Search

The fate of the Fermi surface in bulk electron-doped Sr$_{2}$IrO$_{4}$ remains elusive, as does the origin and extension of its pseudogap phase. Here, we use high-resolution angle-resolved photoelectron spectroscopy (ARPES) to investigate the electronic structure of Sr$_{2-x}$La$_{x}$IrO$_{4}$ up to $x=0.2$, a factor of two higher than in previous work. Our findings reveal that the Fermi surface evolves smoothly with doping. Notably, the antinodal pseudogap persists up to the highest doping level, while nodal quasiparticle coherence increases monotonously. This demonstrates that the sharp increase in Hall carrier density recently observed above $x^{*}=0.16$ [Y.-T. Hsu et al., Nature Physics 20, 1596 (2024)] cannot be attributed to the closure of the pseudogap. Further, we determine a temperature boundary of the pseudogap of $T^{*}\simeq~200~\textrm{K}$ for $x=0.2$, comparable to cuprates. Our results suggest that pseudogaps are a generic feature of doped quasi-2D antiferromagnetic Mott insulators, likely related to short range magnetic correlations., Comment: 8 pages, 3 figures. Supplementary Information: 3 pages, 3 figures

In strongly coupled field theories, perturbation theory cannot be employed to study the low-energy spectrum. Thus, non-perturbative techniques are required. We employ the variational method, a rigorous, non-perturbative approach which provides variational upper bounds on the energy eigenstates of the theory. An essential step in the variational method is the choice of trial wave function. In this work, we study the viability of employing a neural network as our variational ansatz. As a first step towards phenomenologically interesting strongly coupled theories like quantum chromodynamics, we study scalar field theories with quartic couplings., Comment: 5 pages, 6 figures, contribution to the 10th International Quark and Nuclear Physics Conference (QNP2024) held in Barcelona on July 2024

The structure of hadronic form factors at high energies and their deviations from perturbative quantum chromodynamics provide insight on nonperturbative dynamics. Using an approach that is consistent with dispersion relations, we construct a model that simultaneously accounts for the pion wave function, gluonic exchanges, and quark Reggeization. In particular, we find that quark Reggeization can be investigated at high energies by studying scaling violation of the form factor.

Inclusive production processes will be important for the first observations of $XYZ$ states at new generation electron-hadron colliders, as they generally benefit from larger cross sections than their exclusive counterparts. We make predictions of semi-inclusive photoproduction of the $\chi_{c1}(1P)$ and $X(3872)$, whose peripheral production is assumed to be dominated by vector exchanges. We validate the applicability of Vector Meson Dominance in the axial-vector charmonium sector and calculate production rates at center-of-mass energies relevant for future experimental facilities. We find the semi-inclusive cross sections near threshold to be enhanced by a factor of $\sim 2-3$ compared to the exclusive reaction and well suited for a first observation in photoproduction., Comment: 16 pages, 9 figures. Typos fixed and references updated. Link to code provided. Version appearing in PRD

We present the results of multicolour $UBVR_{\text{C}}I_{\text{C}}JHK$ photometry, spectroscopic analysis and spectral energy distribution (SED) modelling for the post-AGB candidate IRAS 02143+5852. We detected Cepheid-like light variations with the full peak-to-peak amplitude $\Delta V\sim0.9$ mag and the pulsation period of about 24.9 d. The phased light curves appeared typical for the W Vir Cepheids. The period-luminosity relation for the Type II Cepheids yielded the luminosity $\log L/L_{\odot}\sim2.95$. From a low-resolution spectrum, obtained at maximum brightness, the following atmospheric parameters were determined: $T_\text{eff}\sim7400$ K and $\log g\sim1.38$. This spectrum contains the emission lines H$\alpha$, BaII $\lambda$6496.9, HeI $\lambda$10830 and Pa$\beta$. Spectral monitoring performed in 2019-2021 showed a significant change in the H$\alpha$ profile and appearance of CH and CN molecular bands with pulsation phase. The metal lines are weak. Unlike typical W Vir variables, the star shows a strong excess of infrared radiation associated with the presence of a heavy dust envelope around the star. We modelled the SED using our photometry and archival data from different catalogues and determined the parameters of the circumstellar dust envelope. We conclude that IRAS~02143+5852 is a low-luminosity analogue of dusty RV Tau stars., Comment: 21 pages, 19 figures, 9 tables, accepted for publication in MNRAS

