arXiv subjects

R. S. Singh

Publications and source records attributed to R. S. Singh.

At least 19 recordsLinked to original sources

arXiv2023

Superconducting Properties of Topological Semimetal 1$T$-RhSeTe

Platinum-group transition-metal dichalcogenides have emerged as a subject of considerable interest in condensed matter physics due to their remarkable topological properties and unconventional superconducting behavior. In this study, we report the synthesis and superconducting characteristics of a new Dirac-type topological semimetallic compound 1$T$-RhSeTe. It shows type-II superconductivity with a superconducting transition temperature of 4.72 K and a high upper critical field. The coexistence of superconductivity and topological properties makes it a prime candidate for hosting topological superconductivity.

cond-mat.supr-con↗

arXiv2022

Superconducting properties of pseudobinary telluride Chevrel Phase Mo$_4$Re$_2$Te$_8$

Unconventional superconductivity in the Chevrel phase offers a wide structural aspect to understand the superconducting ground state. A detailed investigation on the superconducting properties of Re based pseudobinary telluride Chevrel phase Mo$_4$Re$_2$Te$_8$ is reported. It crystallizes in a trigonal structure with the space group $R\bar{3}H$ having superconducting transition temperature at $T_C$ = 3.26(3) K. Specific heat measurements suggests a fully gapped superconducting state; however, the proximity of upper critical field value from the Pauli limiting field can be attributed to unconventional nature.

cond-mat.supr-con↗

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↗

arXiv2020

Superheavy dark matter in $R+R^2$ cosmology with conformal anomaly

Cosmological evolution and particle creation in $R^2$-modified gravity are considered for the case of the dominant decay of the scalaron into a pair of gauge bosons due to conformal anomaly. It is shown that in the process of thermalization superheavy dark matter with the coupling strength typical for the GUT SUSY can be created. Such dark matter would have the proper cosmological density if the particle mass is close to $10^{12}$ GeV.

hep-ph↗

arXiv2019

Performance modeling of electro-optical devices for military target acquisition

Accurate predictions of electro-optical imager performance are important for defence decision-making. The predictions serve as a guide for system development and are used in war game, simulations that directly influence engagement tactics. In the present study, mathematical models have been developed which involves detection of different military targets using their opto-electronics properties in different environmental conditions. The method first calculates the signal-to-noise ratio received by the observing sensors reflected from the target by quantifying the light energy in terms of photons, which is used for evaluating the detection probability.

stat.AP↗

arXiv2019

Dark matter in $R+R^2$ cosmology

Production of massive stable relics in $R^2$-modified gravity is considered. It is shown that the cosmological evolution and kinetics of massive species differs significantly from those in the conventional cosmology. The results are applied to the lightest supersymmetric particles and it is argued that they are viable candidates for the constituents of dark matter, if their mass is about 1000 TeV.

astro-ph.CO↗

arXiv2018

Distortion of the standard cosmology in R+R^2 theory

Universe history in $R^2$-gravity is studied from "beginning" up to the present epoch. It is assumed that initially the curvature scalar $R$ was sufficiently large to induce the proper duration of inflation. Gravitational particle production by the oscillating $R(t)$ led to a graceful exit from inflation, but the cosmological evolution in the early universe was drastically different from the standard one till the universe age reached the value of the order of the inverse decay rate of the oscillating curvature $R(t)$. This deviation from the standard cosmology might have a noticeable impact on the formation of primordial black holes and baryogenesis. At later time, after exponential decay of the curvature oscillations, cosmology may return to normality.

gr-qc↗

arXiv2018

Structural response to the magnetic pre ordering in LiFeSi2O6

We investigate the temperature evolution of the structural parameters of potential ferrotoroidic LiFeSi2O6 compound across structural and magnetic phase transitions. The structural transition (TS)is around 220K and the paramagnetic to antiferromagnetic transition (TN) is around 18K. The lattice parameters exhibit unusual temperature dependence and based on its behaviour, the exper- imental results can be divided into 3 regions.In region I (300K to 240K), the cell parameters are mainly governed by mere thermal effect. As the compound enters region II (below 240K to 50K), the lattice parameters show non linear behaviour. In this region, the exchange pathways that lead to the magnetic interactions within and between the Fe-Fe chains do not show significant response.The region III (below 50K) is dominated by the magnetic contribution where we observe setting up of intra and inter-chain magnetic interaction. This behaviour is unlike other low dimensional com- pounds like Ca3Co2O6, Sr3NiRhO6, MnTiO3 etc. thereby suggesting the magnetism in LiFeSi2O6 is of three dimensional nature. The present results will be helpful in understanding the evolution of the spin rings that give rise to net toroidal moment and hence its multiferroic behaviour.

