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.
Argon belongs to the class of rare and molecular gases that exhibit triple-point wetting, a regime in which adsorbed solid films remain only a few monolayers thick under thermodynamic equilibrium well below the triple point. Here we investigate the behavior of such films under nonequilibrium conditions, with particular emphasis on temperature gradients imposed within the sample cell. We show that these gradients can drive the formation of significantly thicker films than predicted by triple-point wetting theory. Our findings are motivated by, and possibly offer insight into, recent experiments with electron qubits above solid neon films, where film thicknesses substantially exceed equilibrium expectations.
Single crystals of LaxFe1−xSe0.5Te0.5 (x = 0, 0.02, 0.04, 0.06, 0.08) were grown using the self-flux method. A systematic investigation of the effects of La addition revealed changes in the lattice parameters, with the lattice parameter a decreasing and the lattice parameter c showing a slight increasing tendency. The superconducting transition temperature showed no significant dependence on La doping. However, when x reached 0.04, the critical current density derived from magnetization loops using the Bean model increased. The dominant pinning mechanism induced by La in FeSe0.5Te0.5 was identified as normal point pinning at low magnetic fields. At the same time, machine learning was employed to quantitatively model the composition–property relationship between La doping and superconducting and magnetic properties; the results indicate that this method is effective in capturing experimental trends. This work demonstrates that rare earth doping could be a viable strategy for optimizing flux pinning in iron-based superconductors.
We report the design, fabrication, microwave characterization, and room-temperature ESR demonstration of a compact planar loop-gap resonator operating near 12 GHz. The resonator was fabricated by etching a 20-µm-thick copper layer on a glass-composite substrate and consisted of a 4.2-mm-diameter circular conductor with a 0.15-mm gap. Non-contact coupling to a stripline was characterized by varying the relative lateral and vertical positions of the resonator. At the position giving the largest resonance dip, the resonance frequency and loaded Q-factor were 12.2 GHz and 67.8, respectively, corresponding to a bandwidth of approximately 180 MHz. A first-order lumped RLC description was used to interpret the measured resonance characteristics. Room-temperature continuous-wave ESR measurements of DPPH demonstrated spin detection near 12.7 GHz with a signal-to-noise ratio of approximately 20. The present results demonstrate a simple planar fabrication and coupling approach for compact ESR resonators.
Coaxial cables are widely used in radiofrequency and microwave cryogenic setups for condensed matter and quantum experiments. Since the inner conductor of coaxes is often in good thermal contact with the sample to be measured, it is desirable to know the phononic heat channeled by the inner conductor. Although cryogenic attenuators are widely used to thermalize the inner conductor of coaxes, to our knowledge, quantitative information is not available. We present data on the effectiveness of three commercially available 0 dB attenuators as thermal heatsinks. In particular, we measured the temperature of the inner pin of several 0 dB attenuators under a heat load. This information will aid in designing and carefully controlling the thermal environment of samples in high-frequency experiments mounted in dilution refrigerators and on nuclear demagnetization stages.
Abstract $$\hbox {FeSe}_{\mathrm{1-x}} \hbox {S}_{\textrm{x}}$$ FeSe 1 - x S x is known to have a characteristic phase diagram where superconducting (SC), nematic and antiferromagnetic (AFM) phases coexist or compete to each other. We report single crystal growth of $$\hbox {FeSe}_{\mathrm{1-x}} \hbox {S}_{\textrm{x}}$$ FeSe 1 - x S x and pressure effect on superconductivity for the specimens with x =0.02 through the measurements of DC magnetization ( M ) and electrical resistivity ( $$\rho$$ ρ ) as a function of temperature ( T ). Single crystals of $$\hbox {FeSe}_{\mathrm{1-x}} \hbox {S}_{\textrm{x}}$$ FeSe 1 - x S x ( $$x\le 0.17$$ x ≤ 0.17 ) with a maximum dimension of 1.5 $$\times$$ × 1.5 $$\hbox {mm}^2$$ mm 2 were successfully obtained by a chemical vapor transport method. The M ( T ) and $$\rho$$ ρ ( T ) measurements have revealed that a nematic phase is suppressed and disappears at $$\sim$$ ∼ 1.5 GPa, where superconducting transition temperature $$T_{\textrm{c}}$$ T c shows a local minimum, while AFM phases appear separately inside and outside the nematic phase. A crossover of superconductivity near the end point of AFM phase reported in our previous study for $$x\ge 0.04$$ x ≥ 0.04 was not observed for x =0.02.
With nonuniform crossed electric and magnetic fields inside a long nonconducting cylinder, we show that a non-null nonclassical moment of inertia (at zero temperature) and revival time can be obtained for s-wave from the interaction of these fields with the induced electric dipole moment of a neutral particle combined with rotation.
