arXiv subjects

Surendra Singh

Publications and source records attributed to Surendra Singh.

At least 19 recordsLinked to original sources

arXiv2024

Smartphone-based Iris Recognition through High-Quality Visible Spectrum Iris Capture

Iris recognition is widely acknowledged for its exceptional accuracy in biometric authentication, traditionally relying on near-infrared (NIR) imaging. Recently, visible spectrum (VIS) imaging via accessible smartphone cameras has been explored for biometric capture. However, a thorough study of iris recognition using smartphone-captured 'High-Quality' VIS images and cross-spectral matching with previously enrolled NIR images has not been conducted. The primary challenge lies in capturing high-quality biometrics, a known limitation of smartphone cameras. This study introduces a novel Android application designed to consistently capture high-quality VIS iris images through automated focus and zoom adjustments. The application integrates a YOLOv3-tiny model for precise eye and iris detection and a lightweight Ghost-Attention U-Net (G-ATTU-Net) for segmentation, while adhering to ISO/IEC 29794-6 standards for image quality. The approach was validated using smartphone-captured VIS and NIR iris images from 47 subjects, achieving a True Acceptance Rate (TAR) of 96.57% for VIS images and 97.95% for NIR images, with consistent performance across various capture distances and iris colors. This robust solution is expected to significantly advance the field of iris biometrics, with important implications for enhancing smartphone security.

eess.IV↗

arXiv2024

Securing Biometric Data: Fully Homomorphic Encryption in Multimodal Iris and Face Recognition

Multimodal biometric systems have gained popularity for their enhanced recognition accuracy and resistance to attacks like spoofing. This research explores methods for fusing iris and face feature vectors and implements robust security measures to protect fused databases and conduct matching operations on encrypted templates using fully homomorphic encryption (FHE). Evaluations on the QFIRE-I database demonstrate that our method effectively balances user privacy and accuracy while maintaining a high level of precision. Through experimentation, we demonstrate the effectiveness of employing FHE for template protection and matching within the encrypted domain, achieving notable results: a 96.41% True Acceptance Rate (TAR) for iris recognition, 81.19% TAR for face recognition, 98.81% TAR for iris fusion (left and right), and achieving a 100% TAR at 0.1% false acceptance rate (FAR) for face and iris fusion. The application of FHE presents a promising solution for ensuring accurate template matching while safeguarding user privacy and mitigating information leakage.

cs.CR↗

arXiv2024

Longitudinal Evaluation of Child Face Recognition and the Impact of Underlying Age

The need for reliable identification of children in various emerging applications has sparked interest in leveraging child face recognition technology. This study introduces a longitudinal approach to enrollment and verification accuracy for child face recognition, focusing on the YFA database collected by Clarkson University CITeR research group over an 8 year period, at 6 month intervals.

cs.CV↗

arXiv2023

Wait-time Distributions for Photoelectric Detection of Light

Wait-time distributions for the $n$th photo-detection at a detector illuminated by a stationary light beam are studied. Both unconditional measurements, initiated at an arbitrary instant, and conditional measurements, initiated upon a photo-detection, are considered. Simple analytic expressions are presented for several classical and quantum sources of light and are used to quantify and compare photon sequences generated by them. These distributions can be measured in photon counting experiments and are useful in characterizing and generating photon sequences with prescribed statistics. Effects of non-unit detection efficiency are also discussed, and curves are presented to illustrate the behavior.

quant-ph↗

arXiv2023

Coupling of strain and magnetism in manganite-based complex oxide heterostructures

Complex oxide thin films and heterostructures offer a wide range of properties originating from the intrinsic coupling between lattice strain and magnetic/electronic ordering. This article reviews experimental, phenomenological, and theoretical analyses of the coupling of strain with electronic and magnetic properties of mixed valence manganite heterostructures. The influence of epitaxial strain on the magnetic properties of manganite films is measured using macroscopic magnetization measurements and shown mixed reports suggesting, both, an increase and decrease in ferromagnetic phases on the application of the strain. Using polarized neutron reflectivity (PNR), a simultaneous measurement of transport and magnetic properties of manganite thin films showed direct evidence of modification in the magnetic properties on the application of bending strain. The coupling coefficient of strain and magnetism of manganite heterostructures was estimated using PNR, which not only helped to understand the correlation of elastic strain with magnetism but also explained the condition of magnetic phase order change in the phase-separated systems within a phenomenological Ginzburg Landau theory. An overview is also provided of the current perspectives and existing studies on the influence of strain on structure, electronic, magnetic, magnetic anisotropy, phase coexistence and magnetocaloric properties of mixed valence manganite heterostructures. Based on the understanding of a diverse range of perovskite functionalities, detailed perspectives on how the coupling of strain and magnetism open up pathways toward the emergence of novel device design features including the different ways of applying uniform strain, are discussed.

