arXiv subjects

Shekhar Chandra Pandey

Publications and source records attributed to Shekhar Chandra Pandey.

7 recordsLinked to original sources

arXiv2026

High-Efficiency Broadband Mid-Infrared Absorption in Asymmetrically Matched Metallic Meanders: Development of Ti40V60 Alloy based LEKIDs for Mid-Far IR

Fast, highly sensitive, and broadband detectors operating in the mid-to-far-infrared (MIR-FIR) spectral region are essential for applications ranging from astrophysics to time-resolved spectroscopy using laboratory-based sources and beamlines at Infrared Free-Electron Laser (IR-FEL) facilities. Conventional Lumped Element Kinetic Inductance Detectors (LEKID) achieve high optical efficiency using resonant quarter wavelength (λ/4) backshort cavities. However, this cavity-based approach is inherently narrowband and becomes optomechanically challenging at the mid to far infrared (MIR-FIR) wavelengths. Here, we present a completely backshort-free LEKID absorber architecture that achieves broadband absorption exceeding 50%. The meander absorbers were fabricated from a superconducting Ti-V alloy and characterized using IR radiation from the IR-FEL at RRCAT, India. By illuminating through the silicon substrate and matching the meander's sheet resistance to the silicon substrate's wave impedance, the front-side reflection is strongly suppressed. Simultaneously, the sub-wavelength periodicity of the dense meander inhibits propagating transmission into free space via evanescent wave confinement. This combined mechanism drives efficient Ohmic dissipation within the metallic meander, yielding an experimental absorption efficiency ranging from 50% to 90% across the 12.5-30 micrometer wavelength range. The cavity-free design greatly simplifies the fabrication of the focal plane array while providing the broadband response required for next-generation detectors. To assess the suitability of the Ti40V60 alloy as an active superconducting detector material, a test LEKID resonator was also designed, fabricated, and experimentally characterized.

physics.ins-det↗

arXiv2026

Terahertz Electrodynamics and Kinetic Inductance of Disordered Titanium-Vanadium Alloy Thin Films

Disordered superconductors represent an important area in modern condensed matter physics, where superconductivity survives even in the presence of strong electron scattering and localization effects. Understanding how disorder modifies the high-frequency electrodynamic response is not only important from physics point of view, but is also essential for developing next-generation quantum detectors and superconducting devices. In this work, we investigate the terahertz electrodynamics of disordered Ti40V60 alloy thin films using terahertz time-domain spectroscopy (THz-TDS) to understand the relationship between disorder, quasiparticle dynamics, and kinetic inductance. By analysing the complex conductivity, penetration depth and superfluid response, we show that structural disorder can be systematically used to tune the inductive response while maintaining a robust superconducting phase. Unlike conventional nitride superconductors that require tightly controlled reactive growth conditions, Ti40V60 alloys provide a simpler and more adaptable route for tuning the superconducting energy scales directly through the deposition conditions. These findings establish Ti40V60 alloys as a promising material for kinetic inductance detectors and provide useful insights into the electrodynamics of strongly disordered superconductors.

cond-mat.supr-con↗

arXiv2026

Effect of Underlayer Induced Charge Carrier Substitution on the Superconductivity of Ti40V60 Alloy Thin Films

The influence of metallic and semiconducting (V, Al, and Si) under-layer induced charge carrier substitution on the superconducting properties of the Ti40V60 alloy thin films are studied and also compared with a pristine reference film without any under-layer. All the films exhibit metallic behavior in the normal state and a superconducting transition at low temperatures, where the superconducting transition temperature is tunable between 4.77 K and 5.73 K. Hall measurements on the films reveal that the under-layer strongly affects the charge carrier type and density, leading to a correlation between increasing carrier concentration and decreasing TC. The Si under-layer introduces the highest disorder, yet yields the highest TC. This indicates that in the Ti40V60 alloys, a moderate amount of disorder suppresses the spin-fluctuations (inherent to the alloy system) induced pair breaking, thereby enhancing the superconductivity. The comparable TC of the film with V under-layer and the film without under-layer, and the much smaller coherence length (~6.2 nm) as compared to the film thickness (25 nm), confirm the absence of any significant proximity effects. These findings demonstrate that under-layer engineering provides an effective route to tune the superconducting properties of Ti-V alloy thin films.

cond-mat.supr-con↗

arXiv2025

Effect of Deposition Pressure on the Superconductivity of Ti40V60 Alloy Thin Films