The hot end terminal section of a pulse tube refrigerator fundamentally shapes its internal energy transport and irreversibility. In this work, the roles of the terminal compressible volume and the high resistance structure are decoupled using three 2D axisymmetric CFD models. Under no-load conditions, the inertance pulse tube refrigerator achieves effective cooling to 84 K, whereas the model with only the high resistance structure or only the terminal compressible volume shows much poorer cooling performance. Detailed thermodynamic analyses are performed for the pulse tube, regenerator, and cold heat exchanger, with emphasis on cooling behavior, pressure–volume (PV) power and enthalpy flow conversion, and entropy generation. The results show that the main role of terminal resistance is to reduce the losses associated with viscous dissipation in the pulse tube and the pressure drop losses in the regenerator. In contrast, the terminal compressible volume mainly helps maintain stable periodic oscillating flow in the pulse tube and provides a certain phase adjustment effect, thereby improving PV power transmission. Proper matching between these two effects can effectively reduce the irreversible losses of the system and improve energy utilization efficiency. In comparison, the continuous phase shifting capability of the inertance tube plays a more critical role in increasing the transmissible PV power of the system. The calculation results at a cold-end temperature of 120 K further show that the present study can provide theoretical guidance for the optimal design of the phase shifter and the improvement of cooling performance in inertance pulse tube refrigerators.
This work investigates the effect of low-level Fe incorporation (x ≤ 0.009) in YBa2Cu3O7−δ, nominally at the Y site, on the structural and superconducting properties. X-ray diffraction confirms preservation of the orthorhombic phase with subtle changes in lattice parameters, suggesting local distortions and modifications in oxygen ordering. Resistivity measurements reveal a two-stage superconducting transition associated with intragranular pairing and intergranular coherence, consistent with weak-link behavior in polycrystalline samples. A slight maximum in characteristic temperatures is observed at x ≈ 0.2–0.3
The interfacial exchange interaction is key to realize exchange bias (EB) phenomenon in materials consisting of two different magnetic phases, which have immense applications in modern era technological development. LaCrO3 (LCO) is an antiferromagnetic (AFM) oxide, which could be utilized to perceive near room-temperature exchange bias phenomenon. In this work, we report an experimental investigation on the structural, magnetic and dielectric properties of LaCr1−xRuxO3 (0 ≤ x ≤ 0.3) through x-ray diffraction, x-ray photoelectron spectroscopy and temperature- and field-dependent magnetization and dielectric measurements. All samples are found to be crystallized in the orthorhombic structure with space group Pnma, and cell volume reveals a usual ionic radius related enhancement due to Ru4+ ion doping. The AFM transition of pure LCO is modified to ferromagnetic-like (FM-like) transition; while, transition temperature continuously decreases with increase in Ru doping concentration. Magnetization measurements indicate the formation of ferromagnetic cluster-glass state in x = 0.2 sample. We find that a tenfold increase in coercivity value for x = 0.1 as compared to x = 0, suggesting the evolution of moderate FM component. Interestingly, complex interfacial exchange interaction between host AFM matrix of LCO and induced FM phase leads to a significant EB phenomenon in the doped samples. The values of |H_EB| are found to be 2.61 kOe and 1.62 kOe at 200 K for x = 0.1 and x = 0.2, respectively. Moreover, EB effect can be tuned by varying the concentration of Ru dopants in LCO, which is fascinating from technological perspectives.
The CUPID (CUORE Upgrade with Particle IDentification) experiment searches for neutrinoless double beta decay using cryogenic detectors operating at milli-Kelvin temperatures. These systems are highly sensitive to mechanical vibrations introduced by cryocoolers, which can deteriorate calorimetric performance. In this work, we present the application of transmissibility-based Transfer Path Analysis (TPA) to a test cryostat devoted to CUPID. The method allows estimation of vibration transfer at structural interfaces without requiring force measurements, which are often impractical in cryogenic environments. Numerical simulations were performed at the 300 K plate interface using finite element models and component substructuring. The responses computed using transmissibility-based TPA showed excellent agreement with harmonic response simulations, validating the approach. This study establishes the basis for extending the methodology to colder stages (35 K, 3.5 K), where vibration coupling is more critical. Beyond validating the method, the results provide new insights into the dominant transfer paths at room temperature, thereby supporting the design of improved vibration isolation strategies for next-generation cryogenic detectors.
