The competition among superconductivity, stripe-type magnetic order, and a new type of $C_4$ symmetric magnetic order in ${\text{Ba}}_{1-x}{\text{K}}_x{\text{Fe}}_2{\text{As}}_2$ is theoretically studied, focusing on its impact on the global phase diagram. By carrying out a renormalization group analysis of an effective field theory, we obtain the energy-scale dependent flows of all the model parameters, and then apply the results to understand the observed phase diagram. On the basis of the renormalization group analysis, we show that the critical line of nematic order has a negative slope in the superconducting dome and superconductivity is suppressed near the magnetic quantum critical point, which are both consistent with recent experiments. Moreover, we find that, although the observed $C_4$ symmetric magnetic state could be a charge-spin density wave or a spin-vortex crystal at high temperatures, charge-spin density wave is the only stable $C_4$ magnetic state in the low-temperature regime. Therefore, ordering competition provides a method to distinguish these two candidate $C_4$ magnetic states.

Since the discovery of half-filled cuprate to be a Mott insulator, the excitation spectra above the chemical potential for the unoccupied states has attracted much research attention. There were many theoretical works using different numerical techniques to study this problem, but many have reached different conclusions. One of the reasons is the lack of very detailed high-resolution experimental results for the theories to be compared with. Recently, the scanning tunneling spectroscopy [P. Cai et al., Nat. Phys. 12, 1047 (2016); C. Ye et al., Nat. Commun. 4, 1365 (2013)] on lightly doped Mott insulator with an antiferromagnetic order found the presence of in-gap states with energy of order half an eV above the chemical potential. The measured spectral properties with doping are not quite consistent with earlier theoretical works. Although the experiment has disorder and localization effect, but for the energy scale we will study here, a model without disorder is sufficed to illustrate the underlying physics. We perform a diagonalization method on top of the variational Monte Carlo calculation to study the evolution of antiferromagnetic Mott state with doped hole concentration in the Hubbard model. Our results found in-gap states that behave similarly with ones reported by STS. These in-gap states acquire a substantial amount of dynamical spectral weight transferred from the upper Hubbard band. The in-gap states move toward chemical potential with increasing spectral weight as doping increases. Our result also provides information about the energy scale of these in-gap states in relation with the Coulomb coupling strength $U$.

The height distribution of Ag(111) islands grown on Si(111) $7\times 7$ was studied using in situ x-ray reflectivity. This noble metal-on-semiconductor system is of particular interest because the islands exhibit an unusual minimum height that is imposed by the quantum confinement of the conduction electrons. For different coverages and temperatures as well as annealing, it was found that the island heights exhibit a variance that is less than the mean by a constant amount. We argue that this behavior is related to Poisson-like statistics with the imposition of the minimum island height. A modified Poisson height distribution model is presented and shown to provide a good description of the experimentally measured island height distributions. The results, which contribute to a better understanding of the nanoscale growth behavior for an important noble metal, are discussed in terms of mobility that leads to taller islands.

We report ${}^{31}\mathrm{P}$ and ${}^{29}\mathrm{Si}$ NMR in single crystals of ${\mathrm{URu}}_2{\mathrm{Si}}_{2-x}{\mathrm{P}}_x$ for $x=0.09$ and $x=0.33$. The spectra in the $x=0.33$ sample are consistent with a homogenous commensurate antiferromagnetic phase below $T_N\sim 37$ K. The Knight shift exhibits an anomaly at the coherence temperature $T^{*}$ that is slightly enhanced with P doping. Spin-lattice-relaxation rate data indicate that the density of states is suppressed for $x=0.09$ below 30 K, similar to the undoped compound, but there is no evidence of long-range order at this concentration. Our results suggest that Si substitution provides chemical pressure and electronic tuning mediated by filling of the $s/p$ shells with minimal electronic inhomogeneity.

We use x-ray magnetic circular dichroism to evidence the effect of correlations on the local impurity magnetic moment in an archetypal Kondo system, namely, a dilute Cu:Fe alloy. Applying the sum rules on the Fe $L_{2,3}$ absorption edges, the evolution of the spin and orbital moments across the Kondo temperature are determined separately. The spin moment presents a crossover from a nearly temperature-independent regime below the Kondo temperature to a paramagneticlike regime above. Conversely, the weak orbital moment shows a temperature-independent behavior in the whole temperature range, suggesting different Kondo screening temperature scales for the spin and orbital moments.

