arXiv subjects

Asif Ali

Publications and source records attributed to Asif Ali.

At least 19 recordsLinked to original sources

arXiv2026

Rare Radiative Decays of Z boson into S- and P-wave Charmonium within the Bethe-Salpeter Model

We employ the Bethe-Salpeter (BS) model to investigate radiative decays of the Z boson into charmonium. Within the instantaneous approximation of the BS equation, we analyze the relevant decay channels for S-wave charmonium states ($\psi(nS)$, $\eta_{c}(nS)$, $n=1,2,3$) and P-wave charmonium states ($\chi_{c0}(mP)$, $\chi_{c1}(mP)$, $h_{c}(mP)$, $m=1,2$). We compute all branching fractions using leading-order Feynman diagrams. For the $J/\psi$ channel, our BS calculations suggest that prior theoretical results were likely underestimated, making our prediction more promising for future experimental measurements.

hep-ph↗

arXiv2026

Rare Exclusive Decays of the Z-boson into S-wave Quarkonia within the Bethe-Salpeter Formalism

This paper investigates the rare decays of the Z boson into S-wave quarkonia within the Bethe-Salpeter formalism. Both the production of double S-wave quarkonia and radiative decays into single S-wave quarkonium are analyzed. For double quarkonia production, i.e., $Z\to VV$ and $Z\to VP$ (where $V$ and $P$ represent vector and pseudoscalar quarkonia, respectively), we consider the leading order contribution from both QCD as well as electromagnetic transition via virtual photon (QED) amplitudes. The heavy quark limit is adopted to simplify calculations. Additionally, we have introduced another possible leading order channel for Z-boson decays to double S-wave quarkonia, where the Z boson decays into bottomonium plus charmonium via QED amplitude. Such processes may include $Z\to J/\psi+\Upsilon(1S)$, $Z\to\eta_{b}+J/\psi$ and $Z\to\eta_{c}+\Upsilon(1S)$. Moreover, we have also studied radiative Z boson decays to S-wave quarkonium, namely $Z\to X(Q\bar{Q})\gamma$, where $X(Q\bar{Q})=J/\psi$, $\Upsilon$, $\eta_{c}$, and $\eta_{b}$. Interestingly, for double charmonium and radiative charmonium production, our results are larger than the NRQCD finding, while for the bottomonium case, our findings are comparatively smaller. This shows that charmonium is a relativistic particle, while bottomonium is a non-relativistic particle.

hep-ph↗

arXiv2025

Spectroscopic evidence of Kondo resonance in 3$d$ van der Waals ferromagnets

Two-dimensional van der Waals (vdW) ferromagnets drive the advancement in spintronic applications and enable the exploration of exotic magnetism in low-dimensional systems. The entanglement of dual $-$ localized and itinerant $-$ nature of electrons lies at the heart of the correlated electron systems giving rise to exotic ground state properties such as complex magnetism, heavy fermionic behavior, Kondo lattice formation, \textit{etc}. Through temperature-dependent electronic structure of vdW ferromagnets, (Co$_{x}$Fe$_{1-x}$)$_{3}$GeTe$_{2}$, probed using high-resolution photoemission spectroscopy and density functional theory combined with dynamical mean field theory (DFT+DMFT), we provide direct evidence of the emergence of Kondo resonance peak driven by complex interplay between localized and itinerant electrons. In overall agreement with experimental electronic structure and magnetic properties, DFT+DMFT also reveals finite spin band splitting well beyond $T_{C}$. Core levels, valence band photoemission spectra together with DFT+DMFT spectral functions reveal insignificant change across $T_{C}$ indicating non-Stoner magnetism in (Co$_{x}$Fe$_{1-x}$)$_{3}$GeTe$_{2}$. Our results provide a way forward to the understanding of complex interplay between electronic structure, exotic magnetism and heavy fermionic behavior leading to Kondo scenerio in 3$d$ vdW ferromagnets.

cond-mat.str-el↗

arXiv2025

Unraveling the role of disorder in the electronic structure of high entropy alloys

