The Mott insulator ${\beta }^{\prime }\text{−}{\mathrm{EtMe}}_3\mathrm{Sb}{\left[\mathrm{Pd}{\left(\mathrm{dmit}\right)}_2\right]}_2$ belongs to a class of charge transfer solids with highly frustrated triangular lattice of $S=1/2$ molecular dimers and a quantum-spin-liquid ground state. Our experimental and ab initio theoretical studies show the fingerprints of strong correlations and disorder, the important role of cation-dimer bonding in charge redistribution, no sign of intra- and interdimer dipoles, and the decisive van der Waals contribution to interdimer interactions and the ground-state structure. The latter consists of quasidegenerate electronic states related to the different configurations of cation moieties, which permit two different equally probable orientations. Upon reducing the temperature, the low-energy excitations slow down, indicating glassy signatures as the cation motion freezes out.

In this work, we analyze in detail the occurrence of divergences in the irreducible vertex functions for one of the fundamental models of many-body physics: the Anderson impurity model (AIM). These divergences, a surprising hallmark of the breakdown of many-electron perturbation theory, have been recently observed in several contexts, including the dynamical mean-field solution of the Hubbard model. The numerical calculations for the AIM presented in this work, as well as their comparison with the corresponding results for the Hubbard model, allow us to clarify several open questions about the properties of vertex divergences in a particularly interesting context, the correlated metallic regime at low temperatures. Specifically, our analysis (i) rules out explicitly the transition to a Mott-insulating phase, but not the more general suppression of charge fluctuations (proposed in [O. Gunnarsson et al., Phys. Rev. B 93, 245102 (2016)]), as a necessary condition for the occurrence of vertex divergences, (ii) clarifies their relation with the underlying Kondo physics, and, eventually, (iii) individuates which divergences might also appear on the real-frequency axis in the limit of zero temperature, through the discovered scaling properties of the singular eigenvectors.

We study quantum quenches in two-dimensional lattice gauge theories with fermions coupled to dynamical ${\mathbb{Z}}_2$ gauge fields. Through the identification of an extensive set of conserved quantities, we propose a generic mechanism of charge localization in the absence of quenched disorder both in the Hamiltonian and in the initial states. We provide diagnostics of this localization through a set of experimentally relevant dynamical measures, entanglement measures, as well as spectral properties of the model. One of the defining features of the models that we study is a binary nature of emergent disorder, related to ${\mathbb{Z}}_2$ degrees of freedom. This results in a qualitatively different behavior in the strong disorder limit compared to typically studied models of localization. For example, it gives rise to a possibility of a delocalization transition via a mechanism of quantum percolation in dimensions higher than 1D. We highlight the importance of our general phenomenology to questions related to dynamics of defects in Kitaev's toric code, and to quantum quenches in Hubbard models. While the simplest models we consider are effectively noninteracting, we also include interactions leading to many-body localizationlike logarithmic entanglement growth. Finally, we consider effects of interactions that generate dynamics for conserved charges, which gives rise to only transient localization behavior, or quasi-many-body localization.

We report on temperature-dependent terahertz spectroscopy of a three-layer InAs/GaSb/InAs quantum well (QW) with inverted-band structure. The interband optical transitions, measured up to 16 T at different temperatures by Landau-level magnetospectroscopy, demonstrate the inverted-band structure of the QW. The terahertz photoluminescence at different temperatures allows us to directly extract the optical gap in the vicinity of the $\mathrm{\Gamma }$ point of the Brillouin zone. Our results experimentally demonstrate that the gap in the three-layer QWs is temperature independent and exceeds by four times the maximum band gap available in the inverted InAs/GaSb bilayers.

We report the atomic-scale structure of epitaxial films of the parent infinite-layer compound $\mathrm{SrCu}{\mathrm{O}}_2$ prepared on ${\mathrm{SrTiO}}_3$ by molecular beam epitaxy. In situ scanning tunneling microscopy study reveals a stoichiometric copper oxide (${\mathrm{CuO}}_2$) -terminated surface featured by $2\times 2$ reconstruction, caused primarily by structural distortions of four adjacent ${\mathrm{CuO}}_2$ plaquettes. Furthermore, the subsurface Sr atoms have been rarely discernible, showing intra-unit-cell rotational symmetry breaking. These observations can be reasonably modeled by a periodic up-down buckling of oxygen ions on the ${\mathrm{CuO}}_2$ plane. Further postannealing leads to the removal of surface oxygens and an incommensurate stripe phase. Our study provides indispensable structural information to help understand the exotic properties of cuprate superconductors.