The $A$-site-ordered cubic perovskite $\mathrm{LaC}{\mathrm{u}}_3\mathrm{C}{\mathrm{r}}_4{\mathrm{O}}_{12}$, where a partial Cu-Cr intersite charge transfer transition occurs at $T_{\mathrm{CT}}=220\mathrm{K}$, was found to be an unconventional metallic and $G$-type antiferromagnetic oxide. Neutron powder diffraction revealed a $G$-type antiferromagnetic ordering at the Cr sites and no ordered moments at the Cu sites. Ab initio electronic structure calculations revealed that the narrowing of the Cr-O-Cr bands due to heavy tilting of the $\mathrm{Cr}{\mathrm{O}}_6$ octahedra and the strong hybridization of the $\mathrm{Cu}\text{−}3d,\mathrm{Cr}\text{−}3d$, and $\mathrm{O}\text{−}2p$ orbitals near the Fermi level give an unusual electronic structure in the vicinity of a localized-electron regime. The $G$-type magnetic structure is primarily stabilized by nearest-neighbor antiferromagnetic superexchange interactions of the near-localized Cr spins. The ferromagnetic $\left\{111\right\}$ layers of the $G$-type antiferromagnetic Cr-spin sublattice allow the spin-polarized electron transfer through the strongly hybridized Cu orbitals.

We report on observation of a fine structure of microwave-induced resistance oscillations in an ultraclean two-dimensional electron gas. This fine structure is manifested by multiple secondary sharp extrema, residing beside the primary ones, which emerge at high radiation power. Theoretical considerations reveal that this fine structure originates from multiphoton-assisted scattering off short-range impurities. Unique properties of the fine structure allow us to access all experimental parameters, including microwave power, and to separate different contributions to photoresistance. Furthermore, we show that the fine structure offers a convenient means to quantitatively assess the correlation properties of the disorder potential in high-quality systems, allowing separation of short- and long-range disorder contributions to the electron mobility.

The distribution of waiting times between successive tunneling events is an already established method to characterize current fluctuations in mesoscopic systems. Here, I investigate mechanisms generating correlations between subsequent waiting times in two model systems, a pair of capacitively coupled quantum dots and a single-level dot attached to spin-polarized leads. Waiting time correlations are shown to give insight into the internal dynamics of the system; for example they allow distinction between different mechanisms of the noise enhancement. Moreover, the presence of correlations breaks the validity of the renewal theory. This increases the number of independent cumulants of current fluctuation statistics, thus providing additional sources of information about the transport mechanism. I also propose a method for inferring the presence of waiting time correlations based on low-order current correlation functions. This method gives a way to extend the analysis of nonrenewal current fluctuations to the systems for which single-electron counting is not experimentally feasible. The experimental relevance of the findings is also discussed; for example reanalysis of previous results concerning transport in quantum dots is suggested.

We have studied the microwave spectra of a wide quantum well for Landau level fillings, $\nu$, just below 1/2, under conditions where the $\nu =1/2$ fractional quantum Hall effect (FQHE) is present. One resonance in the spectra exhibits intensity variations with $\nu$ in striking agreement with that expected for a pinning mode of a Wigner solid of quasiholes of this FQHE state. This resonance is also quite sensitive to asymmetrization of the growth-direction charge distribution in the quantum well by gate bias. Another resonance in the spectra is associated with a different bilayer Wigner solid that also exists at much lower $\nu$ than the 1/2 FQHE, and that appears to coexist with the 1/2 quasihole solid.

