arXiv subjects

R. S. Islam

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

At least 19 recordsLinked to original sources

arXiv2026

First-Principles Study of Novel Lead-Free Double Perovskite \b{eta}2SnGeX6 (\b{eta} = K, Rb; X = Cl, Br, I) for thermomechanical, optoelectronic and outstanding thermoelectric applications

In this study, the structural, mechanical, electronic, optical, and thermoelectric properties of the novel lead-free halide double perovskite series beta2SnGeX6 (beta = K, Rb; X = Cl, Br, I) are systematically investigated using density functional theory (DFT). Calculated formation energies, Tolerance factors, and octahedral factors confirm that all six compounds exhibit robust thermodynamic stability within a highly symmetric cubic geometry. Mechanical analysis derived from elastic parameters characterizes the entire series as fundamentally ductile, ensuring high processing elasticity and resistance to micro-cracking during device manufacturing. Electronic band structures reveal direct bandgaps showing exceptional composition-dependent tunability from 1.44 eV down to 0.64 eV via progressive halogen substitution. The wide gap chloride variations are optimized for single-junction photovoltaic absorbers, while the narrower-gap bromide and iodide analogs show immense promise for tandem solar architectures and near-infrared photodetectors. Thermoelectrically, heavy constituent atoms introduce strong lattice anharmonicity and intense high-temperature Umklapp phonon scattering, significantly suppressing lattice thermal conductivity. Combined with low carrier effective masses that optimize electrical transport, the iodide compounds achieve higher power factors and outstanding dimensionless figures of merit (ZT = 2.4 for K2SnGeI6 at 1000 K). Ultimately, these lead-free double perovskite family emerges as an environmentally benign and versatile platform for next-generation green optoelectronics and solid-state waste-heat recovery.

cond-mat.mtrl-sci↗

arXiv2025

Pressure dependent ab initio study of the physical properties of hexagonal BeB2C: a possible high-Tc superconductor

This study uses the Density Functional Theory to explore the pressure dependent properties of hexagonal BeB2C. The metallic nature of BeB2C was substantiated at ambient pressure, with pressure induced alterations in electronic band structure and Fermi surface topology suggesting a potential for tunability across various applications. The phonon dispersion and phonon density of states show the dynamical stability under pressure. The thermophysical properties are also investigated under varying pressure conditions. Finally, the exploration of superconducting properties found that the transition temperature is in good agreement with previously reported values, and illustrated that beB2C holds considerable promise as a high-temperature superconductor, with pressure augmenting its superconducting properties.

cond-mat.mtrl-sci↗

arXiv2024

Ab-initio insights into the mechanical, phonon, bonding, electronic, optical and thermal properties of hexagonal W2N3 for potential applications

We investigated the structural, elastic, electronic, vibrational, optical, thermodynamic and a number of thermophysical properties of W2N3 in this study using DFT based formalisms. The mechanical and dynamical stabilities have been confirmed. The Pugh and Poisson ratios are located quite close to the brittle to ductile borderline. The electronic band structure and energy density of states show metallic behavior. The Fermi surface features are investigated. The analysis of charge density distribution map clearly shows that W atoms have comparatively high electron density around than the N atoms. Presence of covalent bondings are anticipated. High melting temperature and high phonon thermal conductivity at room temperature of W2N3 imply that the compound has potential to be used as a heat sink system. The optical characteristics demonstrate anisotropy for W2N3. The compound can be used in optoelectronic device applications due to its high absorption coefficient and low reflectivity in the visible to ultraviolet spectrum. Furthermore, the quasiharmonic Debye model is used to examine temperature and pressure dependent thermal characteristics for the first time.

cond-mat.mtrl-sci↗

arXiv2023

DFT based investigation of structural, elastic, optoelectronic, thermophysical and superconducting state properties of binary Mo3P at different pressures

