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Source–drain contacts seriously affect low frequency noise (LFN) in amorphous IZO (a-IZO) thin-film transistors with bilayer ITO/Mo electrodes at cryogenic temperatures. In the range of 7–300 K, electrical and LFN performances of devices are measured, and the temperature dependence of channel resistances (Rch) and contact resistances (Rsd) is also analyzed. The carrier transport transition both occurs in a-IZO channels at 80 K and in ITO/Mo electrodes at 100 K, which causes the variation in Rsd and Rch. Below 80 K, the variable range hopping conduction dominates in the channels and contacts with Rsd/Rch ratio > 1. The LFN measured results indicate that the noise is contact-dominated. At higher temperatures above 120 K, the band conduction dominates in the channel, with Rsd/Rch ratio < 1, and the noise is channel-dominated. The main mechanism of noise transfers from the mobility fluctuation to the carrier number fluctuation. We consider that the contribution of contact noise to total LFN is determined by the Rsd/Rch ratio. This work provides comments for the selection of electrode materials in devices applied to cryogenic integration circuits. [ABSTRACT FROM AUTHOR]

We introduce a design modification to conventional geometry of the cryogenic three-terminal switch, the nanocryotron (nTron). The conventional geometry of nTrons is modified by including parallel current-carrying channels, an approach aimed at enhancing the device's performance in magnetic field environments. The common challenge in nTron technology is to maintain efficient operation under varying magnetic field conditions. Here, we show that the adaptation of parallel channel configurations leads to an enhanced gate signal sensitivity, an increase in operational gain, and a reduction in the impact of superconducting vortices on nTron operation within magnetic fields up to 1 T. Contrary to traditional designs that are constrained by their effective channel width, the parallel nanowire channels permits larger nTron cross sections, further bolstering the device's magnetic field resilience while improving electro-thermal recovery times due to reduced local inductance. This advancement in nTron design not only augments its functionality in magnetic fields but also broadens its applicability in technological environments, offering a simple design alternative to existing nTron devices. [ABSTRACT FROM AUTHOR]

Electromagnetic noise is one of the main external factors decreasing superconducting qubit coherence. Matched coaxial filters can prevent microwave and IR photons' negative influence on superconducting quantum circuits. In this report, we describe the design and fabrication process of matched coaxial filters for noise-sensitive measurements at millikelvin temperatures. A robust transmission coefficient and ultralow reflection loss of −20 dB in the frequency range up to 20 GHz is achieved. Fabricated low-pass filters have linear transmission and reflection characteristics with 3 dB-cutoff frequency of 1.5–2.5 GHz. A method for extracting the propagation constant and filter impedance from scattering parameter measurements is demonstrated. This method is experimentally approved on a filter with a compound of Cu powder and Stycast epoxy resin and a filter filled with ECCOSORB CR-110 epoxy resin. The proposed design and assembly technology are versatile for various compounds and provide highly repeatable geometric and microwave characteristics. Furthermore, we demonstrate that these low-pass coaxial filters can be effectively utilized to improve superconducting qubit relaxation due to suppressing standing waves originating from reflections in control coaxial cables. [ABSTRACT FROM AUTHOR]

While semiconductor-based spin qubits have demonstrated promising fidelities exceeding 99.9%, their coherence time is limited by the presence of charge noise. However, fast process optimization for reduced charge noise becomes challenging due to the time-consuming nature of cryogenic measurements. Hence, this work explores low frequency analysis methods to determine interface trap densities, their temperature dependence, and correlation with observed noise levels. The herein presented results provide evidence for strong temperature dependence of the interface trap density. Moreover, good agreement is observed between charge pumping and conductance-based methods. Finally, differences in temperature dependent trends of flicker noise are observed, indicating additional influences, which need to be considered for further device optimization. [ABSTRACT FROM AUTHOR]

Color centers in diamond, among them the negatively charged germanium vacancy (GeV−), are promising candidates for many applications of quantum optics, such as a quantum network. For efficient implementation, the optical transitions need to be coupled to a single optical mode. Here, we demonstrate the transfer of a nanodiamond containing a single ingrown GeV− center with excellent optical properties to an open Fabry–Pérot microcavity by nanomanipulation utilizing an atomic force microscope. Coupling of the GeV− defect to the cavity mode is achieved, while the optical resonator maintains a high finesse of F = 7700 , and a 48-fold spectral density enhancement is observed. This article demonstrates the integration of a GeV− defect with a Fabry–Pérot microcavity under ambient conditions with the potential to extend the experiments to cryogenic temperatures toward an efficient spin-photon platform. [ABSTRACT FROM AUTHOR]