The load-controlled mode is routinely used in nanoindentation experiments. Yet there are no simulations or models that predict the generic features of force-displacement $F\text{−}z$ curves, in particular, the existence of several displacement jumps of decreasing magnitude. Here, we show that the recently developed dislocation dynamical model predicts all the generic features when the model is appropriately coupled to an equation defining the load rate. Since jumps in the indentation depth result from the plastic deformation occurring inside the sample, we devise a method for calculating this contribution by setting up a system of coupled nonlinear time evolution equations for the mobile and forest dislocation densities. The equations are then coupled to the force rate equation. We include nucleation, multiplication, and propagation threshold mechanisms for the mobile dislocations apart from other well known dislocation transformation mechanisms between the mobile and forest dislocations. The commonly used Berkovitch indenter is considered. The ability of the approach is illustrated by adopting experimental parameters such as the indentation rate, the geometrical quantities defining the Berkovitch indenter including the nominal tip radius, and other parameters. We identify specific dislocation mechanisms contributing to different regions of the $F\text{−}z$ curve as a first step for obtaining a good fit to a given experimental $F\text{−}z$ curve. This is done by studying the influence of the parameters on the model $F\text{−}z$ curves. In addition, the study demonstrates that the model predicts all the generic features of nanoindentation such as the existence of an initial elastic branch followed by several displacement jumps of decreasing magnitude, and residual plasticity after unloading for a range of model parameter values. Further, an optimized set of parameter values can be easily determined that gives a good fit to the experimental force-displacement curve for Al single crystals of $\left(110\right)$ orientation. The stress corresponding to the maximum force on the elastic branch is close to the theoretical yield stress. We also elucidate the ambiguity in defining the hardness at nanometer scales where the displacement jumps dominate. For larger indentation depths where displacement jumps disappear, the indentation size effect is predicted. The approach also provides insights into several open questions.

In frustrated magnets the Dzyaloshinsky-Moriya interaction (DMI) arising from spin-orbit coupling can induce a magnetic long-range order. Here, we report a theoretical prediction of the thermal Hall effect in frustrated kagome magnets such as ${\mathrm{KCr}}_3{\left(\mathrm{OH}\right)}_6{\left(\text{SO}4\right)}_2$ and ${\mathrm{KFe}}_3{\left(\mathrm{OH}\right)}_6{\left({\mathrm{SO}}_4\right)}_2$. The thermal Hall effects in these materials are induced by scalar spin chirality as opposed to DMI in previous studies. The scalar spin chirality originates from the magnetic-field-induced chiral spin configuration due to noncoplanar spin textures, but in general it can be spontaneously developed as a macroscopic order parameter in chiral quantum spin liquids. Therefore, we infer that there is a possibility of the thermal Hall effect in frustrated kagome magnets such as herbertsmithite ${\mathrm{ZnCu}}_3{\left(\mathrm{OH}\right)}_6{\mathrm{Cl}}_2$ and the chromium compound ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_7{\mathrm{O}}_{28}$, although they also show evidence of magnetic long-range order in the presence of applied magnetic field or pressure.

Yttrium iron garnet is the ubiquitous magnetic insulator used for studying pure spin currents. The exchange constants reported in the literature vary considerably between different experiments and fitting procedures. Here we calculate them from first principles. The local Coulomb correction $(U-J)$ of density-functional theory is chosen such that the parametrized spin model reproduces the experimental Curie temperature and a large electronic band gap, ensuring an insulating phase. The magnon spectrum calculated with our parameters agrees reasonably well with that measured by neutron scattering. A residual disagreement about the frequencies of optical modes indicates the limits of the present methodology.

The oxygen isotope (${}^{16}\mathrm{O}$/${}^{18}\mathrm{O}$) effect (OIE) on the pseudogap (charge-stripe ordering) temperature $T^{*}$ is investigated for the cuprate superconductor ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ as a function of doping $x$ by means of x-ray absorption near edge structure studies. A strong $x$ dependent and sign reversed OIE on $T^{*}$ is observed. The OIE exponent ${\alpha }_{T^{*}}$ systematically decreases from ${\alpha }_{T^{*}}=-0.6\left(1.3\right)$ for $x=0.15$ to ${\alpha }_{T^{*}}=-4.4\left(1.1\right)$ for $x=0.06$, corresponding to increasing $T^{*}$ and decreasing superconducting transition temperature $T_c$. Both $T^{*}\left({}^{16}\mathrm{O}\right)$ and $T^{*}\left({}^{18}\mathrm{O}\right)$ exhibit a linear doping dependence with different slopes and critical end points [where $T^{*}\left({}^{16}\mathrm{O}\right)$ and $T^{*}\left({}^{18}\mathrm{O}\right)$ fall to zero] at $x_c\left({}^{16}\mathrm{O}\right)=0.201\left(4\right)$ and $x_c\left({}^{18}\mathrm{O}\right)=0.182\left(3\right)$, indicating a large positive OIE of $x_c$ with an exponent of ${\alpha }_{x_c}=0.84\left(22\right)$. The remarkably large and strongly doping dependent OIE on $T^{*}$ signals a substantial involvement of the lattice in the formation of the pseudogap, consistent with a polaronic approach to cuprate superconductivity and the vibronic character of its ground state.

