arXiv subjects

U. Patel

Publications and source records attributed to U. Patel.

10 recordsLinked to original sources

arXiv2026

High-resolution calorimetric sample platforms for cryogenic thermodynamic studies with multimodal synchrotron x-ray compatibility

X-ray calorimetric sample platforms combining specific heat and synchrotron x-ray measurements provide a powerful means to investigate fundamental material properties. Calorimeter cell designs featuring a compact heater and thermometer arranged in a sidecar geometry, with the sample positioned directly above the heater at the center of a silicon nitride membrane, are presented. High-yield, wafer-level batch fabrication of precision calorimetric sensor chips, beamline and laboratory cryostat plugins with sensor mounting and packaging are described. Using our calorimetric sensors, we present specific heat measurements on samples with masses ranging from 4 {\mu}g to 145 {\mu}g. The sample and reference cells are characterized with relaxation and ac steady-state measurements. The thermal response is captured using lock-in detection at carefully optimized measurement frequencies, with phase-lag correction ensuring precise extraction of heat capacity. The reference cell's background heat capacity was measured to be under 320 nJ/K at 300 K, decreasing to just 0.4 nJ/K at 0.7 K. The calorimeter performance is illustrated by studying the specific heat of small samples of superconducting Nb and a 4 {\mu}g piece of superconducting Al under different magnetic field strengths. The determination of fundamental thermodynamic quantities from low-temperature electronic and lattice specific heat measurements is discussed. These versatile, high-throughput sample platforms are engineered for small-sample calorimetry across a broad cryogenic temperature range, and they support scalable integration with a wide range of cryostats, including beamline cryostats at the Advanced Photon Source. They accommodate multimodal geometries and enable operation under ultra-high vacuum, millikelvin temperatures, magnetic fields, and x-ray illumination.

physics.ins-det↗

arXiv2022

High-resolution Compton spectroscopy using X-ray microcalorimeters

X-ray Compton spectroscopy is one of the few direct probes of the electron momentum distribution of bulk materials in ambient and operando environments. We report high-resolution inelastic X-ray scattering experiments with high momentum and energy transfer performed at a storage-ring-based high-energy X-ray light source facility using an X-ray microcalorimeter detector. Compton profiles were measured for lithium and cobalt oxide powders relevant to lithium-ion battery research. Spectroscopic analysis of the measured Compton profiles shows high-sensitivity to the low-Z elements and oxidation states. The lineshape analysis of the measured Compton profiles in comparison with computed Hartree-Fock profiles is limited by the resolution of the energy-resolving semiconductor detector. We have characterized an X-ray transition-edge sensor microcalorimeter detector for high-resolution Compton scattering experiments using a bending magnet source at the Advanced Photon Source (APS) with a double crystal monochromator providing monochromatic photon energies near 27.5 keV. The momentum resolution below 0.16 atomic units was measured yielding an improvement of more than a factor of 7 over a state-of-the-art silicon drift detector for the same scattering geometry. Furthermore, the lineshapes of narrow valence and broad core electron profiles of sealed lithium metal were clearly resolved using an X-ray microcalorimeter detector compared to smeared and broadened lineshapes observed when using a silicon drift detector. High-resolution Compton scattering using the energy-resolving detector shown here presents new opportunities for spatial imaging of electron momentum distributions for a wide class of materials with applications ranging from electrochemistry to condensed matter physics.

physics.ins-det↗

arXiv2021

Ground-state and decay properties of neutron-rich 106Nb

The ground-state properties of neutron-rich 106Nb and its beta decay into 106Mo have been studied using the CARIBU radioactive-ion-beam facility at Argonne National Laboratory. Niobium-106 ions were extracted from a 252Cf fission source and mass separated before being delivered as low-energy beams to the Canadian Penning Trap, as well as the X-Array and SATURN beta-decay-spectroscopy station. The measured 106Nb ground-state mass excess of -66202.0(13) keV is consistent with a recent measurement but has three times better precision; this work also rules out the existence of a second long-lived, beta-decaying state in 106Nb above 5 keV in excitation energy. The decay half-life of 106Nb was measured to be 1.097(21) s, which is 8% longer than the adopted value. The level scheme of the decay progeny, 106Mo, has been expanded up to approximately 4 MeV. The distribution of decay strength and considerable population of excited states in 106Mo of J >= 3 emphasises the need to revise the adopted Jpi = 1- ground-state spin-parity assignment of 106Nb; it is more likely to be J => 3.

nucl-ex↗

arXiv2020

Beamline Spectroscopy of Integrated Circuits With Hard X-ray Transition Edge Sensors at the Advanced Photon Source

