arXiv subjects

S. Nawaz

Publications and source records attributed to S. Nawaz.

5 recordsLinked to original sources

arXiv2020

Axion Dark Matter eXperiment: Run 1B Analysis Details

Searching for axion dark matter, the ADMX collaboration acquired data from January to October 2018, over the mass range 2.81--3.31 $μ$eV, corresponding to the frequency range 680--790 MHz. Using an axion haloscope consisting of a microwave cavity in a strong magnetic field, the ADMX experiment excluded Dine-Fischler-Srednicki-Zhitnisky (DFSZ) axions at 100% dark matter density over this entire frequency range, except for a few gaps due to mode crossings. This paper explains the full ADMX analysis for Run 1B, motivating analysis choices informed by details specific to this run.

astro-ph.CO↗

arXiv2020

Axion Dark Matter eXperiment: Detailed Design and Operations

Axion Dark Matter eXperiment (ADMX) ultra low noise haloscope technology has enabled the successful completion of two science runs (1A and 1B) that looked for dark matter axions in the $2.66$ to $3.1$ $μ$eV mass range with Dine-Fischler-Srednicki-Zhitnisky (DFSZ) sensitivity Ref. [1,2]. Therefore, it is the most sensitive axion search experiment to date in this mass range. We discuss the technological advances made in the last several years to achieve this sensitivity, which includes the implementation of components, such as state-of-the-art quantum limited amplifiers and a dilution refrigerator. Furthermore, we demonstrate the use of a frequency tunable Microstrip Superconducting Quantum Interference Device (SQUID) Amplifier (MSA), in Run 1A, and a Josephson Parametric Amplifier (JPA), in Run 1B, along with novel analysis tools that characterize the system noise temperature.

astro-ph.IM↗

arXiv2019

Extended Search for the Invisible Axion with the Axion Dark Matter Experiment

This paper reports on a cavity haloscope search for dark matter axions in the galactic halo in the mass range $2.81$-$3.31$ $μeV$. This search excludes the full range of axion-photon coupling values predicted in benchmark models of the invisible axion that solve the strong CP problem of quantum chromodynamics, and marks the first time a haloscope search has been able to search for axions at mode crossings using an alternate cavity configuration. Unprecedented sensitivity in this higher mass range is achieved by deploying an ultra low-noise Josephson parametric amplifier as the first stage signal amplifier.

hep-ex↗

arXiv2015

Quantum capacitance in monolayers of silicene and related buckled materials

Silicene and related buckled materials are distinct from both the conventional two dimensional electron gas and the famous graphene due to strong spin orbit coupling and the buckled structure. These materials have potential to overcome limitations encountered for graphene, in particular the zero band gap and weak spin orbit coupling. We present a theoretical realization of quantum capacitance which has advantages over the scattering problems of traditional transport measurements. We derive and discuss quantum capacitance as a function of the Fermi energy and temperature taking into account electron-hole puddles through a Gaussian broadening distribution. Our predicted results are very exciting and pave the way for future spintronic and valleytronic devices.

cond-mat.mes-hall↗

arXiv2013

Improved nanopatterning for YBCO nanowires approaching the depairing current

An improved nanopatterning procedure has been developed to obtain YBCO nanowires with cross sections as small as 50x50 nm^2, protected by an Au capping layer. To probe the effective role of the Au protecting layer, we have measured the current-voltage characteristics and the resistive transition in temperature of the nanowires. Critical current densities up to 10^8 A/cm^2 have been achieved at T=4.2 K, approaching the theoretical depairing current limit. The resistance, measured as a function of temperature close to Tc, has been fitted with a thermal activated phase slip model, including the effect of the gold layer. The extracted values of the superconducting coherence length and of the London penetration depth give current densities consistent with the measured ones. These results cannot be achieved with same nanowires, without the Au capping layer.

cond-mat.supr-con↗