Parents want to work with their children's teachers to help them succeed in school. "What Brain Research Says about Student Learning" provides parents and teachers the most recent findings in brain research and learning theory in a very approachable way. The reader will see how the child's brain develops, learns, remembers, and creates new meaning and understanding. User-friendly discussions of learning and teaching theories will show strategies both parents and teachers can use to capitalize on this new understanding about the child's developing brain. Topics include: learning environment, developmental stages, lesson planning, teaching strategies, assignments, and assessments. The book concludes with a variety of actual samples from these topic areas.

In many physical situations in which many-body assemblies exist at temperature $T$, a characteristic quantum-mechanical time scale of approximately $\hbar/k_{B}T$ can be identified in both theory and experiment, leading to speculation that it may be the shortest meaningful time in such circumstances. When this behaviour is investigated by probing the scattering rate of strongly interacting electrons in metals, it is clear that in some cases only electron-electron scattering can be its cause, while in others it arises from high-temperature scattering of electrons from quantised lattice vibrations, i.e. phonons. In metallic oxides, which are among the most studied materials, analysis of electrical transport does not satisfactorily identify the relevant scattering mechanism at 'high' temperatures near room temperature. We employ a contactless optical method to measure thermal diffusivity in two Ru-based layered perovskites, Sr$_3$Ru$_2$O$_7$ and Sr$_2$RuO$_4$, and use the measurements to extract the dimensionless Lorenz ratio. By comparing our results to the literature data on both conventional and unconventional metals we show how the analysis of high-temperature thermal transport can both give important insight into dominant scattering mechanisms, and be offered as a stringent test of theories attempting to explain anomalous scattering., Comment: 27 pages, 8 figures

MgV$_{2}$O$_{4}$ is a spinel based on magnetic V$^{3+}$ ions which host both spin ($S=1$) and orbital ($l_{eff}=1$) moments. Owing to the underlying pyrochlore coordination of the magnetic sites, the spins in MgV$_{2}$O$_{4}$ only antiferromagnetically order once the frustrating interactions imposed by the $Fd\overline{3}m$ lattice are broken through an orbitally-driven structural distortion at T$_{S}$ $\simeq$ 60 K. Consequently, a N\'eel transition occurs at T$_{N}$ $\simeq$ 40 K. Low temperature spatial ordering of the electronic orbitals is fundamental to both the structural and magnetic properties, however considerable discussion on whether it can be described by complex or real orbital ordering is ambiguous. We apply neutron spectroscopy to resolve the nature of the orbital ground state and characterize hysteretic spin-orbital correlations using x-ray and neutron diffraction. Neutron spectroscopy finds multiple excitation bands and we parameterize these in terms of a multi-level (or excitonic) theory based on the orbitally degenerate ground state. Meaningful for the orbital ground state, we report an "optical-like" mode at high energies that we attribute to a crystal-field-like excitation from the spin-orbital $j_{eff}$=2 ground state manifold to an excited $j_{eff}$=1 energy level. We parameterize the magnetic excitations in terms of a Hamiltonian with spin-orbit coupling and local crystalline electric field distortions resulting from deviations from perfect octahedra surrounding the V$^{3+}$ ions. We suggest that this provides compelling evidence for complex orbital order in MgV$_{2}$O$_{4}$. We then apply the consequences of this model to understand hysteretic effects in the magnetic diffuse scattering where we propose that MgV$_{2}$O$_{4}$ displays a high temperature orbital memory of the low temperature spin order., Comment: 21 pages and 13 figures