We study the nonequilibrium properties of a nonergodic random quantum chain in which highly excited eigenstates exhibit critical properties usually associated with quantum critical ground states. The ground state and excited states of this system belong to different universality classes, characterized by infinite-randomness quantum critical behavior. Using strong-disorder renormalization group techniques, we show that the crossover between the zero and finite energy density regimes is universal. We analytically derive a flow equation describing the unitary dynamics of this isolated system at finite energy density from which we obtain universal scaling functions along the crossover.

This paper presents the physical properties of a nonstandard orthorhombic form of ${\mathrm{MnV}}_2{\mathrm{O}}_6$, including a comparison with the isostructural orthorhombic niobate ${\mathrm{MnNb}}_2{\mathrm{O}}_6$, and with the usual ${\mathrm{MnV}}_2{\mathrm{O}}_6$ monoclinic polymorph. Orthorhombic ($Pbcn$) ${\mathrm{MnV}}_2{\mathrm{O}}_6$ is obtained under extreme conditions of high pressure (6.7 GPa) and high temperature ($800{}^{\circ }\mathrm{C}$). A negative Curie-Weiss temperature ${\theta }_{\mathrm{CW}}$ is observed, implying dominant antiferromagnetic interactions at high temperatures, in contrast to the positive ${\theta }_{\mathrm{CW}}$ of the monoclinic form. Specific-heat measurements are reported down to 1.8 K for all three compounds, and corroborate the magnetic-transition temperatures obtained from susceptibility data. Orthorhombic ${\mathrm{MnV}}_2{\mathrm{O}}_6$ presents a transition to an ordered antiferromagnetic state at $T_N=4.7$ K. Its magnetic structure, determined by neutron diffraction, is unique among the columbite compounds, being characterized by a commensurate propagation vector $\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. It presents antiferromagnetic chains running along the $c$ axis, but with a different spin pattern in comparison to the chains observed in ${\mathrm{MnNb}}_2{\mathrm{O}}_6$. By a comparative discussion of our observations in this three compounds, we are able to highlight the interplay between competing interactions and dimensionality that yield their magnetic properties.

We study the entanglement entropy (EE) of Gaussian systems on a lattice with periodic boundary conditions, both in the vacuum and at nonzero temperatures. By restricting the reduced subsystem to periodic sublattices, we can compute the entanglement spectrum and EE exactly. We illustrate this for a free (1+1)-dimensional massive scalar field at a fixed temperature. Consistent with previous literature, we demonstrate that for a sufficiently large periodic sublattice the EE grows extensively, even in the vacuum. Furthermore, the analytic expression for the EE allows us to probe its behavior both in the massless limit and in the continuum limit at any temperature.

Dijkgraaf-Witten (DW) theories are of recent interest to the condensed matter community, in part because they represent topological phases of matter, but also because they characterize the response theory of certain symmetry protected topological (SPT) phases. However, as yet there has not been a comprehensive treatment of the spectra of these models in the field theoretic setting even for Abelian gauge groups, the goal of this work is to fill the gap in the literature, especially for a selection of DW models with Abelian gauge groups but non-Abelian topological order. Particularly, we focus on the appearance of non-Abelian statistics in type-III twisted DW theories with Abelian gauge groups ${\mathbb{Z}}_2^{\otimes 3}$. There are only 22 distinguishable line operators, and their fusion rules and correlation functions are calculated. The flux insertion operators have quantum dimension 2, which clearly demonstrates the non-Abelian topological order of type-III twisted DW theories.