The crystallographic stacking order in multilayer graphene plays an important role in determining its electronic properties. It has been predicted that a rhombohedral (ABC) stacking displays a conducting surface state with flat electronic dispersion. In such a flat band, the role of electron-electron correlation is enhanced, possibly resulting in high $T_{\mathrm{c}}$ superconductivity, charge-density wave, or magnetic orders. Clean experimental band-structure measurements of ABC-stacked specimens are missing because the samples are usually too small in size. Here, we directly image the band structure of large multilayer graphene flakes containing approximately 14 consecutive ABC layers. Angle-resolved photoemission spectroscopy experiments reveal the flat electronic bands near the $K$ point extends by $0.13{\AA }^{-1}$ at the Fermi level at liquid nitrogen temperature. First-principles calculations identify the electronic ground state as an antiferromagnetic state with a band gap of about 40 meV.

Recent discoveries of terrestrial exoplanets distant from our solar system motivate laboratory experiments that provide insight into their formation and thermal evolution. Using laser-driven shock wave experiments, we constrain high-temperature and high-pressure adiabats and the equation of state of ${\mathrm{MgSiO}}_3$, a dominant mantle constituent of terrestrial exoplanets. Critical to the development of a habitable exoplanet is the early thermal history, specifically the formation and freezing of the magma ocean and its role in enabling convection in the mantle and core. We measure the adiabatic sound speed and constrain the melt transition along the Hugoniot and find that the adiabats and melt boundary of silicate magmas are shallower than predicted. This suggests that small changes in the temperature of a super-Earth mantle would result in rapid melting and solidification of nearly the entire mantle.

The response of the one-dimensional antiferromagnetic spin-1/2 chain to the ac staggered magnetic field is studied within the Hartree-Fock-like approximation. For a closed system that field produces oscillations of the magnetization with the frequency of the ac field, modulated by the large number of small Rabi frequencies. In the open system the Rabi oscillations decay due to relaxation processes. It is shown that those oscillations also contribute to the dynamics of the entanglement of the system. The calculated temperature and frequency dependence of the dynamical characteristics is strictly nonmonotonic, reflecting the complicated character of the common action of the homogeneous and staggered dc field.

We report on the first successful growth of single crystals of the noncentrosymmetric superconductor ${\mathrm{Mo}}_3{\mathrm{Al}}_2\mathrm{C}$ obtained by means of a cubic-anvil, high-pressure, and high-temperature technique. Composition, structure, and normal-state transport properties of the crystals were studied by means of x-ray diffraction, energy-dispersive x-ray spectroscopy, magnetic susceptibility, and resistivity measurements as a function of temperature. Variations in critical temperature ($T_c$) between 8.6 and 9.3 K were observed, probably due to the slightly different carbon stoichiometry of the samples. Single-crystal x-ray refinement confirmed the high structural perfection of the grown crystals. Remarkably, the refined Flack parameter values for all the measured crystals using a $P{4}_{1}32$ space-group model were consistently close to either 0 or 1, hence indicating that the considered crystals belong to two enantiomorphic space groups, $P{4}_{1}32$ and $P{4}_{3}32$. An anomaly in the resistivity is observed at $\simeq 130$ K, most likely associated with the onset of a charge-density-wave phase. The superconducting properties (and in particular the symmetry, the amplitude, and the temperature dependence of the superconducting gap) were studied by using point contact Andreev-reflection spectroscopy. The results confirm that ${\mathrm{Mo}}_3{\mathrm{Al}}_2\mathrm{C}$ is a moderately strongly-coupled superconductor with $2\mathrm{\Delta }/k_{\mathrm{B}}{T}_c\simeq 4$ and unambiguously prove that the order parameter has an $s$-wave symmetry despite the asymmetric spin-orbit coupling arising from the lack of inversion symmetry.

