arXiv subjects

M. M. Sharma

Publications and source records attributed to M. M. Sharma.

At least 37 records · Page 2Linked to original sources

arXiv2022

Large amplitude bidirectional anisotropy of cosmic-ray intensity observed with world-wide networks of ground-based neutron monitors and muon detectors in November, 2021

We analyze the cosmic-ray variations during a significant Forbush decrease observed with world-wide networks of ground-based neutron monitors and muon detectors during November 3-5, 2021. Utilizing the difference between primary cosmic-ray rigidities monitored by neutron monitors and muon detectors, we deduce the rigidity spectra of the cosmic-ray density (or omnidirectional intensity) and the first- and second-order anisotropies separately, for each hour of data. A clear two-step decrease is seen in the cosmic-ray density with the first $\sim2\%$ decrease after the interplanetary shock arrival followed by the second $\sim5\%$ decrease inside the magnetic flux rope (MFR) at 15 GV. Most strikingly, a large bidirectional streaming along the magnetic field is observed in the MFR with a peak amplitude of $\sim5\%$ at 15 GV which is comparable to the total density decrease inside the MFR. The bidirectional streaming could be explained by adiabatic deceleration and/or focusing in the expanding MFR, which have stronger effects for pitch angles near 90$^\circ$, or by selective entry of GCRs along a leg of the MFR. The peak anisotropy and density depression in the flux rope both decrease with increasing rigidity. The spectra vary dynamically indicating that the temporal variations of density and anisotropy appear different in neutron monitor and muon detector data.

astro-ph.HE↗

arXiv2022

Topological Superconductor AuSn4: A first principle study

Topological semimetals such as Weyl or Dirac semimetals with superconductivity have emerged as a new class of topological materials to realize and study Majorana Fermion. This article reports the Density Functional Theory (DFT) calculated bulk electronic band structure of recently discovered topological superconductor candidate AuSn4. The study has been performed on AuSn4 considering two space groups symmetries viz. Aea2 and Ccce, as reported earlier. This study is further extended to the calculation of Z2 invariants. The Fermi surfaces corresponding to the bands, which are responsible for non-trivial band topology, along with the surface states, are also mapped. The complete study suggests that AuSn4 is a topological semimetal. On AuSn4, it is the first report in the literature showing the non-trivial band topology based on first-principle calculations.

cond-mat.supr-con↗

arXiv2022

Investigation of structural and magneto-transport properties of PdTe2 single crystals

The growth and structural analysis of topological semimetal (TSM) PdTe2 were carried out in this study. The self-flux method was employed to grow the single crystals which were structurally characterized by XRD, SEM and EDAX, while the vibrational modes were observed by Raman spectroscopy. Further, the transport properties of the grown crystal are also investigated, which show the presence of the weak anti-localization effect. The low field (1Tesla) magnetoconductivity is studied by Hikami-Larkin-Nagaoka (HLN) model, and the physical parameters are extracted. Further, a quadratic term and a linear term in applied field were added in HLN model, which are accounted for quantum and classical contributions in conduction mechanism. The modified HLN model was used to study magneto-conductivity in entire field range and at temperature from 2-100 K. This study not only confirmed the growth of single crystal PdTe2, but also verified the presence of topological surface states (TSS) through the HLN analysis of magneto-transport measurements.

cond-mat.mtrl-sci↗

arXiv2022

Sn2Pd: a possible superconducting material with topological surface states

In this article, we report the detailed magneto transport measurements of the topological semimetal (TSM) candidate, Sn2Pd. Single crystal of Sn2Pd is synthesized through the self-flux method. Phase purity and crystalline morphology are confirmed through powder X ray diffraction (PXRD) pattern and field emission scanning electron microscopy (FESEM) image. Signatures of superconducting transition are seen in both transport and magneto transport measurements, which are further supported by the AC magnetization studies. Sn2Pd is found to show superconductivity onset at below 2.8K, but not the zero resistivity down to 2K. Although, isothermal magneto resistivity measurements below superconducting onset (2.8K) clearly exhibited superconductor-like behavior, but is not observed in heat capacity measurements, indicating the same to be of weak nature. Magnetotransport measurements performed in a normal state of Sn2Pd show the presence of a weak antilocalization (WAL) effect, which is confirmed by modeling of low field magneto-conductivity (MC) through Hikami Larkin Nagaoka (HLN) formalism. Here, it is worth mentioning that the present article is the first report on magneto transport measurements of Sn2Pd, which show the same to be a topological material with a weak superconducting phase below around 2.8K.

