arXiv subjects

Adrian Porch

Publications and source records attributed to Adrian Porch.

5 recordsLinked to original sources

arXiv2022

Superconducting boron doped nanocrystalline diamond microwave coplanar resonator

A superconducting boron doped nanocrystalline diamond (B-NCD) coplanar waveguide resonator (CPR) is presented for kinetic inductance ($L_k$) and penetration depth ($λ_{\rm{L}}$) measurements at microwave frequencies of 0.4 to 1.2 GHz and at temperatures below 3 K. Using a simplified effective medium CPR approach, this work demonstrates that thin granular B-NCD films ($t\approx $ 500 nm) on Si have a large penetration depth ($λ_{\rm{L}}\approx 4.3$ to 4.4 $μ$m), and therefore an associated high kinetic inductance ($L_{k,\square} \approx $ 670 to 690 pH/$\square$). These values are much larger than those typically obtained for films on single crystal diamond which is likely due to the significant granularity of the nanocrystalline films. Based on the measured Q factors of the structure, the calculated surface resistance in this frequency range is found to be as low as $\approx$ 2 to 4 $μΩ$ at $T<2$ K, demonstrating the potential for granular B-NCD for high quality factor superconducting microwave resonators and highly sensitive kinetic inductance detectors.

cond-mat.supr-con↗

arXiv2019

Dielectric spectroscopy of hydrogenated hexagonal boron nitride ceramics

Hexagonal boron nitride (h-BN) is a critical material for 2D electronic devices for graphene and has attracted a considerable amount of attention owing to its structural similarity and semiconducting property. However, modifying its wide-band gap is a challenge. Hydrogenation is a potential method of altering the electrical properties, although is seldom experimentally measured. Here, the complex permittivity of h-BN after various hydrogen treatments have been investigated. For untreated h-BN, a frequency independent dielectric constant was measured ($\sim4.2 \pm0.2$) and an immeasurably low dielectric loss, demonstrating the ideal dielectric nature of h-BN across the $10^3$ to $10^{10}$ Hz range. However, after atomic H-plasma treatment in a microwave chemical vapour deposition (CVD) reactor, the complex permittivity amplifies dramatically, introducing dielectric dispersion through Debye-type dielectric relaxations ($\varepsilon_{\textrm{s}}\approx20\pm2$, $\varepsilon_{\infty}\approx4.2\pm0.2$) and a percolating long range conductivity ($\sim0.32$ mS/m). Annealing in molecular hydrogen at similar CVD temperatures showed minimal effect. Raman spectroscopy also detected minimal change in all samples, implying the increase is not due to other phases. This leads to the experimental conclusion that hydrogenation, through atomic H-plasma treatment, results in a moderate increase in room temperature electrical conductivity, an associated finite dielectric loss factor. The potential as a tunable wide-band gap semiconductor is highlighted however for insulating dielectric substrate applications, microwave CVD may destroy these desirable properties.

physics.app-ph↗

arXiv2000

Phenomenological Model of the Nonlinear Microwave Response of a Superconductor Containing Weak Links

A phenomenological model is proposed which describes the effect of both dc and rf magnetic fields, $H$, on the microwave surface impedance, Z_s=R_s+jX_s, of a superconductor containing weak link. Two cases are considered; a weak link between two grains, shunted by another grain, and a non-shunted weak link. In both cases the dependences of R_s and X_s on applied field H were found to be anomalous. Under certain conditions, the values of Z_s(H) can fall below the zero-field values. Comparison with experiment is performed, and very good qualitative and (in some cases) quantitative agreement is found.

cond-mat.supr-con↗

arXiv2000

Anomalous Features in Surface Impedance of Y-Ba-Cu-O Thin Films: Dependence on Frequency, RF and DC Fields

Two high-quality Y-Ba-Cu-O thin films on MgO substrates have been investigated using the coplanar resonator technique at 8 and 16 GHz. Both films exhibit an anomalous decrease in their surface impedance, Zs as a function of microwave field, Hrf. In zero dc field, Hrf-dependences of Rs and Xs for both the samples are uncorrelated, and only one of the quantities, Rs or Xs, displays anomalous behavior. Here, application of relatively weak (~5 mT) dc magnetic fields, Hdc can produce a correlated decrease of Rs(Hrf) and Xs(Hrf). The dependences of Zs on Hdc in both low and high microwave power regimes were found to be non-monotonic. The frequency dependence of Rs ~ fn, 1.7<n<2.5, remained the same upon the transition from low to high microwave power ranges. The consequences of the reported findings for microwave device applications are briefly discussed

cond-mat.supr-con↗

arXiv1999

Modelling the Nonlinear High-Frequency Response of a Short Josephson Junction under Two-Frequency Irradiation

The nonlinear response of a short Josephson Junction (JJ), being irradiated simultaneously with two high-frequency signals, has been studied in the framework of the nonlinear Resistively-Shunted Junction (RSJ) Model. One of the signals, hereafter referred to as "probe signal", has a small amplitude $I_{pr}<I_c$ ($I_c$ is the critical current of the JJ) and frequency $f_{pr}$, and is used to monitor the response of the junction to the other high-power signal with amplitude $I_{pm}$ and frequency $f_{pm}$, hereafter referred to as "pump signal". Varying the frequency ratio $f_{pm}/f_{pr}$ from 0.5 to 100, and the current amplitude of the probe signal from 0.01 to 0.9 of $I_c$, we found that the dependence of the junction impedance at the frequency $f_{pr}$, $Z_s^{f_{pr}}$, versus $I_{pm}$ preserves its general features, independent of $f_{pm}/f_{pr}$ and $I_{pr}/I_c$ values. At the same time, some particular features, like negative values of $Re(Z_s^{f_{pr}})$ and "fine" structure of the steps in $Z_s^{f_{pr}}(I_{pm})$ are observed for $f_{pm}/f_{pr}<1$ and for particular values of $I_{pr}/I_c$. In general, the behavior of $Z_s^{f_{pr}}(I_{pm})$ is rather different from that predicted by the nonlinear RSJ model for a short JJ in the regime of single-frequency irradiation, when one and the same signal plays the roles of the pump and the probe signals simultaneously. Possible applications of the model are briefly discussed.

cond-mat.supr-con↗