Trapped-ion quantum information processing may benefit from qubits encoded in isotopes that are practically available in only small quantities, e.g., due to low natural abundance or radioactivity. Laser ablation provides a method of controllably liberating neutral atoms or ions from low-volume targets, but energetic ablation products can be difficult to confine in the small ion-electrode distance, micron-scale microfabricated traps amenable to high-speed, high-fidelity manipulation of ion arrays. Here, we investigate ablation-based ion loading into surface-electrode traps of different sizes to test a model describing ion loading probability as a function of effective trap volume and other trap parameters. We characterize loading of ablated barium from a metallic source in two cryogenic surface-electrode traps with 730 and 50 μm ion-electrode distances. Our loading rate agrees with a predictive analytical model, providing insight for the confinement of limited-quantity species of interest for quantum computing, simulation, and sensing. [ABSTRACT FROM AUTHOR]

Compared to traditional semiconductor control electronics (TSCE) located at room temperature, cryogenic single flux quantum (SFQ) electronics can provide qubit measurement and control alternatives that address critical issues related to scalability of cryogenic quantum processors. Single-qubit control and readout have been demonstrated recently using SFQ circuits coupled to superconducting qubits. Experiments where the SFQ electronics are co-located with the qubit have suffered from excess decoherence and loss due to quasiparticle poisoning of the qubit. A previous experiment by our group showed that moving the control electronics to the 3 K stage of the dilution refrigerator avoided this source of decoherence in a high-coherence three-dimensional transmon geometry. In this paper, we also generate the pulses at the 3 K stage but have optimized the qubit design and control lines for scalable two-dimensional transmon devices. We directly compare the qubit lifetime T 1 , coherence time T 2 * , and gate fidelity when the qubit is controlled by the Josephson pulse generator (JPG) circuit vs the TSCE setup. We find agreement within the daily fluctuations for T 1 and T 2 * , and agreement within 10% for randomized benchmarking. We also performed interleaved randomized benchmarking on individual JPG gates demonstrating an average error per gate of 0.46% showing good agreement with what is expected based on the qubit coherence and higher-state leakage. These results are an order of magnitude improvement in gate fidelity over our previous work and demonstrate that a Josephson microwave source operated at 3 K is a promising component for scalable qubit control. [ABSTRACT FROM AUTHOR]

Manipulating heat fluxes at the nanoscale has become increasingly important in modern microelectronics. However, many methods of heat manipulations rely on complex nanofabrication. Here, we propose simple designs for collimation and focusing of thermal phonons based on parabolic mirrors that require no nanofabrication. We perform Monte Carlo simulations of a ballistic phonon transport in silicon membranes with parabolic boundaries. Our simulations demonstrate that parabolic surfaces can act as parabolic mirrors for phonons, thus collimating or focusing phonon fluxes in semiconductors. Such parabolic mirrors can create a directional flux of thermal phonons emitted from a nanoscale hot spot or focus a collimated phonon flux into a hot spot. These devices open new possibilities in the thermal management of low-temperature systems, such as quantum circuits or cryogenic particle detectors. [ABSTRACT FROM AUTHOR]

For optical refrigeration to become a viable option for cryogenics, it is fundamental to improve the overall cooling power of an optical cryocooler. In this paper, we propose a design that might be able to cool down a thermal load to temperatures lower than ever before: the parallel configuration. We explore the possibility of attaching a thermal load to multiple Yb:YLF monocrystals, which would allow us to use more pump intensity without surpassing the saturation limit, and we show that by using two YLF:5% Yb crystals connected to an undoped YLF sample (that acts both as a thermal link and a thermal load) we obtained a ΔT increase in 40% compared to a setup with the load and a single crystal. [ABSTRACT FROM AUTHOR]

We investigate the coupled magnetization dynamics in heterostructures of a single crystal of the chiral magnet Cu 2 OSeO 3 (CSO) and a polycrystalline ferromagnet NiFe (Py) thin film using broadband ferromagnetic resonance (FMR) at cryogenic temperatures. We observe the excitation of a hybrid mode (HM) below the helimagnetic transition temperature of CSO. This HM is attributed to the spin dynamics at the CSO/Py interface. We study the HM by measuring its resonance frequencies for in plane rotations of the external magnetic field. We find that the HM exhibits dominantly fourfold anisotropy in contrast to the FMR of CSO and Py. [ABSTRACT FROM AUTHOR]

Microwave loss in niobium metallic structures used for superconducting quantum circuits is limited by a native surface oxide layer formed over a timescale of minutes when exposed to an ambient environment. In this work, we show that nitrogen plasma treatment forms a niobium nitride layer at the metal–air interface, which prevents such oxidation. X-ray photoelectron spectroscopy confirms the doping of nitrogen more than 5 nm into the surface and a suppressed oxygen presence. This passivation remains stable after aging for 15 days in an ambient environment. Cryogenic microwave characterization shows an average filling-factor-adjusted two-level-system loss tangent F δ TLS of (2.9 ± 0.5) · 10 − 7 for resonators with a 3 μ m center strip and (1.0 ± 0.3) · 10 − 7 for a 20 μ m center strip, exceeding the performance of unpassivated samples by a factor of four. [ABSTRACT FROM AUTHOR]

