CaAgP has been accepted as a nodal-line semimetal exhibiting unusual physical properties, such as anomalous magnetoresistance, high-mobility electron carriers (HMEC), and surface superconductivity. In this study, we performed angular-dependent Hall resistivity and magnetoresistance measurements on Pd-doped CaAgP single crystals, with the applied current oriented parallel (I // c) and perpendicular (I ⟂ c) to the c-axis. Analysis of the Hall resistivity using a two-carrier model reveals that the electron contribution was larger for the I ⟂ c configuration, which was more seriously influenced by the (001) surface. Moreover, the Hall resistivity exhibits different angular dependences between the high- and low-field regimes. These findings indicate that the HMEC are highly concentrated on the (001) surface. Meanwhile, the angular dependences of the magnetoresistance are interpreted as arising from the competition between two-dimensional weak antilocalization and three-dimensional weak localization, consistent with the presence of a torus-shaped nontrivial Fermi surface. Taken together, the Hall resistivity and magnetoresistance results demonstrate that Pd-doped CaAgP is a nodal-line semimetal hosting drumhead surface states on the (001) surface.
In this work, quantum mechanics theory was applied to the thermoacoustic heat pump, and a quantum mechanical model within a one-dimensional harmonic potential well, namely the quantum thermoacoustic heat pump micro-cycle (TAHPMC), was constructed. Based on this model, the coefficient of performance COP and heating rate H of the thermoacoustic heat pump were derived, and dimensionless form H^* of H was defined for further analysis. The effects of the characteristic width of the potential well A and the width ratio y on these two parameters were systematically analyzed. To achieve synergistic optimization of the two performance indicators, an optimization objective function Ω was established. Through numerical optimization, the parameter interval that optimizes the comprehensive performance of COP and H^* was identified, and it was proved that the reduction in heat leakage can significantly improve the heating capability of the thermoacoustic heat pump.
We investigate the quantum transport through a rectangular velocity barrier in the α - 𝒯_3 lattice. The scattering states are solved analytically, and the transport properties including conductance, shot noise, and Fano factor are obtained by following the zero-temperature Landauer–Büttiker formalism. The velocity mismatch across the barrier reshapes oblique tunneling channels while preserving the perfect transmission at normal incidence. In particular, this velocity mismatch shifts the critical incident energy for super-Klein tunneling, where transport becomes nearly noiseless as the conductance approaches unity. At the Dirac point, the velocity modulation leaves the finite conductance minimum of the honeycomb limit intact, accompanied by a universal Fano factor peak. In the dice limit, however, both conductance and shot noise vanish at this point owing to channel depletion. In addition, a slow barrier facilitates the high-energy transport for the dice lattice, while a fast barrier can suppress it in both lattice limits.
Phase-sensitive parametric devices facilitate quadrature-selective amplification with the possibility for sub-quantum-limited noise performance. In this work, we investigate the operation of a SQUID-based Josephson parametric amplifier (JPA), comparing its gain and noise performance in the phase-preserving and phase-sensitive regimes. The device, fabricated using VTT SWAPS technology, is driven in a three-wave mixing configuration and characterized in a reflection-based measurement setup at millikelvin temperatures. To directly probe the noise performance at low JPA gains, we employ a cascaded amplification scheme in which a traveling-wave parametric amplifier (TWPA) provides low-noise preamplification of the JPA output. In a phase-preserving operation, the JPA exhibits near-quantum-limited performance with a system noise temperature of 351± 53 mK at 6 GHz. In contrast, phase-sensitive operation yields a minimum system noise temperature of 94± 12 mK, well below the standard quantum limit of 288 mK. Our results demonstrate that a JPA–TWPA amplifier cascade opens the door to direct, high-fidelity probing of quantum devices without the need for background noise subtraction.