Disorder in high entropy alloys, arising from the random distribution of multiple elements, plays a crucial role in their novel properties desirable for various advanced engineering applications. We investigate the role of compositional and structural disorder on the electronic structure of osmium-based superconducting high entropy alloys, (Ru/Re)$_{0.35}$Os$_{0.35}$Mo$_{0.10}$W$_{0.10}$Zr$_{0.10}$, using photoemission spectroscopy and density functional theory (DFT). Elemental and cumulative core level shifts are found to be commensurate with elemental electronegativities and valence electron counts (VEC), respectively. Valence band spectra together with DFT results indicate that the crystal structure plays an important role in deciding the electronic structure of these high entropy alloys. Through temperature dependent high-resolution spectra, we unveil strongly suppressed spectral density of states (SDOS) in the close vicinity of Fermi level. Energy and temperature dependence of the SDOS in accordance with Altshuler-Aronov theory confirms localization of charge carriers in the presence of strong intrinsic disorder. Computed electron-phonon coupling strength and superconducting transition temperature aligning reasonably well with experiments further shed light on phonon-mediated pairing mechanism and role of disorder in these systems. Our results provide a way forward to the understanding of superconducting high entropy alloys through strategic control of disorder, VEC and crystal structure.

cond-mat.mtrl-sci↗

arXiv2025

Towards Efficient and Secure Cloud-Assisted Autonomous Systems: A Review of Architectures, Algorithms, Security, and Deployment Challenges

Networked Control Systems (NCSs) have been instrumental in realizing fully connected and responsive intelligent environments within the context of real-time virtual control and management. However, traditional NCSs face considerable challenges in handling the vast amounts of data generated by large-scale control applications, particularly in terms of data acquisition, storage, and computational processing. To address these challenges, the emergence of cloud computing and advancements in control theory have empowered the new paradigm known as Cloud Control Systems (CCSs). Recently, CCSs have received substantial attention from industries for their potential properties, such as large-scale data management, complex computations, and data-centric optimized decisions. This study presents an extensive review of recent progress in CCSs spanning over multiple studies published between 2012 and 2025. Specifically, the focus is on providing a taxonomy of the current findings in CCS research, encompassing various perspectives, such as its efficient implementations in industrial automation, security and privacy considerations, and cloud-based control techniques. Each category is examined in depth through selected state-of-the-art analyses of different approaches and contrasting methodologies. Furthermore, we discuss future directions aimed at designing more efficient and practical CCSs. The insights gained from this study can help researchers, practitioners, and decision-makers in their domain for effective CCS design and deployment.

eess.SY↗

arXiv2025

Strongly correlated topological surface states in type-II Dirac semimetal NiTe$_{2}$

Nontrivial topology in type-II Dirac semimetal NiTe$_2$ leading to topologically protected surface states give rise to fascinating phenomena holding great promise for next-generation electronic and spintronic devices. Key parameters $-$ such as lattice parameter, disorder, vacancies, and electron correlation $-$ significantly influence the electronic structure and, subsequently, the physical properties. To resolve the discrepancy between the theoretical description and experimentally observed topological surface states, we comprehensively investigate the electronic structure of NiTe$_2$ using angle-resolved photoemission spectroscopy and density functional theory. Although the bulk electronic structure is found to be well-described within mean field approaches, an accurate description of topological surface states is obtained only by incorporating surface electronic correlation. We reveal that the strongly correlated surface states forming Dirac-like conical crossing much below Fermi level have hybridized Ni 3$d$ and Te 5$p$ character. These findings underscore the intricate interplay between electron correlation and band topology, broadening our understanding of many-body correlation effects on the topological surface states in quantum materials.

cond-mat.str-el↗

arXiv2025

Origin of dimensional crossover in quasi-one-dimensional hollandite K$_{2}$Ru$_{8}$O$_{16}$

Intriguing phenomenon of dimensional crossover is comprehensively studied by experimental and theoretical investigation of electronic structure in quasi-one-dimensional hollandite K$_{2}$Ru$_{8}$O$_{16}$. Valence band photoemission spectra in conjunction with density functional theory within local density approximation combined with dynamical mean field theory (LDA+DMFT) reveal moderately correlated electronic structure. Anomalous temperature dependence of high-resolution spectra in the vicinity of Fermi level suggests Tomonaga-Luttinger liquid state down to 150 K, below which it undergoes a dimensional crossover from one-dimensional to three-dimensional electronic behaviour. Monotonously decreasing spectral intensity at the Fermi level along with Fermi cut-off at low temperature suggests non-Fermi liquid like behaviour. Many body effects captured within LDA+DMFT reveal increased warping of the Fermi surface with lowering temperature. A simple analysis suggests that the warping dominates the thermal energy induced momentum broadening at low temperature, leading to the 3D electronic behaviour. Our results offer valuable insight in understanding the interplay of dimensionality, electron correlation and thermal energy governing various exotic phenomena in quasi-one-dimensional systems.

cond-mat.str-el↗

arXiv2024

High-temperature observation of intralayer, interlayer, and Rydberg excitons in bulk van der Waals alloy single crystals