Various applications of quantum devices call for an accurate calibration of cryogenic amplification chains. To this end, we present an experimentally feasible calibration scheme and use it to accurately measure the total gain and noise temperature of an amplification chain by employing normal-metal–insulator–superconductor (NIS) junctions. Our method is based on the radiation emitted by inelastic electron tunneling across voltage-biased NIS junctions. We derive an analytical expression that relates the generated power to the applied bias voltage which is the only control parameter of the device. After the setup has been characterized using a standard voltage reflection measurement, the total gain and the noise temperature are extracted by fitting the analytical expression to the microwave power measured at the output of the amplification chain. The 1σ uncertainty of the total gain of 51.84 dB appears to be of the order of 0.10 dB. [ABSTRACT FROM AUTHOR]

We present direct imaging measurements of charge transport across a 1 cm × 1 cm × 4 mm crystal of high purity silicon (∼20 kΩ cm) at temperatures between 500 mK and 5 K. We use these data to determine the intervalley scattering rate of electrons as a function of the electric field applied along the ⟨ 111 ⟩ crystal axis, and we present a phenomenological model of intervalley scattering which explains the constant scattering rate seen at low-voltage for cryogenic temperatures. We also demonstrate direct imaging measurements of effective hole mass anisotropy, which is strongly dependent on both temperature and electric field strength. The observed effects can be explained by a warping of the valence bands for carrier energies near the spin-orbit splitting energy in silicon. [ABSTRACT FROM AUTHOR]

HfOxNy thin films were deposited on polished and oxidized silicon wafers at different nitrogen-oxygen gas flow rates by DC magnetron reactive sputtering, and temperature sensors based on these HfOxNy thin films were fabricated using a microelectromechanical system micromachining process. The resistance–temperature dependencies of these sensors were studied in the temperature range of 4.2 K–300 K, and the effect of the sputtering gas flow rate on the initial resistivity and sensitivity [temperature coefficient of resistance and absolute sensitivity (Sa)] was discussed. One of these sensors was subjected to 15 cycles between 300 K and 4.2 K for thermal cycle stability testing. The performances of these sensors were compared to the now available negative temperature coefficient thin film temperature sensors (ZrNx, CrNx, RuO2, and ZrOxNy), and they show very outstanding sensitivity and thermal cycle stability. Furthermore, the conduction mechanism of HfOxNy thin films in the cryogenic region was studied for the first time. [ABSTRACT FROM AUTHOR]

Carrier relaxation in self-assembled InAs/In0.53Ga0.23Al0.24As/InP(001) quantum dots emitting at 1.55 μm and quantum dots coupled to the In0.64Ga0.36As/In0.53Ga0.23Al0.24As quantum well through a thin In0.53Ga0.23Al0.24As barrier is investigated employing high-temporal-resolution (< 0.3 ps), time-resolved spectroscopic techniques at cryogenic temperatures, supported additionally with photoluminescence, photoluminescence excitation, and theoretical modelling. We focused on intra-band carrier relaxation pathways that solely determine the observed non-equilibrium carrier population kinetics. We ascertained relatively fast carrier capture and intra-band relaxation process in a reference structure with quantum dots only (∼8 ps time constant) and even faster initial relaxation in the coupled system (∼4 ps). An evident bottleneck effect is observed for the final relaxation stage in the coupled quantum dots-quantum well system slowing down the overall relaxation process by a factor of 5. The effect is attributed to a peculiar picture of the confined conduction band states in the coupled system exhibiting significant changes in the spatial distribution between the relevant lowest-lying electronic states. [ABSTRACT FROM AUTHOR]

We report the electrical transport properties of graphene for dilute alkali metal decoration (n~2×1012 cm-2) at cryogenic temperatures. Upon deposition of K and Li atoms at T=20 K, graphene devices are doped with electrons, and the charge carrier mobility is decreased. As temperature is increased, the number of electrons donated to the graphene and the number of charged scatterers are reduced, and the mobility of the metal decorated graphene is increased. This differs from the typical temperature-dependent transport in undecorated graphene, where the mobility decreases with increasing temperature. To investigate the kinetic behavior of adatoms on graphene, we estimate the hopping time of the Li and K adatoms on graphene based on the migration barrier in the low concentration regime of the metal adatoms by Density Functional Theory calculations. The calculations reveal that these adatoms are mobile even at cryogenic temperatures and become more mobile with increasing temperature, allowing for cluster formation of adatoms. This indicates that the dominant factor in the electron transport on warming is a cluster formation. [ABSTRACT FROM AUTHOR]

