Journal of Low Temperature Physics最新文献

We argue that the author of a recent paper failed to calculate the partition function correctly and for this reason derived thermodynamic functions that are unsuitable for any physical application.

The study examines a fascinating combination of ferromagnetic leads and double quantum dots in a hybrid system. The "two coupled quantum dots Anderson model" is employed to model the coupled quantum dots and simulate the energy levels of the double coupled quantum dots, which interact with both left and right ferromagnetic leads to investigate the process of spin tunneling. This study discusses the role of coupling interaction between quantum dots the Coulomb correlation within each quantum dot, and their connection with the ferromagnetic leads. We determine the occupation number of the energy levels in the quantum dots and solve it in a self-consistent manner. These solutions are then used to compute each quantum dot's spin accumulation. The results are used to compute the spin current tunneling and examine the system's transport characteristics.

Recent advances in the development of cryogenic particle detectors such as magnetic microcalorimeters allow the fabrication of sensor arrays with an increasing number of pixels. Since these detectors must be operated at the lowest temperatures, the readout of large detector arrays is still quite challenging. This is especially true for the ECHo experiment, which presently aims to simultaneously run 6,000 two pixel detectors to investigate the electron neutrino mass. For this reason, we developed a readout system based on a microwave SQUID multiplexer ((mu)MUX) that is operated by a custom software-defined radio (SDR) at room-temperature. The SDR readout electronics consist of three distinct hardware units: a data processing board with a Xilinx ZynqUS+ MPSoC; a converter board that features DACs, ADCs, and a coherent clock distribution network; and a radio frequency front-end board to translate the signals between the baseband and the microwave domains. Here, we describe the characteristics of the full-scale SDR system. First, the generated frequency comb for driving the (mu)MUX was evaluated. Subsequently, by operating the SDR in direct loopback, the crosstalk of the individual channels after frequency demultiplexing was investigated. Finally, the system was used with a 16-channel (mu)MUX to evaluate the linearity of the SDR, and the noise contributed to the overall readout setup.

It is well-known that diatomic molecules are molecules that consist of two atoms bonded together chemically. The use of diatomic molecules is broad and has various applications in different fields of study, such as physical sciences and life sciences. Therefore, in this study, the effects of magnetic and AB-flux fields on thermodynamic properties of hydrogen (H₂), lithium hydride (LiH), hydrogen chloride (HCl) and carbon monoxide (CO) diatomic molecules are investigated. The analytical expressions for the partition function are derived using the energy equation by employing the Euler–Maclaurin summation formula. These properties obtained are thoroughly analyzed utilizing graphical representations as a function of temperature. It was observed that the entropy of the CO diatomic molecule exhibits a paramagnetic behavior which agrees with the Linde cycle when the system is subjected to the magnetic and AB-flux fields. Our findings will be valuable in various technological and scientific fields such as magnetic refrigeration, magnetic levitation, magnetic separation, magnetic storage, magnetic resonance imaging and magnetic force microscopy.

COSINUS will be among the first underground experiments to operate Transition Edge Sensors in a dry dilution refrigerator, measuring temperature changes on the order of (mu)K. A pulse tube cryocooler is used to cool down to 3K, trading simplified handling, by not using liquid noble gases, for an increased vibration noise level in the acoustic frequency range. As the signals measured with a TES are in the same frequency region, it is necessary to decouple the detectors from all possible noise sources. In COSINUS, a two-level passive decoupling system was developed and tested using piezo-based accelerometers. At the first level, the refrigerator is mechanically isolated from all external noise sources. For the second level an internal spring-based system was developed and tested on a mockup system. On the first level a reduction of the vibrational background up to a factor 4 below 10 Hz could be measured. On the second level a resonance frequency of 1.2 Hz with damping of higher frequencies was achieved.

