macroscopically different properties, emerges from the junction. In free fermionic systems some observables close to the light cone follow a universal behavior, known as Tracy-Widom scaling. Universality means a weak dependence on the system's details, so this is the perfect setting where hydrodynamics could emerge. For the transverse-field Ising chain and the $XX$ model, we show that hydrodynamics captures the scaling behavior close to the light cone. On the other hand, our numerical analysis suggests that hydrodynamics fails in more general models, whenever a condition is not satisfied.

We consider a closed chain of an even number of Majorana zero modes with nearest-neighbor couplings which are different site by site generically, thus having no crystal symmetry. Instead, we demonstrate the possibility of an emergent supersymmetry (SUSY), which is accompanied by gapless fermionic excitations. In particular, the condition can be easily satisfied by tuning only one coupling, regardless of how many other couplings are there. Such a system can be realized by four Majorana modes on two parallel Majorana nanowires with their ends connected by Josephson junctions and their bodies connected by an external superconducting ring. By tuning the Josephson couplings with a magnetic flux $\mathrm{\Phi }$ through the ring, we get the gapless excitations at ${\mathrm{\Phi }}_{\mathrm{SUSY}}=\pm f{\mathrm{\Phi }}_0$ with ${\mathrm{\Phi }}_0=hc/2e$, which is signaled by a zero-bias conductance peak in tunneling conductance. We find this $f$ generally a fractional number and oscillating with increasing Zeeman fields that parallel to the nanowires, which provide a unique experimental signature for the existence of Majorana modes.

Magnetic field driven domain wall velocities in [Co/Ni] based multilayers thin films have been measured using polar magneto-optic Kerr effect microscopy. The low field results are shown to be consistent with the universal creep regime of domain wall motion, characterized by a stretched exponential growth of the velocity with the inverse of the applied field. Approaching the depinning field from below results in an unexpected excess velocity with respect to the creep law. We analyze these results using scaling theory to show that this speeding up of domain wall motion can be interpreted as due to the increase of the size of the deterministic relaxation close to the depinning transition. We propose a phenomenological model to accurately fit the observed excess velocity and to obtain characteristic values for the depinning field $H_d$, the depinning temperature $T_d$, and the characteristic velocity scale $v_0$ for each sample.

We consider a possibility of the topological Kosterlitz-Thouless (KT) transition in the two-dimensional Pokrovsky-Talapov model with a finite misfit parameter and discuss its relevance to the theory of critical behavior in thin films of monoaxial chiral helimagnets. For this purpose, the initial model is reformulated in terms of the two-dimensional relativistic model of massive Thirring fermions and the Wetterich's functional renormalization-group (RG) approach is employed. In the new formalism, the misfit parameter corresponds to an effective gauge field that can be included in the RG scheme on an equal footing with the other parameters of the theory. Our main result is that the presence of the misfit parameter, which may be attributed to the Dzyaloshinskii-Moriya interaction in the magnetic system, rules out the KT transition. To support this finding, we provide an additional intuitive explanation of the KT scenario breakdown by using the mapping onto the Coulomb gas model. In the framework of the model, the misfit parameter has a meaning of an effective in-plane electric field that prevents a formation of bound vortex-antivortex pairs.

We investigate the influence of self-energy diagrams beyond the two-particle vertex level within dual fermion theory. Specifically, we calculate the local three-particle vertex and construct from it selected dual fermion self-energy corrections to dynamical mean field theory. For the two-dimensional Hubbard model, the thus obtained self-energy corrections are small in the parameter space where dual fermion corrections based on the two-particle vertex only are small. However, in other parts of the parameter space, they are of a similar magnitude and qualitatively different from standard dual fermion theory. The high-frequency behavior of the self-energy correction is, surprisingly, even dominated by corrections stemming from the three-particle vertex.

The family of binary lanthanum monopnictides, LaBi and LaSb, has attracted a great deal of attention as it displays an unusual extreme magnetoresistance (XMR) that is not well understood. Two classes of explanations have been offered for this: the presence of nontrivial topology and the compensation between electron and hole densities. Here, by synthesizing a new member of the family, LaAs, and performing transport measurements, angle-resolved photoemission spectroscopy, and density functional theory calculations, we show that (a) LaAs retains all qualitative features characteristic of the XMR effect but with a significant reduction in magnitude compared to LaSb and LaBi, (b) the absence of a band inversion or a Dirac cone in LaAs indicates that topology is insignificant to XMR, (c) the equal number of electron and hole carriers indicates that compensation is necessary for XMR but does not explain its magnitude, and (d) the ratio of electron and hole mobilities is much different in LaAs compared to LaSb and LaBi. We argue that the compensation is responsible for the XMR profile and the mobility mismatch constrains the magnitude of XMR.

Defects in semiconductors can play a vital role in the performance of electronic devices, with native defects often dominating the electronic properties of the semiconductor. Understanding the relationship between structural defects and electronic function will be central to the design of new high-performance materials. In particular, it is necessary to quantitatively understand the energy and lifetime of electronic states associated with the defect. Here, we apply first-principles density functional theory (DFT) and many-body perturbation theory within the GW approximation to understand the nature and energy of the defect states associated with a charged nitrogen vacancy on the electronic properties of gallium nitride (GaN), as a model of a well-studied and important wide gap semiconductor grown with defects. We systematically investigate the sources of error associated with the GW approximation and the role of the underlying atomic structure on the predicted defect state energies. Additionally, analysis of the computed electronic density of states (DOS) reveals that there is one occupied defect state 0.2 eV below the valence band maximum and three unoccupied defect states at energy of 0.2–0.4 eV above the conduction band minimum, suggesting that this defect in the +1 charge state will not behave as a carrier trap. Furthermore, we compare the character and energy of the defect state obtained from GW and DFT using the HSE approximate density functional and find excellent agreement. This systematic study provides a more complete understanding of how to obtain quantitative defect energy states in bulk semiconductors.

