Nature of the field-induced charge-ordered phase (phase II) of $\mathrm{Sm}{\mathrm{Ru}}_4{\mathrm{P}}_{12}$ has been investigated by resonant x-ray diffraction (RXD) and polarized neutron diffraction (PND), focusing on the relationship between the atomic displacements and the antiferromagnetic (AFM) moments of Sm. From the analysis of the interference between the nonresonant Thomson scattering and the resonant magnetic scattering, combined with the spectral function obtained from x-ray magnetic circular dichroism, it is shown that the AFM moment of Sm prefers to be parallel to the field (${\mathit{m}}_{\text{AF}}\parallel \mathit{H}$), giving rise to large and small moment sites around which the ${\mathrm{P}}_{12}$ and Ru cage contract and expand, respectively. This is associated with the formation of the staggered ordering of the ${\mathrm{\Gamma }}_7$-like and ${\mathrm{\Gamma }}_8$-like crystal-field states, providing a strong piece of evidence for the charge order. PND was also performed to obtain complementary and unambiguous conclusion. In addition, isotropic and continuous nature of phase II is demonstrated by the field-direction invariance of the interference spectrum in RXD. Crucial role of the $p-f$ hybridization is shown by resonant soft x-ray diffraction at the P $K$ edge ($1s\leftrightarrow 3p$), where we detected a resonance due to the spin polarized $3p$ orbitals reflecting the AFM order of Sm.

The long carrier lifetime and defect tolerance in metal halide perovskites (MHPs) are major contributors to the superb performance of MHP optoelectronic devices. Large polarons were reported to be responsible for the long carrier lifetime. Yet microscopic mechanisms of the large polaron formation, including the so-called phonon melting, are still under debate. Here, time-of-flight inelastic neutron scattering experiments and first-principles density-functional theory calculations were employed to investigate the lattice vibrations (or phonon dynamics) in methylammonium lead iodide, a prototypical example of MHPs. Our findings are that optical phonons lose temporal coherence gradually with increasing temperature which vanishes at the orthorhombic-to-tetragonal structural phase transition. Surprisingly, however, we found that the spatial coherence is still retained throughout the decoherence process. We argue that the temporally decoherent and spatially coherent vibrations contribute to the formation of large polarons in this metal halide perovskite.

We study the entanglement dynamics in a generic quantum automaton circuit subjected to projective measurements. We design an efficient algorithm which not only allows us to perform large-scale simulation for the Rényi entropy, but also provides a physical picture for the entanglement dynamics, which can be interpreted in terms of a classical bit-string model which belongs to the directed percolation universality class. We study the purification dynamics of a state formed by Einstein-Podolsky-Rosen pairs, and the growth of entanglement starting from a product state. In both cases, we verify numerically that the dynamics is in the universality class of classical directed percolation.

Magnetization isotherms of the $5f$-electron ferromagnets URhGa, UCoGa, and $\mathrm{U}{\mathrm{Co}}_{0.98}{\mathrm{Ru}}_{0.02}\mathrm{Al}$ were measured at temperatures in the vicinity of their Curie temperature to investigate the critical behavior near the ferromagnetic phase transition. These compounds adopt the layered hexagonal ZrNiAl-type structure and exhibit huge uniaxial magnetocrystalline anisotropy. The critical β, γ, and δ exponents were determined by analyzing Arrott-Noakes plots, Kouvel-Fisher plots, critical isotherms, scaling theory, and Widom scaling relations. The values obtained for URhGa and UCoGa can be explained by the results of the renormalization group theory for a two-dimensional (2D) Ising system with long-range interactions similar to URhAl reported by other investigators. On the other hand, the critical exponents determined for $\mathrm{U}{\mathrm{Co}}_{0.98}{\mathrm{Ru}}_{0.02}\mathrm{Al}$ are characteristic of a three-dimensional (3D) Ising ferromagnet with short-range interactions suggested in previous studies also for the itinerant $5f$-electron paramagnet UCoAl situated near a ferromagnetic transition. The change from the 2D to the 3D Ising system is related to the gradual delocalization of $5f$ electrons in the series of the URhGa, URhAl, and UCoGa to $\mathrm{U}{\mathrm{Co}}_{0.98}{\mathrm{Ru}}_{0.02}\mathrm{Al}$ and UCoAl compounds and appears close to the strongly itinerant nonmagnetic limit. This indicates possible new phenomena that may be induced by the change of dimensionality in the vicinity of the quantum critical point.

