Catálogo de publicaciones - revistas

<jats:p>Using a three-dimensional classical ensemble model, we investigate the dependence of relative frequency and relative initial phase for nonsequential double ionization (NSDI) of atoms driven by orthogonal two-color (OTC) fields. Our findings reveal that the NSDI probability is clearly dependent on the relative initial phase of OTC fields at different relative frequencies. The inversion analysis results indicate that adjusting the relative frequency of OTC fields helps control returning probability and flight time of the first electron. Furthermore, manipulating the relative frequency at the same relative initial phases can vary the revisit time of the recolliding electron, leading that the emission direction of Ar<jats:sup>2+</jats:sup> ions is explicitly dependent on the relative frequency.</jats:p>

<jats:p>We reveal a special subset of non-degenerate Akhmediev breather (AB) solutions of Manakov equations that only exist in the focusing case. Based on exact solutions, we present the existence diagram of such excitations on the frequency-wavenumber plane. Conventional single-frequency modulation instability leads to simultaneous excitation of three ABs with two of them being non-degenerate.</jats:p>

<jats:p>A central research topic in condensed matter physics is the understanding of the evolution of various phases and phase transitions under different tuning parameters such as temperature, magnetic field and pressure. To explore the pressure-induced evolution of the magnetism and Fermi surface of the heavy fermion antiferromagnet YbPtBi, we performed tunnel diode oscillator based measurements under pressure at low temperatures in high magnetic fields. Our results reveal that the magnetic order strengthens and the Fermi surface shrinks as the pressure increases, which are consistent with typical observations for Yb-based heavy fermion compounds. In addition, an anomalous change in the quantum oscillation amplitudes is observed above 1.5 GPa, and determining the origin requires further study.</jats:p>

<jats:p>We study ultra-high-mobility two-dimensional (2D) electron/hole systems with high precision capacitance measurement. It is found that the capacitance charge appears only at the fringe of the gate at high magnetic field when the 2D conductivity decreases significantly. At integer quantum Hall effects, the capacitance vanishes and forms a plateau at high temperatures <jats:italic>T</jats:italic> ≳ 300 mK, which surprisingly disappears at <jats:italic>T</jats:italic> ≲ 100 mK. This anomalous behavior is likely a manifestation that dilute particles/vacancies in the top-most Landau level form Wigner crystals, which have finite compressibility and can host polarization current.</jats:p>