We describe the formalism to analyze the mathematical ambiguities arising in partial-wave analysis of two spinless mesons produced with a linearly polarized photon beam. We show that partial waves are uniquely defined when all accessible observables are considered, for a wave set which includes $S$ and $D$ waves. The inclusion of higher partial waves does not affect our results, and we conclude that there are no mathematical ambiguities in partial-wave analysis of two mesons produced with a linearly polarized photon beam. We present Monte Carlo simulations to illustrate our results., Comment: 11 pages, 8 figures

This document presents the initial scientific case for upgrading the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab) to 22 GeV. It is the result of a community effort, incorporating insights from a series of workshops conducted between March 2022 and April 2023. With a track record of over 25 years in delivering the world's most intense and precise multi-GeV electron beams, CEBAF's potential for a higher energy upgrade presents a unique opportunity for an innovative nuclear physics program, which seamlessly integrates a rich historical background with a promising future. The proposed physics program encompass a diverse range of investigations centered around the nonperturbative dynamics inherent in hadron structure and the exploration of strongly interacting systems. It builds upon the exceptional capabilities of CEBAF in high-luminosity operations, the availability of existing or planned Hall equipment, and recent advancements in accelerator technology. The proposed program cover various scientific topics, including Hadron Spectroscopy, Partonic Structure and Spin, Hadronization and Transverse Momentum, Spatial Structure, Mechanical Properties, Form Factors and Emergent Hadron Mass, Hadron-Quark Transition, and Nuclear Dynamics at Extreme Conditions, as well as QCD Confinement and Fundamental Symmetries. Each topic highlights the key measurements achievable at a 22 GeV CEBAF accelerator. Furthermore, this document outlines the significant physics outcomes and unique aspects of these programs that distinguish them from other existing or planned facilities. In summary, this document provides an exciting rationale for the energy upgrade of CEBAF to 22 GeV, outlining the transformative scientific potential that lies within reach, and the remarkable opportunities it offers for advancing our understanding of hadron physics and related fundamental phenomena., Comment: Updates to the list of authors; Preprint number changed from theory to experiment; Updates to sections 4 and 6, including additional figures

The study of $J/\psi$ photoproduction at low energies has consequences for the understanding of multiple aspects of nonperturbative QCD, ranging from mechanical properties of the proton, to the binding inside nuclei, and the existence of hidden-charm pentaquarks. Factorization of the photon-$c \bar c$ and nucleon dynamics or Vector Meson Dominance are often invoked to justify these studies. Alternatively, open charm intermediate states have been proposed as the dominant mechanism underlying $J/\psi$ photoproduction. As the latter violates this factorization, it is important to estimate the relevance of such contributions. We analyse the latest differential and integrated photoproduction cross sections from the GlueX and $J/\psi$-007 experiments. We show that the data can be adequately described by a small number of partial waves, which we parameterize with generic models enforcing low-energy unitarity. The results suggest a nonnegligible contribution from open charm intermediate states. Furthermore, most of the models present an elastic scattering length incompatible with previous extractions based on Vector Meson Dominance, and thus call into question its applicability to heavy mesons. Our results indicate a wide array of physics possibilities that are compatible with present data and need to be disentangled., Comment: 15 pages, 7 figures, 2 tables. Version to appear on Phys. Rev. D

We study the decay $J/\psi\to\pi^{+}\pi^{-}\pi^{0}$ within the framework of the Khuri-Treiman equations. We find that the BESIII experimental di-pion mass distribution in the $\rho(770)$-region is well reproduced with a once-subtracted $P$-wave amplitude. Furthermore, we show that $F$-wave contributions to the amplitude improve the description of the data in the $\pi\pi$ mass region around 1.5 GeV. We also present predictions for the $J/\psi\to\pi^{0}\gamma^{*}$ transition form factor., Comment: 20 pages, 9 figures