At Argonne National Laboratory, we are developing hard X-ray (2 to 20 keV) Transition Edge Sensor (TES) arrays for beamline science. The significantly improved energy resolution provided by superconducting detectors compared to semiconductor-based energy-dispersive detectors, but with better collection efficiency than wavelength-dispersive instruments, will enable greatly improved X-ray emission and absorption spectroscopic measurements. A prototype instrument with 24 microwave-frequency multiplexed pixels is now in testing at the Advanced Photon Source (APS) 1-BM beamline. Initial measurements show an energy resolution ten times better (150 eV compared to < 15 eV) than the silicon-drift detectors currently available to APS beamline users, and in particular demonstrate the ability to resolve closely-spaced emission lines in samples containing multiple transition metal elements, such as integrated circuits. Comparing fluorescence spectra of integrated circuits measured with our TESs at the beamline to those measured with silicon detectors, we find emission lines and elements largely hidden (e.g. Hf alongside Cu) from a semiconductor-based detector but well resolved by a TES. This directly shows the strengths of TES-based instruments in fluorescence mapping.

physics.ins-det↗

arXiv2019

Development of Transition-Edge Sensor X-ray Microcalorimeter Linear Array for Compton Scattering and Energy Dispersive Diffraction Imaging

We present a strip transition-edge sensor microcalorimeter linear array detector developed for energy dispersive X-ray diffraction imaging and Compton scattering applications. The prototype detector is an array of 20 transition-edge-sensors with absorbers in strip geometry arranged in a linear array. We discuss the fabrication steps needed to develop this array including Mo/Cu bilayer, Au electroplating, and proof-of-principle fabrication of long strips of SiNx membranes. We demonstrate minimal unwanted effect of strip geometry on X-ray pulse response, and show linear relationship of 1/pulse height and pulse decay times with absorber length. For the absorber lengths studied, preliminary measurements show energy resolutions of 40 eV to 180 eV near 17 keV. Furthermore, we show that the heat flow to the cold bath is nearly independent of the absorber area and depends on the SiNx membrane geometry.

physics.ins-det↗

arXiv2016

Phonon-Mediated Quasiparticle Poisoning of Superconducting Microwave Resonators

Nonequilibrium quasiparticles represent a significant source of decoherence in superconducting quantum circuits. Here we investigate the mechanism of quasiparticle poisoning in devices subjected to local quasiparticle injection. We find that quasiparticle poisoning is dominated by the propagation of pair-breaking phonons across the chip. We characterize the energy dependence of the timescale for quasiparticle poisoning. Finally, we observe that incorporation of extensive normal metal quasiparticle traps leads to a more than order of magnitude reduction in quasiparticle loss for a given injected quasiparticle power.

cond-mat.supr-con↗

arXiv2012

Coherent Josephson phase qubit with a single crystal silicon capacitor

We have incorporated a single crystal silicon shunt capacitor into a Josephson phase qubit. The capacitor is derived from a commercial silicon-on-insulator wafer. Bosch reactive ion etching is used to create a suspended silicon membrane; subsequent metallization on both sides is used to form the capacitor. The superior dielectric loss of the crystalline silicon leads to a significant increase in qubit energy relaxation times. T1 times up to 1.6 micro-second were measured, more than a factor of two greater than those seen in amorphous phase qubits. The design is readily scalable to larger integrated circuits incorporating multiple qubits and resonators.

cond-mat.supr-con↗

arXiv2009

Magnetoresistance Oscillations in Granular Superconducting Niobium Nitride Nanowires

We report on magnetoresistance oscillations in superconducting NbNx nanowires synthesized through ammonia gas annealing of NbSe3 precursor nanostructures. Even though the transverse dimensions of the nanowires are much larger than the superconducting coherence length, the voltage-current characteristics of these nanowires at low temperatures are reminiscent of one-dimensional superconductors where quantum phase slips are associated with the origin of dissipation. We show that both the magnetoresistance oscillations and voltage-current characteristics observed in this work result from the granular structure of our nanowires.

cond-mat.supr-con↗

arXiv2009

Multi-gap nodeless superconductivity in iron selenide FeSe$_x$: evident from quasiparticle heat transport

The in-plane thermal conductivity $κ$ of the iron selenide superconductor FeSe$_x$ ($T_c$ = 8.8 K) were measured down to 120 mK and up to 14.5 T ($\simeq 3/4 H_{c2}$). In zero field, the residual linear term $κ_0/T$ at $ T \to 0$ is only about 16 $μ$W K$^{-2}$ cm$^{-1}$, less than 4% of its normal state value. Such a small $κ_0/T$ does not support the existence of nodes in the superconducting gap. More importantly, the field dependence of $κ_0/T$ in FeSe$_x$ is very similar to that in NbSe$_2$, a typical multi-gap s-wave superconductor. We consider our data as strong evidence for multi-gap nodeless superconductivity in FeSe$_x$. This kind of superconducting gap structure may be generic for all Fe-based superconductors.

cond-mat.supr-con↗

arXiv2009

Growth and Superconductivity of FeSex Crystals

Iron selenide (FeSex) crystals with lateral dimensions up to millimeters were grown via a vapor self-transport method. The crystals consist of the dominant alpha - phase with trace amounts of beta- phase as identified by powder x-ray diffraction. With four-probe resistance measurements we obtained a zero-resistance critical temperature of 7.5 K and a superconducting onset transition temperature of up to 11.8 K in zero magnetic field as well as an anisotropy of 1.5 +- 0.1 for the critical field. Magnetization measurements on individual crystals reveal the co-existence of superconductivity and ferromagnetism.

cond-mat.supr-con↗