cond-mat.str-el↗

arXiv2017

Hydrodynamic signatures of stationary Marangoni-driven surfactant transport

We experimentally study steady Marangoni-driven surfactant transport on the interface of a deep water layer. Using hydrodynamic measurements, and without using any knowledge of the surfactant physico-chemical properties, we show that sodium dodecyl sulphate and Tergitol 15-S-9 introduced in low concentrations result in a flow driven by adsorbed surfactant. At higher surfactant concentration, the flow is dominated by the dissolved surfactant. Using Camphoric acid, whose properties are {\it a priori} unknown, we demonstrate this method's efficacy by showing its spreading is adsorption dominated.

physics.flu-dyn↗

arXiv2017

Observation of pseudogap in MgB2

Pseudogap phase in superconductors continues to be an outstanding puzzle that differentiates unconventional superconductors from the conventional ones (BCS-superconductors). Employing high resolution photoemission spectroscopy on a highly dense conventional superconductor, MgB2, we discover an interesting scenario. While the spectral evolution close to the Fermi energy is commensurate to BCS descriptions as expected, the spectra in the wider energy range reveal emergence of a pseudogap much above the superconducting transition temperature indicating apparent departure from the BCS scenario. The energy scale of the pseudogap is comparable to the energy of E2g phonon mode responsible for superconductivity in MgB2 and the pseudogap can be attributed to the effect of electron-phonon coupling on the electronic structure. These results reveal a scenario of the emergence of the superconducting gap within an electron-phonon coupling induced pseudogap.

cond-mat.supr-con↗

arXiv2013

Ferromagnetism in CaRuO3 thin films by efficient route of tensile epitaxial strain

We show that a ferromagnetic (FM) order in the orthorhombic CaRuO3, which is a non-magnetic and iso-structural analog of FM system SrRuO3, can be established and stabilized by the means of tensile epitaxial strain. Investigations on the structural and magnetic property correlations in the CaRuO3 films with different degrees of strain reveal that the FM moment increases with increasing the tensile strain. This is an experimental verification to the theoretical predictions of scaling of the tensile epitaxial strain and the magnetic order in this system. Our studies further establish that the tensile strain is more efficient than the chemical route to induce the FM order in CaRuO3 as the magnetic moment in these strained films is larger than that in chemically modified CaRu0.9Cr0.1O3 films.

cond-mat.mtrl-sci↗

arXiv2011

Evolution of the Kondo resonance feature and its relationship to spin-orbit coupling across the quantum critical point in Ce2Rh{1-x}CoxSi3

We investigate the evolution of the electronic structure of Ce2Rh{1-x}CoxSi3 as a function of x employing high resolution photoemission spectroscopy. Co substitution at the Rh sites in antiferromagnetic Ce2RhSi3 leads to a transition from an antiferromagnetic system to a Kondo system, Ce2CoSi3 via the Quantum Critical Point (QCP). High resolution photoemission spectra reveal distinct signature of the Kondo resonance feature (KRF) and its spin orbit split component (SOC) in the whole composition range indicating finite Kondo temperature scale at the quantum critical point. We observe that the intensity ratio of the Kondo resonance feature and its spin orbit split component, KRF/SOC gradually increases with the decrease in temperature in the strong hybridization limit. The scenario gets reversed if the Kondo temperature becomes lower than the magnetic ordering temperature. While finite Kondo temperature within the magnetically ordered phase indicates applicability of the spin density wave picture at the approach to QCP, the dominant temperature dependence of the spin-orbit coupled feature suggests importance of spin-orbit interactions in this regime.

cond-mat.str-el↗

arXiv2009

Importance of conduction electron correlation in a Kondo lattice, Ce2CoSi3

Kondo systems are usually described by the interaction of strong correlation induced local moment with the highly itinerant conduction electrons. Here, we study the role of electron correlations among conduction electrons in the electronic structure of a Kondo lattice compound, Ce$_2$CoSi$_3$, using high resolution photoemission spectroscopy and {\it ab initio} band structure calculations, where Co 3$d$ electrons contribute in the conduction band. High energy resolution employed in the measurements helped to reveal signature of Ce 4$f$ states derived Kondo resonance feature at the Fermi level and dominance of Co 3$d$ contributions at higher binding energies in the conduction band. The line shape of the experimental Co 3$d$ band is found to be significantly different from that obtained from the band structure calculations within the local density approximations, LDA. Consideration of electron-electron Coulomb repulsion, $U$ among Co 3$d$ electrons within the LDA+$U$ method leads to a better representation of experimental results. Signature of electron correlation induced satellite feature is also observed in the Co 2$p$ core level spectrum. These results clearly demonstrate the importance of the electron correlation among conduction electrons in deriving the microscopic description of such Kondo systems.