cond-mat.str-el↗

arXiv2023

Emerging interfacial magnetization in isovalent manganite heterostructures driven by octahedral coupling

The distortion of corner-sharing octahedra in isovalent perovskite transition-metal oxide interfaces is proven to be an excellent way to tailor the electronic and magnetic properties of their heterostructures. Combining depth-dependent magnetic characterization technique; (polarized neutron reflectivity, PNR); and theoretical calculation (density functional theory), we report interface-driven magnetic exchange interactions due to a modification in the octahedral rotations at the interfaces in an isovalent La0.67Ca0.33MnO3 (LCMO)/La0.67Sr0.33MnO3 (LSMO) heterostructures. PNR results determined a length scale of ~ 8 unit cells at the interface, which demonstrated a modification in magnetic properties. The results also predicted a low-temperature exchange bias for these ferromagnetic heterostructures with a maximum exchange bias for the heterostructure, which showed an enhanced antiferromagnetic coupling at the interfaces.

cond-mat.mtrl-sci↗

arXiv2023

Charging capacitors from thermal fluctuations using diodes

We theoretically consider a graphene ripple as a Brownian particle coupled to an energy storage circuit. When circuit and particle are at the same temperature, the second law forbids harvesting energy from the thermal motion of the Brownian particle, even if the circuit contains a rectifying diode. However, when the circuit contains a junction followed by two diodes wired in opposition, the approach to equilibrium may become ultraslow. Detailed balance is temporarily broken as current flows between the two diodes and charges storage capacitors. The energy harvested by each capacitor comes from the thermal bath of the diodes while the system obeys the first and second laws of thermodynamics.

cond-mat.mes-hall↗

arXiv2023

Influence of swift heavy ion irradiation on structure and morphology of La0.25Pr0.375Ca0.375MnO3 perovskite film

The effects of Ag15+ (120 MeV) swift heavy ion irradiation on the structural and morphological properties of epitaxial La0.25Pr0.375Ca0.375MnO3 (LPCMO) thin films was investigated by x-ray scattering and atomic force microscopy (AFM) techniques. LPCMO films of thickness ~ 280 {\AA} were irradiated with an Ag15+ ion beam at different fluences of 1E11, 5E11, and 1E12 ions/cm2. XRD results suggested the development of the tensile stress along the out-of-plane direction of the LPCMO film upon ion irradiation which increased on increasing the ion fluence. The morphology of the film also modified with the irradiation and an increase in the fluence of the ion beam enhanced the in-plane height-height correlation length scale (grain size) with a loss of the fractal behaviour.

cond-mat.mtrl-sci↗

arXiv2023

Neutron Reflectometry: a technique for revealing emergent phenomena at interfaces in heterostructures

Neutron reflectometry (NR) has emerged as a unique technique for the investigation of structure and magnetism of thin films of both biologically relevant and magnetic materials. The advantage of NR with respect to many other surface-sensitive techniques is its sub-nanometer resolution that enables structural characterizations at the molecular level. While in the case of bio-relevant samples, NR can be used to probe thin films at buried interfaces, non-destructively, even adopting a complex sample environment. Whereas the polarized version of NR is best suited for revealing the interface magnetism with a sub-nanometer depth resolution. In this article, I will briefly describe the basic principle of NR with some applications of NR to both bio-relevant samples and magnetic heterostructures.

cond-mat.mtrl-sci↗

arXiv2021

Thermal stability of interfacial mixed layers in c-Ni/a-Zr multilayer during annealing: structural and magnetic properties

Annealing of crystalline multilayers composed of two miscible elements usually causes interfacial mixing of the constituent atoms, possibly leading to the formation of binary alloys at the interfaces. Magnetron sputtered c-Ni/a-Zr multilayers deposited at room temperature were vacuum annealed isochronally at 200degC and 400degC to observe thermal stability of the interfaces constituting the crystalline/amorphous multilayers. Control over the interfacial behaviour can aid the formation of materials with novel properties. The resultant changes in structural and magnetic properties of the multilayers were investigated in detail through X-ray Reflectivity, Polarized Neutron Reflectivity, SIMS and SQUID-based magnetization measurement techniques. The compositional variations in the amorphous mixed layers formed at the Ni-on-Zr and Zr-on-Ni interfaces due to atomic transport, were carefully observed as a function of annealing. Interface widths proceeded to increase with annealing at the expense of the Ni and Zr layers. The Ni-on-Zr interface was seen to be unstable at both temperatures; but the overall response of the interfaces to atomic diffusion was more pronounced when the multilayers were annealed at 400degC. Under conditions of supersaturation of atoms within restricted spaces of the interfacial layers and the limited availability of components within the multilayer, unexpected demixing effects were observed at both the interfaces. A large increase in magnetic moment obtained after annealing at 400degC, was attributed to the high densification of the Ni layers as well as to the incorporation of Ni crystallites into the Zr-on-Ni interface layers.

