arXiv subjects

S. Patnaik

Publications and source records attributed to S. Patnaik.

At least 55 records · Page 3Linked to original sources

arXiv2018

Crystal Growth and Characterization of Bulk Sb2Te3Topological Insulator

The Sb2Te3 crystals are grown using the conventional self flux method via solid state reaction route, by melting constituent elements (Sb and Te) at high temperature (850 C), followed by slow cooling (2 C per hour).The weak anti localization (WAL) related low field (2 Tesla) magneto-conductance at low temperatures (2.5 K and 20 K) has been analysed and discussed using the Hikami- Larkin - Nagaoka (HLN) model. Summarily, the short letter reports an easy and versatile method for crystal growth of bulk Sb2Te3 topological insulator (TI) and its brief physical property characterization.

cond-mat.mtrl-sci↗

arXiv2018

Direct Evidence for Time-Reversal Symmetry Breaking in Topological Superconductor Sr0.1Bi2Se3

The single helical Fermi surface on the surface state of three-dimensional topological insulator Bi2Se3 is constrained by the time-reversal invariant bulk topology to possess a spin-singlet superconducting pairing symmetry. In fact, the Cu-doped, and pressure-tuned superconducting Bi2Se3 show no evidence of the time reversal symmetry breaking. We report on the detection of the time reversal symmetry (TRS) breaking in the topological superconductor Sr0.1Bi2Se3 , probed by zero-field (ZF) μSR measurements. The TRS breaking provides strong evidence for the existence of spin-triplet pairing state. The temperature dependent super-fluid density deduced from transverse-field (TF) μSR measurement yields nodeless superconductivity with low superconducting carrier density and penetration depth λ = 1622(134) nm. From the microscopic theory of unconventional pairing, we find that such a fully gapped spin triplet pairing channel is promoted by the complex interplay between the structural hexagonal warping and higher order Dresselhaus spin-orbit coupling terms. Based on Ginzburg-Landau analysis, we delineate the mixing of singlet to triplet pairing symmetry as the chemical potential is tuned far above from the Dirac cone. Our observation of such spontaneous TRS breaking chiral superconductivity on a helical surface state, protected by the TRS invariant bulk topology, can open new avenues for interesting research and applications.

cond-mat.supr-con↗

arXiv2018

Magnetic field-induced resistivity upturn and exceptional magneto-resistance in Weyl semimetal TaSb2

We study magneto-transport properties in single crystals of TaSb_2, which is a recently discovered topological semimetal. In the presence of magnetic field, the electrical resistivity shows onset of insulating behaviour followed by plateau at low temperature. Such resistivity plateau is generally assigned to topological surface states. TaSb2 exhibits extremely high magneto-resistance with non-saturating field dependence. We find that aspects of extremely large magneto resistance and resistivity plateau are well accounted by classical Kohler scaling. Unambiguous evidence for anomalous Chiral transport is provided with observation of negative longitudinal magneto-resistance. Shubnikov-de Haas oscillations reveal two dominating frequencies, 201 T and 455 T. These aspects categorize TaSb2 as a Type-II Weyl semimetal. At low temperature, the field dependence of Hall resistivity shows non-linear behaviour that indicates the presence of two types of charge carriers in consonance with reported electronic band structure. Analysis of Hall resistivity imply very high electron mobilities.

cond-mat.str-el↗

arXiv2017

Facile synthesis of potassium intercalated p-terphenyl and signatures of a possible high Tc phase

Synthesis methodology for flakes of p-terphenyl through sublimation under inert atmosphere of argon is presented. Flake morphology of p-terphenyl provides a favourable environment for efficient intercalation of potassium. Ratio of potassium and p-terphenyl is adjusted so as to obtain the desired superconducting phase i.e. potassium doped p-terphenyl (K3C18H14). A clear transition is observed at 107 K under Zero Field Cooled (ZFC) and Field Cooled (FC) mode. But overall the moment is positive possibly due to impurity phase dominating characteristics in the presence of negligible superconducting volume fraction. The M-H loop taken at 20 K shows magnetic behaviour in synthesized K- doped p-terphenyl but upon background subtraction, it does exhibit characteristics of a type-2 superconductor.

cond-mat.supr-con↗

arXiv2017

Nature of Magnetoelectric coupling in corundum antiferromagnet Co4Ta2O9

We study the magnetocapacitance (MC) effect and magnetoelectric (ME) coupling in spin-flop driven antiferromagnet Co4Ta2O9. The magnetocapacitance data at high magnetic fields are analyzed by phenomenological Ginzburg-landau theory of ferroelectromagnets and it is found that change in dielectric constant is proportional to the square of magnetization. The saturation polarization and magnetoelectric coupling are estimated to be 52microC/m2 and $γ$ = 1.4 x10-3 (emu/g)-2 respectively at 6 Tesla. Electric polarization is achieved below Neel temperature only when the sample is cooled in the presence of magnetic field and it is established that the ground state is non-ferroelectric implying that magnetic lattice does not lead to spontaneous symmetry breaking in Co4Ta2O9.