In recent years, the investigation of novel materials for various technological applications has gained much importance in materials science research. Tri-molybdenum phosphide (Mo3P), a promising transition metal phosphide (TMP), has gathered significant attention due to its unique structural and electronic properties, which already make it potentially valuable system for catalytic and electronic device applications. Through an in-depth study using the density functional theory (DFT) calculations, this work aims to clarify the basic properties of the Mo3P compound at different pressures. In this work, we have studied the structural, elastic, optoelectronic and thermophysical properties of binary Mo3P compound. In this investigation, we varied uniform hydrostatic pressure from 0 GPa to 30 GPa. A complete geometrical optimization for structural parameters is performed and the obtained values are in good accord with the experimental values where available. It is also found that Mo3P possesses very low level of elastic anisotropy, reasonably good machinability, ductile nature, relatively high Vickers hardness, high Debye temperature and high melting temperature. Thermomechanical properties indicate that the compound has potential to be used as a thermal barrier coating material. The bonding nature in Mo3P has been explored. The electronic band structure shows that Mo3P has no band gap and exhibits conventional metallic behavior. All of the energy dependent optical characteristics demonstrate apparent metallic behavior and agree exactly with the electronic density of states calculations. The compound has excellent reflective and absorptive properties suitable for optical applications. Pressure dependent variations of the physical properties are explored and their possible link with superconductivity has been discussed.

cond-mat.mtrl-sci↗

arXiv2022

Interrelations among critical current density, irreversibility field and pseudogap in hole doped high-Tc cuprates

The effects of hole content (p) and oxygen deficiency (delta) on the zero-field critical current density, Jc0, were investigated for high-quality c-axis oriented Y1-xCaxBa2Cu3O7-delta (x = 0, 0.05, 0.10, and 0.20) thin films. Low temperature critical current density of these films above the optimum doping were found to be high and were primarily determined by the hole concentration, reaching a maximum at p ~ 0.185 +/- 0.005, irrespective of the level of oxygen deficiency. This implies that oxygen disorder plays only a secondary role and the intrinsic Jc0 is primarily governed by the carrier concentration in the copper oxide planes. Further support in favor of this was found from the analysis of the in-plane resistive transitions of c-axis oriented crystalline thin films of YBa2Cu3O7-delta (YBCO) under magnetic fields (H) applied along the c-direction, over a wide range of doped holes. The characteristic magnetic field (H0), linked to the vortex activation energy and the irreversibility field, exhibits similar p-dependence as shown by Jc0(p). We have explained these observations in terms of the doping dependent pseudogap (PG) in the low-energy electronic energy density of states. Both the intrinsic critical current density and the irreversibility field depend directly on the superconducting condensation energy, which in turn is largely controlled by the magnitude of the hole concentration dependent PG in the quasiparticle spectral density.

cond-mat.supr-con↗

arXiv2022

A comparative study of the structural, elastic, thermophysical, and optoelectronic properties of CaZn$_2$X$_2$ (X = N, P, As) semiconductors via ab-initio approach

We present a detailed density functional theory based calculations of the structural, elastic, lattice dynamical, thermophysical, and optoelectronic properties of ternary semiconductors CaZn$_2$X$_2$ (X = N, P, As) in this paper. The obtained lattice parameters are in excellent agreement with the experimental values and other theoretical findings. These elastic constants satisfy the mechanical stability criteria. Moreover, many thermophysical parameters of these compounds are estimated, including the Debye temperature, average sound velocity, melting temperature, heat capacity, lattice thermal conductivity, etc. The comprehensive analysis of the elastic constants and moduli show that CaZn$_2$X$_2$ compounds possess reasonably good machinability, relatively high Vickers hardness and relatively low Debye temperature. The phonon dispersion curves and phonon density of states are investigated for the first time for the compounds CaZn$_2$P$_2$ and CaZn$_2$As$_2$. It is observed from the phonon dispersion curves that the bulk CaZn$_2$X$_2$ (X = N, P, As) compounds are dynamically stable. Electronic properties have been studied through the band structures and electronic energy density of states. The electronic band structures show that CaZn$_2$N$_2$ and CaZn$_2$As$_2$ possess direct band gaps while the compound CaZn$_2$P$_2$ show indirect band gap. The bonding characters of CaZn$_2$X$_2$ (X = N, P, As) compounds are investigated. Energy dependent optical parameters exhibit good correspondence with the electronic energy density of states features. We have thoroughly discussed the reflectivity, absorption coefficient, refractive index, dielectric function, optical conductivity and loss function of these semiconductors. The optical absorption, reflectivity spectra and the refractive index of CaZn$_2$X$_2$ (X = N, P, As) show that the compounds hold promise to be used in optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Pressure-dependent semiconductor-metal transition and elastic, electronic, optical, and thermophysical properties of SnS binary chalcogenide

