arXiv subjects

R. P. Singh

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

At least 109 records · Page 6Linked to original sources

arXiv2018

Superconducting properties of the noncentrosymmetric superconductor LaPtGe

We report superconducting properties of noncentrosymmetric superconductor LaPtGe which crystallizes in noncentrosymmetric $ α$-ThSi$ _{2} $ structure. The magnetization, resistivity and specific heat measurements confirm that LaPtGe is a type-II bulk superconductor with a transition temperature T$ _{c} $ = 3.05 $ \pm $ 0.05 K. Muon-spin relaxation/rotation measurements confirms that time reversal preserved in the superconducting ground state.

cond-mat.supr-con↗

arXiv2018

Enhancement of the superconducting transition temperature by Re doping in Weyl semimetal MoTe$_{2}$

This work presents the emergence of superconductivity in Re substituted topological Weyl semimetal MoTe$_{2}$. Re substitution for Mo sites lead to a sizable enhancement in the superconducting transition temperature (T$_{c}$). A record high T$_{c}$ at ambient pressure in a 1T$'$-MoTe$_{2}$ (room temperature structure) related sample is observed for the Mo$_{0.7}$Re$_{0.3}$Te$_{2}$ composition (T$_{c}$ = 4.1 K, in comparison MoTe$_{2}$, shows a T$_{c}$ of 0.1 K). The experimental and theoretical studies indicate that Re substitution is doping electrons and facilitates the emergence of superconductivity by enhancing the electron-phonon coupling and density of states at the Fermi level. Our findings, therefore, open a new way to further manipulate and enhance the superconducting state together with the topological states in 2D van der Waals materials.

cond-mat.supr-con↗

arXiv2018

$ \boldsymbolγ $-vibration in $^{198}$Hg

Low lying states of $^{198}$Hg have been investigated via $^{197}$Au($^{7}$Li, $ α$2n$ γ$)$ ^{198} $Hg reaction at E$ _{\text{beam}} $ = 33 MeV and 38 MeV and the members of $ γ$-vibrational band have been identified. Results are compared with the systematic of this mass region and found in agreement. Observed band structures have been interpreted using the theoretical framework of microscopic triaxial projected shell model (TPSM) approach and it is shown that TPSM results are in fair agreement with the observed energies.

nucl-ex↗

arXiv2018

Fully-gapped superconductivity in single crystals of noncentrosymmetric Re$_6$Zr with broken time-reversal symmetry

The noncentrosymmetric superconductor Re$_6$Zr has attracted much interest due to the observation of broken time-reversal symmetry in the superconducting state. Here we report an investigation of the superconducting gap structure of Re$_6$Zr single crystals by measuring the magnetic penetration depth shift $Δλ(T)$ and electronic specific heat $C_e(T)$. $Δλ(T)$ exhibits an exponential temperature dependence behavior for $T~\ll~T_c$, which indicates a fully-open superconducting gap. Our analysis shows that a single gap $s$-wave model is sufficient to describe both the superfluid density $ρ_s(T)$ and $C_e(T)$ results, with a fitted gap magnitude larger than the weak coupling BCS value, providing evidence for fully-gapped superconductivity in Re$_6$Zr with moderate coupling.

cond-mat.supr-con↗

arXiv2018

Superconductivity in equimolar Nb-Re-Hf-Zr-Ti high entropy alloy

Herein, we report the synthesis and detailed superconducting properties of a new high entropy alloy superconductor with nominal composition Nb$_{20}$Re$_{20}$Zr$_{20}$Hf$_{20}$Ti$_{20}$ using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), magnetization, transport, and thermodynamic measurements. The room temperature powder XRD confirms that the alloy is arranged on a simple body centered cubic crystal lattice with lattice parameter a = 3.38 (1) $\textÅ$. EDX measurement yields an average composition of Nb$_{21}$Re$_{16}$Zr$_{20}$Hf$_{23}$Ti$_{20}$ (in atomic $\%$). Transport, magnetic and heat capacity measurements reveal that the material is a type-II superconductor with the bulk superconducting transition at $T_{c}$ = 5.3 K, lower critical field $H_{c1}$(0) = 33 mT and upper critical field $H_{c2}$(0) = 8.88 T. Low temperature specific heat measurement indicates that the sample is a moderately coupled superconductor, and the electronic specific heat data fits well with the single-gap BCS model.