We experimentally report the bidirectional reconfiguration of an out-of-plane deformable microcantilever based metamaterial for advanced and dynamic manipulation of terahertz waves. The microcantilever is made of a bimaterial stack with a large difference in the coefficient of thermal expansion of the constituent materials. This allows for the continuous deformation of microcantilevers in upward or downward direction in response to positive or negative temperature gradient, respectively. The fundamental resonance frequency of the fabricated microcantilever metamaterial is measured at 0.4 THz at room temperature of 293 K. With decreasing temperature, the resonance frequency continuously blue shifts by 30 GHz at 77 K. On the other hand, with increasing temperature, the resonance frequency gradually red shifts by 80 GHz and saturates at 0.32 THz for 400 K. Furthermore, as the temperature is increased above room temperature, which results in the downward actuation of the microcantilever, a significant resonance line-narrowing with an enhanced quality factor is observed due to tight field confinement in the metamaterial structure. The thermal control of the microcantilever possesses numerous inherent advantages such as enhanced tunable range (~37.5% in this work compared to previously reported microcantilever metamaterials), continuous tunability, and repeatable operations. The microcantilever metamaterial also shows high robustness to operate at cryogenic conditions and hence opens up the possibility of using meta-devices in harsh environments such as space, polar, and deep sea applications. [ABSTRACT FROM AUTHOR]

This study investigates the plastic behavior of the Al0.5CoCrCuFeNi high-entropy alloy at cryogenic temperatures. The samples are uniaxially compressed at 4.2K, 7.5 K, and 9 K. A jerky evolution of stress and stair-like fluctuation of strain are observed during plastic deformation. A scaling relationship is detected between the released elastic energy and strain-jump sizes. Furthermore, the dynamical evolution of serrations is characterized by the largest Lyapunov exponent. The largest Lyapunov exponents of the serrations at the three temperatures are all negative, which indicates that the dynamical regime is non-chaotic. This trend reflects an ordered slip process, and this ordered slip process exhibits a more disordered slip process, as the temperature decreases from 9K to 4.2K or 7.5 K. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) electromechanical resonators have demonstrated unprecedented sensitivities for detecting small masses and forces. The detection speed in a cryogenic setup is usually limited by the CNT contact resistance and parasitic capacitance of cabling. We report the use of a cold heterojunction bipolar transistor amplifying circuit near the device to measure the mechanical amplitude at microsecond timescales. A Coulomb rectification scheme, in which the probe signal is at much lower frequency than the mechanical drive signal, allows investigation of the strongly non-linear regime. The behaviour of transients in both the linear and non-linear regimes is observed and modeled by including Duffing and non-linear damping terms in a harmonic oscillator equation. We show that the non-linear regime can result in faster mechanical response times, on the order of 10 μs for the device and circuit presented, potentially enabling the magnetic moments of single molecules to be measured within their spin relaxation and dephasing timescales. [ABSTRACT FROM AUTHOR]

Porous materials are commonly used in microelectronics, as they can meet the demand for continuously shrinking electronic feature dimensions. However, they are facing severe challenges in plasma etching, due to plasma induced damage. In this paper, we present both the plasma characteristics and surface processing during the etching of porous materials. We explain how the damage occurs in the porous material during plasma etching for a wide range of chuck temperatures and the responsible mechanism for plasma damage-free etching at cryogenic temperature, by a combination of experiments and numerical modeling. [ABSTRACT FROM AUTHOR]

We investigate the electronic transport properties of GaSb/AlAsSb double barrier resonant tunneling diodes with pseudomorphically grown ternary GaAsxSb1-x emitter prewells over a broad temperature range. At room temperature, resonant tunneling is observed and the peak-to-valley current ratio (PVCR) is enhanced with the increasing As mole fraction from 1:88 (GaAs0.07Sb0.93 prewell), to 2:08 (GaAs0.09Sb0.91 prewell) up to 2:36 (GaAs0.11Sb0.89 prewell). The rise in PVCR is attributed to an enhanced carrier density at the Γ-valley within the emitter prewell. On the contrary at cryogenic temperatures, increasing the As mole fractions reduces the PVCR. At a temperature of T = 4:2K, reference samples without incorporation of an emitter prewell containing As show PVCRs up to 20:4. We attribute the reduced PVCR to a degraded crystal quality of the resonant tunneling structure caused by As incorporation and subsequently an enhanced defect scattering at the interfaces. [ABSTRACT FROM AUTHOR]

We propose paramagnetic semiconductors as active media for refrigeration at cryogenic temperatures by adiabatic demagnetization. The paramagnetism of impurity dopants or structural defects can provide the entropy necessary for refrigeration at cryogenic temperatures. We present a simple model for the theoretical limitations to specific entropy and cooling power achievable by demagnetization of various semiconductor systems. Performance comparable to that of the commonly used paramagnetic salt cerous magnesium nitrate hydrate is predicted. [ABSTRACT FROM AUTHOR]

We report on a high repetition rate proton source produced by high-intensity laser irradiation of a continuously flowing, cryogenic hydrogen jet. The proton energy spectra are recorded at 1Hz for Draco laser powers of 6, 20, 40, and 100 TW. The source delivers ~1013 protons/MeV/sr/min. We find that the average proton number over one minute, at energies sufficiently far from the cut-off energy, is robust to laser-target overlap and nearly constant. This work is therefore a first step towards pulsed laser-driven proton sources for time-resolved radiation damage studies and applications which require quasi-continuous doses at MeV energies. [ABSTRACT FROM AUTHOR]