The layered-ruthenate family of materials possess an intricate interplay of structural, electronic and magnetic degrees of freedom that yields a plethora of delicately balanced ground states. This is exemplified by Ca$_{3}$Ru$_{2}$O$_{7}$, which hosts a coupled transition in which the lattice parameters jump, the Fermi surface partially gaps and the spins undergo a $90^{\circ}$ in-plane reorientation. Here, we show how the transition is driven by a lattice strain that tunes the electronic bandwidth. We apply uniaxial stress to single crystals of Ca$_{3}$Ru$_{2}$O$_{7}$, using neutron and resonant x-ray scattering to simultaneously probe the structural and magnetic responses. These measurements demonstrate that the transition can be driven by externally induced strain, stimulating the development of a theoretical model in which an internal strain is generated self-consistently to lower the electronic energy. We understand the strain to act by modifying tilts and rotations of the RuO$_{6}$ octahedra, which directly influences the nearest-neighbour hopping. Our results offer a blueprint for uncovering the driving force behind coupled phase transitions, as well as a route to controlling them., Comment: 12 pages, 6 figures (+ 12 pages, 6 figures of supplemental material)

We present the resolved properties of the $z=2.82$ Hyper Luminous Infrared Galaxy (HyLIRG) HS170850.1, the brightest 850$\mu$m source found in the SCUBA-2 followup to the Keck Baryonic Structure Survey fields (S$_{\rm 850 \mu m}=$19.5 mJy), and amongst the most luminous starbursts known at any redshift. Using the IRAM-NOEMA interferometer in the highest resolution A-configuration, we resolve the source into two components separated by $\sim$8 kpc, visible as blue shifted and red shifted $^{12}$CO(5-4) lines, exhibiting the expected kinematic properties of a major merger between two gas-rich galaxies. The combined merger system is traced over 2.3$''$ or 18.3 kpc. Each component of the merger shows ordered gas motions suggestive of a massive, turbulent disk. We measure the masses of the blue and red disks as (1.5 $\pm$ 0.2) $\times10^{11}$ M$_\odot$ and (0.71 $\pm$ 0.22) $\times10^{11}$ M$_\odot$ respectively. The more massive disk component shows broad wings in the CO line, offset by $\sim$3 kpc from the disk centroid along the major axis, and extending to velocities $\sim\pm$1000 km $ \rm{s^{-1}}$ from systemic velocity. We interpret this as either a possible bipolar outflowing component, or more likely a warping or tidal structure in the CO disk. Comparing the properties of HS170850.1 to other submillimeter detected galaxies with comparably bright 850$\mu$m luminosities suggests that ongoing gas-rich mergers, or at least a clustered/group environment lead to these most extreme starburst phases., Comment: 13 pages, 5 Figures, 2 Tables

We report a comprehensive experimental investigation of the magnetic structure of the cycloidal phase in Ca$_3$Ru$_2$O$_7$, which mediates the spin reorientation transition, and establishes its magnetic phase diagram. In zero applied field, single-crystal neutron diffraction data confirms the scenario deduced from an earlier resonant x-ray scattering study: between $46.7$~K $< T < 49.0$~K the magnetic moments form a cycloid in the $a-b$ plane with a propagation wavevector of $(\delta,0,1)$ with $\delta \simeq 0.025$ and an ordered moment of about 1 $\mu_{\rm{B}}$, with the eccentricity of the cycloid evolving with temperature. In an applied magnetic field applied parallel to the $b$-axis, the intensity of the $(\delta,0,1)$ satellite peaks decreases continuously up to about $\mu_0 H \simeq 5$ T, above which field the system becomes field polarised. Both the eccentricity of the cycloid and the wavevector increase with field, the latter suggesting an enhancement of the anti$-$symmetric Dzyaloshinskii$-$Moriya interaction via magnetostriction effects. Transitions between the various low-temperature magnetic phases have been carefully mapped out using magnetometry and resistivity. The resulting phase diagram reveals that the cycloid phase exists in a temperature window that expands rapidly with increasing field, before transitioning to a polarised paramagnetic state at 5 T. High-field magnetoresistance measurements show that below $T\simeq 70$ K the resistivity increases continuously with decreasing temperature, indicating the inherent insulating nature at low temperatures of our high-quality, untwinned, single-crystals. We discuss our results with reference to previous reports of the magnetic phase diagram of Ca$_3$Ru$_2$O$_7$ that utilised samples which were more metallic and/or poly-domain., Comment: 12 pages, 11 figures

