We add a Heisenberg interaction term $\propto \lambda$ in the one-dimensional $\text{SU}\left(2\right)\otimes \mathit{\text{XY}}$ spin-orbital model introduced by Kumar. At $\lambda =0$ the spin and orbital degrees of freedom can be separated by a unitary transformation leading to an exact solution of the model. We show that a finite $\lambda >0$ leads to spontaneous dimerization of the system which in the thermodynamic limit becomes a smooth phase transition at $\lambda \to 0$, whereas it remains discontinuous within the first-order perturbation approach. We present the behavior of the entanglement entropy, energy gap, and dimerization order parameter in the limit of $\lambda \to 0$ confirming the critical behavior. Finally, we show the evidence of another phase transition in the Heisenberg limit, $\lambda \to \infty$, and give a qualitative analytical explanation of the observed dimerized states both in the limit of small and large $\lambda$.

We measured the electronic structure of Fe-substituted Bi2212 using angle-resolved photoemission spectroscopy. We find that the substitution does not change the momentum dependence of the superconducting gap but induces a very anisotropic enhancement of the scattering rate. A comparison of the effect of Fe substitution to that of Zn substitution suggests that the Fe reduces $T_c$ so effectively because it suppresses very strongly the coherence weight around the antinodes.

Bilayer quantum Hall systems, realized either in two separated wells or in the lowest two subbands of a wide quantum well, provide an experimentally realizable way to tune between competing quantum orders at the same filling fraction. Using newly developed density matrix renormalization group techniques combined with exact diagonalization, we return to the problem of quantum Hall bilayers at filling $\nu =1/3+1/3$. We first consider the Coulomb interaction at bilayer separation $d$, bilayer tunneling energy ${\mathrm{\Delta }}_{\mathrm{SAS}}$, and individual layer width $w$, where we find a phase diagram which includes three competing Abelian phases: a bilayer Laughlin phase (two nearly decoupled $\nu =1/3$ layers), a bilayer spin-singlet phase, and a bilayer symmetric phase. We also study the order of the transitions between these phases. A variety of non-Abelian phases has also been proposed for these systems. While absent in the simplest phase diagram, by slightly modifying the interlayer repulsion we find a robust non-Abelian phase which we identify as the “interlayer-Pfaffian” phase. In addition to non-Abelian statistics similar to the Moore-Read state, it exhibits a novel form of bilayer-spin charge separation. Our results suggest that $\nu =1/3+1/3$ systems merit further experimental study.

The temporal evolution of quantal Joule heating of two-dimensional (2D) electrons in a GaAs quantum well placed in quantizing magnetic fields is studied using a difference-frequency method. The method is based on measurements of the electron conductivity oscillating at the beat frequency $f=f_1-f_2$ between two microwaves applied to the 2D system at frequencies $f_1$ and $f_2$. The method provides direct access to the dynamical characteristics of the heating and yields the inelastic-scattering time ${\tau }_{in}$ of 2D electrons. The obtained ${\tau }_{in}$ is strongly temperature dependent, varying from 0.13 ns at 5.5 K to 1 ns at 2.4 K in magnetic field $B=0.333 \mathrm{T}$. When the temperature $T$ exceeds the Landau-level separation, the relaxation rate $1/{\tau }_{in}$ is proportional to $T^2$, indicating electron-electron interaction as the dominant mechanism limiting the quantal heating. At lower temperatures, the rate tends to be proportional to $T^3$, indicating considerable contribution from electron-phonon scattering.

GaN/AlN nanowire heterostructures can display photoluminescence (PL) decay times on the order of microseconds that persist up to room temperature. Doping the GaN nanodisk insertions with Ge can reduce these PL decay times by two orders of magnitude. These phenomena are explained by the three-dimensional electric field distribution within the GaN nanodisks, which has an axial component in the range of a few MV/cm associated to the spontaneous and piezoelectric polarization, and a radial piezoelectric contribution associated to the shear components of the lattice strain. At low dopant concentrations, a large electron-hole separation in both the axial and radial directions is present. The relatively weak radial electric fields, which are about one order of magnitude smaller than the axial fields, are rapidly screened by doping. This bidirectional screening leads to a radial and axial centralization of the hole underneath the electron, and consequently, to large decreases in PL decay times, in addition to luminescence blue shifts.

We study experimentally the intermittent progress of the mechanically induced martensitic transformation in a Cu-Al-Be single crystal through a full-field measurement technique: the grid method. We utilize an in-house, specially designed gravity-based device, wherein a system controlled by water pumps applies a perfectly monotonic uniaxial load through very small force increments. The sample exhibits hysteretic superelastic behavior during the forward and reverse cubic-monoclinic transformation, produced by the evolution of the strain field of the phase microstructures. The in-plane linear strain components are measured on the sample surface during the loading cycle, and we characterize the strain intermittency in a number of ways, showing the emergence of power-law behavior for the strain avalanching over almost six decades of magnitude. We also describe the nonstationarity and the asymmetry observed in the forward versus reverse transformation. The present experimental approach, which allows for the monitoring of the reversible martensitic transformation both locally and globally in the crystal, proves useful and enhances our capabilities in the analysis and possible control of transition-related phenomena in shape-memory alloys.

