Dissipationless currents from topologically protected states are promising for disorder-tolerant electronics and quantum computation. Here, we photogenerate giant anisotropic terahertz nonlinear ...currents with vanishing scattering, driven by laser-induced coherent phonons of broken inversion symmetry in a centrosymmetric Dirac material ZrTe5. Our work suggests that this phononic terahertz symmetry switching leads to formation of Weyl points, whose chirality manifests in a transverse, helicity-dependent current, orthogonal to the dynamical inversion symmetry breaking axis, via circular photogalvanic effect. The temperature-dependent topological photocurrent exhibits several distinct features: Berry curvature dominance, particle–hole reversal near conical points and chirality protection that is responsible for an exceptional ballistic transport length of ~10 μm. These results, together with first-principles modelling, indicate two pairs of Weyl points dynamically created by B1u phonons of broken inversion symmetry. Such phononic terahertz control breaks ground for coherent manipulation of Weyl nodes and robust quantum transport without application of static electric or magnetic fields.Femtosecond optical pulses are used to generate coherent phonons that break inversion symmetry and drive anisotropic terahertz photocurrents in the topological material ZrTe5.
Si-nanosheets (Si-NSs) have recently attracted considerable attention due to their potential as next-generation materials for electronic, optoelectronic, spintronic, and catalytic applications. Even ...though monolayer Si-NSs were first synthesized over 150 years ago via topotactic deintercalation of CaSi2, there is a lack of consensus within the literature regarding the structure and optical properties of this material. Herein, we provide conclusive evidence of the structural and chemical properties of Si-NSs produced by the deintercalation of CaSi2 with cold (∼−30 °C) aqueous HCl and characterize their optical properties. We use a wide range of techniques, including XRD, FTIR, Raman, solid-state NMR, SEM, TEM, EDS, XPS, diffuse reflectance absorbance, steady-state photoluminescence, time-resolved photoluminescence, and thermal decomposition; when they are combined together, these techniques enable unique insight into the structural and optical properties of the Si-NSs. Additionally, we support the experimental findings with density functional theory (DFT) calculations to simulate FTIR, Raman, solid-state NMR, interband electronic transitions, and band structures. We determined that the Si-NSs consist of buckled Si monolayers that are primarily monohydride terminated. We characterize the nanosheet optical properties, finding they have a band gap of ∼2.5 eV with direct-like behavior and an estimated quantum yield of ∼9%. Given the technological importance of Si, these results are encouraging for a variety of optoelectronic technologies, such as phosphors, light-emitting diodes, and CMOS-compatible photonics. Our results provide critical structural and optical properties to help guide the research community in integrating Si-NSs into optoelectronic and quantum devices.
Topologically protected surface current is highly promising for next-generation low-dissipation and disorder-tolerant quantum electronics and computing. Yet, electric transport from the co-existing ...bulk state dominates the responses of the Dirac surface state, especially at elevated temperatures relevant to technological applications. Here, we present an approach that convincingly showcases the generation, disentanglement, and precise control of enduring surface charge carriers on a topological insulator, Bi2Se3, with high bulk conductivity, all achieved at room temperature. By using pump–probe modulation spectroscopy under ultrabroadband driving tunable from 4 meV to 1.55 eV, we show the terahertz (THz) field-induced surface carriers by discovering their initial temporal responses dominant over high density trivial bulk carriers. Strikingly, the response of the induced surface carrier responses persists for more than ∼5 ps and is enhanced by reducing pump photon energy. The dynamics and lifetime of the distinct surface response manifest themselves as the enhanced THz pump-induced THz transmission, which directly correlates with the transient negative THz conductivity. Increasing the THz driving field reduces the induced surface carrier lifetime and identifies, particularly, an optimal pump field of Es ∼ 224 kV cm−1 for generating the dominant surface response relative to the bulk. This surface carrier dominant regime is suppressed by a joint effect of enhanced surface-bulk scattering and a more rapid saturation of surface excitation compared to the bulk that sets in above Es. The controllability of room temperature topologically surface carriers through pump photon energy offer compelling possibilities for extending this approach to other topological complex materials.
We use cryogenic spatial–temporal photoluminescence (PL) imaging measurements down to 10 K and with short-wavelength, 405 nm laser excitation to study surface charge generation, trapping, and ...recombination at single bright and dark grains as well as their boundaries in model methylammonium lead iodide (MAPbI3) polycrystalline thin films. These salient conditions are shown to be critical for identifying both the detrimental and cooperative roles of grain microstructures where the dark grains serve as the PL quenching center, while the grain boundaries are largely benign and may promote electron–hole separation.
Abstract
The challenge underlying superconducting quantum computing is to remove materials bottleneck for highly coherent quantum devices. The nonuniformity and complex structural components in the ...underlying quantum circuits often lead to local electric field concentration, charge scattering, dissipation and ultimately decoherence. Here we visualize interface dipole heterogeneous distribution of individual Al/AlO
x
/Al junctions employed in transmon qubits by broadband terahertz scanning near-field microscopy that enables the non-destructive and contactless identification of defective boundaries in nano-junctions at an extremely precise nanoscale level. Our THz nano-imaging tool reveals an asymmetry across the junction in electromagnetic wave-junction coupling response that manifests as hot (high intensity) vs cold (low intensity) spots in the spatial electrical field structures and correlates with defected boundaries from the multi-angle deposition processes in Josephson junction fabrication inside qubit devices. The demonstrated local electromagnetic scattering method offers high sensitivity, allowing for reliable device defect detection in the pursuit of improved quantum circuit fabrication for ultimately optimizing coherence times.
