A systematic comparative study of the electronic transport and ferromagnetic resonance of ultrathin trilayers (TLs) of ${\mathrm{SrRuO}}_3/{\mathrm{LaNiO}}_3/{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ on (001)- and (111)-oriented ${\mathrm{SrTiO}}_3$ (STO) substrates has been reported. An unusual upturn in resistivity $\rho (T$) at low temperature (so called Kondo-like behavior) accompanied by the negative magnetoresistance has been observed. For temperatures larger than the Kondo temperature $\left(T_{\text{K}}\right)$, $\rho (T$) is in good agreement with the Hamann's impurity resistivity model $\rho (T>T_{\text{K}})\propto {(ln(T/T_{\text{K}}))}^{-2}$ for spin $S=1/2$ and 3/2 for the TLs on (001)-STO and (111)-STO, respectively. At the temperatures $T\gg T_{\text{K}}$, electron-electron $[\rho \left(T\right)\propto T^2]$ contribution dominates over those appearing due to the electron-phonon interaction $[\rho \left(T\right)\propto T^5]$ and 2-Magnon scattering. Using the ferromagnetic resonance near the Curie temperature of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$, we evaluated the contribution of surface anisotropies $\left(K_{\text{s}}\right)$ as well as in-plane volume anisotropies $\left(K_{\nu }\right)$ : $K_{\text{s}}\sim -9.57\times {10}^{-4}$ ($-6.68\times {10}^{-4}$) ${\mathrm{J}/\mathrm{m}}^2$ and $K_{\nu }\sim 4.04\times {10}^5(3.31\times {10}^5$) ${\mathrm{J}/\mathrm{m}}^3$ for the TLs on (001)-STO (TLs on (111)-STO). In addition, the Gilbert damping constant is determined which varies between 0.32 (0.23) and 0.16 (0.19) having spin mixing conductance, ${\mathrm{g}}^{\uparrow \downarrow }=5.2\times {10}^{19}$ ($13.38\times {10}^{19}$) ${\mathrm{m}}^{-2}$ for TLs on (001)-STO ((111)-STO).

Topological semimetals with a nodal line is a class of topological matter extending the concept of topological matter beyond topological insulators and Weyl/Dirac semimetals. Here we show theoretically that a Floquet topological semimetal with a helical nodal line can be generated in 2+1 dimensions by irradiating graphene or the surface of a topological insulator with circularly polarized light. The helical nodal line is the nodal line running across the Brillouin zone with helical winding. Specifically, it is shown that the dynamics of irradiated graphene is described by the time Stark Hamiltonian, which can host a Floquet topological insulator and a weakly driven Floquet topological semimetal with a helical nodal line in the high and low frequency limits, respectively. One of the most striking features of the Floquet topological semimetal at low frequency is that the Berry phase accumulated along the time direction, also known as the Zak phase, has a topological discontinuity of $\pi$ across the projected helical nodal line. It is predicted that such a topological discontinuity of the Berry phase manifests itself as the topological discontinuity of the Floquet states. At intermediate frequency, this topological discontinuity can create an interesting change of patterns in the quasienergy dispersion of the Floquet states.

Polarized optical microscopy and spectroscopy are progressively becoming key methods for the high-throughput characterization of individual carbon nanotubes (CNTs) and other one-dimensional nanostructures, on substrate and in devices. The optical response of CNTs on substrate in cross polarization experiments is usually limited by the polarization conservation of the optical elements in the experimental setup. We developed a theoretical model taking into account the depolarization by the setup and the optical response of the substrate. We show that proper modelization of the experimental data requires to take into account both noncoherent and coherent light depolarization by the optical elements. We also show how the nanotube signal can be decoupled from the complex reflection factor of the antireflection substrate, which is commonly used to enhance the optical contrast. Finally, we describe an experimental protocol to extract the depolarization parameters and the complex nanotube susceptibility, and how it can improve the chirality assignment of individual carbon nanotubes in complex cases.

We study the effect of a Chern-Simons term on dynamical gap generation in a low-energy effective theory that describes some features of monolayer suspended graphene. We use a nonperturbative Schwinger-Dyson approach. We solve a set of coupled integral equations for eight independent dressing functions that describe fermion and photon degrees of freedom. We find a strong suppression of the gap and corresponding increase in the critical coupling as a function of increasing Chern-Simons coefficient.