<jats:p>We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr<jats:sub>2</jats:sub>GaN. A magnetic phase transition is identified at <jats:italic>T</jats:italic> ≈ 170 K, whereas no trace of structural transition is observed down to 6 K. Combining Rietveld refinement with irreducible representations, the spin configuration of Cr ions in Cr<jats:sub>2</jats:sub>GaN is depicted as an incommensurate sinusoidal modulated structure characterized by a propagating vector <jats:italic>k</jats:italic> = (0.365, 0.365, 0). Upon warming up to the paramagnetic state, the magnetic order parameter closely resembles to the temperature dependence of <jats:italic>c</jats:italic>-axis lattice parameter, suggesting strong magneto-elastic coupling in this compound. Therefore, Cr<jats:sub>2</jats:sub>GaN provides a potential platform for exploration of magnetically tuned properties such as magnetoelectric, magnetostrictive and magnetocaloric effects, as well as their applications.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have achieved the robust nonadiabatic holonomic two-qubit controlled gate in one step based on the ground-state blockade mechanism between two Rydberg atoms. By using the Rydberg-blockade effect and the Raman transition mechanism, we can produce the blockade effect of double occupation of the corresponding ground-state, i.e. ground-state blockade, to encode the computational subspace into the ground-state, thus effectively avoiding the spontaneous emission of the excited Rydberg state. On the other hand, the feature of geometric quantum computation independent on the evolutionary details makes the scheme robust to control errors. In this way, the controlled quantum gate constructed by our scheme not only greatly reduces the gate infidelity caused by spontaneous emission but is also robust to control errors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on experimental measurements of the transition dipole moments (TDMs) between the intermediate state $5\mathrm{s}5\mathrm{p}\, ^3\textrm{P}_1$ and the triplet Rydberg series $5\mathrm{s}n\mathrm{s}\, ^3\textrm{S}_1$ in an ultracold strontium gas. Here $n$ is the principal quantum number ranging from 19 to 40. The transition $5\mathrm{s}5\mathrm{p}\, ^3\textrm{P}_1$ − $5\mathrm{s}n\mathrm{s}\, ^3\textrm{S}_1$ is coupled via an UV beam, inducing Autler-Townes splitting of both states. Such a splitting of the intermediate state is spectroscopically measured using absorption imaging on a narrow transition $5\mathrm{s}^2\, ^1\textrm{S}_0$ − $5\mathrm{s}5\mathrm{p}\, ^3\textrm{P}_1$ in an ultracold gas of strontium atoms. The power and size of the UV beam are carefully determined, with which the TDMs are extracted from the measured Autler-Townes splitting. The experimentally obtained TDMs are compared to calculations based on a parametric core potential, on a Coulomb potential with quantum defect, and on the open-source library Alkali Ryderg Calculator (ARC), finding good agreement with the former two models and significant deviation with the latter.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we utilize both analytical and numerical methods to study the superconducting transition temperature <jats:italic>T</jats:italic> <jats:sub> <jats:italic>c</jats:italic> </jats:sub> near a fermionic quantum critical point (QCP) using a model constructed in Ref. [1] as an example. In this model, the bosonic critical fluctuation plays the role of pairing glue for the Cooper pairs, and we use a Bardeen-Cooper-Schrieffer-type mean-field theory to estimate <jats:italic>T</jats:italic> <jats:sub> <jats:italic>c</jats:italic> </jats:sub>. We further argue that the <jats:italic>T</jats:italic> <jats:sub> <jats:italic>c</jats:italic> </jats:sub> computed from the BCS theory approximates a pseudogap temperature <jats:italic>T</jats:italic> <jats:sub>PG</jats:sub>, instead of the Berenzinskii-Kosterlitz-Thouless-transition temperature <jats:italic>T</jats:italic> <jats:sub>KT</jats:sub>, which is confirmed by our determinant quantum Monte Carlo (DQMC) simulation. Moreover, due to the fact that electron density of state starts to deplete at <jats:italic>T</jats:italic> <jats:sub>PG</jats:sub>, the critical scaling of the underlying QCP is also affected below <jats:italic>T</jats:italic> <jats:sub>PG</jats:sub>. Thus, when studying the critical behavior of fermonic QCPs, we need to monitor that the temperature is above <jats:italic>T</jats:italic> <jats:sub>PG</jats:sub> instead of <jats:italic>T</jats:italic> <jats:sub>KT</jats:sub>. This was often ignored in previous studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We experimentally investigate second-harmonic transverse voltage response to ac electrical current for a magnetic nodal-line semimetal Fe$_3$GeTe$_2$. For zero magnetic field, the observed second-harmonic voltage depends as a square of the longitudinal current, as it should be expected for non-linear Hall effect. The magnetic field behavior is found to be sophisticated:while the first-harmonic response shows the known anomalous Hall hysteresis in FGT, the second-harmonic Hall voltage is characterized by the pronounced high-field hysteresis and flat ($B$-independent) region with curves touching at low fields. The high-field hysteresis strongly depends on the magnetic field sweep rate, so it reflects some slow relaxation process. For the lowest rates, it is also accomplished by multiple crossing points. Similar shape of the second-harmonic hysteresis is known for skyrmion spin textures in non-linear optics. Since skyrmions have been demonstrated for FGT by direct visualization techniques, we can connect the observed high-field relaxation with deformation of the skyrmion lattice. Thus, the second-harmonic Hall voltage response can be regarded as a tool to detect spin textures in transport experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The switchability between the two ferroelectric (FE) states of a FE material makes ferroelectrics (FEs) widely used in memory and other electronic devices. However, for conventional FEs, its FE switching only occurs between the two FE states whose spatial inversion symmetry is broken. The search for FE materials is therefore subject to certain limitations. In this work, we propose a new type of FEs whose FE states still contain spatial inversion centers. The change in polarization of this new type of FEs originates from electronic transfer between two centrosymmetric FE states under an external electric field. Taking BaBiO<jats:sub>3</jats:sub> as an example, we show that charge-ordering systems can be a typical representative of this new type of FEs. Moreover, unlike traditional ferroelectrics, the change in polarization in this new type of FEs is quantum in nature with the direction dependent on the specific FE transition path. Our work therefore not only extends the concept of FEs but may also open up a new way to find multiferroics.</jats:p>