cond-mat.supr-con↗

arXiv2022

Bulk superconductivity and non-trivial band topology analysis of Pb2Pd

A perfect topological superconductor can be realized by the simultaneous existence of bulk superconductivity along with topological non-trivial surface states. In this article, we report single crystal growth of superconducting binary compound Pb2Pd. The crystal is well characterized through X-Ray Diffraction (XRD), Selected Area electron diffraction (SAED), Transmission Electron Microscopy (TEM), Field emission Scanning electron Microscopy (FESEM) and X-Ray Photoelectron spectroscopy (XPS). The bulk superconducting nature of the studied crystal is determined through AC susceptibility and magneto-heat capacity measurements. The specific heat jump at superconducting transition suggests Pb2Pd to be a moderately coupled s-wave superconductor. The topological non-trivial character of Pb2Pd is evidenced through bulk electronic band structure and Z2 invariants, which are calculated under the protocols of Density Functional Theory (DFT). This is the first report on topological invariant of Pb2Pd, showing Pb2Pd to possess non-trivial topological band structure

cond-mat.supr-con↗

arXiv2022

Probing the topological surface states in superconducting Sn4Au single crystal: A magneto transport study

Materials exhibiting bulk superconductivity along with magnetoresistance (MR) in their normal state have emerged as suitable candidates for topological superconductivity. In this article, we report a flux free method to synthesize single crystal of topological superconductor candidate Sn4Au. The phase purity and single crystalline nature are confirmed through various characterizations viz. X-Ray diffraction (XRD), field emission scanning electron microscopy (FESEM), selected Area electron diffraction (SAED), and transmission electron microscopy (TEM). Chemical states of the constituent element viz. Sn and Au are analyzed through X-Ray photoelectron spectroscopy (XPS). Superconductivity in synthesized Sn4Au single crystal is evident form R-T plot and critical field (Hc) is determined through R-H plot at 2K i.e., just below critical temperature Tc. A positive magnetoresistance (MR) is observed in R-H measurements at different temperatures above Tc, viz. at 3K, 5K, 10K and 20K. Further, the magnetoconductivity (MC) is analyzed by using Hikami-Larkin-Nagaoka (HLN) formalism, which signifies the presence of weak antilocalization (WAL) effect in Sn4Au. Angle dependent magneto-transport measurement has been performed to detect the origin of the observed WAL effect in Sn4Au single crystal. Normalized MC vs HcosTheta plot shows presence of topological surface states (TSS) in the studied system. It is evident that Sn4Au is a 2.6K topological superconductor.

cond-mat.supr-con↗

arXiv2022

A comprehensive review on topological superconducting materials and interfaces

Superconductivity in topological materials has drawn a significant interest of the scientific community as these materials provide a hint of the existence of Majorana fermions conceived from the quantized thermal conductivity, a zero-biased conduction peak and the anomalous Josephson effect. In this review, we make a systematic study of recent advances in the field of topological superconductivity. The article comprises of both bulk systems as well as heterostructures. A brief description of Majorana fermions and their relationship with topological superconductors and heterostructures is also carried out. Also, this review consists of details of key experimental techniques to characterize candidates of topological superconductivity. Moreover, we summarize the potential material candidate that may demonstrate topological superconductivity. We also consider some intrinsic odd-parity superconductors, non-centrosymmetric, centrosymmetric superconductors, doped topological insulators, doped topological crystalline insulators and some other materials that are expected to show superconductivity along with topological non-trivial states in bulk from. The effect of pressure, emergence of superconductivity in topological materials and Muon Spin Rotation studies are also summarized in this article.