We present the results of muon spin relaxation ($\mu$SR) and neutron scattering on the Ce-based quasikagome lattice CeRh$_{1-x}$Pd$_{x}$Sn ($x=0.1$ to 0.75). Our ZF-$\mu$SR results reveal the absence of static long-range magnetic order down to 0.05~K in $x = 0.1$ single crystals. The weak temperature-dependent plateaus of the dynamic spin fluctuations below 0.2~K in ZF-$\mu$SR together with its longitudinal-field (LF) dependence between 0 and 3~kG indicate the presence of dynamic spin fluctuations persisting even at $T$ = 0.05~K without static magnetic order. On the other hand, $C_{\text{4f}}$/$T$ increases as --log $T$ on cooling below 0.9~K, passes through a broad maximum at 0.13~K and slightly decreases on further cooling. The ac-susceptibility also exhibits a frequency independent broad peak at 0.16~K, which is prominent with an applied field $H$ along $c$-direction. We, therefore, argue that such a behavior for $x=0.1$ (namely, a plateau in spin relaxation rate ($\lambda$) below 0.2~K and a linear $T$ dependence in $C_{\text{4f}}$ below 0.13~K) can be attributed to a metallic spin-liquid (SL) ground state near the quantum critical point in the frustrated Kondo lattice. The LF-$\mu$SR study suggests that the out of kagome plane spin fluctuations are responsible for the SL behavior. Low energy inelastic neutron scattering (INS) of $x$ = 0.1 reveals gapless magnetic excitations, which are also supported by the behavior of $C_{\text{4f}}$ proportional to $T^{1.1}$ down to 0.06~K., Comment: 19 pages and 9 figures

Protected by the interplay of on-site Coulomb interactions and spin-orbit coupling, Sr$_2$IrO$_4$ at high pressure is a rare example of a Mott insulator with a paramagnetic ground state. Here, using optical Raman scattering, we measure both the phonon and magnon evolution in Sr$_2$IrO$_4$ under pressure, and identify three different magnetically-ordered phases, culminating in a spin-disordered state beyond 18 GPa. A strong first-order structural phase transition drives the magnetic evolution at $\sim$10 GPa with reduced structural anisotropy in the IrO$_6$ cages, leading to increasingly isotropic exchange interactions between the Heisenberg spins and a spin-flip transition to $c$-axis-aligned antiferromagnetic order. In the disordered phase of Heisenberg $J_\mathrm{eff}=1/2$ pseudospins, the spin excitations are quasi-elastic and continuous to 10 meV, potentially hosting a gapless quantum spin liquid in Sr$_2$IrO$_4$.

$B$-site ordered 4$d^1$ and 5$d^1$ double perovskites have a number of potential novel ground states including multipolar order, quantum spin liquids and valence bond glass states. These arise from the complex interactions of spin-orbital entangled $J_{eff}$ = 3/2 pseudospins on the geometrically frustrated fcc lattice. The 4$d^1$ Mo$^{5+}$ perovskite Ba$_2$YMoO$_6$ has been suggested to have a valence bond glass ground state. Here we report on the low temperature properties of powder samples of isostructural Ba$_2$LuMoO$_6$: the only other known cubic 4$d^1$ perovskite with one magnetic cation. Our muon spectroscopy experiments show that magnetism in this material remains dynamic down to 60 mK without any spin freezing or magnetic order. A singlet-triplet excitation with a gap of $\Delta$ = 28 meV is observed in inelastic neutron scattering. These results are interpreted as a disordered valence bond glass ground state similar to Ba$_2$YMoO$_6$. Our results highlight the differences of the 4$d^1$ double perovskites in comparison to cubic 5$d^1$ analogues, which have both magnetic and multipolar order., Comment: 23+4 pages, 5+5 figures

