rf-SQUID measurements of anomalous Josephson effect

We discuss the response of an rf-SQUID formed by anomalous Josephson junctions embedded in a superconducting ring with a non-negligible inductance. We demonstrate that a properly sweeping in-plane magnetic field can cause both the total flux and the current circulating in the device to modulate and to behave hysteretically. The bistable response of the system is analyzed as a function of the anomalous phase shift at different values of the screening parameter, in order to highlight the parameter range within which a hysteretic behavior can be observed. The magnetic flux piercing the SQUID ring is demonstrated to further modulate the hysteretical response of the system. Moreover, we show that the anomalous phase shift can be conveniently determined through the measurement of the out-of-plane magnetic field at which the device switches to the voltage state and the number of trapped flux quanta changes. Finally, we compare the response of two different device configurations, namely, a SQUID including only one or two anomalous junctions. In view of these results, the proposed device can be effectively used to detect and measure the anomalous Josephson effect

Optoelectronic memory in 2D MoS2 field effect transistor

2D layered materials with their tunable bandgap and unique crystal structures are excellent candidates for 2D optoelectronic memories. In this work, we present a simple approach for the realization of a nonvolatile optoelectronic memory device based on a MoS2 transistor with light induced charge storage capability. The MoS2 transistor shows 10^8 on/off current ratio and hysteresis width modulation by air pressure under normal and quiet measurement conditions. Moreover, the device shows persistent photoconductivity and exhibits excellent photo responsive memory performance with a current switching ratio of two orders of magnitude and a photocurrent that increases linearly with the incident light power. We show that a combination of gate voltage and light can be used to control the transistor current and increase the memory window by two orders of magnitude. The obtained results are a significant step toward the improvement of optoelectronic devices, showing that the combination of gate voltage and light can enable a multilevel memory device

Hysteresis and Photoconductivity of Few‐Layer ReSe2 Field Effect Transistors Enhanced by Air Pressure

This study reports the optoelectronic characterization of few-layer ReSe2 field effect transistors at different pressures. The output curves reveal dominant n-type behavior and a low Schottky barrier at the metal contacts. The transfer curves show a significant hysteresis that can be exploited in memory devices with an order of magnitude memory window and good cycling. The devices are dramatically affected by air pressure; their conductance and mobility increase with the lowering pressure that desorbs electronegative air molecules from the surface of the material. The photoresponse under white super-continuum laser illumination reveals that the device exhibits positive photoconductivity (PPC) at ambient and low (≈1 mbar) pressure and negative photoconductivity (NPC) in a higher vacuum (≈10−4 mbar). The transition from PPC to NPC can be explained by considering that the photoresponse is affected by molecule desorption, which yields PPC at higher pressure, and defect trapping of photogenerated carriers, which can dominate at lower pressures. The transient behavior of the device exposed to laser pulses shows a faster response and a higher photodetection efficiency at ambient pressure, with the highest signal-to-noise ratio at the valley of the transfer curve between p- and n-type conduction

Investigation of crystallization in nanolayered TiO2-based superlattices

In the realm of high precision optical applications, such as gravitational wave detectors, the quest for optical coatings with exceptional characteristics, such as high reflectivity, high optical density, and low thermal noise, requires meticulous attention. Achieving the requested optical quality demands a comprehensive approach encompassing design, production, and characterization. A recent study by I.M. Pinto et al. explored the potential of nanolayer-based superlattices as a valuable alternative to the high refractive index component of dielectric Bragg-like mirrors [https://dcc.ligo.org/LIGO-G1301061, https://dcc.ligo.org/LIGO-G1902307]. Following the proposed approach, we have produced and investigated binary nanolayers, employing a combination of TiO2 with other oxides, such as SiO2, Ta2O5, Al2O3, and ZrO2. Within our superlattice structures, each layer's thickness ranges from a few to a few tens of nanometers. It is tailored, together with the number of nanolayers composing the structure, to cater to optical applications involving a light wavelength of 1064 nm (as for the laser of gravitational wave detectors). Our findings indicate that the superlattice structures fulfill the morphological and structural requirements for application in high precision optics when TiO2 is as thin as 2 nm. In this case, the surface attains a level of flatness on the nanometer scale – making spurious light scattering negligible – and its crystallization temperature Tc, a key parameter for reaching high optical quality, exceeds 500 °C. Finally, we demonstrate that further tuning of Tc is possible by varying the interface energy, thus changing the material coupled with TiO2 within the superlattice. This discovery paves the way for even greater control and optimization of these proposed metamaterials

A Josephson phase battery

A classical battery converts chemical energy into a persistent voltage bias that can power electronic circuits. Similarly, a phase battery is a quantum device that provides a persistent phase bias to the wave function of a quantum circuit. It represents a key element for quantum technologies based on phase coherence. Here we demonstrate a phase battery in a hybrid superconducting circuit. It consists of an n-doped InAs nanowire with unpaired-spin surface states, that is proximitized by Al superconducting leads. We find that the ferromagnetic polarization of the unpaired-spin states is efficiently converted into a persistent phase bias φ0 across the wire, leading to the anomalous Josephson effect1,2. We apply an external in-plane magnetic field and, thereby, achieve continuous tuning of φ0. Hence, we can charge and discharge the quantum phase battery. The observed symmetries of the anomalous Josephson effect in the vectorial magnetic field are in agreement with our theoretical model. Our results demonstrate how the combined action of spin–orbit coupling and exchange interaction induces a strong coupling between charge, spin and superconducting phase, able to break the phase rigidity of the system

Two-dimensional α-In2Se3 field effect transistor for wide-band photodetection and non-volatile memory

Mechanically exfoliated two-dimensional -In2Se3 flakes are used as the channel material in field effect transistors. N-type conduction with 0.14 (cm^2)/Vs carrier mobility is reported. The good gate modulation and the pronounced hysteresis make the device suitable for a wide range of applications, from digital logics to memories. An order of magnitude current increase is observed under illumination by a blue light at the incident optical power of 19 nW. The devices can work as visible-to-infrared wide-band photodetectors with time response of few-hundred milliseconds, responsivity up to 40 A/W and specific detectivity D^*= 5⋅10^11 Jones at low light intensity