We employ a quantum master equations approach based on a vectorial Maxwell-pseudospin model to compute the quantum evolution of the spin populations and coherences in the fundamental singlet trion transition of a negatively charged quantum dot embedded in a micropillar cavity. Excitation of the system is achieved through an ultrashort, either circularly or linearly polarized resonant pulse. By implementing a realistic micropillar cavity geometry, we numerically demonstrate a giant optical phase shift ($\sim \pm \pi /2$) of a resonant circularly polarized pulse in the weak-coupling regime. The phase shift that we predict considerably exceeds the experimentally observed Kerr rotation angle $(\sim 6^{\circ })$ under a continuous-wave, linearly polarized excitation. By contrast, we show that a linearly polarized pulse is rotated to a much lesser extent of a few degrees. Depending on the initial boundary conditions, this is due to either retardation or advancement in the amplitude buildup in time of the orthogonal electric field component. Unlike previous published work, the dominant spin relaxation and decoherence processes are fully accounted for in the system dynamics. Our dynamical model can be used for optimization of the optical polarization rotation angle for realization of spin-photon entanglement and ultrafast polarization switching on a chip.

We show that long-range ferromagnetic interactions in quantum spin chains can induce spatial quasilocalization of topological magnetic defects, i.e., domain walls, even in the absence of quenched disorder. Utilizing matrix-product-states numerical techniques, we study the nonequilibrium evolution of initial states with one or more domain walls under the effect of a transverse field in variable-range quantum Ising chains. Upon increasing the range of these interactions, we demonstrate the occurrence of a sharp transition characterized by the suppression of spatial diffusion of the excitations during the accessible time scale: the excess energy density remains localized around the initial position of the domain walls. This quasilocalization is accurately reproduced by an effective semiclassical model, which elucidates the crucial role that long-range interactions play in this phenomenon. The predictions of this Rapid Communication can be tested in current experiments with trapped ions.

Oxide heterostructures are versatile platforms with which to research and create novel functional nanostructures. We successfully develop one-dimensional (1D) quantum-wire devices using quantum point contacts on MgZnO/ZnO heterostructures and observe ballistic electron transport with conductance quantized in units of $2e^2/h$. Using dc-bias and in-plane field measurements, we find that the $g$ factor is enhanced to around 6.8, more than three times the value in bulk ZnO. We show that the effective mass $m^{*}$ increases as the electron density decreases, resulting from the strong electron-electron interactions. In this strongly interacting 1D system we study features matching the “0.7” conductance anomalies up to the fifth subband. This Rapid Communication demonstrates that high-mobility oxide heterostructures such as this can provide good alternatives to conventional III-V semiconductors in spintronics and quantum computing as they do not have their unavoidable dephasing from nuclear spins. This paves a way for the development of qubits benefiting from the low defects of an undoped heterostructure together with the long spin lifetimes achievable in silicon.

We report a dramatic enhancement of the lateral optical forces induced on electrically polarizable Rayleigh particles near hyperbolic and extremely anisotropic metasurfaces under simple plane-wave illumination. Such enhancement is enabled by the interplay between the ultraconfined surface plasmons supported by these structures and the out-of-plane polarization spin acquired by the particle. The resulting giant lateral forces appear over a broad frequency range and may open unprecedented venues for routing, trapping, and assembling nanoparticles.

Electron-electron interactions in topological $p-n$ junctions consisting of vertically stacked topological insulators are investigated. $n$-type ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and $p$-type ${\mathrm{Sb}}_2{\mathrm{Te}}_3$ of varying relative thicknesses are deposited using molecular beam epitaxy and their electronic properties measured using low-temperature transport. The screening factor is observed to decrease with increasing sample thickness, a finding which is corroborated by semiclassical Boltzmann theory. The number of two-dimensional states determined from electron-electron interactions is larger compared to the number obtained from weak antilocalization, in line with earlier experiments using single layers.