By using first principles in combination with atomistic spin dynamics calculational methods, we determine the temperature-dependent free energies of the $L{2}_1$- and $L{1}_0-{\mathrm{Ni}}_2\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right)\text{Ga}\left(0\le x\le 1\right)$, including phonon vibrational and magnetic energies. The $x$-dependent martensitic phase transformation (MPT) temperature $\left(T_M\right)$ and the Curie temperature $\left(T_C\right)$ are well represented. It is found that, the abnormal nonmonotonic behavior of $T_M\sim x$ mainly originates from the phonon vibrational free energy. The magnetic energy, which does not change the trend of $T_M$ against $x$ but decreases the driving force of the MPT, is indispensable as well to get reasonable $T_M$ values. This insight provides a good understanding of the physical mechanisms driving the MPT of ${\mathrm{Ni}}_2\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\right)\text{Ga}$, and promotes the improvement of their magnetic shape memory properties.

The statics-dynamics correspondence in spin glasses relate nonequilibrium results on large samples (the experimental realm) with equilibrium quantities computed on small systems (the typical arena for theoretical computations). Here we employ statics-dynamics equivalence to study the Ising spin-glass critical behavior in three dimensions. By means of Monte Carlo simulation, we follow the growth of the coherence length (the size of the glassy domains), on lattices too large to be thermalized. Thanks to the large coherence lengths we reach, we are able to obtain accurate results in excellent agreement with the best available equilibrium computations. To do so, we need to clarify the several physical meanings of the dynamic exponent close to the critical temperature.

In this paper, the effect of the geometrical shape on the radiative thermal transfer between a periodic array of beams and a planar substrate is investigated. Specifically, we analyze the changes in the thermal transfer that occur when the cross-sectional shape of SiC beams is modified from rectangular to ellipsoidal and finally triangular. Numerical calculations are done based on the rigorous coupled wave analysis. These exact results from this analysis are compared to modified proximity and far-field approximations, which become valid for small and large spacings, respectively. Moreover, these results are also compared to effective medium theory, which becomes increasingly accurate in the limit of small periodicities. We show that a reduction in the periodicity will lead to a reduced thermal transfer for triangular and ellipsoidal shaped beams. Even though, in the limit of very small periodicity, thermal transfer for the case of rectangular shaped beams also decreases by decreasing the periodicity, this decrease is slower as compared to other cross-sectional shapes. Finally, we show that even though changing periodicity will change the magnitude of thermal transfer, the scaling law for its variation with the beam to substrate spacing is primarily determined by the cross-sectional shape rather than the periodicity. We analytically prove this fact by investigating the large and small periodicity regimes.

Superconductors hosting long-sought excitations called Majorana fermions may ultimately be used as qubits of fault-tolerant topological quantum computers. A crucial challenge for the development of practical topological quantum computers is the implementation of quantum operations of nearly degenerate quantum states as a dynamical process of Majorana fermions. In this paper, we investigate the braiding dynamics of Majorana fermions on superconducting nanowires. In a finite-size system, a nonadiabatic dynamical process between nearly degenerate states dominates the braiding that operates qubits of Majorana fermions. Our simulations clarify how qubits behave in the real-time braiding process and elucidate the optimum superconducting nanowire conditions for efficient topological quantum operation.

Motivated by recent experimental progress in the context of ultracold multicolor fermionic atoms in optical lattices, we have investigated the properties of the $\mathrm{SU}{\left(N\right)}_{}$ Heisenberg chain with totally antisymmetric irreducible representations, the effective model of Mott phases with $m<N$ particles per site. These models have been studied for arbitrary $N$ and $m$ with non-Abelian bosonization [I. Affleck, Nucl. Phys. B 265, 409 (1986); I. Affleck, Nucl. Phys. B 305, 582 (1988)], leading to predictions about the nature of the ground state (gapped or critical) in most but not all cases. Using exact diagonalization and variational Monte Carlo based on Gutzwiller projected fermionic wave functions, we have been able to verify these predictions for a representative number of cases with $N\le 10$ and $m\le N/2$, and we have shown that the opening of a gap is associated to a spontaneous dimerization or trimerization depending on the value of $m$ and $N$. We have also investigated the marginal cases where Abelian bosonization did not lead to any prediction. In these cases, variational Monte Carlo predicts that the ground state is critical with exponents consistent with conformal field theory.

In previous studies, the pressure dependence of the magnetic ordering temperature $T_{\text{o}}$ of Dy was found to exhibit a sharp increase above its volume collapse pressure of 73 GPa, appearing to reach temperatures well above ambient at 157 GPa. In a search for a second such lanthanide, electrical resistivity measurements were carried out on neighboring Tb to 141 GPa over the temperature range 3.8–295 K. Below Tb's volume collapse pressure of 53 GPa, the pressure dependence $T_{\text{o}}\left(P\right)$ mirrors that of both Dy and Gd. However, at higher pressures $T_{\text{o}}\left(P\right)$ for Tb becomes highly anomalous. This result, together with the very strong suppression of superconductivity by dilute Tb ions in Y, suggests that extreme pressure transports Tb into an unconventional magnetic state with an anomalously high magnetic ordering temperature.