cond-mat.mtrl-sci↗

arXiv2020

Fluctuation-induced current from freestanding graphene: toward nanoscale energy harvesting

At room temperature, micron-sized sheets of freestanding graphene are in constant motion even in the presence of an applied bias voltage. We quantify the out-of-plane movement by collecting the displacement current using a nearby small-area metal electrode and present a Langevin model for the motion coupled to a circuit containing diodes. The system reaches thermal equilibrium and the rates of heat, work, and entropy production tend quickly to zero. However, there is power generated by graphene which is equal to the power dissipated by the load resistor. The exact power formula is similar to Nyquist's noise power formula, except that the rate of change of diode resistance significantly boosts the output power, and the movement of the graphene shifts the power spectrum to lower frequencies.

cond-mat.mes-hall↗

arXiv2019

Annealing driven positive and negative exchange bias in Fe-Cu-Pt heterostructures at room temperature

We report annealing induced exchange bias in Fe-Cu-Pt based heterostructures with Cu as an intermediate layer (Fe/Cu/Pt heterostructure) and capping layer (Fe/Pt/Cu heterostructure). Exchange bias observed at room temperature (300 K) is found to be dependent on the annealing temperature. We obtained positive exchange bias of 120 Oe on annealing both the heterostructures at 400 oC, while on annealing these heterostructures at 500 and 600 oC a negative exchange bias of ~ -100 Oe was found. X-ray reflectivity and polarized neutron reflectivity measurements provided evolution of depth dependent structure and magnetic properties of the heterostructures on annealing at different temperatures and revealed coexistence of soft and hard (alloy) magnetic phases across the thickness of the films. Rapid and long range interdiffusion at interfaces on annealing the systems at a temperature above 400 oC resulted into formation of a ternary alloy phase. These results can be understood within the context of a very unusual interface exchange interaction at the interface of hard/soft magnetic phases, which are dependent on the annealing temperature.

cond-mat.mtrl-sci↗

arXiv2019

Antisymmetric magnetoresistance and helical magnetic structure in compensated Gd/Co multilayer

Using spin dependent specular and off-specular polarized neutron reflectivity (PNR), we report the observation of a twisted helical magnetic structure with planar 2{\pi} domain wall (DW) and highly correlated magnetic domains in a Gd/Co multilayer. Specular PNR with polarization analysis reveals the formation of planar 2{\pi}DWs below a compensation temperature (TComp), resulting to positive exchange bias in this system. Off-specular PNR with spin polarization showed development of magnetic inhomogenities (increase in magnetic roughness) for central part (thickness ~ 25-30 {\AA}) of each Gd layer, where magnetization is aligned perpendicular (in-plane) to an applied field. These magnetic roughness are vertically correlated and results into Bragg sheet in spin flip channel of Off-specular PNR data, which is contributing towards an antisymmetric magnetoresistance at TComp in the system. The growth and tunability of highly correlated magnetic inhomogeneities (roughness) and domain structure around TComp in combination of twisted helical magnetic structure with planar 2{\pi}DWs will be key for application in all-spin-based technology.

cond-mat.mes-hall↗

arXiv2019

Superconductivity-driven magnetization modulation in YBa2Cu3O7-{\delta} /SrTiO3/La0.67Sr0.33MnO3 heterostructures

Using spin polarized neutron reflectivity experiments, we demonstrate an unusual proximity behaviour when the superconductor (SC) and the ferromagnet (FM) are coupled through an insulator (I) in YBa2Cu3O7-{\delta} (SC)/SrTiO3 (I)/La0.67Sr0.33MnO3 (FM) heterostructures. We have observed an unexpected magnetic modulation at the interface region of the FM below the superconducting transition temperature. The magnetization of the FM layer at the I/FM interface was drastically reduced as compared to the magnetization in the rest of the FM layer. This result indicates that the Cooper pairs tunnel across the insulator and interact with the local magnetization at the interface region (extending ~ 30 {\AA}) of the FM causing modification of the magnetization at the interface. This unexpected magnetic behavior cannot be explained on the basis of the existing theoretical models. However, the length scale associated here clearly suggests the long range proximity effect as a result of tunneling of Cooper pairs.

