Catálogo de publicaciones - revistas

<jats:p> <jats:italic>We investigate strong exciton-plasmon coupling and plasmon-mediated hybridization between the Frenkel (F) and Wannier–Mott (WM) excitons of an organic-inorganic hybrid system consisting of a silver ring separated from a monolayer WS</jats:italic> <jats:sub>2</jats:sub> <jats:italic>by J-aggregates. The extinction spectra of the hybrid system calculated by employing the coupled oscillator model are consistent with the results simulated by the finite-difference time-domain method. The calculation results show that strong couplings among F excitons, WM excitons, and localized surface plasmon resonances (LSPRs) lead to the appearance of three plexciton branches in the extinction spectra. The weighting efficiencies of the F exciton, WM exciton and LSPR modes in three plexciton branches are used to analyze the exciton-polaritons in the system. Furthermore, the strong coupling between two different excitons and LSPRs is manipulated by tuning F or WM exciton resonances.</jats:italic> </jats:p>

<jats:p> <jats:italic>We establish a quantum field theory of phase transitions in gapless superconductor CeCoIn</jats:italic> <jats:sub>5</jats:sub>. <jats:italic>It is found that uniform Cooper pair gases with pure gradient interactions with negative coefficient can undergo a Bardeen–Cooper–Schrieffer (BCS) condensation below a critical temperature. In the BCS condensation state, bare Cooper pairs with opposite wave vectors are bound into Cooper molecules, and uncoupled bare Cooper pairs are transformed into a new kind of quasiparticle, i.e., the dressed particles. The Cooper molecule system is a condensate or a superfluid, and the dressed particle system is a normal fluid. The critical temperature is derived analytically. The critical temperature of the superconductor CeCoIn</jats:italic> <jats:sub>5</jats:sub> <jats:italic>is obtained to be T</jats:italic> <jats:sub>c</jats:sub> = 2.289 <jats:italic>K, which approaches the experimental data. The transition from the BCS condensation state to the normal state is a first-order phase transition.</jats:italic> </jats:p>

<jats:p> <jats:italic>Time reversal symmetry (TRS) is a key symmetry for classification of unconventional superconductors, and the violation of TRS often results in a wealth of novel properties. Here we report the synthesis and superconducting properties of the partially filled skutterudite Pr</jats:italic> <jats:sub>1 − <jats:italic>δ</jats:italic> </jats:sub> <jats:italic>Pt</jats:italic> <jats:sub>4</jats:sub> <jats:italic>Ge</jats:italic> <jats:sub>12</jats:sub>. <jats:italic>The results from x-ray diffraction and magnetization measurements show that the [Pt</jats:italic> <jats:sub>4</jats:sub> <jats:italic>Ge</jats:italic> <jats:sub>12</jats:sub> <jats:italic>] cage-forming structure survives and bulk superconductivity is preserved below the superconducting transition temperature T</jats:italic> <jats:sub>c</jats:sub> = 7.80 <jats:italic>K. The temperature dependence of both the upper critical field and the electronic specific heat can be described in terms of a two-gap model, providing strong evidence of multi-band superconductivity. TRS breaking is observed using zero field muon-spin relaxation experiments, and the magnitude of the spontaneous field is nearly half of that in PrPt</jats:italic> <jats:sub>4</jats:sub> <jats:italic>Ge</jats:italic> <jats:sub>12</jats:sub>.</jats:p>

<jats:p> <jats:italic>We use neutron powder diffraction to study the non-superconducting phases of ThFeAsN</jats:italic> <jats:sub>1−<jats:italic>x</jats:italic> </jats:sub> <jats:italic>O</jats:italic> <jats:sub> <jats:italic>x</jats:italic> </jats:sub> <jats:italic>with x</jats:italic> = 0.15, 0.6. <jats:italic>In our previous results of the superconducting phase ThFeAsN with T</jats:italic> <jats:sub>c</jats:sub> = 30 <jats:italic>K, no magnetic transition is observed by cooling down to 6 K, and possible oxygen occupancy at the nitrogen site is shown in the refinement [Europhys. Lett. 117 (2017) 57005]. Here in the oxygen doped system ThFeAsN</jats:italic> <jats:sub>1−<jats:italic>x</jats:italic> </jats:sub> <jats:italic>O<jats:sub>x</jats:sub>, two superconducting regions</jats:italic> (0 ⩽ x ⩽ 0.1 <jats:italic>and</jats:italic> 0.25 ⩽ <jats:italic>x</jats:italic> ⩽ 0.55) <jats:italic>are identified by transport experiments [J. Phys.: Condens. Matter 30 (2018) 255602]. However, within the resolution of our neutron powder diffraction experiment, neither the intermediate doping x</jats:italic> = 0.15 <jats:italic>nor the heavily overdoped compound x</jats:italic> = 0.6 <jats:italic>shows any magnetic order from 300 K to 4 K. Therefore, while it shares the common phenomenon of two superconducting domes as most 1111-type iron-based superconductors, the magnetically ordered parent compound may not exist in this nitride family.</jats:italic> </jats:p>