cond-mat.mtrl-sci↗

arXiv2017

Enhanced Ferromagnetism in Lacey Reduced Graphene Oxide Nano-ribbon

Incorporation of magnetism in graphene based compounds holds great promise for potential spintronic applications. By optimizing point defects and high edge density of defects, we report many-fold increase in the ferromagnetic saturation moment in lacey reduced graphene oxide nanoribbons (LRGONR) as compared to other graphene derivatives. The samples were synthesized using chemical unzipping methodology. Detailed structural and morphological characterizations are discussed that include XRD, Raman, SEM, HRTEM and XPS measurements. Brilluoin function analysis to magnetization data reflects best fit for J = 7/2 with a saturation moment of 1.1 emu/g. The microscopic origin of magnetization in LRGONR is assigned to high edge defect density which has also been correlated to microstructure.

physics.app-ph↗

arXiv2017

Evidence for conventional superconductivity in Sr0.1Bi2Se3 from high pressure studies

SrxBi2Se3 is recently reported to be a superconductor derived from topological insulator Bi2Se3. It shows a maximum resistive Tc of 3.25 K at ambient pressure. We report magnetic (upto 1 GPa) and transport properties (upro 8 Gpa) under pressure for single crystalline Sr0.1Bi2Se3 superconductor. Magnetic measurements show that Tc decreases from ~2.6 K (0 GPa) to ~1.9 K (0.81 GPa). Similar behavior is observed in transport properties as well without much change in the metallic characteristics in normal state resistivity. No reentrant superconducting phase (Physical Review B 93, 144514 (2016)) is observed at high pressure. Normal state resistivity near Tc is explained by Fermi liquid model. Above 100 K, a polaronic hopping conduction mechanism with two parallel channels for current flow is indicated. Band structure calculations indicate decreasing density of states at Fermi level with pressure. In consonance with transition temperature suppression in conventional BCS low Tc superconductors, the pressure effect in SrxBi2Se3 is well accounted by pressure induced band broadening.

cond-mat.supr-con↗

arXiv2017

Unusual non saturating Giant Magneto-resistance in single crystalline Bi2Te3 topological insulator

We report synthesis, structural details and electrical transport properties of topological insulator Bi2Te3. The single crystalline specimens of Bi2Te3 are obtained from high temperature (950C) melt and slow cooling (2C/hour). The resultant crystals were shiny, one piece (few cm) and of bright silver color. The Bi2Te3 crystal is found to be perfect with clear [00l] alignment. The powder XRD pattern being carried out on crushed crystals showed that Bi2Te3 crystallized in R3m symmetry with a = b = 4.3866(2) A, c = 30.4978(13) A and Gamma = 120degree. The Bi position is refined to (0, 0, 0.4038 (9)) at Wyckoff position 6c and of Te are (0, 0, 0) at Wyckoff position 3a and at (0, 0, 0.2039(8)) at 6c. Ambient pressure and low temperature (down to 2K) electrical transport measurements revealed metallic behavior. Magneto transport measurements under magnetic field showed huge non saturating magneto resistance (MR) reaching up to 250% at 2.5K and under 50KOe field. Summarily, the short communication clearly demonstrates that Bi2Te3 topological insulator exhibit non-saturating large positive MR at low temperature of say below 10K. The non saturating MR is seen right up to room temperature albeit with much decreased magnitude. Worth mentioning is the fact that these crystals are bulk in nature and hence the anomalous MR is clearly an intrinsic property and not due to the size effect as reported for nano-wires or thin films of the same.

cond-mat.str-el↗

arXiv2016

Exceptional magneto-electric coupling and spontaneous electric polarization in anti-ferromagnet Co4Nb2O9

Synthesis and extensive structural, pyroelectric, magnetic, dielectric and magneto-electric characterizations are reported for polycrystalline Co4Nb2O9 towards unraveling the multiferroic state especially in reference to the magnetic spin flop transition. Magnetic measurements confirm the Co4Nb2O9 becomes antiferromagnetic (AFM) at around 28 K but no clear evidence for spin-flop effect was found. Associated with the magnetic phase transition, a sharp peak in pyroelectric current indicates the appearance of the strong magneto-electric coupling below Neel temperature (TN) with a large coupling constant upto 17.8 uC/m^2T. Using temperature oscillation technique, we establish Co4Nb2O9 to be a genuine multiferroic with spontaneous electric polarization in the anti-ferromagnetic state.

