arXiv subjects

Nagendra Singh

Publications and source records attributed to Nagendra Singh.

6 recordsLinked to original sources

arXiv2026

Pressure induced electronic band evolution and observation of superconductivity in the Dirac semimetal ZrTe5

We report a comprehensive investigation of the pressure effects on the magnetotransport properties of the topological material ZrTe5 within 1 to 8 GPa pressure range. With increasing pressure, the characteristic peak (Tp) in its electrical resistivity first shifts to higher temperature and then moves quickly towards the lower temperature before disappearing eventually at 6 GPa. Beyond 6 GPa, the system exhibits metallic behavior across the entire temperature range, and superconductivity emerges below Tc = 1.8 K at 8 GPa. Based on the systematic magnetotransport measurement under pressure, we demonstrate that the superconductivity occurs following a significant electronic structure modulation possibly due to pressure induced structural changes near 6 GPa, which coincides with dramatic enhancement of the magnetoresistance (MR) reaching up to 1400 percent. Our experimental results are substantiated by density functional theory calculations as the application of pressure drastically alters the density of states near the Fermi level. Notably, multiple hole pockets emerge at the Fermi level from 4 GPa onward, and their contributions are further enhanced with increasing pressure. The combined experimental and theoretical investigation reveals a comprehensive evolution of electronic structure of Dirac semimetal ZrTe5 under pressure and suggest a possible link between the Fermi surface reconstruction in the pressure range of structural transition and emergence of superconductivity

cond-mat.mtrl-sci↗

arXiv2025

Effect of pressure on the transport properties and thermoelectric performance of Dirac semimetal ZrTe5

In this study, we have investigated and compared the effect of hydrostatic pressure up to ~20 kbar on the transport properties of ZrTe5 single crystals grown by chemical vapor transport (CVT) and flux methods. With the application of pressure, the electrical resistivity Rho(T) and thermopower S(T) of both crystals were found to increase in the whole temperature range unlike the other known thermoelectric materials, such as Bi2Te3, SnSe etc. This observation is supported by the complementary first-principles band structure calculation as the application of pressure widens the direct bandgap at Γ point. Moreover, the analysis of the pressure dependent magneto-transport and Shubnikov de-Hass oscillation results revealed an increase in carrier concentration and effective mass along with the reduction of mobility as pressure rises. Furthermore, with the application of pressure, the flux-grown ZrTe5 crystals display a transition from unipolar to bipolar charge transport as evidenced by the emergence of resistivity peak at T* under high pressure, unlike the CVT-grown ZrTe5 crystals where the bipolar charge transport near its characteristic resistivity peak (Tp) remains unaffected.

cond-mat.mtrl-sci↗

arXiv2024

On relationships between vector variational inequalities and optimization problems using convexificators on Hadamard manifold

An important concept of convexificators has been extended to Hadamard manifolds in this paper. The mean value theorem for convexificators on the Hadamard manifold has also been derived. Monotonicity of the bounded convexificators has been discussed and an important characterization for the bounded convexificators to be $\partial_{*}^{*}$-geodesic convexity has been derived. Furthermore, a vector variational inequalities problem using convexificators on Hadamard manifold has been considered. In addition, the necessary and sufficient conditions for vector optimization problems in terms of Stampacchia and Minty type partial vector variational inequality problem ($\partial_{*}^{*}$-VVIP) have been derived.

math.OC↗

arXiv2024

Relations between nonsmooth vector variational inequalities and nonsmooth vector optimization problems on Hadamard manifold in terms of bifunction

In this paper, we discuss the concepts of bifunction and geodesic convexity for vector valued functions on Hadamard manifold. The Hadamard manifold is a particular type of Riemannian manifold with non-positive sectional curvature. Using bifunction, we introduce a definition of generalized geodesic convexity in the context of the Hadamard manifold. To support the definition, we construct a non-trivial example that demonstrates the property of geodesic convexity on Hadamard manifold. Additionally, we define the geodesic $h$-convexity, geodesic $h$-pseudoconvexity and geodesic $h$-quasiconvexity for vector valued function using bifunction and study their several properties. Furthermore, we demonstrate the uniqueness of the solution for nonsmooth vector variational inequality problem (NVVIP) and prove the characterization property for the solution of NVVIP and the Minty type NVVIP (MNVVIP) on Hadamard manifold in terms of bifunction. Afterward, we consider a nonsmooth vector optimization problem (NVOP) and investigate the relationships among the solutions of NVOP, NVVIP, and MNVVIP.

math.OC↗

arXiv2022

Thermo-acoustics and its detection in a premixed flame

A new optical technique based on light-matter interaction is devised in-house to detect thermo-acoustic disturbances generated after ignition and during propagation of a premixed flame front in a half open channel. The technique involves passing a polarized laser light through a medium whose density or refractive index varies due to the passage of acoustic waves and/or flame front and then capturing the leaked depolarised light through an analyser by a photo-detector. The technique is applied to combustor involving premixed flame propagation and tulip inversion. The thermo-acoustic signals and the flame front are distinguished by comparing the oscilloscope signal with high speed photography of the flow-field. Acoustic waves are found to intercept the flame propagation at various axial locations and time instants.

physics.flu-dyn↗

arXiv2013

Ion pseudoheating by low-frequency Alfvén waves revisited

Pseudoheating of ions in the presence of Alfvén waves is studied. We show that this process can be explained by $E\times B$ drift. The analytic solution obtained in this paper are quantitatively in accordance with previous results. Our simulation results show that the Maxwellian distribution is broadened during the pseudoheating; however, the shape of the broadening distribution function depends on the number of wave modes (i.e., a wave spectrum or a monochromatic dispersionless wave) and the initial thermal speed of ions ($v_{p}$). It is of particular interests to find that the Maxwellian shape is more likely to maintain during the pseudoheating under a wave spectrum compared with a monochromatic wave. It significantly improves our understanding of heating processes in interplanetary space where Alfvénic turbulences exist pervasively. Compared with a monochromatic Alfvén wave, $E\times B$ drift produces more energetic particles in a broad spectrum of Alfvén waves, especially when the Alfvénic turbulence with phase coherent wave modes is given. Such particles may escape from the region of interaction with the Alfvén waves and can contribute to fast particle population in astrophysical and space plasmas.

physics.plasm-ph↗