Transition metal dichalcogenides (TMDs) exhibit remarkable optical properties due to the diverse number of strongly bound excitons, which can be fine-tuned by alloying. Despite a flurry of research activity in characterizing these excitons, a comprehensive and profound understanding of their behavior with temperature is lacking. Here, we report the rich spectrum of excitonic features within bulk van der Waals alloy Mo$_{0.5}$W$_{0.5}$S$_2$ and Mo$_{0.5}$W$_{0.5}$Se$_2$ single crystals through temperature-dependent reflectance spectroscopy and first-principle calculations. We observed Rydberg excitons and interlayer excitons in both the single crystals. Notably, we provide the first experimental evidence of highly energetic A$^\prime$ and B$^\prime$ excitons in Mo$_{0.5}$W$_{0.5}$S$_2$ at room temperature. The strong carrier-phonon scattering significantly broadens the A$^\prime$, B$^\prime$ and interlayer excitons at room temperature in bulk Mo$_{0.5}$W$_{0.5}$S$_2$ single crystal compared to its selenide. Our findings, supported by density functional theory and Bethe-Salpeter equation calculations, signify the crucial role of carrier-phonon interactions. These results open pathways for next-generation optoelectronic devices and quantum technologies operating at high temperature.

cond-mat.mtrl-sci↗

arXiv2024

Influence of anti-ferromagnetic ordering and electron correlation on the electronic structure of MnTiO$_3$

Electron correlation and long-range magnetic ordering have a significant impact on the electronic structure and physical properties of solids. Here, we investigate the electronic structure of ilmenite MnTiO$_{3}$ using room temperature photoemission spectroscopy and theoretical approaches within density functional theory (DFT), DFT+$U$ and DFT+dynamical mean field theory (DMFT). Mn 2$p$ (Ti 2$p$) core level photoemission spectra, confirming Mn$^{2+}$ (Ti$^{4+}$) oxidation state, exhibit multiple satellites which are very similar to that of MnO (TiO$_{2}$), suggesting similar strength of various interactions in this system. Valence band spectra collected at different photon energies suggest dominant Mn 3$d$ character in the highest occupied band with a wide insulating gap. DFT(+$U$) correctly predicts the experimentally observed anti-ferromagnetic (AFM) insulating ground state for MnTiO$_3$ where the requirement of a large $U$ to reproduce the experimental values of magnetic moment and band gap signifies the importance of electron correlation. Magnetically disordered paramagnetic (PM) phase could be well captured within DFT+DMFT, which provides an excellent agreement for the experimental band gap, paramagnetic moment, valence band spectra as well as dominant Mn 3$d$ character in the highest occupied band. The calculated spectral function remains largely unaffected and exhibits sharper features in the magnetically ordered AFM phase. We show that the electronic structure of MnTiO$_{3}$ in both the PM and AFM phases can be accurately described within DFT+DMFT.

cond-mat.str-el↗

arXiv2024

Manifestation of incoherent-coherent crossover and non-Stoner magnetism in the electronic structure of Fe$_3$GeTe$_2$

Two-dimensional (2D) van der Waals ferromagnets have potential applications as next-generation spintronic devices and provide a platform to explore the fundamental physics behind 2D magnetism. The dual nature (localized and itinerant) of electrons adds further complexity to the understanding of correlated magnetic materials. Here, we present the temperature evolution of electronic structure in 2D van der Waals ferromagnet, Fe$_{3}$GeTe$_{2}$, using photoemission spectroscopy in conjunction with density functional theory (DFT) plus dynamical mean field theory (DMFT). With the appearance of quasiparticle peak and its evolution in the vicinity of Fermi energy, we unveil empirical evidences of incoherent-coherent crossover at around 125 K. DFT+DMFT results show that the quasiparticle lifetime surpasses thermal energy for temperature below 150 K, confirming incoherent-coherent crossover in the system. No appreciable change in the Fe 2$p$ core level, overall valence band spectra across the magnetic transition, and temperature dependent ferromagnetic DFT+DMFT results, provide substantial evidence for non-stoner magnetism in Fe$_{3}$GeTe$_{2}$. We elucidate the temperature dependent intimate relation between magnetism and electronic structure in Fe$_{3}$GeTe$_{2}$. Sommerfeld coefficient of $\sim$ 104 mJ mol$^{-1}$ K$^{-2}$ obtained in the low temperature limit from DFT+DMFT calculations resolve the long standing issue of large Sommerfeld coefficient ($\sim$ 110 mJ mol$^{-1}$ K$^{-2}$) obtained from specific heat measurements.

cond-mat.str-el↗

arXiv2023

Role of electron correlation and disorder on the electronic structure of layered nickelate (La$_{0.5}$Sr$_{0.5}$)$_2$NiO$_4$