<jats:p> <jats:italic>In paired Fermi systems, strong many-body effects exhibit in the crossover regime between the Bardeen–Cooper–Schrieffer (BCS) and the Bose–Einstein condensation (BEC) limits. The concept of the BCS–BEC crossover, which is studied intensively in the research field of cold atoms, has been extended to condensed matters. Here by analyzing the typical superconductors within the BCS–BEC phase diagram, we find that FeSe-based superconductors are prone to shift their positions in the BCS–BEC crossover regime by charge doping or substrate substitution, since their Fermi energies and the superconducting gap sizes are comparable. Especially at the interface of single-layer FeSe on SrTiO</jats:italic> <jats:sub>3</jats:sub> <jats:italic>substrate, the superconductivity is relocated closer to the crossover unitary than other doped FeSe-based materials, indicating that the pairing interaction is effectively modulated. We further show that hole-doping can drive the interfacial system into the phase with possible pre-paired electrons, demonstrating its flexible tunability within the BCS–BEC crossover regime.</jats:italic> </jats:p>

<jats:p> <jats:italic>Ferroelectric Pb(Zr</jats:italic> <jats:sub>0.60</jats:sub> <jats:italic>Ti</jats:italic> <jats:sub>0.40</jats:sub> <jats:italic>)O</jats:italic> <jats:sub>3</jats:sub> <jats:italic>thin films deposited on the niobium-doped SrTiO</jats:italic> <jats:sub>3</jats:sub> <jats:italic>and Pt (111)/Ti/SiO</jats:italic> <jats:sub>2</jats:sub> <jats:italic>/Si substrates are fabricated by a sol-gel method. X-ray diffraction indicates that the films have a ‘cube-on-cube’ growth with highly (100) preferred orientation and good surface qualities. Using piezoelectric force microscopy, we investigate domain structures and butterfly amplitude loops of ferroelectric thin films. The results indicate that the film deposited on Nb:SrTiO</jats:italic> <jats:sub>3</jats:sub> <jats:italic>has both kinds of 180° polarizations perpendicular or parallel to the surface while the film deposited on Pt/Ti/SiO</jats:italic> <jats:sub>2</jats:sub> <jats:italic>/Si has irregular phase differences. Excellent piezoelectric polarization are observed in the films on niobium-doped SrTiO</jats:italic> <jats:sub>3</jats:sub> <jats:italic>with local</jats:italic> <jats:inline-formula> <jats:tex-math> <?CDATA ${d}_{33}^{\ast }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>d</mml:mi> <mml:mrow> <mml:mn>33</mml:mn> </mml:mrow> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_36_10_107701_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>values around 45 pm/V three times more than that of the films around 13 pm/V deposited on Pt (111)/Ti/SiO</jats:italic> <jats:sub>2</jats:sub> <jats:italic>/Si. Our findings emphasize that nano-domain switching ability and non-180° domains will contribute significantly to enhance piezoelectric responses of ferroelectric thin films.</jats:italic> </jats:p>

<jats:p> <jats:italic>We perform a computational simulation of the fluid dynamics of sodium doublet (Na-D) line emissions from one sonoluminescing bubble among the cavitation bubbles in argon-saturated Na hydroxide (NaOH) aqueous solutions. Our simulation includes the distributions of acoustic pressures and the dynamics of cavitation bubbles by numerically solving the cavitation dynamic equation and bubble-pulsation equation. The simulation results demonstrate that when the maximum temperature inside a luminescing bubble is relatively low, two emission peaks from excited Na are prominent within the emission spectra, at wavelengths of 589.0 and 589.6 nm. As the maximum temperature of the bubble increases, the two peaks merge into one peak and the full width at half maximum of this peak increases. These calculations match with the observations of Na-D line emissions from MBSL occurring in aqueous solutions of NaOH under an argon gas.</jats:italic> </jats:p>

<jats:p> <jats:italic>Heterojunction phototransistors (HPTs) with scaling emitters have a higher optical gain compared to HPTs with normal emitters. However, to quantitatively describe the relationship between the emitter-absorber area ratio (A<jats:sub>e</jats:sub>/A<jats:sub>a</jats:sub>) and the performance of HPTs, and to find the optimum value of A</jats:italic> <jats:sub>e</jats:sub> <jats:italic>/A</jats:italic> <jats:sub>a</jats:sub> <jats:italic>for the geometric structure design, we develop an analytical model for the optical gain of HPTs. Moreover, five devices with different A</jats:italic> <jats:sub>e</jats:sub>/A<jats:sub>a</jats:sub> <jats:italic>are fabricated to verify the numerical analysis result. As is expected, the measurement result is in good agreement with the analysis model, both of them confirmed that devices with a smaller A</jats:italic> <jats:sub>e</jats:sub> <jats:italic>/A</jats:italic> <jats:sub>a</jats:sub> <jats:italic>exhibit higher optical gain. The device with area ratio of 0.0625 has the highest optical gain, which is two orders of magnitude larger than that of the device with area ratio of 1 at 3 V. However, the dark current of the device with the area ratio of 0.0625 is forty times higher than that of the device with the area ratio of 1. By calculating the signal-to-noise ratios (SNRs) of the devices, the optimal value of A</jats:italic> <jats:sub>e</jats:sub> <jats:italic>/A</jats:italic> <jats:sub>a</jats:sub> <jats:italic>can be obtained to be 0.16. The device with the area ratio of 0.16 has the maximum SNR. This result can be used for future design principles for high performance HPTs.</jats:italic> </jats:p>