cond-mat.supr-con↗

arXiv2022

Detailed magneto-heat capacity analysis of SnAs topological superconductor

In this article, we report magneto-heat capacity analysis of superconducting SnAs, which is characterized through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and magneto-transport measurements. The studied SnAs superconductor evidenced the presence of superconductivity at around 4K, and the same is seen to persist up to an applied field of 250Oe. The bulk nature of superconductivity is determined through AC susceptibility along with heat capacity measurements. Magneto-heat capacity measurements show SnAs to be a fully gapped s wave superconductor. This finding is well supported by calculated superconducting physical parameters. Further, the calculation of the residual Sommerfeld coefficient at different fields confirms node-less superconductivity in SnAs.

cond-mat.supr-con↗

arXiv2022

Growth, structure, micro-structure and magneto transport of an easy route synthesized bulk polycrystalline TiSe2

This article reports an easy route synthesis of bulk polycrystalline TiSe2. Phase purity and microstructure are determined through powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FESEM) respectively. Vibrational modes of TiSe2 as being analyzed by Raman spectroscopy, show the occurrence of both Ag and Eg modes. Charge density wave (CDW) is observed in transport measurements of TiSe2 with hysteresis in cooling and warming measurements at around 180K. Further, studied TiSe2 showed negative magnetoresistance (MR) below the CDW and a small positive MR above the CDW.

cond-mat.mtrl-sci↗

arXiv2021

Andreev reflection spectroscopy on SnAs single crystals

Binary compounds of SnT family(T= As, Sb, Te, S, Se, P) exhibit novel properties like superconductivity, topologically protected states etc. Some of these compounds crystallize in NaCl type structure or in layered structure, both of which are considered potentially important for high-temperature/unconventional superconductivity. It was previously shown that K-doped BaBiO$_3$ with NaCl type structure exhibits superconducting state below $\sim$ 30 K. SnAs has crystallographic configuration that is exactly similar to K-doped BaBiO$_3$ and this warrants for the investigation of superconductivity in this material. Previously it was reported that SnAs exhibits weakly coupled type I superconductivity with an energy gap of 0.7 meV. Recently, the electronic bandstructure calculations has hinted to the existence of possible topologically protected states in SnAs. This has motivated us to investigate the superconducting nature of SnAs using point contact Andreev reflection spectroscopy. Our investigation revealed that superconductivity in SnAs can be well explained within the BCS framework in the weak coupling limit.

cond-mat.supr-con↗

arXiv2021

SnAs: a 4K weak type-II superconductor with non-trivial band topology

Superconductors with non-trivial band topology are emerging as one of the best avenues to study quantum anomalies and experimental realization of Majorana Fermions. This article reports the successful crystal growth of superconducting SnAs, which can have topologically non-trivial states, as evidenced in DFT (Density Functional Theory) calculations, Z2 invariants, and topologically surface state. Here, we followed a two-step method to grow SnAs crystal. The powder XRD (X-ray Diffractometry) pattern of synthesized crystal ensures that the crystal is grown in a single phase with a NaCl type cubic structure and the EDAX (Energy Dispersive X-ray Analysis) endorses the stoichiometry of the as-grown sample. The DFT calculations performed with and without the inclusion of spin-orbit coupling (SOC) show band inversion at various K symmetry points near the Fermi level. The recorded Raman spectra show two different modes, which are assigned as A1 and ETO vibrations. The ZFC (Zero-Field Cooled) & FC (Field Cooled), as well as the isothermal M-H (Magnetization vs. field) measurements, are also performed for the topological non-trivial SnAs superconductor, which eventually confirms the weak type-II superconductivity at 4K. Various other superconductivity parameters viz. kappa parameter, coherence length, and penetration depth are also calculated to probe the as-grown sample's characteristics.