Backward angle (u-channel) scattering provides complementary information for studies of hadron spectroscopy and structure, but has been less comprehensively studied than the corresponding forward angle case. As a result, the physics of u-channel scattering poses a range of new experimental and theoretical opportunities and questions. We summarize recent progress in measuring and understanding high energy reactions with baryon charge exchange in the u-channel, as discussed in the first backward angle (u-channel) Physics Workshop. In particular, we discuss backward angle measurements and their theoretical description via both hadronic models and the collinear factorization approach, and discuss planned future measurements of u-channel physics. Finally, we propose outstanding questions and challenges for u-channel physics.

When the transition temperature of a continuous phase transition is tuned to absolute zero, new ordered phases and physical behaviour emerge in the vicinity of the resulting quantum critical point. Sr3Ru2O7 can be tuned through quantum criticality with magnetic field at low temperature. Near its critical field Bc it displays the hallmark T-linear resistivity and a T log(1/T) electronic heat capacity behaviour of strange metals. However, these behaviours have not been related to any critical fluctuations. Here we use inelastic neutron scattering to reveal the presence of collective spin fluctuations whose relaxation time and strength show a nearly singular variation with magnetic field as Bc is approached. The large increase in the electronic heat capacity and entropy near Bc can be understood quantitatively in terms of the scattering of conduction electrons by these spin-fluctuations. On entering the spin density wave (SDW) phase present near Bc, the fluctuations become stronger suggesting that the SDW order is stabilised through an "order-by-disorder" mechanism.

Evidence for broken time reversal symmetry (TRS) has been found in the superconducting states of the $R_5$Rh$_6$Sn$_{18}$ (R = Sc, Y, Lu) compounds with a centrosymmetric caged crystal structure, but the origin of this phenomenon is unresolved. Here we report neutron diffraction measurements of single crystals with $R$=Lu, as well as measurements of the temperature dependence of the magnetic penetration depth using a self-induced tunnel diode-oscillator (TDO) based technique, together with band structure calculations using density functional theory. Neutron diffraction measurements reveal that the system crystallizes in a tetragonal caged structure, and that one of nominal Lu sites in the Lu$_5$Rh$_6$Sn$_{18}$ structure is occupied by Sn, yielding a composition Lu$_{5-x}$Rh$_6$Sn$_{18+x}$ ($x=1$). The low temperature penetration depth shift $\Delta\lambda(T)$ exhibits an exponential temperature dependence below around $0.3T_c$, giving clear evidence for fully gapped superconductivity. The derived superfluid density is reasonably well accounted for by a single gap $s$-wave model, whereas agreement cannot be found for models of TRS breaking states with two-component order parameters. Moreover, band structure calculations reveal multiple bands crossing the Fermi level, and indicate that the aforementioned TRS breaking states would be expected to have nodes on the Fermi surface, in constrast to the observations., Comment: 9 pages, 6 figures

Discrepancies in the low-energy quasiparticle dispersion extracted from angle resolved photoemission, scanning tunneling spectroscopy and quantum oscillation data are common and have long haunted the field of quantum matter physics. Here, we directly test the consistency of results from these three techniques by comparing data from the correlated metal Sr$_2$RhO$_4$. Using established schemes for the interpretation of the experimental data, we find good agreement for the Fermi surface topography and carrier effective masses. Hence, the apparent absence of such an agreement in other quantum materials, including the cuprates, suggests that the electronic states in these materials are of different, non-Fermi liquid like nature. Finally, we discuss the potential and challenges in extracting carrier lifetimes from photoemission and quasiparticle interference data.

This paper will present observations on the design, artistic, and human factors of creating digital music controllers. Specific projects will be presented, and a set of design principles will be supported from those examples., Comment: Proceedings of the International Conference on New Interfaces for Musical Expression, 2001