cond-mat.supr-con↗

arXiv2017

High density nonmagnetic cobalt in thin films

Recently high density (HD) nonmagnetic (NM) cobalt has been discovered in a cobalt thin film, grown on Si(111). This cobalt film had a natural cobalt oxide at the top. The oxide layer forms when the film is taken out of the electron-beam deposition chamber and exposed to air. Thin HD NM cobalt layers were found near the cobalt/silicon and the cobalt-oxide/cobalt interfaces, while the thicker mid-depth region of the film was hcp cobalt with normal density and normal magnetic moment. If an ultrathin film of gold is grown on the cobalt layer, before exposing it to air, the oxidation of the cobalt surface layer is prevented. It is important to investigate whether the growth of HD NM cobalt layers in the thin film depends on (i) capping of the film by the gold layer, (ii) the film thickness and (iii) the nature of the substrate. The results of such investigations, presented here, indicates that for cobalt films capped with a thin gold layer, and for various film thicknesses, HD NM cobalt layers are still observed. However, instead of a Si substrate, when the cobalt films are grown on oxide substrates, such as silicon oxide or cobalt oxide, HD NM cobalt layers are not observed.

cond-mat.mtrl-sci↗

arXiv2016

Evidence of Formation of Superdense Nonmagnetic Cobalt

Magnetism of 3d transition metals at high density has always received wide interest due to existence of magnetism at the core of the Earth. For ferromagnetic cobalt, although there is a theoretical prediction that its magnetic moment would vanish when the density increases to about 1.4 times the normal value, so far there is no experimental evidence. We have discovered the existence of ultrathin superdense nonmagnetic cobalt layers in a polycrystalline cobalt thin film. The densities of these layers are about 1.3-1.4 times the normal density of Co. This has been revealed by X-ray reflectometry experiments, which provide a depth profile of the electron scattering length density, and corroborated by polarized neutron reflectometry (PNR) experiments. The superdense Co layer has an fcc structure, unlike hcp structure for bulk Co, as revealed by transmission electron microscopy. The magnetic depth profile, obtained by PNR, shows that the superdense Co layers at the film-substrate interface and near the top of the film are nonmagnetic. The major part of the Co film has the usual density and magnetic moment.

cond-mat.mtrl-sci↗

arXiv2016

Antiferromagnetic Coupling between Surface and Bulk Magnetization and Anomalous Magnetic Transport in Electro-deposited Co Film

We report an interesting magnetic behavior of a Co film (thickness ~ 350 {\AA}) grown on Si/Ti/Cu buffer layer by electro-deposition (ED) technique. Using depth sensitive X-ray reflectivity and polarized neutron reflectivity (PNR) we observed two layer structures for the Co film grown by ED with a surface layer (thickness ~ 100 {\AA}) of reduced density (~ 68% of bulk) compared to rest of the Co film (thickness ~ 250 {\AA}). The two layer structure is consistent with the histogram profile obtained from atomic force microscope (AFM) of the film. Interestingly, using PNR, we found that the magnetization in the surface Co layer is inversely (antiferomagnetically) coupled (negative magnetization for surface Co layer) with the rest of the Co layer for the ED grown film. While we compare PNR result for a Co film of similar layered structure grown by sputtering, the film showed a uniform magnetization as expected. We also show that the depth dependent unusual magnetic behavior of ED grown Co film may be responsible for anomalous anisotropic magnetoresistance observed in low field in this film as compared to the Co film grown by sputtering. Combining X-ray scattering, AFM, superconducting quantum interface device magnetometry (SQUID), PNR and magneto-transport measurements we attempted to correlate and compare the structural, magnetic and morphological properties with magneto-transport of Co films grown by ED and sputtering. The study indicates that the interesting surface magnetic property and magneto-transport property of the ED film is caused by its unique surface morphology.

cond-mat.mtrl-sci↗

arXiv2015

Composition dependence of electronic, magnetic, transport and morphological properties of mixed valence manganite thin films

We present a comparison of the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1-xCaxMnO3 films with x = 0.33 and 0.375, across the metal to insulator transition (MIT) temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films near the MIT. The charge-magnetic correlation length (~ 12000 {\AA}) for x = 0.33 was much larger (~4 times) than the charge-charge correlation length (~ 3200 {\AA}) at 20 K. Whereas for x = 0.375 the charge-magnetic correlation length (~ 7500 {\AA}) was smaller than the charge-charge correlation length (~ 9000 {\AA}).

cond-mat.str-el↗