We show that the fundamental gaps of quantum dots can be accurately estimated at the computational effort of a standard ground-state calculation supplemented with a non-self-consistent step of negligible cost, all performed within density-functional theory at the level of the local-density approximation.

${\mathrm{ZrTe}}_5$ is a layered pentatelluride with very weak interlayer coupling, high in-plane carrier mobility, and strong electron-electron interaction. We investigate the hot carrier dynamics of ${\mathrm{ZrTe}}_5$ by ultrafast time-resolved optical reflectivity. Our results reveal a phonon-mediated across-gap recombination and an electron-phonon scattering channel in thermalization, with timescales of few and sub-ps, respectively. In addition we find a fast relaxation right after the initial photoexcitation with a time constant of $\sim 250$ fs, possibly arising from an electron-electron scattering channel. Our findings indicate that correlated many-body effects play an important role for the transient dynamics of ${\mathrm{ZrTe}}_5$.

Magnetotransport investigation of a half-Heusler antiferromagnet DyPdBi revealed hallmark features of Weyl semimetal: huge negative longitudinal magnetoresistance and planar Hall effect. Both effects have recently been linked to a chiral magnetic anomaly—axial charge pumping between Weyl nodes. Magnetoresistance (MR) of single crystals of DyPdBi is very pronounced. In magnetic field longitudinal to electrical current direction it reaches $-80\%$ and its relative difference with respect to that measured in transverse field (expressed as anisotropic magnetoresistance) is extremely strong: $-60\%$ at 10 K and 14 T. The planar Hall effect in DyPdBi depends on temperature and magnetic field in nonmonotonous way, which has not been previously reported. We compare magnetoresistance measured with voltage contacts on midline of the sample with that measured with contacts on its edge, and show that the role of current-jetting, an extrinsic source of anisotropic negative magnetoresistance, is marginal. We discuss that nature of the compound and sample quality exclude intrinsic sources of negative and anisotropic magnetoresistance other than weak localization and the chiral magnetic anomaly.

We develop a theory of cooperative emission mediated by cooperative energy transfer (CET) from an ensemble of quantum emitters (QEs) to plasmonic antenna at a rate equal to the sum of individual QE-plasmon energy transfer rates. If the antenna radiation efficiency is sufficiently high, the transferred energy is radiated away at approximately the same cooperative rate that scales with the ensemble size. We derive explicit expressions, in terms of local fields, for cooperative Purcell factor and enhancement factor for power spectrum valid for plasmonic structures of any shape with characteristic sizes smaller than the radiation wavelength. The radiated power spectrum retains the plasmon resonance lineshape with overall amplitude scaling with the ensemble size. If QEs are located in a region with nearly constant plasmon local density of states (LDOS), e.g., inside a plasmonic nanocavity, we demonstrate that the CET rate scales linearly with the number of excited QEs, consistent with the experiment, and can be tuned in a wide range by varying the excitation power. For QEs distributed in an extended region saturating the plasmon mode volume, we show that the cooperative Purcell factor has universal form independent of the system size. The CET mechanism incorporates the plasmon LDOS enhancement as well, giving rise to possibilities of controlling the emission rate beyond field enhancement limits.

${\mathrm{CeRhSi}}_3$ is a superconductor under pressure coexisting with a weakly antiferromagnetic phase characterized by a Bragg peak at ${\vec{q}}_0=(\sim 0.2,0,0.5)$ [N. Aso et al., J. Magn. Magn. Mater. 310, 602 (2007)]. The compound is also a heavy-fermion material with a large specific heat coefficient $\gamma =110$ mJ ${\mathrm{mol}}^{-1}{\mathrm{K}}^{-2}$ and a high Kondo temperature of $T_K=50$ K, indicating ${\mathrm{CeRhSi}}_3$ is in a strongly Kondo screened state. We apply high-resolution neutron spectroscopy to investigate the magnetic fluctuations in the normal phase, at ambient pressures, and at low temperatures. We measure a commensurate dynamic response centered around the $\vec{Q}=(0,0,2)$ position that gradually evolves to $H\sim 0.2$ with decreasing temperature and/or energy transfers. The response is broadened both in momentum and energy and is not reminiscent of sharp spin wave excitations found in insulating magnets where the electrons are localized. We parametrize the excitation spectrum and temperature dependence using a heuristic model utilizing the random-phase approximation to couple relaxing ${\mathrm{Ce}}^{3+}$ ground-state Kramers doublets with a Kondo-like dynamic response. With a Ruderman-Kittel-Kasuya-Yosida exchange interaction within the $ab$ plane and an increasing single-site susceptibility, we can qualitatively reproduce the neutron spectroscopic results in ${\mathrm{CeRhSi}}_3$ and, namely, the trade-off between scattering at commensurate and incommensurate positions. We suggest that the antiferromagnetic phase in ${\mathrm{CeRhSi}}_3$ is driven by weakly correlated relaxing localized Kramers doublets and that ${\mathrm{CeRhSi}}_3$ at ambient pressures is on the border between a Rudderman-Kittel-Yosida antiferromagnetic state and a Kondo-screened phase where static magnetism is predominately absent.

