Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Universal size-dependent nonlinear charge transport in single crystals of the Mott insulator Ca2_2RuO4_4

The surprisingly low current density required for inducing the insulator to metal transition has made Ca$_2$RuO$_4$ an attractive candidate material for developing Mott-based electronics devices. The mechanism driving the resistive switching, however, remains a controversial topic in the field of strongly correlated electron systems. Here we probe an uncovered region of phase space by studying high-purity Ca$_2$RuO$_4$ single crystals, using the sample size as principal tuning parameter. Upon reducing the crystal size, we find a four orders of magnitude increase in the current density required for driving Ca$_2$RuO$_4$ out of the insulating state into a non-equilibrium (also called metastable) phase which is the precursor to the fully metallic phase. By integrating a microscopic platinum thermometer and performing thermal simulations, we gain insight into the local temperature during simultaneous application of current and establish that the size dependence is not a result of Joule heating. The findings suggest an inhomogeneous current distribution in the nominally homogeneous crystal. Our study calls for a reexamination of the interplay between sample size, charge current, and temperature in driving Ca$_2$RuO$_4$ towards the Mott insulator to metal transition

Crystal growth and Hall effect of the non-centrosymmetric superconductor α-BiPd and the topological superconductor β-Bi2Pd

Due to the rarity of triplet pairing, topological superconductors (SCs) have primarily been realized experimentally in manufactured topological phases, such as heterostructures, where the proximity effect causes triplet pairing with traditional s-wave SCs. Recently, there has been a lot of interest in investigating novel quantum materials with spin-triplet pairs in order to develop Majorana physics and creating quantum computers. Bi-based superconductors are speculated to hold promise for realizing spin-triplet pairing due to its large spin orbit coupling. In this work, we present the growth of α-BiPd and β-Bi2Pd single crystals using the optical floating zone technique and their characterization. The single crystals of α-BiPd and β-Bi2Pd are found to crystallize in monoclinic and tetragonal crystalline system with space group P21 and I4/mmm, respectively. The composition and microstructure of the grown crystals were analyzed with a scanning electron microscope, through energy dispersive spectroscopy (EDS) and electron backscattered diffraction (EBSD) analysis. The superconducting behavior and Hall effect of both α-BiPd and β-Bi2Pd single crystals have been investigated through resistivity measurements

Impact of Acetate-Based Hydrogel Electrolyte on Electrical Performance and Stability of Eco-Friendly Supercapacitors

The electrochemical characteristics and stability of hydrogel-based environmentally friendly supercapacitors employing sodium acetate as salt have been investigated. To ensure the overall sustainability of the devices, chitosan (a biomaterial from renewable resources) and activated carbon (derived from coconut shells) have been used as a binder and filler within the electrodes, respectively. Cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy measurements have been performed to compare the electrochemical properties of the fabricated devices. Compared to reference electrolytes containing NaCl, the utilization of sodium acetate exhibited enhancements in energy performance and stability up to 50000 cycles. The most efficient device has been delivered approximately 10.6?Wh/kg of energy at a high-power density of about 3940?W/kg. A comprehensive investigation of the electrochemical performances has been carried out, considering both faradaic and non-faradaic processes as charge storage mechanisms within the devices. A model has been proposed to describe the storage mechanisms and to provide insights into the ageing phenomena observed during the cycling procedure

Current-driven insulator-to-metal transition without Mott breakdown in Ca2RuO4

The electrical control of a material's conductivity is at the heart of modern electronics. Conventionally, this control is achieved by tuning the density of mobile charge carriers. A completely different approach is possible in Mott insulators such as Ca2RuO4, where an insulator-to-metal transition (IMT) can be induced by a weak electric field or current. While the driving force of the IMT is poorly understood, it has been thought to be a breakdown of the Mott state. Using in operando angle-resolved photoemission spectroscopy, we show that this is not the case: The current-induced conductivity is caused by the formation of in-gap states with only a minor reorganization of the Mott state. Electronic structure calculations show that these in-gap states form at the boundaries of structural domains that emerge during the IMT. At such boundaries, the overall gap is drastically reduced, even if the structural difference between the domains is small and the individual domains retain their Mott character. The inhomogeneity of the sample is thus key to understanding the IMT, as it leads to a nonequilibrium semimetallic state that forms at the interface of Mott domains

Modeling of Josephson Traveling Wave Parametric Amplifiers

The recent developments in quantum technologies, as well as advanced detection experiments, have raised the need to detect extremely weak signals in the microwave frequency spectrum. To this aim, the Josephson travelling wave parametric amplifier, a device capable of reaching the quantum noise limit while providing a wide bandwidth, has been proposed as a suitable cryogenic front-end amplifier. This work deals with the numerical study of a Josephson travelling wave parametric amplifier, without approximations regarding the nonlinearity of the key elements. In particular, we focus on the investigation of the system of coupled nonlinear differential equations representing all the cells of the Josephson travelling wave parametric amplifier, with proper input and output signals at the boundaries. The investigation of the output signals generated by the parametric amplification process explores the phase-space and the Fourier spectral analysis of the output voltage, as a function of the parameters describing the pump and signal tones that excite the device. Beside the expected behavior, i.e., the signal amplification, we show that, depending on the system operation, unwanted effects (such as pump tone harmonics, incommensurate frequency generation, and noise rise), which are not accounted for in simple linearized approaches, can be generated in the whole nonlinear system