cond-mat.supr-con↗

arXiv2018

Time Reversal Symmetry Breaking in noncentrosymmetric superconductor Re6Ti

We have investigated the superconducting state of the noncentrosymmetric superconductor Re6Ti (Tc = 6.0 K) using muon-spin rotation/relaxation (muSR) technique. The zero-field muon experiment shows the presence of spontaneous magnetic fields in the superconducting state, indicating time-reversal symmetry breaking (TRSB). However, the low-temperature transverse field muon measurements suggest nodeless s-wave superconductivity. The time reversal symmetry breaking further confirmed in the stoichiometric composition Re24Ti5. These results indicate that the pairing symmetry is not affected by spin-orbital coupling Re6X family of compounds. Altogether these studies suggest unconventional nature (TRSB) of superconductivity is intrinsic to Re6X family of compounds and paves the way for further studies of this family of materials.

cond-mat.supr-con↗

arXiv2017

Abrupt phase change of the core rotation in the 143 Sm nucleus

Dipole sequences in the 143 Sm nucleus have been investigated via the 124 Sn ( 24 Mg, 5n) reaction at E lab = 107 MeV using the Indian National Gamma Array (INGA). The spin-parity of the associated levels have been firmly established from the spectroscopic measurement. Level lifetimes of several levels in the dipole bands have been measured using the Doppler Shift Attenuation Method. The decreasing trend of the measured B(M1) and B(E2) transition strengths in one of the sequence (DB I) spells out its origin as Magnetic Rotation (MR). The trends of B(M1) and B(E2) in DB I are reproduced well in the theoretical calculations using the Shears mechanism with the Principal Axis Cranking (SPAC) model. However, the calculations fail to reproduce the sharp rise in the B(M1)/B(E2) ratio at the highest spins in DB I and the same has been interpreted from the decreasing of the core rotation along the sequence. The experimental observations along with the the theoretical calculations for the second dipole band (DB II), indicate that the core rotation, rather than the shears mechanism, is being favored for angular momentum generation. This represents a unique observation of forking of the shears band DB I from an abrupt phase change of the core from spherical into the deformed one.

nucl-ex↗

arXiv2017

Time-reversal symmetry breaking in noncentrosymmetric superconductor Re6Hf:further evidence for unconventional behaviour in the alpha-Mn family of materials

The discovery of new families of unconventional superconductors is important both experimentally and theoretically, especially if it challenges current models and thinking. By using muon spin relaxation in zero-field, time-reversal symmetry breaking has been observed in Re6Hf. Moreover, the temperature dependence of the superfluid density exhibits s-wave superconductivity with an enhanced electron-phonon coupling. This, coupled with the results from isostructural Re6Zr, shows that the Re6X family are indeed a new and important group of unconventional superconductors.

cond-mat.supr-con↗

arXiv2017

Superconducting properties of the noncentrosymmetric superconductor TaOs

The noncentrosymmetric superconductor TaOs has been characterized using x-ray diffraction, resistivity, magnetization, and specific heat measurements. Magnetization and specific heat measurements show a bulk superconducting transition at 2.07 K. These measurements suggest that TaOs is a weakly coupled type-II superconductor. The electronic specific heat in the superconducting state can be explained by the single-gap BCS model, suggesting s-wave superconductivity in TaOs.

cond-mat.supr-con↗

arXiv2017

Superconducting and normal-state properties of the noncentrosymmetric superconductor Re6Zr