The number of elements in most cryogenic sensor arrays is limited by the technology available to multiplex signals from the arrays into a smaller number of wires and readout amplifiers. The largest demonstrated arrays of transition-edge sensor (TES) microcalorimeters contain roughly 250 detectors and use time-division multiplexing with Superconducting Quantum Interference Devices (SQUIDs). The bandwidth limits of this technology constrain the number of sensors per amplifier chain, a quantity known as the multiplexing factor, to several 10s. With microwave SQUID multiplexing, we can expand the readout bandwidth and enable much larger multiplexing factors. While microwave SQUID multiplexing of TES microcalorimeters has been previously demonstrated with small numbers of detectors, we now present a fully scalable demonstration in which 128 TES detectors are read out on a single pair of coaxial cables. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of a Fabry-Perot microcavity enclosing a thin diamond membrane at cryogenic temperatures. The cavity is designed to enhance resonant emission of single nitrogen-vacancy centers by allowing spectral and spatial tuning while preserving the optical properties observed in bulk diamond. We demonstrate cavity finesse at cryogenic temperatures within the range of F = 4000-12 000 and find a sub-nanometer cavity stability. Modeling shows that coupling nitrogen-vacancy centers to these cavities could lead to an increase in remote entanglement success rates by three orders of magnitude. [ABSTRACT FROM AUTHOR]

Exciton spin and related optical polarization in self-assembled InAs/In0.53Ga0.23Al0.24As/InP(001) quantum dashes emitting at 1.55 μm are investigated by means of polarization- and time-resolved photoluminescence, as well as photoluminescence excitation spectroscopy, at cryogenic temperature. We investigate the influence of highly non-resonant and quasi-resonant optical spin pumping conditions on spin polarization and spin memory of the quantum dash ground state. We show that a spin pumping scheme, utilizing the longitudinal-optical-phonon-mediated coherent scattering process, can lead to the polarization degree above 50%. We discuss the role of intrinsic asymmetries in the quantum dash that influence values of the degree of polarization and its time evolution. [ABSTRACT FROM AUTHOR]

Detection jitter quantifies variance introduced by the detector in the determination of photon arrival time. It is a crucial performance parameter for systems using superconducting nanowire single photon detectors (SNSPDs). In this work, we have demonstrated that the detection timing jitter is limited in part by the spatial variation of the photon detection events along the length of the wire. We define this jitter source as a geometric jitter since it is related to the length and area of the SNSPD. To characterize the geometric jitter, we have constructed a differential cryogenic readout with less than 7 ps of an electronic jitter that can amplify the pulses generated from the two ends of an SNSPD. By differencing the measured arrival times of the two electrical pulses, we were able to partially cancel out the difference of the propagation times and thus reduce the uncertainty of the photon arrival time. We proved that the variation of the differential propagation time was a few ps for a 3 μm ×3 lm device, while it increased up to 50 ps for a 20 lm ×20 μm device. In a 20 lm×20 μm large SNSPD, we achieved a 20% reduction in the overall detection timing jitter for detecting the telecom-wavelength photons by using the differential cryogenic readout. [ABSTRACT FROM AUTHOR]

For magnetic nanowire devices, the precise control of both domain wall (DW) motion and pinning behaviour is essential for reliable functional performance. The domain wall velocity and wall structure are typically sensitive to the driving field or spin-polarized current, and the pinning behaviour depends on the walls' structure and chirality, leading to variability in behaviour. Here, a systematic study combining experimental measurements and micromagnetic simulations of planar nanowires with small fixed-angle structural modulations on both edges was undertaken to study the domain wall reversal regime. A phase diagram for the reversal field as a function of modulation amplitude was obtained that shows that three DW reversal regime. A range of field and modulation amplitudes were identified in which stable DW reversal occurs, where the wall velocity is constant as a function of field and the wall structure is stable, which is well suited to applications. [ABSTRACT FROM AUTHOR]

A single-beam atomic magnetometer being operated near zero-field and measuring three-axis fields simultaneously is demonstrated. We produce a rotating field on the x-0-y plane with the frequency of 90 Hz and a modulation field in the z axis at 130Hz. The rotating field enables a nonzero z axis output when the transverse fields are zeroed using feedback systems. Based on the phase difference of π/2, x and y axes fields can be measured using one lock-in amplifier. Magnetic field sensitivities of 300 fT/Hz1/2 in x and y axes and 3 pT/Hz1/2 in the z axis are achieved. [ABSTRACT FROM AUTHOR]

We investigate how to manipulate the ratio between thermal conductivity (κ) and yield strength (σy) in face-centered cubic solid-solutions by varying the number of principal elements (NPEs) and temperature. The influence of NPEs on κ and its electronic (κe) and lattice (κl) contribution is evaluated using the Wiedemann-Franz law. Positive Dκ/DT and the highest κl/κe ratio in high-entropy alloys (HEAs) can be understood by considering severe lattice distortion and compositional complexity. Among the solid-solutions from Ni to quinary alloys, the NiCoFeCrMn HEA exhibits the lowest κ. However, σy increases with increasing NPEs and decreasing temperature. Thus, the NiCoFeCrMn HEA exhibits the highest σy/κ ratio, higher than those of representative cryogenic alloys, which can be distinctively increased with a decrease in temperature. These results would give us a guideline on how to manipulate properties using HEA design concept in order to develop idealized cryogenic materials. [ABSTRACT FROM AUTHOR]

