Catálogo de publicaciones - revistas

<jats:p>The noncentrosymmetricity of a prototypical correlated electron system Ca<jats:sub>3</jats:sub>Ru<jats:sub>2</jats:sub>O<jats:sub>7</jats:sub> renders extensive interest in the possible polar metallic state, along with multiple other closely competing interactions. However, the structural domain formation in this material often complicates the study of intrinsic material properties. It is crucial to fully characterize the structural domains for unrevealing underlying physics. Here, we report the domain imaging on Ca<jats:sub>3</jats:sub>Ru<jats:sub>2</jats:sub>O<jats:sub>7</jats:sub> crystal using the reflection of polarized light at normal incidence. The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal, and gives rise to a peculiar contrast. The domain walls are found to be the interfaces between 90° rotated twin crystals by complementary magnetization measurements. A distinct contrast in reflectance is also found in the opposite cleavage surfaces, owing to the polar mode of the RuO<jats:sub>6</jats:sub> octahedra. More importantly, the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain. Such an approach provides an efficient yet feasible method for structural domain characterization, which can also find applications in noncentrosymmetric crystals in general.</jats:p>

<jats:p>To obtain various Ni/Mn orderings, we use a low-temperature synthesized method to modulate the Ni/Mn ordering of the ferromagnetic-ferroelastic La<jats:sub>2</jats:sub>NiMnO<jats:sub>6</jats:sub> compound, and the Ni/Mn ordering is estimated by the low-temperature saturation magnetism. The microstructures, crystal structures and magnetic properties are investigated, and the Landau theory are used to describe the form and magnitude of the coupling effects between Ni/Mn ordering and magnetic order parameters. It is predicted that the Ni/Mn ordering would be a strong coupling effect with the Curie transition temperatures if the La<jats:sub>2</jats:sub>NiMnO<jats:sub>6</jats:sub> sample stoichiometry is close.</jats:p>

<jats:p>Planar graphene metalens has demonstrated advantages of ultrathin thickness (200 nm), high focusing resolution (343 nm) and efficiency (&gt;32%) and robust mechanical strength and flexibility. However, diffraction-limited imaging with such a graphene metalens has not been realized, which holds the key to designing practical integrated imaging systems. In this work, the imaging rule for graphene metalenses is first derived and theoretically verified by using the Rayleigh-Sommerfeld diffraction theory to simulate the imaging performance of the 200 nm ultrathin graphene metalens. The imaging rule is applicable to graphene metalenses in different immersion media, including water or oil. Based on the theoretical prediction, high-resolution imaging using the graphene metalens with diffraction-limited resolution (500 nm) is demonstrated for the first time. This work opens the possibility for graphene metalenses to be applied in particle tracking, microfluidic chips and biomedical devices.</jats:p>

<jats:p>Stacking-dependent magnetism in van der Waals materials has caught intense interests. Based on the first principle calculations, we investigate the coupling between stacking orders and interlayer magnetic orders in bilayer H-VSe<jats:sub>2</jats:sub>. It is found that there are two stable stacking orders in bilayer H-VSe<jats:sub>2</jats:sub>, named AB-stacking and A′B-stacking. Under standard DFT framework, the A′B-stacking prefers the interlayer AFM order and is semiconductive, whereas the AB-stacking prefers the FM order and is metallic. However, under the DFT+<jats:italic>U</jats:italic> framework both the stacking orders prefer the interlayer AFM order and are semiconductive. By detailedly analyzing this difference, we find that the interlayer magnetism originates from the competition between antiferromagnetic interlayer super-superexchange and ferromagnetic interlayer double exchange, in which both the interlayer Se-4<jats:italic>p<jats:sub>z</jats:sub> </jats:italic> orbitals play a crucial role. In the DFT+<jats:italic>U</jats:italic> calculations, the double exchange is suppressed due to the opened bandgap, such that the interlayer magnetic orders are decoupled with the stacking orders. Based on this competition mechanism, we propose that a moderate hole doping can significantly enhance the interlayer double exchange, and can be used to switch the interlayer magnetic orders in bilayer VSe<jats:sub>2</jats:sub>. This method is also applicable to a wide range of semiconductive van der Waals magnets.</jats:p>

<jats:p>In cavity quantum electrodynamics, the multiple reflections of a photon between two mirrors defining a cavity is exploited to enhance the light-coupling of an intra-cavity atom. We show that this paradigm for enhancing the interaction of a flying particle with a localized object can be generalized to spintronics based on van der Waals 2D magnets. Upon tunneling through a magnetic bilayer, we find that the spin transfer torques per electron incidence can become orders of magnitude larger than <jats:italic>ℏ</jats:italic>/2, made possible by electron’s multi-reflection path through the ferromagnetic monolayers as an intermediate of their angular momentum transfer. Over a broad energy range around the tunneling resonances, the damping-like spin transfer torque per electron tunneling features a universal value of (<jats:italic>ℏ</jats:italic>/2)tan (<jats:italic>θ</jats:italic>/2), depending only on the angle <jats:italic>θ</jats:italic> between the magnetizations. These findings expand the scope of magnetization manipulations for high-performance and high-density storage based on van der Waals magnets.</jats:p>