cond-mat.str-el↗

arXiv2009

Importance of Co 3d electron correlation in a Ce-based Kondo lattice, Ce(2)CoSi(3)

We study the role of electron correlations among Co 3d electrons contributing to the conduction band of a Kondo lattice compound, Ce2CoSi3, using high resolution photoemission spectroscopy and ab initio band structure calculations. Experimental results reveal signature of Ce 4$f$ states derived Kondo resonance feature at the Fermi level and dominance of Co 3d contributions at higher binding energies in the valence band. The line shape of the experimental Co 3$d$ band is found to be significantly different from that obtained from the band structure calculations within the local density approximations. Consideration of electron-electron Coulomb repulsion among Co 3d electrons leads to a better representation of experimental results. The correlation strength among Co 3$d$ electrons is found to be about 3 eV. Signature of electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. Thus, these results demonstrate the importance of the electron correlation among conduction electrons to derive the microscopic description of such Kondo systems.

cond-mat.str-el↗

arXiv2007

Electronic structure of PrCoO_3 and its temperature evolution

We investigate the detailed electronic structure of PrCoO$_3$ and its temperature evolution using state-of-the-art photoemission spectroscopy and ab initio band structure calculations. We observe that in addition to the correlation effect, spin-orbit interaction plays an important role in determining the electronic properties of this system. Pr 4$f$ states are found to be strongly hybridized with the O 2$p$ and Co 3$d$ valence electronic states, and thus influences the electronic properties significantly. The calculated results corresponding to the intermediate spin state of Co provide a good description of the experimental spectra at 300 K. The decrease in temperature from 300 K leads to a gradual enhancement of the low spin state contributions in the electronic structure. The temperature evolution of the band gap is found to be consistent with the transport data.

cond-mat.str-el↗

arXiv2007

Evidence for strong 5d electron correlations and electron-magnon coupling in a pyrochlore, Y2Ir2O7

We report the observation of an unusual behavior of highly extended 5d electrons in Y2Ir2O7 belonging to pyrochlore family of great current interest using high resolution photoemission spectroscopy. The experimental bulk spectra reveal an intense lower Hubbard band in addition to weak intensities in the vicinity of the Fermi level, e_F. This provides a direct evidence for strong electron correlation among the 5d electrons, despite their highly extended nature. The high resolution spectrum at room temperature exhibits a pseudogap at e_F and |e - e_F|^2 dependence demonstrating the importance of electron correlation in this system. Remarkably, in the magnetically ordered phase (T < 150 K), the spectral lineshape evolves to a |e - e_F|^1.5 dependence emphasizing the dominant role of electron-magnon coupling.

cond-mat.str-el↗

arXiv2007

Investigation of the spin state of Co in LaCoO3 at room temperature

We investigate the spin state of LaCoO3 using state-of-the-art photoemission spectroscopy and ab initio band structure calculations. The GGA+U calculations provide a good description of the ground state for the experimentally estimated value of electron correlation strength, U. In addition to the correlation effect, spin-orbit interaction is observed to play a significant role in the case of intermediate spin and high spin configurations. The comparison of the calculated Co 3d and O 2p partial density of states with the experimental valence band spectra indicates that at room temperature, Co has dominant intermediate spin state configuration and that the high spin configuration may not be significant at this temperature. The lineshape of the La 5p and O 2s core level spectra could be reproduced well within these ab initio calculations.

cond-mat.str-el↗

arXiv2007

Bianchi Type V Universes with Bulk Viscosity in General Relativity

Bianchi type V bulk viscous fluid cosmological models are investigated. Using a generation technique (Camci {\it et al.}, 2001), it is shown that the Einstein's field equations are solvable for any arbitrary cosmic scale function. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. Solutions for particular forms of cosmic scale functions are also obtained. Some physical and geometric aspects of the models are also discussed.

gr-qc↗