We investigate the role of electron correlation and disorder on the electronic structure of layered nickelate (La$_{0.5}$Sr$_{0.5}$)$_2$NiO$_4$ using core level and valence band photoemission spectroscopy in conjunction with density functional theory (DFT) and dynamical mean field theory (DMFT) calculations. Sr 3$d$ and La 4$d$ core level spectra exhibit multiple features associated with photoemission final state effects. An increase of unscreened features in the Sr 3$d$ and La 4$d$ core level spectra with lowering temperature suggests the reduction in density of states (DOS) at the Fermi level, $E_F$. Valence band spectra collected using different photon energies reveal finite intensity at $E_F$ and overall spectra are well captured by DFT+DMFT. Strong renormalization of partially filled $e_g$ bands in DFT+DMFT result indicates strong correlation in this system. Mass enhancement factor, $m^*/m_{\text{DFT}} \sim$ 3, agrees well with values obtained from specific heat measurements. High resolution spectra in the vicinity of $E_F$ show monotonically decreasing spectral intensity with lowering temperature, which evolves to exhibit a Fermi cut-off at low temperatures indicating metallic character in contrast to insulating transport, suggesting Anderson insulating state. $|E-E_F|^{1/2}$ dependence of the spectral DOS and square root temperature dependence of spectral DOS at $E_F$ evidences the role of disorder in the electronic structure of (La$_{0.5}$Sr$_{0.5}$)$_2$NiO$_4$.

cond-mat.str-el↗

arXiv2023

Evidence of electron correlation and weak bulk plasmon in SrMoO$_{3}$

We investigate the electronic structure of highly conducting perovskite SrMoO$_{3}$ using valence band photoemission spectroscopy and electronic structure calculations. Large intensity corresponding to coherent feature close to Fermi level is captured by density functional theory (DFT) calculation. An additional satellite at $\sim$ 3 eV binding energy remains absent in DFT, hybrid functional (DFT-hybrid) and dynamical mean field theory (DFT + DMFT) calculations. Mo 4$d$ spectra obtained with different surface sensitive photoemission spectroscopy suggest different surface and bulk electronic structures. DFT + DMFT spectral function is in excellent agreement with the coherent feature in the bulk Mo 4$d$ spectra, revealing moderate electron correlation strength. A large plasmon satellite and signature of strong electron correlation are observed in the surface spectra, while the bulk spectra exhibits a $weak$ plasmon satellite.

cond-mat.str-el↗

arXiv2023

Revelation of Mott insulating state in layered honeycomb lattice Li$_2$RuO$_3$

We investigate the role of electron correlation in the electronic structure of honeycomb lattice Li$_2$RuO$_3$ using photoemission spectroscopy and band structure calculations. Monoclinic Li$_2$RuO$_3$ having Ru network as honeycomb lattice undergoes magneto-structural transition at T$_c$ $\sim$ 540 K from high temperature phase $C2/m$ to low temperature dimerized phase $P2_1/m$. Room temperature valence band photoemission spectra reveal an insulating ground state with no intensity at Fermi level ($E_F$). Ru 4$d$ band extracted from high and low photon energy valence band photoemission spectra reveal that the surface and bulk electronic structures are very similar in this system. Band structure calculations using generalized gradient approximation (GGA) leads to metallic ground state while screened hybrid (YS-PBE0) functional reveals opening up of a gap in almost degenerate $d_{zx}$/$d_{yz}$ orbital, whereas $d_{xy}$ orbital is already gapped. Ru 3$d$ core level spectra with prominent unscreened feature provides direct evidence of strong electron correlation among Ru 4$d$ electrons which is also manifested by $|E-E_F|^2$ dependence of spectral density of states (DOS) in the vicinity of $E_F$ in the high-resolution spectra, establishing Li$_2$RuO$_3$ as Mott insulator.

cond-mat.str-el↗

arXiv2023

Role of disorder and strong 5$d$ electron correlation in the electronic structure of Sr2TiIrO6

Transport and magnetic properties along with high resolution valence band photoemission study of disordered double perovskite Sr$_{2}$TiIrO$_{6}$ has been investigated. Insulator to insulator transition along with a magnetic transition concurrently occurs at 240 K. Comparison of valence band photoemission with band structure calculations suggests that the spin orbit coupling as well as electron correlation are necessary to capture the line shape and width of the Ir 5$d$ band. Room temperature valence band photoemission spectra show negligibly small intensity at Fermi energy, $E_{F}$. Fermi cut-off is observed at low temperatures employing high resolution. The spectral density of states at room temperature exhibits $|E-E_{F}|^{2}$ energy dependence signifying the role of electron-electron interaction. This energy dependence changes to $|E-E_{F}|^{3/2}$ below the magnetic transition evidencing the role of electron-magnon coupling in magnetically ordered state. The evolution of pseudogap ($\pm$12 meV) explains the sudden increase in resistivity ($\rho$) below 50 K in this disordered system. The temperature dependent spectral density of states at $E_{F}$ exhibiting $T^{1/2}$ behaviour verifies Altshuler-Aronov theory for correlated disordered systems.