Density functional theory based study of the pressure dependent physical properties of binary SnS compound has been carried out. The computed elastic constants reveal that SnS is mechanically stable and brittle under ambient conditions. With increasing pressure, the compound becomes ductile. The Poisson's ratio also indicates brittle-ductile transition with increasing pressure. The hardness of SnS increases significantly with pressure. The compound possesses elastic anisotropy. The ground state electronic band structure is semiconducting with a small band gap which becomes metallic under pressure. The band becomes more and more dispersive with the increase in pressure while the electronic correlations decrease as pressure is raised. Both the Debye temperature and the phonon thermal conductivity of SnS increase sharply with pressure. The Melting temperature of the compound is low. Mixed bonding characteristics are found with ionic and covalent contributions. SnS is a good absorber of ultraviolet light. The reflectivity of the material increases with the increase in pressure. The reflectivity is nonselective over a wide spectral range. The low energy refractive index is high. All these optical characteristics are useful for prospective optoelectronic device applications. The optical anisotropy is low.

cond-mat.mtrl-sci↗

arXiv2022

Comparative analysis of physical properties of some binary transition metal carbides XC (X = Nb, Ta, Ti): Insights from a comprehensive ab-initio study

Binary metallic carbides belong to a technologically prominent class of materials. We have explored the structural, mechanical, electronic, optical, and some thermophysical properties of XC (X = Nb, Ta, Ti) binary metallic carbides in details employing first-principles method. Some of the results obtained are novel. A comparative analysis has been made.

cond-mat.mtrl-sci↗

arXiv2021

First-principles prediction of pressure dependent mechanical, electronic, optical, and superconducting state properties of NaC6: A potential high-Tc superconductor

Very recently carbon-rich NaC6 with sodalite-like structure has been predicted to show superconducting transition temperature above 100 K at relatively low applied (compared to high-Tc hydrides) hydrostatic pressures. We have investigated the pressure dependent structural, elastic, electronic, superconducting state, and optoelectronic properties of NaC6 in this study. Some important thermophysical properties have also been explored. The elastic properties along with Poisson's and Pugh's ratios and optoelectronic parameters are investigated for the first time. NaC6 was found to be structurally stable only at high pressures at and above 40 GPa, in agreement with previous study. The compound is highly ductile and the chemical bonding is predominantly metallic in nature. The Debye temperature shows strong pressure dependence. The Gruneisen parameter also exhibits significant pressure dependence. The electronic band structure reveals metallic character and consists of highly dispersive and almost flat bands crossing the Fermi level. Both the electronic density of states at the Fermi level and repulsive Coulomb pseudopotential increase gradually with increasing pressure in the range 40 GPa to 70 Gpa. The degree of dispersion in the E(k) curves depend weakly on pressure both in the valence and conduction bands. The optical parameters spectra, studied for the first time, correspond well with the electronic band structure. NaC6 absorbs and reflects electromagnetic radiation quite efficiently in the mid-ultraviolet region. Superconducting transition temperatures of NaC6 have been estimated at different pressures and compared with previously reported values. The effects of various parameters on Tc have been discussed in details.

cond-mat.supr-con↗

arXiv2021

Ab-initio insights into the elastic, bonding, phonon, optoelectronic and thermophysical properties of SnTaS2