cond-mat.supr-con↗

arXiv2021

Superconductivity with Topological non-trivial surface states in NbC

Quantum materials with non-trivial band topology and bulk superconductivity are considered superior materials to realize topological superconductivity. In this regard, we report detailed Density Functional Theory (DFT) calculations and Z2 invaraints for the NbC superconductor, exhibiting its band structure to be topologically non-trivial. Bulk superconductivity at 8.9K is confirmed through DC magnetization measurements under Field Cooled (FC) and Zero Field Cooled (ZFC) protocols. This superconductivity is found to be of type-II nature as revealed by isothermal M-H measurements and thus calculated the Ginzberg-Landau parameter. A large intermediate state is evident from the phase diagram, showing NbC to be a strong type-II superconductor. Comparing with earlier reports on superconducting NbC, a non-monotonic relationship of critical temperature with lattice parameters is seen. In conclusion, NbC is a type-II around 10K superconductor with topological non-trivial surface states.

cond-mat.supr-con↗

arXiv2021

Structural and WAL analysis of Topological single-crystal SnSb2Te4

Here, we report successful single crystal growth of SnSb2Te4 using the self-flux method. Unidirectional crystal growth is confirmed through X Ray Diffraction (XRD) pattern taken on mechanically cleaved crystal flake while the rietveld refined Powder XRD (PXRD) pattern confirms the phase purity of the grown crystal. Scanning Electron Microscopy (SEM) image and Energy Dispersive X-Ray analysis (EDAX) confirm crystalline morphology and exact stoichiometry of constituent elements. Vibrational Modes observed in Raman spectra also confirm the formation of the SnSb2Te4 phase. DC resistivity measurements confirm the metallic character of the grown crystal. Magneto-transport measurements up to 5T show a nonsaturating low magneto-resistance percentage. V type cusp and Hikami Larkin Nagaoka (HLN) fitting at lower field confirms the Weak Anti-localization (WAL) effect in SnSb2Te4. Density Functional Theory (DFT) calculations were showing topological non-trivial electronic band structure. It is the first-ever report on MR study and WAL analysis of SnSb2Te4 single crystal.

cond-mat.mtrl-sci↗

arXiv2021

A Peculiar ICME Event in August 2018 Observed with the Global Muon Detector Network

We demonstrate that global observations of high-energy cosmic rays contribute to understanding unique characteristics of a large-scale magnetic flux rope causing a magnetic storm in August 2018. Following a weak interplanetary shock on 25 August 2018, a magnetic flux rope caused an unexpectedly large geomagnetic storm. It is likely that this event became geoeffective because the flux rope was accompanied by a corotating interaction region and compressed by high-speed solar wind following the flux rope. In fact, a Forbush decrease was observed in cosmic-ray data inside the flux rope as expected, and a significant cosmic-ray density increase exceeding the unmodulated level before the shock was also observed near the trailing edge of the flux rope. The cosmic-ray density increase can be interpreted in terms of the adiabatic heating of cosmic rays near the trailing edge of the flux rope, as the corotating interaction region prevents free expansion of the flux rope and results in the compression near the trailing edge. A northeast-directed spatial gradient in the cosmic-ray density was also derived during the cosmic-ray density increase, suggesting that the center of the heating near the trailing edge is located northeast of Earth. This is one of the best examples demonstrating that the observation of high-energy cosmic rays provides us with information that can only be derived from the cosmic ray measurements to observationally constrain the three-dimensional macroscopic picture of the interaction between coronal mass ejections and the ambient solar wind, which is essential for prediction of large magnetic storms.

physics.space-ph↗

arXiv2020

Excited-state dynamics of structurally characterized crystal of SnxSb1-x

The topological behavior of heavy metal alloys opens a vast area for incredible research and future technology. Here, we extend our previous report about the superconducting properties of Sn0.4Sb0.6 along with the compositional variation of Sn and Sb in SnxSb1-x (with (X=0.5 and 0.6)) to study the detailed optical properties. Structural and morphological details of grown crystal are carried from the previous study. Further, the samples are excited by a pump of 2.61 eV with a broad probe of 0.77-1.54 eV in the NIR regime for transient reflectance ultrafast studies (TRUS) measurements. The differential reflectance profile shows an unprecedented negative magnitude, and the average power-dependent analysis of this negative trend has been analyzed. This article not only provides evidence of band filling phenomenon in the samples but also shows that with the variation of average power, there is a definite increase in the excited charge carriers, and thereby enhancing the band filling response. The estimated value of the bandgap between the band filled states and valence state is also determined from these studies. The nonlinear properties and bandgap analysis of the studied topological alloys and similar materials help in the advancement of various nonlinear optical applications.

