Catálogo de publicaciones - revistas

<jats:p>We systematically study the low-temperature specific heats for the two-dimensional kagome antiferromagnet, Cu<jats:sub>3</jats:sub>Zn(OH)<jats:sub>6</jats:sub>FBr. The specific heat exhibits a <jats:italic>T</jats:italic> <jats:sup>1.7</jats:sup> dependence at low temperatures and a shoulder-like feature above it. We construct a microscopic lattice model of <jats:italic>Z</jats:italic> <jats:sub>2</jats:sub> quantum spin liquid and perform large-scale quantum Monte Carlo simulations to show that the above behaviors come from the contributions from gapped anyons and magnetic impurities. Surprisingly, we find the entropy associated with the shoulder decreases quickly with grain size <jats:italic>d</jats:italic>, although the system is paramagnetic to the lowest temperature. While this can be simply explained by a core-shell picture in that the contribution from the interior state disappears near the surface, the 5.9-nm shell width precludes any trivial explanations. Such a large length scale signifies the coherence length of the nonlocality of the quantum entangled excitations in quantum spin liquid candidate, similar to Pippard’s coherence length in superconductors. Our approach therefore offers a new experimental probe of the intangible quantum state of matter with topological order.</jats:p>

<jats:p>To understand the intriguing many-body states and effects in the correlated quantum materials, inference of the microscopic effective Hamiltonian from experiments constitutes an important yet very challenging inverse problem. Here we propose an unbiased and efficient approach learning the effective Hamiltonian through the many-body analysis of the measured thermal data. Our approach combines the strategies including the automatic gradient and Bayesian optimization with the thermodynamics many-body solvers including the exact diagonalization and the tensor renormalization group methods. We showcase the accuracy and powerfulness of the Hamiltonian learning by applying it firstly to the thermal data generated from a given spin model, and then to realistic experimental data measured in the spin-chain compound copper nitrate and triangular-lattice magnet TmMgGaO<jats:sub>4</jats:sub>. The present automatic approach constitutes a unified framework of many-body thermal data analysis in the studies of quantum magnets and strongly correlated materials in general.</jats:p>

<jats:p>Li<jats:sub>6.4</jats:sub>La<jats:sub>3</jats:sub>Zr<jats:sub>1.4</jats:sub>Ta<jats:sub>0.6</jats:sub>O<jats:sub>12</jats:sub> (LLZTO) is a promising inorganic solid electrolyte due to its high Li<jats:sup>+</jats:sup> conductivity and electrochemical stability for all-solid-state batteries. Mechanical characterization of LLZTO is limited by the synthesis of the condensed phase. Here we systematically measure the elastic modules, hardness, and fracture toughness of LLZTO polycrystalline pellets of different densities using the customized environmental nanoindentation. The LLZTO samples are sintered using the hot-pressing method with different amounts of Li<jats:sub>2</jats:sub>CO<jats:sub>3</jats:sub> additives, resulting in the relative density of the pellets varying from 83% to 98% and the largest grain size of 13.21 ± 5.22 μm. The mechanical properties show a monotonic increase as the sintered sample densifies, elastic modulus and hardness reach 158.47 ± 10.10 GPa and 11.27 ± 1.38 GPa, respectively, for LLZTO of 98% density. Similarly, fracture toughness increases from 0.44 to 1.51 MPa⋅m<jats:sup>1/2</jats:sup>, showing a transition from the intergranular to transgranular fracture behavior as the pellet density increases. The ionic conductivity reaches 4.54 × 10<jats:sup>−4</jats:sup> S/cm in the condensed LLZTO which enables a stable Li plating/stripping in a symmetric solid-state cell for over 100 cycles. This study puts forward a quantitative study of the mechanical behavior of LLZTO of different microstructures that is relevant to the mechanical stability and electrochemical performance of all-solid-state batteries.</jats:p>

<jats:p>Sulfur and lanthanum hydrides under compression display superconducting states with high observed critical temperatures. It has been recently demonstrated that carbonaceous sulfur hydride displays room temperature superconductivity. However, this phenomenon has been observed only at very high pressure. Here, we theoretically search for superconductors with very high critical temperatures, but at much lower pressures. We describe two of such sodalite-type clathrate hydrides, YbH<jats:sub>6</jats:sub> and LuH<jats:sub>6</jats:sub>. These hydrides are metastable and are predicted to superconduct with <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> ∼ 145 K at 70 GPa and <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> ∼ 273 K at 100 GPa, respectively. This striking result is a consequence of the strong interrelationship between the <jats:italic>f</jats:italic> states present at the Fermi level, structural stability, and the final <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> value. For example, TmH<jats:sub>6</jats:sub>, with unfilled 4<jats:italic>f</jats:italic> orbitals, is stable at 50 GPa, but has a relatively low value of <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> of 25 K. The YbH<jats:sub>6</jats:sub> and LuH<jats:sub>6</jats:sub> compounds, with their filled <jats:italic>f</jats:italic>-shells, exhibit prominent phonon “softening”, which leads to a strong electron-phonon coupling, and as a result, an increase in <jats:italic>T</jats:italic> <jats:sub>c</jats:sub>.</jats:p>

<jats:p>High-fidelity two-qubit gates are essential for the realization of large-scale quantum computation and simulation. Tunable coupler design is used to reduce the problem of parasitic coupling and frequency crowding in many-qubit systems and thus thought to be advantageous. Here we design an extensible 5-qubit system in which center transmon qubit can couple to every four near-neighboring qubits via a capacitive tunable coupler and experimentally demonstrate high-fidelity controlled-phase (CZ) gate by manipulating central qubit and one near-neighboring qubit. Speckle purity benchmarking and cross entropy benchmarking are used to assess the purity fidelity and the fidelity of the CZ gate. The average purity fidelity of the CZ gate is 99.69±0.04% and the average fidelity of the CZ gate is 99.65±0.04%, which means that the control error is about 0.04%. Our work is helpful for resolving many challenges in implementation of large-scale quantum systems.</jats:p>