We report the selective intercalation of polyiodide chains (I5-) inside the interstitial sites of singlewall carbon nanotube (SWCNT) bundles of which internal sites are pre-encapsulated with monatomic sulfur chains. By using metallic- and semiconducting-enriched SWCNTs with diameter of ∼1 nm, our direct-current electric transport measurements reveal that the I5- intercalation on the metallic- and semiconducting-enriched SWCNT networks exhibits an opposite trend on the temperature dependence of the electric resistance at cryogenic temperature. Based on our analysis using the fluctuation-induced tunneling conduction model, the intercalation of I5- chains into the semiconducting-SWCNTs leads to the increase in energy barriers required for tunneling processes. Since the charge transfer is negligible between I5- chains and the semiconducting-SWCNTs, the main effect of the intercalated I5- on the semiconducting-SWCNTs is to behave as a scattering center below 50 K. In contrast to the semiconducting-SWCNTs, the intercalation of I5- chains into the metallic-SWCNTs results in the suppression of tunneling barriers due to the charge transfer interaction. The energy barrier is further reduced by the encapsulation of I5- chains inside the metallic-SWCNT, implying that the doping effect could be more effectively enhanced by the interaction through the inner spaces of SWCNTs. [ABSTRACT FROM AUTHOR]

We address nonradiative recombination pathways by leveraging surface passivation and dislocation management in lm-scale arrays of Ge crystals grown on deeply patterned Si substrates. The time decay photoluminescence (PL) at cryogenic temperatures discloses carrier lifetimes approaching 45 ns in band-gap engineered Ge micro-crystals. This investigation provides compelling information about the competitive interplay between the radiative band-edge transitions and the trapping of carriers by dislocations and free surfaces. Furthermore, an in-depth analysis of the temperature dependence of the PL, combined with capacitance data and finite difference time domain modeling, demonstrates the effectiveness of GeO2 in passivating the surface of Ge and thus in enhancing the room temperature PL emission. [ABSTRACT FROM AUTHOR]

We use a cryogenic high-electron-mobility transistor circuit to amplify the current from a single electron transistor, allowing for demonstration of single shot readout of an electron spin on a single P donor in Si with 100 kHz bandwidth and a signal to noise ratio of ~9. In order to reduce the impact of cable capacitance, the amplifier is located adjacent to the Si sample, at the mixing chamber stage of a dilution refrigerator. For a current gain of ~2:7 x 10³, the power dissipation of the amplifier is 13 µW, the bandwidth is ~1.3MHz, and for frequencies above 300 kHz the current noise referred to input is ≤ 70 fA√Hz. With this amplification scheme, we are able to observe coherent oscillations of a P donor electron spin in isotopically enriched 28Si with 96% visibility. [ABSTRACT FROM AUTHOR]

Graphene quantum-dots (GQDs) have been predicted and demonstrated with fascinating optical and magnetic properties. However, the magnetic effect on the optical properties remains experimentally unexplored. Here, we conduct a magneto-photoluminescence study on the blue-luminescence GQDs at cryogenic temperatures with magnetic field up to 10 T. When the magnetic field is applied, a remarkable enhancement of photoluminescence emission has been observed together with an insignificant change in circular polarization. The results have been well explained by the scenario of magnetic-field-controlled singlet-triplet mixing in GQDs owing to the Zeeman splitting of triplet states, which is further verified by temperature-dependent experiments. This work uncovers the pivotal role of intersystem crossing in GQDs, which is instrumental for their potential applications such as light-emitting diodes, photodynamic therapy, and spintronic devices. [ABSTRACT FROM AUTHOR]

Techniques that can probe the thermal properties of cells are used in many applications ranging from cryogenic preservation to hyperthermia therapy, and provide powerful tools to investigate diseased conditions. The structural complexity of cells, however, requires innovative modalities operating at a subcell scale. We developed a label-free, non-ionizing technique based on a thermoelastic lens. With this device, we captured images of single cells with a ~2 μm resolution based on thermal properties as the contrast mechanism. To investigate the thermorheological behaviour of cells, we present simultaneous acoustic imaging using an inverted opto-acoustic microscope. Acoustic impedances extracted from the acoustic images support the effusivity obtained from the thermal images. This technique should provide diagnostic tools at the single cell scale. [ABSTRACT FROM AUTHOR]