The growth and characterization of high quality superconducting thin films is essential for fundamental understanding and also for the use of these films in technological applications. In the present study, Ti40V60 alloy thin films have been deposited using DC magnetron co sputtering of Ti and V at ambient temperatures. The effect of deposition pressure on the film morphology, superconducting and normal state properties has been studied. Measurement of electrical resistance as a function of temperature indicates that up to a certain deposition pressure, the 20 nm thick Ti40V60 films exhibit metallic behavior in the normal state and superconductivity at low temperatures. Beyond a threshold pressure, the films show a negative temperature coefficient of resistance with a residual resistance ratio less than one. Electrical transport measurements in the presence of magnetic field were performed to find the current voltage characteristics of the thin films. Analysis of the I V curves indicates that the Ti40V60 alloy thin films have a large transport critical current density (JC) e.g. 1.475E10 A per m2 in zero magnetic field and 2.657E09 A per m2 in 4 T (both at 4 K). Analysis of the field dependence of flux line pinning force density indicates a combined effect of core delta k surface and core delta k point pinning mechanisms (where k is the Ginzburg Landau parameter). Additionally, spatial variations in the superconducting critical temperature (TC ) across the sample contribute to delta TC pinning. In higher magnetic fields, a contribution from delta l pinning (where l is the electron mean free path) also becomes significant. The findings indicate the potential of Ti40V60 alloy thin film for superconducting device applications like cryogenic radiation detectors.

cond-mat.supr-con↗

arXiv2025

Extending the optical absorption in a lumped element meander structure to far-infrared wavelengths

Superconducting radiation detectors typically exhibit detection and single photon sensitivity limited to the mid infrared wavelength range. Extending their detection capabilities into the far infrared range (>10 um) requires careful selection of substrate materials and detector geometries. The overall detection efficiency is linked to absorption and coupling efficiencies. In this study, the resonator geometry and absorption efficiency were estimated using electromagnetic simulations in CST Microwave Studio for a lumped-element meander structure. Simulations were performed for the 12 to 50 um wavelength range, corresponding to the Infrared Free Electron Laser (IR FEL) at RRCAT, Indore. Absorption in the meander inductor was influenced by the substrate material, thickness, and impedance matching between the detector and incident photon medium. The results indicate that SiO2 and diamond substrates are suitable for developing lumped-element kinetic inductance detectors (LEKID) in this range. Optimized meander geometries on diamond substrates demonstrated absorption efficiencies of up to 95% for narrow bandwidths and over 50% for wide bandwidths. A 30-pixel LEKID structure was fabricated using electron beam lithography on a 500 um SiO2 coated Si substrate, with a 20 nm thick Ti40V60 alloy resonator. Experimental absorption efficiency was determined through transmission and reflection measurements. Results show that in the 14 to 26 um IR-FEL range, the LEKID achieved up to 75% absorption efficiency. These studies demonstrate that the LEKID structure is ideal for detecting far infrared wavelengths above 10 um, with high absorption efficiency.

cond-mat.supr-con↗

arXiv2025

Sputtering Current Driven Growth & Transport Characteristics of Superconducting Ti40V60 Alloy Thin Films

The room temperature growth, characterization, and electrical transport properties of magnetron sputtered superconducting Ti40V60 alloy thin films are presented. The films exhibit low surface roughness and tunable transport properties. As the sputtering current increases, the superconducting transition move towards higher temperatures. Rietveld refinement of two dimensional XRD (2D XRD) pattern reveals the presence of stress in the films, which shifts from tensile to compressive as the sputtering current increases. Additionally, the crystallite size of the films increases with higher sputtering currents. The films exhibit a strong preferential orientation, contributing to their texturing. The crystallite size and texturing are found to be correlated with the superconducting transition temperature (TC) of the films. As the crystallite size and texturing increase, the TC of the films also rises.

cond-mat.supr-con↗

arXiv2023

Ambient Temperature Growth and Superconducting Properties of Ti-V Alloy Thin Films

A study on the optimization of ambient temperature growth and superconducting properties of Ti-V alloy thin films grown on SiO2-coated Si substrate is reported here. These films have been synthesized by co-sputtering of Ti and V targets, and films having different Ti concentrations were deposited to get the optimized critical temperature (TC) of thin films close to the bulk value. The maximum TC of 5.2 K has been obtained in the Ti40V60 composition, which is further increased to 6.2 K when a 10 nm thick Ti underlayer is added below the Ti-V film. GIXRD measurements confirm the formation of Ti-V alloys in the desired crystal structure. The upper critical field (HC2) of the thin films has been estimated with the help of magnetotransport measurements. The utility of Ti-V alloy thin films in superconducting radiation detection applications is ascertained.

cond-mat.supr-con↗