High-temperature phase behavior in the system $\mathrm{L}{\mathrm{i}}_x\mathrm{N}{\mathrm{a}}_{1-x}\mathrm{Nb}{\mathrm{O}}_3$ has been studied by using high-resolution neutron powder diffraction. Each of the three compositions studied in the Na-rich part of the phase diagram (viz., $x=0.03,0.08$, and 0.12) shows evidence for distinct and complex structural modulations based on different tilting schemes of ${\mathrm{NbO}}_6$ octahedral units. Whilst octahedral tilting is prevalent in the structural chemistry of perovskites the details of the long-range tilt phases are distinct from those previously observed in $\mathrm{NaNbO}{}_3$ itself. A phase with a well-defined fourfold superlattice is observed for the composition ${\mathrm{Li}}_{0.12}{\mathrm{Na}}_{0.88}{\mathrm{NbO}}_3$, and yet more complex phases with modulations based on 20-fold and 30-fold repeats are observed for ${\mathrm{Li}}_{0.03}{\mathrm{Na}}_{0.97}{\mathrm{NbO}}_3$ and ${\mathrm{Li}}_{0.08}{\mathrm{Na}}_{0.92}{\mathrm{NbO}}_3$, respectively. This peculiar structural frustration makes the system $\mathrm{L}{\mathrm{i}}_x\mathrm{N}{\mathrm{a}}_{1-x}\mathrm{Nb}{\mathrm{O}}_3$ a most structurally complex “simple” perovskite.

Density-wave instabilities have been observed and studied in a multitude of materials. Most recently, in the context of unconventional superconductors like the iron-based superconductors, they have excited considerable interest. We analyze the fluctuation corrections to the equation of state of the density-wave order parameter for commensurate charge-density waves and spin-density waves due to perfect nesting. For XY magnets, we find that contributions due to longitudinal and transverse fluctuations cancel each other, making the mean-field analysis of the problem controlled. This is consistent with the analysis of fluctuation corrections to the BCS theory of superconductivity [Š. Kos, A. J. Millis, and A. I. Larkin, Phys. Rev. B 70, 214531 (2004)]. However, this cancellation does not occur in density-wave systems when the order parameter is a real $N$-component object with $N\ne 2$. Then, the number of transverse fluctuating modes differs from the number of longitudinal fluctuating modes. Indeed, in the case of charge-density waves as well as spin-density waves with Heisenberg symmetry, we find that fluctuation corrections are not negligible, and hence mean-field theories are not justified. These singular fluctuations originate from the intermediate length-scale regime, with wavelengths between the lattice constant and the $T=0$ correlation length. The resulting logarithmic fluctuation contributions to the gap equation originate from the derivative of the anomalous polarization function, and the crucial process is an interaction of quasiparticles through the exchange of fluctuations.

The ground state of the $t\text{−}{t}^{\prime }\text{−}J$ ladder with four legs favors a striped charge distribution for the parameters corresponding to hole-doped cuprate superconductors. We investigate the dynamical spin and charge structure factors of the model by using the dynamical density matrix renormalization group (DMRG) and clarify the influence of the stripe on the structure factors. The dynamical charge structure factor along the momentum direction from $\mathbf{q}=(0,0)$ to $(\pi ,0)$ clearly shows low-energy excitations corresponding to the stripe order in hole doping. On the other hand, the stripe order weakens in electron doping, resulting in fewer low-energy excitations in the charge channel. In the spin channel, we find incommensurate spin excitations near $\mathbf{q}=(\pi ,\pi )$ forming an hourglass behavior in hole doping, while in electron doping we find clearly spin-wave-like dispersions starting from $\mathbf{q}=(\pi ,\pi )$. Along the $(0,0)\text{−}(\pi ,0)$ direction, the spin excitations are strongly influenced by the stripes in hole doping, resulting in two branches that form a discontinuous behavior in the dispersion. In contrast, the electron-doped systems show a downward shift in energy toward $(\pi ,0)$. These behaviors along the $(0,0)\text{−}(\pi ,0)$ direction are qualitatively similar to momentum-dependent spin excitations recently observed by resonant inelastic x-ray scattering experiments in hole- and electron-doped cuprate superconductors.