<jats:p>Fundamental understanding of interfacial charge behaviors is of great significance for the optoelectronic and photovoltaic applications. However, the crucial roles of perovskite terminations in charge transport processes have not been completely clear. We investigate the charge transfer behaviors of the CsPbI<jats:sub>3</jats:sub>/black phosphorus (BP) van der Waals heterostructure by using the density functional theory calculations with a self-energy correction. The calculations at the atomic level demonstrate the type-II band alignments of the CsPbI<jats:sub>3</jats:sub>/BP heterostructure, which make electrons transfer from the perovskite side to monolayer BP. Moreover, the stronger interaction and narrower physical separation of the interfaces can lead to higher charge tunneling probabilities in the CsPbI<jats:sub>3</jats:sub>/BP heterostructure. Due to different electron affinities, the PbI<jats:sub>2</jats:sub>-terminated perovskite slab tends to collect electrons from the adjacent materials, whereas the CsI-termination prefers to inject electrons into transport materials. In addition, the interface coupling effect enhances the visible-light-region absorption of the CsPbI<jats:sub>3</jats:sub>/BP heterostructure. This study highlights the importance of the perovskite termination in the charge transport processes and provides theoretical guidelines to develop high-performance photovoltaic and optoelectronic devices.</jats:p>

<jats:p>Recently, the theoretically predicted lanthanum superhydride, LaH<jats:sub>10 ± <jats:italic>δ</jats:italic> </jats:sub>, with a clathrate-like structure was successfully synthesized and found to exhibit a record high superconducting transition temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> ≈ 250 K at ∼ 170 GPa, opening a new route for room-temperature superconductivity. However, since <jats:italic>in situ</jats:italic> experiments at megabar pressures are very challenging, few groups have reported the ∼ 250 K superconducting transition in LaH<jats:sub>10 ± <jats:italic>δ</jats:italic> </jats:sub>. Here, we establish a simpler sample-loading procedure that allows a relatively large sample size for synthesis and a standard four-probe configuration for resistance measurements. Following this procedure, we successfully synthesized LaH<jats:sub>10 ± <jats:italic>δ</jats:italic> </jats:sub> with dimensions up to 10 × 20 <jats:italic>μ</jats:italic>m<jats:sup>2</jats:sup> by laser heating a thin La flake and ammonia borane at ∼ 1700 K in a symmetric diamond anvil cell under the pressure of 165 GPa. The superconducting transition at <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> ≈ 250 K was confirmed through resistance measurements under various magnetic fields. Our method will facilitate explorations of near-room-temperature superconductors among metal superhydrides.</jats:p>

<jats:p>Metal–insulator transition (MIT) is one of the most conspicuous phenomena in correlated electron systems. However such a transition has rarely been induced by an external magnetic field as the field scale is normally too small compared with the charge gap. We present the observation of a magnetic-field-driven MIT in a magnetic semiconductor <jats:italic>β</jats:italic>-EuP<jats:sub>3</jats:sub>. Concomitantly, we find a colossal magnetoresistance in an extreme way: the resistance drops billionfold at 2K in a magnetic field less than 3T. We ascribe this striking MIT as a field-driven transition from an antiferromagnetic and paramagnetic insulator to a spin-polarized topological semimetal, in which the spin configuration of Eu<jats:sup>2+</jats:sup> cations and spin-orbital coupling play a crucial role. As a phosphorene-bearing compound whose electrical properties can be controlled by the application of field, <jats:italic>β</jats:italic>-EuP<jats:sub>3</jats:sub> may serve as a tantalizing material in the basic research and even future electronics.</jats:p>

<jats:p>We investigate the magnetic damping parameter of Fe<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>Cr<jats:sub> <jats:italic>x</jats:italic> </jats:sub> thin films using the time-resolved magneto-optical Kerr effect technique. It is demonstrated that the overall effective damping parameter is enhanced with the increasing Cr concentration. The effective damping at high field <jats:italic>α</jats:italic> <jats:sub>0</jats:sub> is found to be significantly enhanced when increasing the Cr concentration with the <jats:italic>α</jats:italic> <jats:sub>0</jats:sub> = 0.159 in the Fe<jats:sub>45</jats:sub>Cr<jats:sub>55</jats:sub> enhanced by 562% compared with that of <jats:italic>α</jats:italic> <jats:sub>0</jats:sub> = 0.024 in the pure Fe film. This study provides a new approach of controlling the effective damping parameter with a desired magnitude via varying Cr composition.</jats:p>

<jats:p>We systematically investigate the magnetic properties of Cu<jats:sub>4 – <jats:italic>x</jats:italic> </jats:sub>Zn<jats:sub> <jats:italic>x</jats:italic> </jats:sub>(OH)<jats:sub>6</jats:sub>FBr using the neutron diffraction and muon spin rotation and relaxation (<jats:italic>μ</jats:italic>SR) techniques. Neutron-diffraction measurements suggest that the long-range magnetic order and the orthorhombic nuclear structure in the <jats:italic>x</jats:italic> = 0 sample can persist up to <jats:italic>x</jats:italic> = 0.23 and 0.43, respectively. The temperature dependence of the zero-field <jats:italic>μ</jats:italic>SR spectra provides two characteristic temperatures, <jats:italic>T</jats:italic> <jats:sub> <jats:italic>A</jats:italic> <jats:sub>0</jats:sub> </jats:sub> and <jats:italic>T<jats:sub>λ</jats:sub> </jats:italic>, which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation, respectively. Comparison between <jats:italic>T</jats:italic> <jats:sub> <jats:italic>A</jats:italic> <jats:sub>0</jats:sub> </jats:sub> and <jats:italic>T</jats:italic> <jats:sub>M</jats:sub> from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to <jats:italic>x</jats:italic> = 0.82. On the other hand, the doping level where <jats:italic>T<jats:sub>λ</jats:sub> </jats:italic> becomes zero is about 0.66, which is much higher than threshold of the long-range order, i.e., ∼0.4. Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above <jats:italic>x</jats:italic> = 0.66 with the perfect kagome planes.</jats:p>