We describe the formation of charge- and spin-density patterns induced by spin-selective photoexcitations of interacting fermionic systems in the presence of a microstructure. As an example, we consider a one-dimensional Hubbard-like system with a periodic magnetic microstructure, which has a uniform charge distribution in its ground state, and in which a long-lived charge-density pattern is induced by the spin-selective photoexcitation. Using tensor-network methods, we study the full quantum dynamics in the presence of electron-electron interactions and identify doublons as the main decay channel for the induced charge pattern. Our setup is compared to the optically induced spin transfer (OISTR) mechanism, in which ultrafast optically induced spin transfer in Heusler and magnetic compounds is associated to the difference of the local density of states of the different elements in the alloys. We find that applying a spin-selective excitation there induces spatially periodic patterns in local observables. Implications for pump-probe experiments on correlated materials and experiments with ultracold gases on optical lattices are discussed.

We predict that CeBi in the ferromagnetic state is a Weyl semimetal. Our calculations within density functional theory show the existence of two pairs of Weyl nodes on the momentum path $(0,0,k_z)$ at $15\mathrm{meV}$ above and $100\mathrm{meV}$ below the Fermi level. Two corresponding Fermi arcs are obtained on surfaces of mirror-symmetric (010)-oriented slabs at $E=15\mathrm{meV}$ and both arcs are interrupted into three segments due to hybridization with a set of trivial surface bands. By studying the spin texture of surface states, we find the two Fermi arcs are strongly spin polarized but in opposite directions, which can be detected by spin-polarized ARPES measurements. Our theoretical study of quasiparticle interference (QPI) for a nonmagnetic impurity at the Bi site also reveals several features related to the Fermi arcs. Specifically, we predict that the spin polarization of the Fermi arcs leads to a bifurcation-shaped feature only in the spin-dependent QPI spectrum, serving as a fingerprint of the Weyl nodes.

The performance of density functional theory depends largely on the approximation applied for the exchange functional. We propose here a screened exchange potential for semiconductors, with parameters based on the physical properties of the underlying microscopic screening and obeying the requirements for proper asymptotic behavior. We demonstrate that this functional is Koopmans compliant and reproduces a wide range of band gaps. We also show, that the only tunable parameter of the functional can be kept constant upon changing the cation or the anion isovalently, making the approach suitable for treating alloys.

We theoretically investigate the effects of spin frustration on the nonequilibrium dynamics of photoexcited carriers in a half-filled two-dimensional Hubbard model. Using a nonequilibrium generalization of the dynamical cluster approximation, we compare the relaxation dynamics in lattices which interpolate between the triangular lattice and square lattice configuration. To clarify the influence of the density of states of the different lattices, we also consider the corresponding single-site dynamical mean-field theory results. Our study shows that the cooling effect resulting from the disordering of the spin background is less effective in the triangular case because of the frustration. This manifests itself in a longer relaxation time of the photodoped population, as measured by the time-resolved photoemission signal, and a higher effective temperature of the photodoped carriers in the nonthermal steady state after the intra-Hubbard-band thermalization.

We present a general study of a large family of exactly integrable quantum chains with multispin interactions. The exact integrability follows from the algebraic properties of the energy density operators defining the quantum chains. The Hamiltonians are characterized by a parameter $p=1,2,\cdots$ related to the number of interacting spins in the multispin interaction. In the general case, the quantum spins are of infinite dimension. In special cases, characterized by the parameter $N=2,3,...$, the quantum chains describe the dynamics of $Z\left(N\right)$ quantum spin chains with open boundary conditions. The simplest case $p=1$ corresponds to the free fermionic quantum Ising chain ($N=2$) or the $Z\left(N\right)$ free parafermionic quantum chain. The eigenenergies of the quantum chains are given in terms of the roots of special polynomials, and for general values of $p$ the quantum chains are characterized by a free fermionic ($N=2$) or free parafermionic ($N>2$) eigenspectrum. The models have a special critical point when all coupling constants are equal. At this point, the ground-state energy is exactly calculated in the bulk limit, and our analytical and numerical analyses indicate that the models belong to universality classes of critical behavior with dynamical critical exponent $z=(p+1)/N$ and specific-heat exponent $\alpha =max\{0,1-(p+1)/N\}$.

Ground states that appear in a quantizing magnetic field in an imbalanced bilayer electron system hosted by a dual-gated, wide GaAs quantum well are explored with a magnetocapacitance technique that enables detection of the compressibility of each layer separately, the characterization of the charge distribution, as well as the distinction of single- or double-layer-like behavior. Magnetic field induced reentrant quantum phase transitions are observed between a compressible double-layer ground state and a single-layer-like incompressible phase for both total fillings 1 and 2. The transitions are accompanied by a charge redistribution across the well. Our observations indicate for both incompressible states easy-plane pseudospin ferromagnetism as the origin.