cond-mat.mtrl-sci↗

arXiv2020

Raman Spectroscopy of Bi2Se3-xTex (x= 0 to 3) Topological Insulator Crystals

We report crystal growth and Raman spectroscopy characterization of pure and mixed bulk topological insulators. The series comprises of both binary and ternary tetradymite topological insulators. We analyzed in detail the Raman peaks of vibrational modes as out of plane Ag, and in plane Eg for both binary and ternary tetradymite topological insulators. Both out of plane Ag exhibit obvious atomic size dependent peak shifts and the effect is much lesser for the former than the latter. The situation is rather interesting for in plane Eg, which not only shows the shift but rather a broader hump like structure. The de convolution of the same show two clear peaks, which are understood in terms of the presence of separate in plane BiSe and BiTe modes in mixed tetradymite topological insulators. Summarily, various Raman modes of well-characterized pure and mixed topological insulator single crystals are reported and discussed in this article.

cond-mat.mtrl-sci↗

arXiv2020

Type-II Superconductivity below 4K in Sn0.4Sb0.6

In this article, we report the occurrence of superconductivity in Sn0.4Sb0.6 single crystal at below 4K. Rietveld refined Powder XRD data confirms the phase purity of as grown crystal, crystallizing in rhombohedral R-3m space group with an elongated (2xc) unit cell in c-direction. Scanning Electron Microscope (SEM) image and EDAX measurement confirm the laminar growth and near to desired stoichiometry ratio. Raman Spectroscopy data shows the vibrational modes of Sn-Sb and Sb-Sb modes at 110 and 135cm-1. ZFC (Zero-Field-Cooled) magnetization measurements done at 10Oe showed sharp superconducting transitions at 4K along with a minor step at 3.5K. On the other hand, Paramagnetic Meissner Effect (PME) is observed in FC measurements. Magnetization vs applied field (M-H) plots at 2, 2.2, 2.5, 2.7, 3, 3.2, 3.5, and 3.7K shows typical Type-II nature of observed superconductivity with lower and upper critical fields (Hc1 and Hc2) at 69.42Oe and 630Oe respectively at 2K. Type-II superconductivity is also confirmed by calculated Ginzburg-Landau Kappa parameter value of 3.55. Characteristics length viz. coherence length and penetration depth are also calculated. Weak granular coupling is observed from R-T plot, in which resistance is not dropping to zero down to 2K.

cond-mat.supr-con↗

arXiv2019

Bulk Superconductivity below 6K in PdBi2Te3 topological single crystal

We study the structural and bulk superconducting properties of self flux grown PdBi2Te3 single crystal. Phase purity of as grown crystal is confirmed by Rietveld refinement of gently crushed powder XRD of the same. PdBi2Te3 crystallizes in rhombohedral structure with R-3 m space group along with small impurity of Bi. Scanning Electron Microscopy (SEM) images showed layered structure and the elemental analysis by energy dispersive X Ray analysis (EDAX) done on same confirmed the stoichiometry to be near to PdBi2Te3. Characteristic vibrational modes viz. A11g, Eg2, A21g are clearly observed in Raman spectrum, and are slightly shifted from that as in case of Bi2Te3. Bulk superconductivity is confirmed by FC and ZFC magnetization measurements (M-T) exhibiting diamagnetic transition with Tconset at around 6K. M-H plots at different temperatures of 2K, 2.5K, 3K, 3.5K, 4K, 4.5K, 5K and 6K showed clear opening of the loop right up to 6K. Both M-T and M-H clearly establish the appearance of bulk type II superconductivity below 6K in studied PdBi2Te3. The lower critical field Hc1 and upper critical field Hc2 are at 180Oe at 4800Oe respectively at 2K for as grown PdBi2Te3 crystal. Other critical parameters of superconductivity such as coherence length, penetration depth and kappa parameter are also calculated.

cond-mat.supr-con↗