In this work, we present a method for measuring the refractive index of liquids at cryogenic temperature by shearing interferometry. The method is self-calibrated and easy to use over the range from cryogenic to room temperature. We validated the accuracy of our approach by comparing the measured refractive index of liquid propane with data reported in the literature. Moreover, we measured the refractive indices of three as yet uncharacterized fluorinated liquids that are of great interest as immersion fluids in the field of cryogenic light microscopy. [ABSTRACT FROM AUTHOR]

Broad-area 10-stage interband cascade lasers (ICLs) emitting at λ = 3.0-3.2 μm are shown to maintain continuous-wave (cw) wallplug efficiencies exceeding 40% at temperatures up to 125 K, despite having a design optimized for operation at ambient and above. The cw threshold current density at 80 K is only 11 A/cm² for a 2 mm cavity with anti-reflection/high-reflection coatings on the two facets. The external differential quantum efficiency for a 1-mm-long cavity with the same coatings is 70% per stage at 80 K, and still above 65% at 150 K. The results demonstrate that at cryogenic temperatures, where free carrier absorption losses are minimized, ICLs can convert electrical to optical energy nearly as efficiently as the best specially designed intersubband-based quantum cascade lasers. [ABSTRACT FROM AUTHOR]

The effective bandgap is a crucial design parameter of heterojunction tunneling field-effect transistors. In this letter, we demonstrate a method to measure the effective bandgap directly from the band-to-band tunneling current of a heterojunction Esaki diode, of which we only require knowledge of the electrostatic potential profile. The method is based on a characteristic exponentially increasing current with forward bias, caused by sharp energy filtering at cryogenic temperature. We apply this method experimentally to a n+In0.53Ga0.47As/pGaAs0.5Sb0.5 Esaki diode and define requirements to apply it to other heterojunctions. [ABSTRACT FROM AUTHOR]

We report on the implementation of 5 THz quantum well photodetector exploiting a patch antenna cavity array. The benefit of our plasmonic architecture on the detector performance is assessed by comparing it with detectors made using the same quantum well absorbing region, but processed into a standard 45° polished facet mesa. Our results demonstrate a clear improvement in responsivity, polarization insensitivity, and background limited performance. Peak detectivities in excess of 5 × 1012 cmHz1/2/W have been obtained, a value comparable with that of the best cryogenic cooled bolometers. [ABSTRACT FROM AUTHOR]

Many future particle accelerators require hundreds of superconducting radiofrequency (SRF) cavities operating with high duty factor. The large dynamic heat load of the cavities causes the cryogenic plant to make up a significant part of the overall cost of the facility. This contribution can be reduced by replacing standard niobium cavities with ones coated with a low-dissipation superconductor such as Nb3Sn. In this paper, we present results for single cell cavities coated with Nb3Sn at Cornell. Five coatings were carried out, showing that at 4.2 K, high Q0 out to medium fields was reproducible, resulting in an average quench field of 14 MV/m and an average 4.2K Q0 at quench of 8×109. In each case, the peak surface magnetic field at quench was well above Hc1, showing that it is not a limiting field in these cavities. The coating with the best performance had a quench field of 17 MV/m, exceeding gradient requirements for state-of-the-art high duty factor SRF accelerators. It is also shown that--taking into account the thermodynamic efficiency of the cryogenic plant--the 4.2K Q0 values obtained meet the AC power consumption requirements of state-of-the-art high duty factor accelerators, making this a proof-of-principle demonstration for Nb3Sn cavities in future applications. [ABSTRACT FROM AUTHOR]

We report the experimental evidence of uncovering a photoresponse amplification mechanism in heavily doped, partially compensated silicon p-n junctions under very low bias voltage. We show that the observed photocurrent gain occurs at a bias that is more than an order of magnitude below the threshold voltage for conventional impact ionization. Moreover, contrary to the case of avalanche detectors and p-i-n diodes, the amplified photoresponse is enhanced rather than suppressed with increasing temperature. These distinctive characteristics lead us to hypothesize that the inelastic scattering between energetic electrons (holes) and the ionized impurities in the depletion and charge neutral regions of the p-n junction in a cyclic manner plays a significant role in the amplification process. Such an internal signal amplification mechanism, which occurs at much lower bias than impact ionization and favors room temperature over cryogenic temperature, makes it promising for practical device applications. [ABSTRACT FROM AUTHOR]

The onset of the efficiency droop in GaInN/GaN blue light-emitting diodes (LEDs), i.e., the maximum-efficiency point, typically occurs at current densities of 1-10 A/cm² and the efficiency decreases monotonically beyond the onset. At typical operating current densities (10-100 A/cm²), LEDs are strongly affected by the droop. At cryogenic temperatures, an increase in the efficiency, i.e., a "U-turn" feature, is found in the droop regime of the efficiency-versus-current curve. The occurrence of the U-turn feature coincides with a distinct increase in device conductivity, which is attributed to an enhancement in p-type conductivity that in turn increases the injection efficiency. [ABSTRACT FROM AUTHOR]