<jats:p>Since Yukawa proposed that the pion is responsible for mediating the nucleon-nucleon interaction, meson exchanges have been widely used in understanding hadron-hadron interactions. The most studied mesons are the <jats:italic>σ</jats:italic>, <jats:italic>π</jats:italic>, <jats:italic>ρ</jats:italic>, and <jats:italic>ω</jats:italic>, while other heavier mesons are often argued to be less relevant because they lead to short range interactions. However, whether the range of interactions is short or long should be judged with respect to the size of the system studied. We propose that one charmonium exchange is responsible for the formation of the <jats:italic>Ω<jats:sub>ccc</jats:sub>Ω<jats:sub>ccc</jats:sub> </jats:italic> dibaryon, recently predicted by lattice QCD simulations. The same approach can be extended to the strangeness and bottom sectors, leading to the prediction on the existence of <jats:italic>ΩΩ</jats:italic> and <jats:italic>Ω<jats:sub>bbb</jats:sub>Ω<jats:sub>bbb</jats:sub> </jats:italic> dibaryons, while the former is consistent with the existing lattice QCD results, the latter remains to checked. In addition, we show that the Coulomb interaction may break up the <jats:italic>Ω<jats:sub>ccc</jats:sub>Ω<jats:sub>ccc</jats:sub> </jats:italic> pair but not the <jats:italic>Ω<jats:sub>bbb</jats:sub>Ω<jats:sub>bbb</jats:sub> </jats:italic> and <jats:italic>ΩΩ</jats:italic> dibaryons.</jats:p>

<jats:p>We report the production of <jats:sup>87</jats:sup>Rb Bose–Einstein condensate in an asymmetric crossed optical dipole trap (ACODT) without the need of an additional dimple laser. In our experiment, the ACODT is formed by two laser beams with different radii to achieve efficient capture and rapid evaporation of laser cooled atoms. Compared to the cooling procedure in a magnetic trap, the atoms are firstly laser cooled and then directly loaded into an ACODT without the pre-evaporative cooling process. In order to determine the optimal parameters for evaporation cooling, we optimize the power ratio of the two beams and the evaporation time to maximize the final atom number left in the ACODT. By loading about 6 × 10<jats:sup>5</jats:sup> laser cooled atoms in the ACODT, we obtain a pure Bose–Einstein condensate with about 1.4 × 10<jats:sup>4</jats:sup> atoms after 19 s evaporation. Additionally, we demonstrate that the fringe-type noises in optical density distributions can be reduced via principal component analysis, which correspondingly improves the reliability of temperature measurement.</jats:p>

<jats:p>Identification of the glass formation process in various conditions is of importance for fundamental understanding of the mechanism of glass transitions as well as for developments and applications of glassy materials. We investigate the role of pinning in driving the transformation of crystal into glass in two-dimensional colloidal suspensions of monodisperse microspheres. The pinning is produced by immobilizing a fraction of microspheres on the substrate of sample cells where the mobile microspheres sediment. Structurally, the crystal-hexatic-glass transition occurs with increasing the number fraction of pinning <jats:italic>ρ</jats:italic> <jats:sub>pinning</jats:sub>, and the orientational correlation exhibits a change from quasi-long-range to short-range order at <jats:italic>ρ</jats:italic> <jats:sub>pinning</jats:sub> = 0.02. Interestingly, the dynamics shows a non-monotonic change with increasing the fraction of pinning. This is due to the competition between the disorder that enhances the dynamics and the pinning that hinders the particle motions. Our work highlights the important role of the pinning on the colloidal glass transition, which not only provides a new strategy to prevent crystallization forming glass, but also is helpful for understanding of the vitrification in colloidal systems.</jats:p>

<jats:p>Graphene oxide membranes (GOMs), as one of the most promising novel materials, have gained great interest in the field of adsorption. However, the oxygen content of graphene oxide is directly related to its adsorption properties, such as suspension stability, adsorption capacity, and reusability of GOMs. Here, a series of reduced GOMs with oxygen content from 28% to 12% were conveniently prepared by the thermally reduced and the corresponding interlayer spacing of these membranes changed from 8.0 Å to 3.7 Å. These prepared GOMs have remarkable Ca<jats:sup>2+</jats:sup> adsorption capacity, which increases with the oxygen content or interlayer spacing of GOMs. Importantly, the max adsorption capacity of the mass ratio between adsorbed Ca<jats:sup>2+</jats:sup> and pristine GOMs can reach up to 0.481 g/g, which is about one order of magnitude higher than the adsorption capacity of activated sludge, magnetic Fe<jats:sub>3</jats:sub>O<jats:sub>4</jats:sub>, functionalized silica, zeolite molecular sieve, and other reported previously. Moreover, GOMs show excellent stability and the Ca<jats:sup>2+</jats:sup> can be easily desorbed by water, so that the GOMs can be reused. Our previous theoretical analysis suggests that this remarkable adsorption is attributable to the strong interactions between Ca<jats:sup>2+</jats:sup> and GO sheets, including the ion-<jats:italic>π</jats:italic> interactions between Ca<jats:sup>2+</jats:sup> and aromatic graphitic rings as well as the electrostatic interaction between Ca<jats:sup>2+</jats:sup> and oxygen-containing groups.</jats:p>