An electron field emission (FE) mechanism, which includes Coulomb blockade and quantum confinement effects, is revealed for heterostructured emitters composed of quantum dots and nanowires self-assembled at diamond nanotips. The total energy distributions of the emitted electrons show multiple peaks attributed to the discrete electronic states of the quantum-confined emitter with the corresponding energy levels oscillating as a function of the applied voltage due to the Coulomb blockade. The FE current-voltage characteristics exhibit a modified Coulomb staircase with additional steps becoming more pronounced with increasing voltage. The experimentally observed behavior is consistent with numerical simulations based on the model of Coulomb blockade in quantum dots in combination with the theory of FE from sharp tips.

Within the chemical substitution series ${\mathrm{URu}}_2{\mathrm{Si}}_{2-x}{\mathrm{P}}_x$, there is an evolution in the ground-state behavior from hidden ordered (HO) for $x\lesssim 0.03$, to Kondo lattice behavior with no ordering (NO) for $0.03\lesssim x\lesssim 0.26$, to antiferromagnetism (AFM-2) for $0.26\lesssim x\lesssim 0.5$ [A. Gallagher et al., Nat. Commun. 7, 10712 (2016); A. Gallagher et al., J. Phys.: Condens. Matter 29, 024004 (2016)]. To better understand what factors control this behavior, temperature-dependent electrical resistivity measurements are performed for this series under applied pressures $P$ up to 20.5 kbar. Specimens in the HO $x$ region show similarities to the parent compound, where HO transforms into antiferromagnetism (AFM-1) at a critical pressure ($P_{\mathrm{c}}$). $P_{\mathrm{c}}$ decreases with increasing $x$ and collapses towards $P=0$ near $x\approx 0.03$, suggesting that AFM-1 occurs at ambient pressure for this concentration. No pressure-induced phase transitions are observed in the NO $x$ region and the AFM-2 state is only weakly suppressed by $P$. Measurements further reveal that AFM-1 and AFM-2 are distinct from each other. Calculations of the wave functions using the tight-binding Hartree-Fock approximation are performed and show (i) that the radial probability distributions for the phosphorus ions are more tightly bound than those for the silicon and (ii) that the energy difference between the orbitals decreases with increasing $x$. The cumulative effect of these two factors is that $\mathrm{Si}\to \mathrm{P}$ substitution decreases the hybridization strength, which correlates with the weakening of HO. At large $x$, additional effects such as electrical charge tuning also play an important role in determining the ground-state behavior.

We present a combined soft x-ray and high-resolution vacuum-ultraviolet angle-resolved photoemission spectroscopy study of the electron-overdoped cuprate ${\mathrm{Pr}}_{1.3-x}{\mathrm{La}}_{0.7}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ (PLCCO). Demonstration of its highly two-dimensional band structure enabled precise determination of the in-plane self-energy dominated by electron-electron scattering. Through analysis of this self-energy and the Fermi liquid cut-off energy scale, we find—in contrast to hole-doped cuprates—a momentum isotropic and comparatively weak electron correlation in PLCCO. Yet, the self-energies extracted from multiple oxide systems combine to demonstrate a logarithmic divergent relation between the quasiparticle scattering rate and mass. This constitutes a spectroscopic version of the Kadowaki-Woods relation with an important merit—the demonstration of Fermi liquid quasiparticle lifetime and mass being set by a single energy scale.

In connection with the recent Harvard group experiment on graphene-based four-terminal Josephson junctions containing a grounded loop, we consider voltage biasing at opposite voltages on the quartet line and establish lowest-order perturbation theory in the tunnel amplitudes between a two-dimensional (2D) metal and four superconducting leads in the dirty limit. We present in addition general nonperturbative and nonadiabatic results. The critical current on the quartet line $I_c(\mathrm{\Phi }/{\mathrm{\Phi }}_0)$ depends on the reduced flux $\mathrm{\Phi }/{\mathrm{\Phi }}_0$ via interference between the three-terminal quartets (3TQs) and the nonstandard four-terminal split quartets (4TSQs). The 4TSQs result from synchronizing two Josephson junctions by exchange of two quasiparticles “surfing” on the 2D quantum wake, and this mechanism is already operational at equilibrium. Perturbation theory in the tunnel amplitudes shows that the 3TQs are $\pi$-shifted but the 4TSQs are 0-shifted if the contacts have linear dimension which is large compared to the elastic mean free path. We establish the gate voltage dependence of the quartet critical current oscillations $I_c(\mathrm{\Phi }/{\mathrm{\Phi }}_0)$. It is argued that “observation of $I_c\left(0\right)\ne I_c(1/2)$” implies “evidence for the four-terminal 4TSQ” for finite bias voltage on the quartet line and arbitrary interface transparencies. This statement relies on physically motivated approximations leading to the Ambegaokar-Baratoff-type formula for the quartet critical current-flux relation. It is concluded that the recent experiment mentioned above finds evidence for the four-terminal 4TSQ.