Based on the dissipative Gross–Pitaevskii equation, effects of dissipation strength and interaction strength on the linear instability and the splitting processes of quadruply quantized vortices are studied. Using the linear perturbation theory to calculate out the elementary excitation modes of the quadruply quantized vortices, we reveal a novel and very important dynamical transition of the most unstable mode. It is found that the most unstable mode is the twofold rotational symmetry mode at a small dissipation strength, while it is the fourfold rotational symmetry mode at a larger dissipation strength. What’s more, the transition dissipation strength decreases with the increase in the interaction strength. The full nonlinear numerical simulations further demonstrate the process of such a dynamical transition. Our work has shed light on the long-standing puzzle in Bose–Einstein condensate, why the fourfold rotational symmetry splitting pattern of quadruply quantized vortex has not yet been observed in the laboratory. We propose a promising direction to solve this problem by increasing the dissipation strength or the interaction strength. Our predictions are likely to be tested in the laboratory in the near future.

We describe a compact calorimeter that opens ultra-low-temperature heat capacity studies of small metal crystals in moderate magnetic fields. The performance is demonstrated on the canonical heavy fermion metal YbRh(_{2})Si(_{2}). Thermometry is provided by a fast current sensing noise thermometer. This single thermometer enables us to cover a wide temperature range of interest from 175 µK to 90 mK with temperature-independent relative precision. Temperatures are tied to the international temperature scale with a single-point calibration. A superconducting solenoid surrounding the cell provides the sample field for tuning its properties and operates a superconducting heat switch. Both adiabatic and relaxation calorimetry techniques, as well as magnetic field sweeps, are employed. The design of the calorimeter results in an addendum heat capacity which is negligible for the study reported. The keys to sample and thermometer thermalisation are the lack of dissipation in the temperature measurement and the steps taken to reduce the parasitic heat leak into the cell to the tens of fW level.

COSINUS is a new cryogenic observatory for rare event searches located in the Laboratori Nazionali del Gran Sasso in Italy. COSINUS’s first goal is to clarify whether the signal detected by the DAMA/LIBRA experiment originates from dark matter particle interactions or has a different nature. To this aim, sodium iodide (NaI) cryogenic scintillating calorimeters read out by transition edge sensors (TESs) are developed. To preserve the NaI crystal from the TES fabrication process, COSINUS implemented a novel design, the remoTES, where the TES is deposited on a separate wafer and coupled to the absorber through a Au-bonding wire and a Au-phonon collector. This design has reached baseline resolutions below 100 eV for Si, 200 eV for (hbox {TeO}_2) and 400 eV for NaI absorbers. These results show that the remoTES not only brings COSINUS close to its performance goal of 1 keV energy threshold, but also offers the possibility to employ delicate crystals previously excluded for cryogenic applications as absorbers and to avoid the exposure of the absorbers to the TES fabrication process. It therefore extends the choice of target materials of the rare event searches using TES. In this work, we will provide a detailed description of the remoTES design and present the results of the latest prototypes.

In this work, we study the proximity effects in a single- and two-band superconducting three-dimensional heterostructure, described by two condensates (condensate 1 and condensate 2) in the presence of an external magnetic field perpendicular to the heterostructure. The distance between the interfaces of both condensates is given by the parameter (lambda '). We solve the time-dependent Ginzburg-Landau equations considering a Josephson-like coupling to explore properties such as magnetization, Gibbs free energy, and the Abrikosov vortex state. We propose three cases: case 1, both condensates are composed of a single-band; case 2, the condensates are composed of two bands; and case 3, condensate 1 has a single-band and condensate 2 has two bands. As a result, we highlight the variation of the first critical field and the novel vortex configurations induced by the proximity effect between the superconducting condensates. This phenomenon substantially influences the arrangement of vortices in each of the superconducting bands.

In this paper, the proposal for a new multichroic pixel camera for the QUBIC instrument is presented, which aims to measure the B-mode polarization of the cosmic microwave background. The camera features antenna-coupled magnetic microbolometers (MMB) read out by a microwave SQUID multiplexer and software-defined radio-based room-temperature electronics, which are specifically optimized for MMB readout. The architecture of the detectors and their readout system is introduced, and the main design considerations are also discussed. The initial results of the simulation study suggest that MMBs are capable of achieving background-limited detection of the sky when used in an instrument like QUBIC. Additionally, the time response of these detectors appears to be sufficiently fast for the given telescope scan speed and beam size.