Frequency tunability of three dimensional (3D) microwave cavities opens up numerous possibilities for their use in hybrid quantum systems and related technologies. For many applications, it is desirable to tune the resonance at cryogenic temperatures without mechanical actuation. We show that a superconducting 3D microwave cavity can be tuned at the percent level by taking advantage of the dielectric properties of superfluid 4He at millikelvin temperatures, without affecting its intrinsic quality factor-reaching 3×105 in the present experiment. [ABSTRACT FROM AUTHOR]

Thermal Nyquist noise fluctuations of high-Q bulk acoustic wave cavities have been observed at cryogenic temperatures with a DC superconducting quantum interference device amplifier. High Q modes with bandwidths of few tens of milliHz produce thermal fluctuations with a signal-to-noise ratio of up to 23 dB. The estimated effective temperature from the Nyquist noise is in good agreement with the physical temperature of the device, confirming the validity of the equivalent circuit model and the non-existence of any excess resonator self-noise. The measurements also confirm that the quality factor remains extremely high (Q > 108 at low order overtones) for very weak (thermal) system motion at low temperatures, when compared to values measured with relatively strong external excitation. This result represents an enabling step towards operating such a high-Q acoustic device at the standard quantum limit. [ABSTRACT FROM AUTHOR]

The complex optical index ñ n + i k) of InAs/GaSb type-II superlattice (T2SL) was determined in the 1-6 μm range from reflectivity measurements of resonant structures at 80 K. Several air/superlattice/gold cavities of various thicknesses were fabricated and their reflectivity was measured. As the large variations induced by the cavity resonances in the studied range can be accurately modeled, we were able to determine the complex optical index ñ of InAs/GaSb T2SL with an error of only a few percent. We found that the in-plane refractive index n of the T2SL lies between 3.65 and 3.77 in the mid-infrared wavelength range, and the absorption coefficient j decreases from 0.23 to 0.001 as the wavelength increases from 1.25 to 5.65 μm. The subtractive Kramers-Kronig relation allowed us to verify our determination of ñ. [ABSTRACT FROM AUTHOR]

We model, using the macrospin approximation, the magnetic reversal of a perpendicularly magnetized nanostructured free layer formed on a normal, heavy-metal nanostrip, subjected to spin-orbit torques (SOTs) generated by short (≤0.5 ns) current pulses applied to the nanostrip, to examine the potential for SOT-based fast, efficient cryogenic memory. Due to thermal fluctuations, if solely an anti-damping torque is applied, then, for a device with sufficiently low anisotropy (H°anis ~ 1 kOe) suitable for application in cryogenic memory, a high magnetic damping parameter (a ~ 0.1 -- 0.2) is required for reliable switching over a significant variation of pulse current. The additional presence of a substantial field-like torque improves switching reliability even for low damping (α < 0.03) [ABSTRACT FROM AUTHOR]

We present an all-optical method for measuring the average size, density, and mass fraction of large (>50 nm) clusters produced in cryogenically cooled, continuous gas jets. The technique combines three optical diagnostics--forward/backward Mie scattering detection, 90° scattering imaging, and neutral gas interferometry. Our measurement shows that cryogenic cooling and high backing gas pressure greatly enhance both cluster size and clustering ratio in continuous gas flow. Such a cluster source can be used as a potential target for intense, high-repetition-rate (>kHz) laser pulses. [ABSTRACT FROM AUTHOR]

Recently, a pump beam size dependence of thermal conductivity was observed in Si at cryogenic temperatures using time-domain thermal reflectance (TDTR). These observations were attributed to quasiballistic phonon transport, but the interpretation of the measurements has been semiempirical. Here, we present a numerical study of the heat conduction that occurs in the full 3D geometry of a TDTR experiment, including an interface, using the Boltzmann transport equation. We identify the radial suppression function that describes the suppression in heat flux, compared to Fourier's law, that occurs due to quasiballistic transport and demonstrate good agreement with experimental data. We also discuss unresolved discrepancies that are important topics for future study. [ABSTRACT FROM AUTHOR]

Vacancy depth profiles in silicon wafers—installed by Rapid Thermal Annealing and monitored by Pt diffusion—show, upon subsequent annealing at 975 or 950 °C, a peculiar evolution: the concentration profile goes down without any trace of vacancy out-diffusion. The estimated apparent diffusivity is less than 10–7 cm2/s at 975 °C. The monitored vacancy species is tentatively identified as a "slow vacancy" that was recently concluded to exist along with other (highly mobile) vacancy species. [ABSTRACT FROM AUTHOR]

The photoluminescence quantum efficiencies of a series of Ga(N,As,P)/GaP multiple quantum wells are analyzed. The external quantum efficiencies are derived from the absorbed and the emitted light intensities measured using an integrating sphere mounted inside a closed-cycle helium cryostat. By taking into account the device layer sequences as well as internal reflections and reabsorption, the internal quantum efficiencies yield values above 90% for all samples at cryogenic temperatures. The temperature-dependence of the quantum efficiencies as a function of active quantum well layer design reveal the internal interfaces as remaining growth challenge in these heterostructures. [ABSTRACT FROM AUTHOR]