An unbiased zero-temperature auxiliary-field quantum Monte Carlo method is employed to analyze the nature of the semimetallic phase of the two-dimensional Hubbard model on the honeycomb lattice at half filling. It is shown that the quasiparticle weight $Z$ of the massless Dirac fermions at the Fermi level, which characterizes the coherence of zero-energy single-particle excitations, can be evaluated in terms of the long-distance equal-time single-particle Green's function. If this quantity remains finite in the thermodynamic limit, the low-energy single-particle excitations of the correlated semimetallic phase are described by a Fermi-liquid-type single-particle Green's function. Based on the unprecedentedly large-scale numerical simulations on finite-size clusters containing more than 10 000 sites, we show that the quasiparticle weight remains finite in the semimetallic phase below a critical interaction strength. This is also supported by the long-distance algebraic behavior ($\sim r^{-2}$, where $r$ is distance) of the equal-time single-particle Green's function that is expected for the Fermi liquid. Our result thus provides a numerical confirmation of Fermi-liquid theory in two-dimensional correlated metals.

We investigate the optical response properties of three-dimensional Luttinger semimetals with the Fermi energy close to a quadratic band touching point. In particular, in order to address recent experiments on the spectroscopy of pyrochlore iridates and half-Heusler superconductors, we derive expressions for the optical conductivity in both the normal and general superconducting states in the linear response regime within the random phase approximation. The response functions can be decomposed into contributions from intraband and interband transitions, the latter comprising a genuine signature of the quadratic band touching point. We demonstrate the importance of interband transitions in the optical response in the normal state both in the homogeneous and quasistatic limit. Our analysis reveals a factorization property of the homogeneous conductivity in the spatially anisotropic case and the divergence of the conductivity for strong spatial anisotropy. In the quasistatic limit, the response is dominated by interband transitions and significantly different from systems with a single parabolic band. As an applications of the formalism in the superconducting state we compute the optical conductivity and superfluid density for the $s$-wave singlet superconducting case for both finite and vanishing chemical potential.

Geometrical moiré patterns, generic for almost aligned bilayers of two-dimensional crystals with similar lattice structure but slightly different lattice constants, lead to zone folding and miniband formation for electronic states. Here, we show that moiré superlattice (mSL) effects in $\mathrm{MoSe}{}_2/\mathrm{WS}{}_2$ and $\mathrm{MoTe}{}_2/\mathrm{MoSe}{}_2$ heterobilayers that feature alignment of the band edges are enhanced by resonant interlayer hybridization, and anticipate similar features in twisted homobilayers of transition-metal dichalcogenides (TMDs), including examples of narrow minibands close to the actual band edges. Such hybridization determines the optical activity of interlayer excitons in TMD heterostructures, as well as energy shifts in the exciton spectrum. We show that the resonantly hybridized exciton energy should display a sharp modulation as a function of the interlayer twist angle, accompanied by additional spectral features caused by umklapp electron-photon interactions with the mSL. We analyze the appearance of resonantly enhanced mSL features in absorption and emission of light by the interlayer exciton hybridization with both intralayer $A$ and $B$ excitons in $\mathrm{MoSe}{}_2/\mathrm{WS}{}_2, \mathrm{MoTe}{}_2/\mathrm{MoSe}{}_2, \mathrm{MoSe}{}_2/\mathrm{MoS}{}_2, \mathrm{WS}{}_2/\mathrm{MoS}{}_2$, and $\mathrm{WSe}{}_2/\mathrm{MoSe}{}_2$.