SnTaS2 is a recently discovered layered semimetal exhibiting type-II low transition temperature superconductivity. Except some superconductivity related parameters, most of the physical properties, namely, elastic, mechanical, bonding, phonon dispersion, acoustic, thermophysical, and optical properties of SnTaS2 are unexplored till now. In this study, we have investigated these hitherto unexplored properties of SnTaS2 for the first time employing density functional theory (DFT) based first-principles method. SnTaS2 is a mechanically stable, elastically anisotropic compound with strongly layered feature. The bond hardness and Vickers hardness have been calculated. The material under study is ductile, soft and highly machinable. The chemical bonding feature has mixed character with significant contribution coming from the ionic channel. Phonon dispersion curves disclose dynamical stability. Electronic band structure calculations show simple metallic character. The Fermi surface consists of both electron-like and hole-like sheets with varying degrees of dispersion. The low energy (including visible part of the spectrum) refractive index of SnTaS2 is high. The reflectivity is fairly nonselective over a wide range of photon energy and the absorption coefficient is large in the mid ultraviolet region. The Debye temperature and thermal conductivity of SnTaS2 are low. The electron-phonon coupling constant has been calculated. The compound under study possesses optical anisotropy with respect to the polarization direction of the incident electric field.

cond-mat.mtrl-sci↗

arXiv2021

Hole content dependent fluctuation diamagnetism in YBa2Cu3O7-δ: possible role of the pseudogap

This study focuses on the temperature and hole content dependent fluctuation diamagnetism of hole doped YBa2Cu3O7-delta (Y123) high-Tc superconductors. Two different compositions of Y123 have been considered with in-plane hole content (p): 0.161 (optimally doped) and 0.143 (underdoped). The fluctuation induced excess diamagnetic susceptibility, Delta_chi(T), has been investigated via the mean-field Gaussian-Ginzburg-Landau (MFGGL) formalism with and without a total energy cut-off in the fluctuating modes. It has been found that inclusion of total energy cut-off describes the Delta_chi(T) data significantly better. Furthermore, the pseudogap (PG) itself induces an anomalous decrease in the normal state magnetic susceptibility. By means of the analysis of Delta_chi(T)/T at different hole concentrations, we have explored the possible role of the PG on diamagnetic fluctuations. It has been found that MFGGL formalism is not able to reproduce the Delta_chi(T)/T features for the underdoped compound over a broad range of reduced temperature, Epsilon [= ln(T/Tc)]. The discrepancy becomes prominent in the temperature range where PG dominates the normal state magnetic susceptibility data. The agreement between the theoretical prediction and experimental Delta_chi(T) is better for the optimally doped compound with p = 0.161, where the effect of the PG is small. This notable difference implies that PG induced reduction in the magnetic susceptibility is not related directly to the superconducting fluctuations which in turn indicate that electronic correlations giving rise to the PG and Cooper pairing are independent to each other.

cond-mat.supr-con↗

arXiv2021

Structural, elastic, bonding, optoelectronic, and some thermo-physical properties of transition metal dichalcogenides ZrX2 (X = S, Se, Te): Insights from ab-initio calculations

Transition metal dichalcogenides (TMDCs) belong to technologically important compounds. We have explored the structural, elastic, bonding, optoelectronic and some thermo-physical properties of ZrX2 (X = S, Se, Te) TMDCs in details via ab-initio technique in this study. Elastic anisotropy indices, atomic bonding character, optoelectronic properties and thermo-physical parameters including melting temperature and minimum phonon thermal conductivity are investigated for the first time. All the TMDCs under investigation possess significant elastic anisotropy and layered structural features. ZrX2 (X = S, Se, Te) compounds are fairly machinable, and ZrS2 and ZrSe2 are moderately hard. ZrTe2, on the other hand, is significantly softer. Both covalent and ionic bondings contribute in the crystals. Electronic band structure calculations display semiconducting behavior for ZrS2 and ZrSe2 and metallic behavior for ZrTe2. Energy dependent optoelectronic parameters exhibit good correspondence with the underlying electronic energy density of states features. ZrX2 (X = S, Se, Te) compounds absorb ultraviolet radiation effectively. The reflectivity spectrum, R(w), remains over 50% in the energy range from 0 eV to 20 eV for ZrTe2. Therefore, this TMDC has wide band and nonselective high reflectivity and can be used as an efficient reflector to reduce solar heating. Debye temperature, melting point and minimum phonon thermal conductivity of the compounds under study are low and show excellent correspondence with each other and also with the elastic and bonding characteristics.