We investigate multiple-Q magnetic states in a triangular-lattice spin model with a D_3d -type anisotropic interaction under in-plane magnetic fields. Focusing on the interplay between anisotropy and field orientation, we examine how the magnetic phases evolve when the field is applied along two inequivalent in-plane directions. By means of simulated annealing, we identify a wide variety of field-induced phases, including both topological and non-topological multiple-Q states. In the strong-anisotropy regime, the skyrmion crystal with a higher topological number of two, stabilized at zero field, is transformed into the conventional skyrmion crystal with a topological number of one under increasing magnetic field. This transition occurs without a change in the principal ordering wave vectors, indicating that a subtle reorganization of the triple-Q components governs the change in topology. In contrast, in the weak-anisotropy regime, the magnetic behavior is sensitive to the direction of the applied magnetic field. The system eventually selects a single-Q state for the x-directional magnetic field, while it continues to reside within the multiple-Q states, exhibiting several distinct triple-Q states characterized by different intensity distributions among the symmetry-related ordering wave vectors for the y-directional magnetic field. These results demonstrate that the direction of an in-plane magnetic field plays an active role in selecting competing magnetic states, not only modifying phase boundaries but also controlling the topology and internal structure of the spin textures. Our findings highlight a route to manipulate multiple-Q states in centrosymmetric magnets through the combined effect of anisotropic interactions and field orientation.
We study the quantum metrological properties of two coupled double quantum dots, where coherent tunneling and Coulomb interaction jointly govern the system dynamics. Using the quantum Fisher information framework, we evaluate the ultimate precision limits for estimating the interaction strength and temperature. We compare simultaneous and independent estimation strategies and show that parameter correlations strongly influence the achievable precision. In the simultaneous scheme, correlations may induce near-singular behavior of the quantum Fisher information matrix, leading to pronounced precision degradation in specific parameter regions. By contrast, independent estimation yields a more stable and robust precision profile. A quantitative comparison between the two strategies identifies the regimes where each approach is advantageous. Our results demonstrate that the metrological performance of coupled quantum dots is determined not only by intrinsic quantum sensitivity but also by interaction-induced correlations, providing guidance for optimizing quantum sensing protocols in solid-state nanoscale systems.
Superconductors in nano-sized shape are investigated. Superconductor and also electrons which form superconductivity have quantum nature. This means when size of superconductor is small, there appear quantum effects. The critical temperature T_c becomes higher than that of a bulk superconductor. In the extremely dirty nano-sized superconductor, the critical temperature becomes much higher than that of a clean nano-sized superconductor. This is because a part of superconducting electrons concentrates in a localized state and has a high density of states. However, if the superconducting state remains localized below T_c , resistivity may not be zero just below T_c . Therefore we investigate how this localized state of superconductivity develops with decreasing temperature below T_c . We show this localized state extends to whole superconductor just below T_c .
Rare earth sesquisulfides α - R_2 S _3 (R = Dy, Sm) possess an orthorhombic crystal structure having two crystallographically inequivalent rare earth sites, R1 and R2. The compound α - Dy_2S_3 exhibits successive antiferromagnetic transitions at T_N1 = 11.4 K and T_N2 = 6.4 K, while α -Sm _2 S _3 shows successive weak-ferromagnetic transitions at T_C1 = 3.6 K and T_C2 = 1.8 K. Furthermore, they are fascinating because they exhibit a very large increase and recovery in electrical resistivity within a narrow temperature range just above T_N2 and T_C1 , respectively. In this study, the AC magnetic susceptibility was measured near T_N1 and T_N2 using α -Dy _2 S _3 single crystals, and near T_C1 using α -Sm _2 S _3 single crystals. The imaginary part of AC susceptibility for each compound exhibited sharp peak near T_N2 or T_C1 , respectively, clearly indicating a phase delay in the magnetic moment motion within each temperature range, where it could not follow the changes in the AC magnetic field. Furthermore, it was found that in α -Dy _2 S _3 , the peak height increases with increasing AC magnetic field frequency, whereas in α -Sm _2 S _3 , it decreases, reflecting the difference in magnetic ordering between the two compounds.
PdSb _2 is a metal in which band structure calculations suggest the presence of sixfold-degenerate fermions. Surface bands emerging from the sixfold-degenerate point may exhibit nontrivial topological properties. Here, we present Scanning Tunneling Microscopy (STM) measurements of PdSb _2 between 4.2 and 60 K and under magnetic fields up to 14 T. We identify a gap-like feature with a width of approximately 20 meV around the Fermi level. We additionally provide Density Functional Theory (DFT) calculations and discuss the possible connection between the observed tunneling conductance and the surface band structure. We find a small incomplete gap-like feature in the density of states which has a similar size as the feature observed in the experiment but is located slightly above the Fermi level. We furthermore estimate surface relaxation of atomic positions and find that Sb suffers larger relaxations than Pd atoms. This could influence the position in energy of the features found in the band structure. Our measurements show that PdSb _2 is a good metal, with a density of states which presents, however, interesting features close to the Fermi level.
Polylactic acid (PLA) is a material often used in 3D printing. However, its low-temperature thermal properties are not well known. In this paper, we present results of measurements of the thermal contraction of two samples of PLA made by different manufacturers. We constructed a capacitance dilatometer and used it to measure the length variations of PLA continuously from room temperature to 4K. We found that in both cases, the sample’s length changed by approximately 1–1.2