Magnetic susceptibility measurements of 3–4 ML Fe/W(001) ferromagnetic films demonstrate that this is a 2DXY system in which a finite-size Kosterlitz-Thouless (KT) transition occurs. The films are grown in ultrahigh vacuum and their magnetic response is measured using the magneto-optic Kerr effect (MOKE). The analysis of many independently grown films shows that the paramagnetic tail of the susceptibility is described by $\chi \left(T\right)={\chi }_{0}exp[B/{(T/T_{\text{KT}}-1)}^a]$, where $a=0.50\pm 0.03$ and $B=3.48\pm 0.16$, in quantitative agreement with KT theory. Below the finite size L transition temperature $T_C\left(L\right)$, the behavior is complicated by dissipation (likely related to the re-emergence of fourfold anisotropy and magnetic domains). A subset of measurements with very small dissipation most closely represents the idealized system treated by theory. For these measurements, there is a temperature interval of order tens of K between the fitted Kosterlitz-Thouless transition temperature and the finite-size transition temperature, in agreement with theory. The normalized interval $T_C\left(L\right)/T_{\text{KT}}-1=0.065\pm 0.016$ yields an estimate of the finite size $L$ affecting the film of order micrometers. This gives experimental support to the idea that even a mesoscopic limitation of the vortex-antivortex gas results in a substantial finite-size effect at the KT transition. In contrast, fitting the paramagnetic tail to a power law, appropriate to a second-order critical transition, gives unphysical parameters. The effective critical exponent ${\gamma }_{\text{eff}}\approx 3.7\pm 0.7$ does not correspond to a known universality class, and the fitted transition temperature $T_{\gamma }$ is much further below the peak in the susceptibility than is physically reasonable.

We propose a scaling theory for the many-body localization (MBL) phase transition in one dimension, building on the idea that it proceeds via a “quantum avalanche.” We argue that the critical properties can be captured at a coarse-grained level by a Kosterlitz-Thouless (KT) renormalization group (RG) flow. On phenomenological grounds, we identify the scaling variables as the density of thermal regions and the length scale that controls the decay of typical matrix elements. Within this KT picture, the MBL phase is a line of fixed points that terminates at the delocalization transition. We discuss two possible scenarios distinguished by the distribution of rare, fractal thermal inclusions within the MBL phase. In the first scenario, these regions have a stretched exponential distribution in the MBL phase. In the second scenario, the near-critical MBL phase hosts rare thermal regions that are power-law-distributed in size. This points to the existence of a second transition within the MBL phase, at which these power laws change to the stretched exponential form expected at strong disorder. We numerically simulate two different phenomenological RGs previously proposed to describe the MBL transition. Both RGs display a universal power-law length distribution of thermal regions at the transition with a critical exponent ${\alpha }_c=2$, and continuously varying exponents in the MBL phase consistent with the KT picture.

We investigate a model of hard-core bosons with infinitely repulsive nearest- and next-nearest-neighbor interactions in one dimension, introduced by Fendley, Sengupta, and Sachdev [Phys. Rev. B 69, 075106 (2004)]. Using a combination of exact diagonalization, tensor network, and quantum Monte Carlo simulations, we show how an intermediate incommensurate phase separates a crystalline and a disordered phase. We base our analysis on a variety of diagnostics, including entanglement measures, fidelity susceptibility, correlation functions, and spectral properties. According to theoretical expectations, the disordered-to-incommensurate-phase transition point is compatible with Berezinskii-Kosterlitz-Thouless universal behavior. The second transition is instead nonrelativistic, with dynamical critical exponent $z>1$. For the sake of comparison, we illustrate how some of the techniques applied here work at the Potts critical point present in the phase diagram of the model for finite next-nearest-neighbor repulsion. This latter application also allows us to quantitatively estimate which system sizes are needed to match the conformal field theory spectra with experiments performing level spectroscopy.