cond-mat.mtrl-sci↗

arXiv2018

Critical current density of hole doped high-Tc cuprates and heavy fermion superconductors: relevance to the possible quantum critical behavior

The superconducting critical current density, Jc, in hole doped cuprates show strong dependence on the doped hole content, p, within the copper oxide plane(s). The doping dependent Jc mainly exhibits the variation of the intrinsic depairing critical current density as p is varied. Jc(p) tends to peak at p ~ 0.185 in copper oxide superconductors. This particular value of the hole content, often termed as the critical hole concentration, has several features putative to a quantum critical point (QCP). Very recently, pressure dependences of the superconducting transition temperature (Tc) and the critical current (Ic) in pure CeRhIn5 and Sn doped CeRhIn5 heavy fermion compounds have been reported (Nature Communications (2018) 9:44, DOI: 10.1038/s41467-018-02899-5). The critical pressure demarcates an antiferromagnetic quantum critical point where both Tc and Ic are maximized. We have compared and contrasted this behavior with those found for Y1-xCaxBa2Cu3O7-d in this brief communication. The resemblance of the systematic behavior of the critical current with pressure and hole content between heavy fermion systems and hole doped cuprates is significant. This adds to the circumstantial evidence that quantum critical physics probably plays a notable role beyond the unconventional normal and superconducting state properties of copper oxide superconductors.

cond-mat.supr-con↗

arXiv2018

Pair-Breaking, Pseudogap, and Superconducting Tc of Hole Doped Cuprates: Interrelations and Implications

Irrespective of the class they belong to, all the hole doped high-Tc cuprate superconductors show an anti-correlation between the superconducting transition temperature and the characteristic pseudogap energy in the underdoped region. The doping dependent pseudogap in the quasiparticle spectral density is believed to remove low-energy electronic states and thereby reduce the superconducting condensate. Impurities within the CuO2 plane, on the other hand, break Cooper pairs in the unitarity limit and diminish superfluid density. Both pseudogap in pure cuprates and impurity scattering in disordered cuprates reduces Tc very effectively. In this study we have compared and contrasted the mechanisms of Tc degradation due to pseudogap and impurity scattering in hole doped cuprates. We have suggested a framework where both these factors can be treated on somewhat equal footing. Beside impurity and pseudogap dependent superconducting transition temperature, the proposed scenario has been employed to investigate the disorder and hole content dependent isotope exponent in high-Tc cuprates in this work.

cond-mat.supr-con↗

arXiv2017

Zn-induced in-gap electronic states in La214 probed by uniform magnetic susceptibility: relevance to the suppression of superconducting Tc

Substitution of isovalent non-magnetic defects, such as Zn, in CuO2 plane strongly modifies the magnetic properties of strongly electron correlated hole doped cuprate superconductors. The reason for enhanced uniform magnetic susceptibility, \c{hi}, in Zn substituted cuprates is debatable. So far, the observed magnetic behavior has been analyzed mainly in terms of two somewhat contrasting scenarios, (a) that due to independent localized moments appearing in the vicinity of Zn arising because of the strong electronic/magnetic correlations present in the host compound and (b) that due to transfer of quasiparticle spectral weight and creation of weakly localized low energy electronic states associated with each Zn atom in place of an in-plane Cu. If the second scenario is correct, one should expect a direct correspondence between Zn induced suppression of superconducting transition temperature, Tc, and the extent of the enhanced magnetic susceptibility at low temperature. In this case, the low-T enhancement of \c{hi} would be due to weakly localized quasiparticle states at low energy and these electronic states will be precluded from taking part in Cooper pairing. We explore this second possibility by analyzing the \c{hi}(T) data for La2-xSrxCu1-yZnyO4 with different hole contents, p (= x), and Zn concentrations (y) in this paper. Results of our analysis support this scenario.

cond-mat.supr-con↗

arXiv2015

An investigation of the in-plane dc fluctuation conductivity of optimally doped and overdoped cuprates: implication and origin of the pseudogap