cond-mat.mtrl-sci↗

arXiv2016

Evolution of Microstructure and Relaxor Ferroelectric Properties in (La_zBa_(1-z)(Ti0.80Sn0.20)O3

We report a study on a series of lanthanum doped barium stannate-titanate (LBTS) ceramics towards correlating their microstructure with ferroelectric properties. The samples were prepared by solid state reaction technique and the XRD analysis indicated predominantly single phase microstructure. Scanning Electron Microscopy revealed that while a low La doping of 1 atomic % yielded inhibited grain growth in 1LBTS, higher amounts of La doping yield larger leafy grains. This peculiar grain growth and microstructure evolution could be attributed to the combination of the following two competing factors: (i) suppression of O vacancies due to La doping leading to grain growth inhibition and (ii) enhancement of mechanism leading to nucleation and growth of 2-D (leafy) grains for La doping higher than 2 atomic % due to eutectic phenomena. Dielectric permittivity measurements indicate that addition of La enhances diffused phase transition in BTS, but its frequency dependence is observed only at 2 atomic % La doping. This signature relaxor behaviour and the increase in the intensity of a particular Raman peak with La doping, as well as non-saturated PE hysteresis loops confirm the presence of polar nano-regions for 2 and 3 atomic % La doped BTS. However significant enhancement in dielectric permittivity could not be achieved due to reduced grain size.

cond-mat.mtrl-sci↗

arXiv2016

Evidence for trivial Berry phase and absence of chiral anomaly in semimetal NbP

We report a detailed magneto-transport study in single crystals of NbP. High quality crystals were grown by vapour transport method. An exceptionally large magnetoresistance is confirmed at low temperature which is non-saturating and is linear at high fields. Models explaining the linear magnetoresistance are discussed and it is argued that in NbP this is linked to charge carrier mobility fluctuations. Negative longitudinal magnetoresistance is not seen, unlike several other Weyl monopnictides, suggesting lack of well defined chiral anomaly in NbP. Unambiguous Shubnikov-de-Haas oscillations are observed at low temperatures that are correlated to Berry phases. The Landau fan diagram indicates trivial Berry phase in NbP crystals corresponding to Fermi surface extrema at 30.5 Tesla.

cond-mat.mtrl-sci↗

arXiv2016

Weak ferromagnetism in non-centrosymmetric BiPd 4K superconductor

We report synthesis of non-centrosymmetric BiPd single crystal by self flux method. The BiPd single crystal is crystallized in monoclinic structure with the P21 space group. Detailed SEM (Scanning Electron Microscopy) results show that the crystals are formed in slab like morphology with homogenous distribution of Bi and Pd. The magnetic susceptibility measurement confirmed that the BiPd compound is superconducting below 4K. Further, BiPd exhibits weak ferromagnetism near the superconducting transition temperature in isothermal magnetization (MH) measurements. The temperature dependent electrical resistivity also confirmed that the BiPd single crystal is superconducting at Tc=4K. Magneto transport measurements showed that the estimated Hc2(0) value is around 7.0kOe. We also obtained a sharp peak in heat capacity Cp(T) measurements at below 4K due to superconducting ordering. The normalized specific-heat jump, DC/γTc, is 1.52, suggesting the BiPd to be an intermediate BCS coupled superconductor. The pressure dependent electrical resistivity shows the Tc decreases with increasing applied pressure and the obtained dTc/dP is -0.62K/Gpa.

cond-mat.supr-con↗

arXiv2015

Improved superconducting properties of skutterudite La3Co4Sn13 with indium substitution

We report on two fold increase in superconducting transition temperature of La3Co4Sn13 by substituting indium at the tin site. The transition temperature of this skutterudite is observed to increase from 2.5 K to 5.1 K for 10 % indium substituted sample. The band structure and density of states calculations also indicate such a possibility. The compounds exhibit type - II superconductivity and the values of lower critical field (Hc1), upper critical field (Hc2), Ginzburg - Landau coherence length , penetration depth and GL parameter are estimated to be 0.0028 T, 0.68 T, 21.6 nm, 33.2 nm and 1.53 respectively for La3 Co4Sn11.7In1.3. Hydrostatic external pressure leads to decrease in transition temperature and the calculated pressure coefficient is -0.311 K/GPa . Flux pinning and vortex activation energies also improved with indium addition. Only positive frequencies are observed in phonon dispersion curve that relate to the absence of charge density wave or structural instability in the normal state.