Generalizing the classical Thomson problem to the quantum regime provides an ideal model to explore the underlying physics regarding electron correlations. In this work, we systematically investigate the combined effects of the geometry of the substrate and the symmetry of the wave function on correlations of geometrically confined electrons. By the numerical configuration interaction method in combination with analytical theory, we construct symmetrized ground-state wave functions; analyze the energetics, correlations, and collective vibration modes of the electrons; and illustrate the routine for the strongly correlated, highly localized electron states with the expansion of the sphere. This work furthers our understanding about electron correlations on confined geometries and shows the promising potential of exploiting confinement geometry to control electron states.

In previous work, we have argued that the optical properties of moderately doped two-dimensional semiconductors can be described in terms of excitons dressed by their interactions with a degenerate Fermi sea of additional charge carriers. These interactions split the bare exciton into attractive and repulsive exciton-polaron branches. The collective excitations of the coupled system are many-body generalizations of the bound trion and unbound states of a single electron interacting with an exciton. In this paper, we consider exciton-polarons in the presence of an external magnetic field that quantizes the kinetic energy of the electrons in the Fermi sea. Our theoretical approach is based on a transformation to a new basis that respects the underlaying symmetry of magnetic translations. We find that the attractive exciton-polaron branch is only weakly influenced by the magnetic field, whereas the repulsive branch exhibits magnetic oscillations and splits into discrete peaks that reflect combined exciton-cyclotron resonance.

An important goal in quantum information processing is to reduce the duration of quantum-logical operations. Motivated by this, we provide a theoretical analysis of electrically induced fast dynamics of a single-electron spin-orbit qubit. We study the example of a one-dimensional quantum dot with Rashba spin-orbit interaction and harmonic driving, and focus on the case of strong driving, when the real-space oscillation amplitude of the driven electron is comparable to the width of its wave function. We provide simple approximate analytical relations between the qubit Larmor frequency, the shortest achievable qubit-flip time, and the driving amplitude required for the shortest achievable qubit flip. We find that these relations compare well with results obtained from numerical simulations of the qubit dynamics. Based on our results, we discuss practical guidelines to maximize speed and quality of electric single-qubit operations on spin-orbit qubits.

Long-range energy transfer in organic molecules has been experimentally obtained by strongly coupling their electronic excitations to a confined electromagnetic cavity mode. Here, we shed light into the polariton-mediated mechanism behind this process for different configurations: donor and acceptor molecules either intermixed or physically separated. We numerically address the phenomenon by means of Bloch-Redfield theory, which allows us to reproduce the effect of complex vibrational reservoirs characteristic of organic molecules. Our findings reveal the key role played by the middle polariton as the nonlocal intermediary in the transmission of excitations from donor to acceptor molecules. We also provide analytical insights on the key physical magnitudes that help to optimize the efficiency of the long-range energy transfer.

Accurate description of electronic band structure of strongly correlated $d$- or $f$-electron materials has been regarded as a great challenge for first-principles electronic structure theory. Previous theoretical studies based on the $GW$ approach has met mixed success, and in particular, the one-short ($G_0{W}_0$) or partially self-consistent (${GW}_0$) approaches with the local or semilocal density functional approximations plus the Hubbard $U$ correction ($GW$@LDA+$U$) as the reference systematically underestimate the binding energies of occupied $d$ or $f$ states. In this work we have investigated quasiparticle electronic band structures of a series of $d$- or $f$-electron oxides including late transition metal mono-oxides (TMO, TM = Mn, Fe, Co, and Ni), ${\mathrm{La}}_2{\mathrm{O}}_3$, ${\mathrm{CeO}}_2$, ${\mathrm{Ce}}_2{\mathrm{O}}_3$, and ${\mathrm{UO}}_2$. It is shown that a large part of the errors observed in previous $GW$ studies can be attributed to numerical errors related to the inaccuracy of unoccupied states and the incompleteness of the summation of states, which can be effectively overcome by including high-energy local orbitals (HLOs) in the linearized augmented plane waves (LAPW) framework.