In conventional superconductors the magnitude of the pairing fluctuation is primarily determined by Tc and the superconducting (SC) coherence length, ξ. In systems with strong structural and electronic anisotropies, the interlayer separation, s, plays a significant role. In cuprates, the pseudogap (PG) correlation induces a downturn in the temperature dependent resistivity. As Tc is approached from above, this downturn in the resistivity is supposed to either i) add to or ii) join smoothly to that due to paraconductivity caused by short-lived Cooper pairs. It is important to differentiate between these two possibilities since they are closely linked to the origin of the PG. It would be reasonable to assume that if the first scenario is correct then the PG has a non-SC origin, while the second scenario, if found to hold, would relate precursor pairing to the PG correlations. We have studied the in-plane fluctuation conductivity of two c-axis oriented thin films of Y0.95Ca0.05Ba2Cu3O7-d with similar hole contents (p), p = 0.165 (optimally doped) and p = 0.184 (slightly overdoped). The hole contents are fixed at these values so that the PG affects the resistivity data only at temperatures close to Tc. Analysis of paraconductivity, Δσab(T), within the mean-field Gaussian Ginzburg-Landau (MFGGL) framework reveals different features for the optimally doped (OPD) and the slightly overdoped (SOD) compounds. The excess conductivity due to Cooper pair fluctuations of the SOD sample can be described reasonably well by the MFGGL formalism. The excess conductivity of the OPD compound, on the other hand, cannot be accounted for by the MFGGL formalism with reasonable set of parameters. There is a significant added contribution to Δσab(T) for the OPD sample which appears to come from the presence of a PG. These findings point towards a non-pairing origin of the PG.

cond-mat.supr-con↗

arXiv2014

Doping dependent vortex activation energy and pseudogap in Y123

The temperature and magnetic field dependent activation energy, U(T, H), is one of the most important parameter in the field of applied superconductivity as it primarily determines both the crtical current density and the irreversibility field. Previously, we have determined the doping dependent U(T, H) from the analysis of field dependent resistive transitions in high-quality c-axis oriented crytalline thin films of Y123 (arXiv:1207.4312). In this short communication, we have showed a direct link between the characteristic field Ho that sets the magnitude of U(T, H) and the pseudogap temperature, T*. The strong dependence of Ho on the in-plane hole content, p, seems to follow from the p-dependent evolution of the pseudogap energy scale (T*, when expressed in temperature) which reduces the superconducting condensation energy as hole concentration decreases.

cond-mat.supr-con↗

arXiv2013

Effects of non-magnetic defects in hole doped cuprates: exploration of the roles of the underlying electronic correlations

The effects of non-magnetic iso-valent defects inside the CuO2 plane(s) on superconducting transition temperature, Tc, dc charge transport, and the bulk magnetic susceptibility, \c{hi}(T), were investigated for the YBa2(Cu1-yZny)3O7-d (Zn-YBCO) and La2-xSrxCu1-yZnyO4 (Zn-LSCO) superconductors over a wide range of hole concentrations, p, and Zn contents (y) in the CuO2 plane(s). From the analysis of the \c{hi}(T, y) data, the pseudogap energy scale, εg, was found to be almost independent of the defect content at a given value of p. The Zn induced rate of suppression of Tc, dTc(p)/dy, was found to be strongly p-dependent and showed a systematic variation with hole concentration, except in the vicinity of p ~ 0.125, i.e., near the so-called 1/8th anomaly where the charge and spin stripe orderings are at their strongest in various families of hole doped cuprates. Near p ~ 0.125, the static striped charge ordering is largely believed to dominate the T-p electronic phase diagram. dTc(p)/dy decreased strongly around this composition, i.e., Zn abruptly became less effective in degrading Tc when p ~ 0.125. This observation, together with the facts that (i) Zn suppresses Tc most effectively and (ii) the characteristic pseudogap energy scale remains insensitive to the level of Zn substitution, provide us with important clues regarding the nature and interplay of the underlying electronic correlations present in high-Tc cuprates. We have discussed the possible connections among the stripe ordering, superconducting correlations and the pseudogap phenomenon in details in view of the above findings.

cond-mat.supr-con↗