cond-mat.supr-con↗

arXiv2015

Superconductivity by Sr Intercalation in Layered Topological Insulator Bi2Se3

Strontium intercalation between van der Waals bonded layers of topological insulator Bi2Se3 is found to induce superconductivity with a maximum Tc of 2.9 K. Transport measurement on single crystal of optimally doped sample Sr0.1Bi2Se3 shows weak anisotropy (1.5) and upper critical field Hc2(0) equals to 2.1 T for magnetic field applied per-pendicular to c -axis of the sample. The Ginzburg-Landau coherence lengths are Xi-ab = 15.3 Å and Xi_c = 10.2 Å. The lower critical field and zero temperature penetration depth Lambda(0) are estimated to be 0.35 mT and 1550 nm respectively. Hall and Seebeck measurements confirm the dominance of electronic conduction and the carrier concentration is surprisingly low (n = 1.85 x 10^19 cm-3) at 10 K indicating possibility of unconventional superconductivity.

cond-mat.supr-con↗

arXiv2015

Single gap s-wave superconductivity in Nb2PdS5

Superconducting order parameter and its symmetry are important parameters towards deciphering the pairing mechanism in newly discovered superconducting systems. We report a study on penetration depth measurement on Nb2PdS5 that has recently been reported with extremely high upper critical field with possible triplet pairing mechanism. Our data show that at low temperatures the change in penetration depth is best fitted with BCS s-wave model for single gap. The zero-temperature value of the superconducting energy gap is estimated to be Δ0 = 1.05 meV. The superfluid density in the entire temperature range is well described by single gap for λ (0) = 220 nm.

cond-mat.supr-con↗

arXiv2015

Effect of pressure on superconductivity in doped topological crystalline insulator Sn0.5In0.5Te

We report on the impact of hydrostatic pressure on the superconductivity of optimally (Indium) doped SnTe which is established to be derived from a topological crystalline insulating phase. Single crystals of Sn1-xInxTe were synthesized by a modified Bridgman method that exhibited maximum superconducting Tc of 4.4 K for x= 0.5. Hydrostatic pressure upto 2.5 GPa was applied on the crystals of Sn0.5In0.5Te and electrical resistivity as a function of temperature and pressure was measured. We observed decrease in onset superconducting transition temperature from 4.4 K to 2.8 K on increasing pressure from ambient to 2.5 GPa. The normal state resistivity also decreased abruptly by an order of magnitude at 0.5 GPa but for higher pressures, the same decreased marginally. From onset, offset and zero resistivity values, dTc/dP of -0.6K/GPa was confirmed. The low temperature normal state resistivity followed T^2 dependence suggesting Fermi liquid behaviour both for ambient and high pressure data. This increase in metallic characteristics accompanied by normal state Fermi liquid behaviour is in accordance with a dome structure for Tc variation with varying carrier concentration.

cond-mat.supr-con↗

arXiv2014

Effect of dilution of both A- and B- sites on the multiferroic properties of spinal Mott insulators

The structural, magnetic, electrical and transport properties of FeV2O4, by doping Li and Cr ions respectively in A and B sites, have been studied. Dilution of A-site by Li doping increases the ferri-magnetic ordering temperature and decreases the ferroelectric transition temperature. This also decreases the V-V distances which in effect increases the A-V coupling. This increased A-V coupling dominates over the decrease in A-V coupling due to doping of non-magnetic Li. On the other hand, Cr doping increases the ferri-magnetic ordering temperature but does not alter the ferroelectric transition temperature which is due to the fact that the polarization origin to the presence of almost non-substituted regions.

cond-mat.str-el↗

arXiv2014

Improper Ferroelectricity in Helicoidal Antiferromagnet Cu3Nb2O8

Cu3Nb2O8 is an unusual multiferroic compound that undergoes a series of magnetic ordering at low temperatures. Concurrent development of electric polarization has been reported at TN1 ~25 K corresponding to a non-collinear helicoidal ordering (Phys. Rev. Lett. 107, 137205 (2011)). But questions remain on the microscopic origin of such phenomena. In this communication, we report a detailed study of induced polar ordering in Cu3Nb2O8 by performing polarization, magnetization, dielectric constant and heat capacity measurements over a broad range of temperature and magnetic field. The dielectric constant shows suppression in the magnetic field but it does not shift to lower temperature with the application of external field. The appearance of magneto-dielectric effect signifies the contribution of q-dependent magnetic correlation function with enhanced weightage in the presence of magnetic field. This magnetic correlation function is associated with the ferro-axial vector and our overall results support this mechanism for the observation of muliferroicity in Cu3Nb2O8.

cond-mat.str-el↗