In this paper, we consider a quantum dot connected to four superconducting terminals biased at opposite voltages on the quartet line. The grounded superconductor contains a loop threaded by the magnetic flux $\mathrm{\Phi }$. We provide Keldysh microscopic calculations and physical pictures for the voltage-$V$ dependence of the quartet current. Superconductivity is expected to be stronger at $\mathrm{\Phi }/{\mathrm{\Phi }}_0=0$ than at $\mathrm{\Phi }/{\mathrm{\Phi }}_0=\frac{1}{2}$. However, inversion $I_{q,c}(V,0)<I_{q,c}(V,\frac{1}{2})$ is obtained in the critical current $I_{q,c}(V,\mathrm{\Phi }/{\mathrm{\Phi }}_0)$ on the quartet line in the voltage-$V$ ranges which match avoided crossings in the Floquet spectrum at $(V,\mathrm{\Phi }/{\mathrm{\Phi }}_0=0)$ but not at $(V,\frac{1}{2})$. A reduction in $I_{q,c}$ appears in the vicinity of those avoided crossings, where Landau-Zener tunneling produces dynamical quantum mechanical superpositions of the Andreev bound states. In addition, $\pi$-0 and 0-$\pi$ crossovers emerge in the current-phase relations as $V$ is further increased. The voltage-induced $\pi$ shift is interpreted as originating from the nonequilibrium Floquet populations produced by voltage biasing. The numerical calculations reveal that the inversion is robust against strong Landau-Zener tunneling and many levels in the quantum dot. Our theory provides a simple “Floquet level and population” mechanism for inversion tuned by the bias voltage $V$, which paves the way towards more realistic models for the recent Harvard group experiment where the inversion is observed.

The collective behavior of thermally active structures offers clues on the emergent degrees of freedom and the physical mechanisms that determine the low-energy state of a variety of systems. Here, the thermally active dynamics of magnetic dipoles at square plaquettes is modeled in terms of Brownian oscillators in contact with a heat bath. Solution of the Langevin equation for a set of interacting $x\text{−}y$ dipoles allows the identification of the timescales and correlation length that reveal how interactions, temperature, damping, and inertia may determine the frequency modes of edge and bulk magnetic mesospins in artificial dipolar systems.

We study the superconductivity in typical $d$-band elemental superconductors V and Nb with the recently developed nonempirical computational scheme based on the density functional theory for superconductors. The effect of ferromagnetic fluctuation (paramagnon) on the superconducting transition temperature $T_{\mathrm{c}}$, which, in principle, suppresses the $s$-wave superconducting pairing, is quantified without any empirical parameter. We show that the strong paramagnon effect cancels the $T_{\mathrm{c}}$-enhancing effects of the phonon-mediated pairing and dynamical screened Coulomb interaction.

In artificial spin ice systems, an interplay of defects and dipolar interactions is expected to play important roles in stabilizing different collective magnetic states. In this work, we investigated the magnetization reversal of individual defective square artificial spin ice vertices where defects break fourfold rotational symmetry of the system. By varying the angle between the applied field and the geometrical axis of individual vertices, we are able to access different energy landscapes of the system. Thus, we find a tuning parameter to stabilize different collective magnetic configurations of a defective vertex. Interesting among them is the collective low-energy state which is otherwise observed in a fully demagnetized state. Micromagnetic simulations are performed for the exact experimental conditions the results of which are consistent with the experimental data.

Using a functional renormalization-group approach, we show that at low temperatures and in a certain range of magnetic fields, the longitudinal dynamic structure factor of quantum Heisenberg ferromagnets in dimensions $D\le 2$ exhibits a well-defined quasiparticle peak with linear dispersion that we identify as zero-magnon sound. In $D>2$, the larger phase space available for the decay into transverse spin waves leads only to a broad hump centered at zero frequency whose width scales linearly in momentum.

Topological Weyl semimetal (WSM) is a solid-state realization of chiral Weyl fermions, whose phonon behaviors provide in-depth knowledge of their electronic properties. In this work, anisotropic Fano resonance is observed in a type-II WSM candidate LaAlSi by polarized Raman spectroscopy. The asymmetric line shape occurs for the $B_1^2$ phonon mode of LaAlSi only for 488- and 532-nm laser excitations but not for 364-, 633-, and 785-nm excitations, suggesting the excitation selectivity. The asymmetry, frequency, and linewidth of the $B_1^2$ phonon mode, along with the spectral background, all show fourfold rotational symmetry as a function of the polarization angle in the polarized Raman spectra. While the shift of Raman frequency in a metal or semimetal is typically attributed to Kohn anomaly, here we show that the anisotropic frequency shift in LaAlSi cannot be explained by the effect of Kohn anomaly, but potentially by the anisotropic scattering background of Fano resonance. Origins of the excitation-energy dependence and anisotropic behavior of the Fano resonance are discussed by the first-principles calculated electronic band structure and phonon dispersion.