We systematically investigate the normal and superconducting properties of non-centrosymmetric Re$_{6}$Zr using magnetization, heat capacity, and electrical resistivity measurements. Resistivity measurements indicate Re$_{6}$Zr has poor metallic behavior and is dominated by disorder. Re$_6$Zr undergoes a superconducting transition at $T_{\mathrm{c}} = \left(6.75\pm0.05\right)$ K. Magnetization measurements give a lower critical field, $μ_{0}H_{\mathrm{c1}} = \left(10.3 \pm 0.1\right)$ mT. The Werthamer-Helfand-Hohenberg model is used to approximate the upper critical field $μ_{0}H_{\mathrm{c2}} = \left(11.2 \pm 0.2\right)$ T which is close to the Pauli limiting field of 12.35 T and which could indicate singlet-triplet mixing. However, low-temperature specific-heat data suggest that Re$_{6}$Zr is an isotropic, fully gapped s-wave superconductor with enhanced electron-phonon coupling. Unusual flux pinning resulting in a peak effect is observed in the magnetization data, indicating an unconventional vortex state.

cond-mat.supr-con↗

arXiv2017

Scattering of Poincare beams: polarization speckles

Polarization speckle is a fine granular light pattern having spatially varying random polarization profile. We generate these speckle patterns by using the scattering of Poincaré beams, a special class of vector vortex beams, through a ground glass plate. Here, the Poincaré beams are generated using a polarization sensitive spatial light modulator displaying an on-axis hologram corresponding to an optical vortex phase profile. The different inhomogeneities of the rough surface experience different polarizations, which control the ability for scattered waves to interfere at the detection plane and causes a spatially varying polarization profile. We experimentally determined the spatial variation of local degree of polarization and orientation of the polarization ellipse for these speckle patterns from the Stokes analysis. We also determined the size of scalar speckles using the auto-correlation function of Stokes parameter S0 and the size of polarization speckles using the sum of auto-correlation functions of remaining three Stokes parameters. We found that the scalar speckle size is independent of index of the vector beam but the size of polarization speckles decreases with the increase in index of the vector beam.

physics.optics↗

arXiv2017

Direct transfer of pump amplitude to parametric down-converted photons

We numerically and experimentally show that all photons generated by spontaneous parametric down-conversion (SPDC) follow a transverse amplitude similar to that of the pump. This amplitude transfer from pump to SPDC is revealed in the Fourier image plane of the down-converted photons restricted by an aperture. We also observe a considerable shift of the image plane from the actual Fourier plane, when size of the aperture is gradually increased. The shift of the Fourier image of down-converted photons affects the quality of spatial mode-based projection in various quantum correlation experiments with parametric down-converted photon pairs. The results may be useful in applications of down-converted photons for quantum imaging and quantum communication.

quant-ph↗

arXiv2017

Superconducting Properties and $μ$SR Study of the Noncentrosymmetric Superconductor Nb$_{0.5}$Os$_{0.5}$

The properties of the noncentrosymmetric superconductor ($α$-$\textit{Mn}$ structure) Nb$_{0.5}$Os$_{0.5}$ is investigated using resistivity, magnetization, specific heat, and muon spin relaxation and rotation ($μ$SR) measurements. These measurements suggest that Nb$_{0.5}$Os$_{0.5}$ is a weakly coupled ($λ_{e-ph}$ $\sim$ 0.53) type-II superconductor ($κ_{GL}$ $\approx$ 61) having a bulk superconducting transition temperature $T_c$ = 3.07 K. The specific heat data in the superconductive regime fits well with the single-gap BCS model indicating nodeless s-wave superconductivity in Nb$_{0.5}$Os$_{0.5}$. The $μ$SR measurements also confirm $\textit{s}$-wave superconductivity with the preserved time-reversal symmetry.

cond-mat.supr-con↗

arXiv2017

Multiband Superconductivity in the time reversal symmetry broken superconductor Re6Zr

We report point contact Andreev Reflection (PCAR) measurements on a high-quality single crystal of the non-centrosymmetric superconductor Re6Zr. We observe that the PCAR spectra can be fitted by taking two isotropic superconducting gaps with Delta_1 ~ 0.79 meV and Delta_2 ~ 0.22 meV respectively, suggesting that there are at least two bands which contribute to superconductivity. Combined with the observation of time reversal symmetry breaking at the superconducting transition from muon spin relaxation measurements (Phys. Rev. Lett. 112, 107002 (2014)), our results imply an unconventional superconducting order in this compound: A multiband singlet state that breaks time reversal symmetry or a triplet state dominated by interband pairing.