•A new hybrid system includes a molten carbonate fuel cell and a thermionic generator.•Losses in reforming, electrochemical, and heat transfer processes are considered.•Performances of the hybrid ...system and the single MCFC are compared.•Optimal regions of some key parameters including two loads are determined.•Advantages of the present system over other MCFC-based hybrid systems are shown.
A new hybrid system consisting of an internal reforming molten carbonate fuel cell (IR-MCFC) and a vacuum thermionic generator (TIG) is constructed. By considering the main irreversible losses in two subsystems and the coupling process, general expressions for the power output and efficiency of the hybrid system are derived. The performance characteristics of the hybrid system are revealed, and the optimal regions, including the power output, efficiency, and load resistances, are determined. It is found that the maximum power output density of the IR-MCFC/TIG system increases by 22% compared to that of a single MCFC, and among the IR-MCFC- and MCFC-based hybrid systems reported in the literature, the present hybrid system can most efficiently harvest the waste heat from the MCFC.
The thermodynamic performance and optimization of a three-terminal quantum dot nano-device consisting of two capacitively coupled quantum dots connected to electron reservoirs in the Coulomb-blockade ...regime are investigated. Based on the master equation, the existing model with configuration A and a previously unreported model with configuration B of the device are studied and compared systematically. The maximum power output and efficiency of the two configurations under different given conditions are analyzed. The results obtained indicate that the working regions of the output voltage and Coulomb interaction of configuration B are significantly larger than those of configuration A. Moreover, the optimum ranges of the output voltage and Coulomb interaction of both configuration A and B are determined. A key measure of performance, i.e. the efficiency at the maximum power output, is further studied. It is found that the efficiency at the maximum power output is approximately equal to 0.035 for configuration A and 0.058 for configuration B. When the temperature difference between the two electron reservoirs is large enough, the maximum power output and efficiency at the maximum power output of configuration B are significantly larger than those of configuration A.
•Two configurations of three-terminal quantum dot engines are established.•Effects of the output voltage and Coulomb interaction are discussed.•Maximum power outputs and efficiencies of two configurations are calculated.•Performances of two configurations are optimally analyzed and compared.•Optimum ranges of the output voltage and Coulomb interaction are determined.
Abstract The coupling between superconductors and oscillation cycles of light pulses, i.e., lightwave engineering, is an emerging control concept for superconducting quantum electronics. Although ...progress has been made towards terahertz-driven superconductivity and supercurrents, the interactions able to drive non-equilibrium pairing are still poorly understood, partially due to the lack of measurements of high-order correlation functions. In particular, the sensing of exotic collective modes that would uniquely characterize light-driven superconducting coherence, in a way analogous to the Meissner effect, is very challenging but much needed. Here we report the discovery of parametrically driven superconductivity by light-induced order-parameter collective oscillations in iron-based superconductors. The time-periodic relative phase dynamics between the coupled electron and hole bands drives the transition to a distinct parametric superconducting state out-of-equalibrium. This light-induced emergent coherence is characterized by a unique phase–amplitude collective mode with Floquet-like sidebands at twice the Higgs frequency. We measure non-perturbative, high-order correlations of this parametrically driven superconductivity by separating the terahertz-frequency multidimensional coherent spectra into pump–probe, Higgs mode and bi-Higgs frequency sideband peaks. We find that the higher-order bi-Higgs sidebands dominate above the critical field, which indicates the breakdown of susceptibility perturbative expansion in this parametric quantum matter.
A model of the three-terminal nano-scaled energy conversion system as a heat engine based on two capacitively coupled quantum dots in the Coulomb-blockade regime is established within four quantum ...states that include the essential physical features. The dynamical properties of the model are calculated by master equation approach account for the quantitative behavior of such a system. Expressions for the power output and efficiency of the three-terminal quantum dot heat engine are derived. The characteristic curves between the power output and the efficiency are plotted. Moreover, the optimal values of main performance parameters are determined by the numerical calculation. The influence of dissipative tunnel processes on the optimal performance is discussed in detail. The results obtained here can provide some theoretical guidelines for the design and operation of practical three-terminal quantum dot heat engines.
•A new model of three-terminal nano-scaled quantum dot heat engines is established.•Expressions for the power output and efficiency are derived by master equation.•The general performance characteristics of the heat engine are revealed.•The effects of dissipative tunnel processes are discussed in detail.•Some important criteria of the parametric optimum design are obtained.
On the basis of the theory of irreversible thermodynamics and an elementary model of the molecular motors converting chemical energy by ATP hydrolysis to mechanical work exerted against an external ...force, the efficiencies of the molecular motors at two different optimization configurations for trade-off figure of merit representing a best compromise between the useful energy and the lost energy are calculated. The upper and lower bounds for the efficiency at two different optimization configurations are determined. It is found that the optimal efficiencies at the two different optimization configurations are always larger than 1/2.
•The optimization of molecular motors under a trade-off figure of merit criterion is studied.•The efficiencies of molecular motors at two different optimization configurations are calculated.•The upper and lower bounds for the efficiency of molecular motors are determined.•The optimal efficiencies at the two different optimization configurations are always larger than 1/2.
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