We examine the consequences of a strongly interface-concentrated perpendicular magnetic anisotropy (PMA) energy in CoFeB thin films currently in wide use in magnetic tunnel junctions (MTJs) for spin-torque-related memory applications. The direct consequence of such an anisotropy energy distribution, in combination with a moderate exchange coupling of the interface moment to the rest of the film, is a phenomenological appearance of a fourth-order anisotropy term as the film is viewed by ferromagnetic resonance. The presence of a fourth-order anisotropy also affects the apparent thermal activation energy of a patterned nanomagnet with such thin films, and it could lead to an apparent increase in the spin-torque switching efficiency as represented by the ratio of the thermal activation energy and the threshold switching current. However, for interface-sensitive quantities such as tunnel magnetoresistance's hard-axis behavior, as well as for spin-torque excitation processes, the specifics of such separation of interface versus film-interior moment rotation could become important.

Spin rectification in a single crystal Fe/Au/Fe sandwich is electrically detected for collinear and noncollinear magnetization and external magnetic field configurations. The line shape, linewidth, and signal polarity are analyzed. The spin rectification theory has been much extended by taking the magnetocrystalline anisotropy and shape anisotropy into account, which explains noncollinear resonances and agrees very well with experimental data. Thus, a comprehensive understanding of spin rectification in ferromagnetic metal is demonstrated in this work.

The electric-field control of magnetic properties of $\mathrm{P}{\mathrm{r}}_{0.67}\mathrm{S}{\mathrm{r}}_{0.33}\mathrm{Mn}{\mathrm{O}}_3$ (PSMO) film on piezoelectric $\mathrm{Pb}\left(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}\right){\mathrm{O}}_3-\mathrm{PbTi}{\mathrm{O}}_3$ (PMNT) substrate was investigated. The piezoelectric response of the PMNT substrate to the electric field produced strain that was coupled to the PSMO film. The in-plane compressive (tensile) strain increased (decreased) the magnetization. The change of magnetic moment was associated with the Mn ions. First-principles simulations showed that the strain-induced electronic redistribution of the two ${\mathit{e}}_g$ orbitals $(3d_z^2$ and $3d_{x^2-y^2})$ of Mn ions was responsible for the change of magnetic moment. This work demonstrates that the magnetoelectric effect in manganite/piezoelectric heterostructures originates from the change in ${\mathit{e}}_g$ orbital occupancy of Mn ions induced by strain rather than the interfacial effect.

In this paper, the interplay between frustration and entanglement is investigated in the family of ring-shaped chromium nanomagnets that exhibit various types of frustration. To this end, the exact measures of frustration and bipartite entanglement are calculated numerically in the ground state. It is demonstrated that though larger frustration generates stronger entanglement between complementary spin blocks and weaker between nearest-neighbor spins, the relation between entanglement and frustration is not strictly monotonic and can be used to reconcile different classifications of frustration. It is shown that in the geometrically frustrated phase the region in which the lower bound on the universal frustration measure is saturated increases as geometric frustration is diluted. The entanglement between particular complementary spin blocks can attain almost the maximal value for a proper choice of Hamiltonian parameters.

We study the nonequilibrium aging behavior of the $\pm J$ Edwards-Anderson model in three dimensions for samples of size up to $N={128}^3$ and for up to ${10}^8$ Monte Carlo sweeps. In particular we are interested in the change of the aging when crossing from the spin-glass phase to the ferromagnetic phase. The necessary long simulation times are reached by employing a CUDA-based GPU implementation, which allows for single-spin flip times as small as 8 ps. We measure typical spin-glass correlation functions in space and time to determine the growing length scale and extract the constituting exponents. We observe a clear signature of the disorder-driven equilibrium transition in the nonequilibrium behavior.

We report discovery of ${\mathrm{KFe}}_{1.05}{\mathrm{Ag}}_{0.88}{\mathrm{Te}}_2$ single crystals with semiconducting spin glass ground state. Composition and structure analyses suggest nearly stoichiometric $I4/\mathit{mmm}$ space group but allow for the existence of vacancies, absent in long-range semiconducting antiferromagnet ${\mathrm{KFe}}_{0.85}{\mathrm{Ag}}_{1.15}{\mathrm{Te}}_2$. The subtle change in stoichometry in Fe-Ag sublattice changes magnetic ground state but not conductivity, giving further insight into the semiconducting gap mechanism.

We determine the joint probability density function (JPDF) of reflection eigenvalues in three Dyson's ensembles of normal-conducting chaotic cavities coupled to the outside world through both ballistic and tunnel point contacts. Expressing the JPDF in terms of hypergeometric functions of matrix arguments (labeled by the Dyson index $\beta$), we further show that reflection eigenvalues form a determinantal ensemble at $\beta =2$ and a new type of a Pfaffian ensemble at $\beta =4$. As an application, we derive a simple analytic expression for the concurrence distribution describing production of orbitally entangled electrons in chaotic cavities with tunnel point contacts when time-reversal symmetry is preserved.