cond-mat.supr-con↗

arXiv2016

Griffiths phase and critical behavior in layered Sr$_2$IrO$_4$ ferromagnet

We report the existence of Griffiths phase (GP) and its influence on critical phenomena in layered Sr$_2$IrO$_4$ ferromagnet (T$_C$ = 221.5 K). The power law behavior of inverse magentic susceptibility, 1/$χ$(T) with exponent $λ= 0.18(2)$ confirm the GP in the regime T$_C$ $<$ T $\leq$ T$_G$ = 279.0(5) K. Moreover, the detailed critical analysis via modified Arrott plot method exhibits unrealistic critical exponents $β$ = 0.77(1), $γ$ = 1.59(2) and $δ= 3.06(4)$, in corroboration with magneto-caloric study. The abnormal exponent values have been viewed in context of ferromagnetic-Griffiths phase transition. The GP has been further analyzed using Bray model, which yields a reliable value of $β$ = 0.19(2), belonging to the two-dimensional (2D) XYh$_4$ universality class with strong anisotropy present in Sr$_2$IrO$_4$. The present study proposes Bray model as a possible tool to investigate the critical behavior for Griffiths ferromagnets in place of conventional Arrott plot analysis. The possible origins of GP and its correlation with insulating nature of Sr$_2$IrO$_4$ have been discussed.

cond-mat.str-el↗

arXiv2016

Quantum Information with Even/Odd States of Orbital Angular Momentum of Light

We address the possibility of using even/odd states of orbital angular momentum (OAM) of photons for the quantum information tasks. Single photon qubit states and two photon entangled states in even/odd basis of OAM are considered. We present a method for the tomography and general projective measurement in even/odd basis. With the general projective measurement, we show the Bell violation and quantum cryptography with Bell's inequality. We also describe hyper and hybrid entanglement of even/odd OAM states along with polarization, which can be applied in the implementation of quantum protocols like super dense coding.

quant-ph↗

arXiv2016

Pancharatnam phase in non-separable states of light

We generate the non-separable state of polarization and orbital angular momentum (OAM) using a laser beam. The generated state undergoes a cyclic polarization evolution which introduces a Pancharatnam geometric phase to the polarization state and in turn a relative phase in the non-separable state. We experimentally study the violation of Bell - CHSH inequality for different Pancharatnam phases introduced by various cyclic polarization evolutions with linear and circular states as measurement bases. While measuring in linear bases, the Bell-CHSH parameter oscillates with Pancharatnam phase. One can overcome this dependence by introducing a relative phase in one of the projecting state. However for measurement in circular bases, the Pancharatnam phase does not affect the Bell-CHSH violation.

physics.optics↗

arXiv2016

Superconducting Properties of the Non-Centrosymmetric Superconductor Re6Hf

The synthesis and detailed characterization of the noncentrosymmetric superconductor Re$_{6}$Hf using powder x-ray diffraction (XRD), magnetization, transport and thermodynamic measurements are reported. XRD confirms the crystal structure of Re$_{6}$Hf to be cubic noncentrosymmetric $α$-\textit{Mn} with a lattice parameter a = 9.6850(3)\textÅ. Resistivity, DC and AC magnetization confirms the bulk superconducting transition T$_{c}^{onset} \sim $ ~ 5.96 K. The lower critical field H$_{C1}(0)\approx$ 5.6 mT and upper critical H$_{C2}(0)$ was found to be around 12.2 T which is greater than the Pauli limiting field, indicating unconventional behavior in Re$_{6}$Hf and leads to the possibility of triplet pairing. A sharp discontinuity in the specific heat data was observed around T$_{c}$ indicating bulk superconductivity, and the normalized specific heat jump is $ΔC_{el}$/$γ_{n}$T$_{c}$ = 1.53 which is in close agreement with BCS value. Superconducting electronic specific heat data is fitted reasonably well for an exponential relation with Sommerfeld coefficient ($γ$) showing a linear relation with magnetic field suggesting that in Re$_{6}$Hf dominant pairing channel is s-wave with isotropic superconducting gap parameter without nodes.

cond-mat.supr-con↗