We demonstrate that the spin injection/extraction efficiency is enhanced by an ultrathin Mg insertion layer (⩽2 nm) in $\mathrm{Fe}\text{/}\mathrm{Mg}\text{/}\mathrm{MgO}\text{/}{n}^{+}\text{−}\mathrm{Si}$ tunnel junctions. In diode-type vertical three-terminal devices fabricated on a Si substrate, we observe the narrower three-terminal Hanle (N-3TH) signals indicating true spin injection into Si and estimate the spin polarization in Si to be 16% when the thickness of the Mg insertion layer is 1 nm, whereas no N-3TH signal is observed without the Mg insertion. This means that the spin injection/extraction efficiency is enhanced by suppressing the formation of a magnetically dead layer at the Fe/MgO interface. We also observe clear spin transport signals, such as nonlocal Hanle signals and spin-valve signals, in a lateral four-terminal device with the same $\mathrm{Fe}\text{/}\mathrm{Mg}\text{/}\mathrm{MgO}\text{/}{n}^{+}\text{−}\mathrm{Si}$ tunnel junctions fabricated on a Si-on-insulator substrate. It is found that both the intensity and linewidth of the spin signals are affected by the geometrical effects (device geometry and size). We have derived analytical functions taking into account the device structures, including channel thickness and electrode size, and estimated important parameters: spin lifetime and spin polarization. Our analytical functions explain the experimental results very well. Our study shows the importance of suppressing a magnetically dead layer and provides a unified understanding of spin injection/detection signals in different device geometries.

Understanding the structural and physical origins of low thermal conductivity behavior is essential for improving and searching for high-efficiency thermoelectric materials. Natural minerals are cheap and usually have low thermal conductivities. The lattice thermal conductivities of two isostructural natural materials, chalcostibite ${\mathrm{CuSbS}}_2$ and emplectite ${\mathrm{CuBiS}}_2$, are substantially low in experimental measurements. In particular, the lattice thermal conductivity of ${\mathrm{CuBiS}}_2$ is much lower than that of ${\mathrm{CuSbS}}_2$. Using first-principles Debye-Callaway calculations, we found that the lattice thermal conductivities of ${\mathrm{CuSbS}}_2$ and ${\mathrm{CuBiS}}_2$ are 1.44 W/mK and 0.46 W/mK at 300 K, respectively, which are in good agreement with the experimental measurements. From the calculated vibrational properties, we demonstrate that the stereochemically active lone-pair electrons at the Sb sites are major contributors to the low thermal conductivity of ${\mathrm{CuSbS}}_2$. However, for ${\mathrm{CuBiS}}_2$, the dual effects of the lone-pair electrons at the Bi sites and the rattling of the Cu ions are the primary reasons for the ultralow thermal conductivity. Because of the ultralow thermal conductivity in ${\mathrm{CuBiS}}_2$, our predicted highest $ZT$ value in the material could reach 0.91 for $n$-type doping at 700 K and 0.77 for $p$-type doping at 780 K, which implies that ${\mathrm{CuBiS}}_2$ can be utilized as a potential low-cost thermoelectric material for both $n$ and $p$ type. The present work emphasizes the importance of lone-pair electrons and rattling modes in impelling the phonon anharmonicity, providing a useful guide to seek and design new thermoelectric materials with ultralow thermal conductivity and high efficiency.

Exciton-polaritons in semiconductor microcavities are ideal for the study of the exciton-light interaction and its dependence on light polarization. In this work, we report on the optical response and the dependence on polarization of a polariton microcavity using microreflectance anisotropy spectroscopy ($\mu$-RAS) with a spatial resolution of $10.0\times 10.0\mu {\mathrm{m}}^2$. We have found that, in contrast to optical reflection, the $\mu$-RAS spectra are quite inhomogeneous along the microcavity surface. We demonstrate the existence of microscopic local domains with differences in optical anisotropy of up to $20\%$ within $100\mu \mathrm{m}$. These variations are independent of the detuning between the optical and excitonic resonances, which in our sample is close to 0 meV. The $\mu$-RAS line shape can be understood by using a model based on the anisotropic strain fields induced at the interfaces of the microcavity. The model agrees quite well with the experimental results and allows us to quantify the split of the energy levels of the exciton-polariton branches induced by the local break of symmetry at the microcavity interfaces.

Goncharov and Geballe reanalyze [Phys. Rev. B 96, 157101 (2017)] experimental data using a finite element analysis and cannot reproduce our experimental heating curves; they use incomplete and incorrect material properties. They analyze optical data at the onset of the insulator-to-metal transition to show that it cannot be fit to a Drude model, not realizing that the Drude model does not describe metallic hydrogen in this transition region. Yet, they ignore the region where the reflectance is saturated and the data can be fit to the Drude model. They suggest that we observe semiconducting behavior rather than metallic behavior, but a straightforward calculation shows that reflectance from a semiconductor cannot explain our observed reflectance.

Howie, Dalladay-Simpson, and Gregoryanz Phys. Rev. B 96, 157102 (2017) comment on our observation of liquid metallic hydrogen (LMH). All of their objections are answered in our response. The experimental observation of LMH at static pressures stands on firm ground.