cond-mat.str-el↗

arXiv2022

Evidence of Lattice Strain as a Precursor to Superconductivity in BaPb$_{0.75}$Bi$_{0.25}$O$_3$

In this work, we have investigated the precursor effects to superconductivity in BaPb$_{0.75}$Bi$_{0.25}$O$_3$ using temperature dependent resistivity, x-ray diffraction technique and photoemission spectroscopy. The present compound exhibits superconductivity around 11 K ($T_C$). The synthesis procedure adopted is much simpler as compared to the procedure available in the literature. In the temperature range (10 K-25 K) i.e. above $T_C$, our results show an increase in both the orthorhombic and tetragonal strain. The well screened features observed in Bi and Pb 4$f_{7/2}$ core levels are indicative of the metallic nature of the sample. The compound exhibits finite intensity at the Fermi level at 300 K and this intensity decreases with decrease in temperature and develops into a pseudogap; the energy dependence of the spectral density of states suggests disordered metallic state. Furthermore, our band structure calculations reveal that the structural transition upon Pb doping results in the closing of the band gap at the Fermi level.

cond-mat.supr-con↗

arXiv2022

Realizing Giant Spin-Selective Reflection based on a Chiral Meta-structure Operating in the Visible-Infrared Regime

The spin-selective reflection to introduce chirality which can have a lot of applications in real life such as spectroscopy, optical setups, media industry etc. In this paper, a reflection based metasurface proposed to introduce the giant chiroptical effects at broadband visible and infrared (IR) regimes. The optimization and results of basic unit also termed as nanostructure are demonstrated here. The reflectance at the optimal parameters for the proposed nanostructure shows the inclusion of multiband giant chiroptical effects in reflection mode. The results show that this metasurface can elicit large spin-selective reflection coefficients with moderate chirality covering the broadband wavelength. The circular dichroism in the visible and IR regime shows its potential applicability for a lot of applications in our daily life. This work also provides a new approach to achieve giant Spin Hall Effect at broadband wavelength ranges with low loss.

physics.optics↗

arXiv2020

Electronic structure of ternary palladates and effect of hole doping: A valence band photoemission spectroscopic study

We investigate the electronic structure of ternary palladates $A$Pd$_3$O$_4$ ($A$ = Sr, Ca) using valence band photoemission spectroscopy and band structure calculations. Overall width of the valence band and energy positions of various features in experimental valence band spectra are well captured by band structure calculations using hybrid functional. Band structure calculations within local density approximations lead to metallic ground state while the calculations using hybrid functional provide band gap of 0.25 eV and 0.22 eV for CaPd$_3$O$_4$ and SrPd$_3$O$_4$ respectively, suggesting moderated to strong electron correlation strength in these narrow band gap semiconducting palladates. High resolution spectra reveals negligibly small intensity at Fermi level for parent compounds while hole doped SrPd$_3$O$_4$ (by 15\% Li substitution at Sr site) exhibits a Fermi cut-off suggesting metallic character in contrast to semiconducting transport. These observations reveal the importance of localization of electrons in case where the Fermi edge falls in the mobility edge.

cond-mat.str-el↗

arXiv2020

Electron-phonon coupling in APd3O4: A = Ca, Sr, and Sr0.85Li0.15

Here we have investigated the role of electron-phonon coupling on the Raman spectrum of narrow bandgap semiconductors APd3O4 (A = Ca, Sr) and hole-doped system Sr0.85Li0.15Pd3O4. Four Raman active phonons are observed at room temperature for all three compounds as predicted by factor group analysis. The lowest energy phonon (~190/202 cm-1) associated with Pd vibrations is observed to exhibit an asymmetric Fano-like lineshape in all the three compounds, indicating the presence of an interaction between the phonon and the electronic continuum. The origin of the electronic continuum states and electron-phonon coupling are discussed based on our laser power- and temperature-dependent Raman results. We have observed an enhanced strength of electron-phonon coupling in Sr0.85Li0.15Pd3O4 at low temperatures which can be attributed to the metallicity in this doped compound.

cond-mat.str-el↗