Multi-band superconductivity driven by a site-selective mechanism in Mo8_8Ga41_{41}

The family of the endohedral gallide cluster compounds recently emerged as a new family of superconductors which is expected to host systems displaying unconventional physics. Mo$_8$Ga$_{41}$ is an important member of this family which shows relatively large $T_c \sim$ 10 K and has shown indications of strong electron-phonon coupling and multi-band superconductivity. Here, through direct measurement of superconducting energy gap by scanning tunneling spectroscopy (STS) we demonstrate the existence of two distinct superconducting gaps of magnitude 0.85 meV and 1.6 meV respectively in Mo$_8$Ga$_{41}$. Both the gaps are seen to be conventional in nature as they evolve systematically with temperature as per the predictions of BCS theory. Our band structure calculations reveal that only two specific Mo sites in an unit cell contribute to superconductivity where only $d_{xz}$/$d_{yz}$ and $d_{x^2-y^2}$ orbitals have strong contributions. Our analysis indicates that the site-elective contribution govern the two-gap nature of superconductivity in Mo$_8$Ga$_{41}$.Comment: 6 pages, 5 figure

Algorithm based new Tone Reservation method for mitigating PAPR in OFDM systems

There are abundant methods to mitigate PAPR in OFDM signals among which algorithm based tone reservation is of great popularity owing to its low complexity as well as decent BER. Here we have put forward a new distinct algorithm based Tone Reservation technique which is not only less complex and calculates its own threshold as well as PRT signal (unlike other algorithms requiring predetermined threshold and PRT) but also aptly modifies the data by bit by bit comparison with a modified copy of itself (algorithm modified) thus scaling the peaks as and providing a decent BER and good PAPR reduction.

Head-to-Head and Tail-to-Tail Domain Wall in Hafnium Zirconium Oxide: A First Principles Analysis of Domain Wall Formation and Energetics

180{\deg} domains walls (DWs) of Head-to-Head/Tail-to-Tail (H-H/T-T) type in ferroelectric (FE) materials are of immense interest for a comprehensive understanding of the FE attributes as well as harnessing them for new applications. Our first principles calculation suggests that such DW formation in Hafnium Zirconium Oxide (HZO) based FEs depends on the unique attributes of the HZO unit cell, such as polar-spacer segmentation. Cross pattern of the polar and spacer segments in two neighboring domains along the polarization direction (where polar segment of one domain aligns with the spacer segment of another) boosts the stability of such DWs. We further show that low density of oxygen vacancies at the metal-HZO interface and high work function of metal electrodes are conducive for T-T DW formation. On the other hand, high density of oxygen vacancy and low work function of metal electrode favor H-H DW formation. Polarization bound charges at the DW get screened when band bending from depolarization field accumulates holes (electrons) in T-T (H-H) DW. For a comprehensive understanding, we also investigate their FE nature and domain growth mechanism. Our analysis suggests that a minimum thickness criterion of domains has to be satisfied for the stability of H-H/T-T DW and switching of the domains through such DW formation.Comment: 10 figure

Direction-Dependent Lateral Domain Walls in Ferroelectric Hafnium Zirconium Oxide and their Gradient Energy Coefficients: A First Principles Study

To understand and harness the physical mechanisms of ferroelectric Hafnium Zirconium Oxide (HZO)-based devices, there is a need for a clear understanding of the domain interactions, domain density, nucleation, domain wall motion, negative capacitance effects, and other multi-domain characteristics. All these crucial attributes strongly depend on the coupling between neighboring domains in HZO which is quantified by gradient energy coefficient (g). Furthermore, HZO has unique orientation-dependent lateral multidomain configurations, which plays a key role for directional dependence of g. To develop an in-depth understanding of these effects, there is a need for a thorough analysis of g in HZO, including its orientation and strain-dependence. In this work, we analyze the energetics of multidomain configurations, domain growth mechanism and gradient energy coefficients of HZO corresponding to lateral domain walls using first-principle Density Functional Theory (DFT) calculations. The dependence of g on domain width and strain is also analyzed to provide a comprehensive understanding of this crucial parameter. Our results indicate that one lateral direction exhibits the following characteristics: (i) domain growth occurs unit-cell-by-unit-cell, (ii) the value of g is negative and in the order of $10^{-12} Vm^{3}C^{-1}$, and (iii) g is much sensitive to strain. In contrast, in the other lateral direction, the following attributes are observed: (i) domain growth occurs in quanta of half-unit-cell, (ii) g is positive and in the order of $10^{-10} Vm^{3}C^{-1}$ and (iii) g shows negligible sensitivity to strain (up to the 1% strain limit considered in this work)

Probing the superconducting ground state of ZrIrSi: A μ\muSR study

The superconducting ground state of newly reported ZrIrSi is probed by means of $\mu$SR technique along with resistivity measurement. The occurrence of superconductivity at $T_\mathrm{C}$ = 1.7 K is confirmed by resistivity measurement. ZF-$\mu$SR study revealed that below $T_\mathrm{C}$, there is no spontaneous magnetic field in the superconducting state, indicates TRS is preserved in case of ZrIrSi. From TF-$\mu$SR measurement, we have estimated the superfluid density as a function of temperature, which is described by an isotropic $s-$wave model with a superconducting gap $2\Delta(0)/k_\mathrm{B}T_\mathrm{C}$ = 5.1, indicates the presence of strong spin-orbit coupling. {\it Ab-initio} electronic structure calculation indicates that there are four bands passing through the Fermi level, forming four Fermi surface pockets. We find that the low-energy bands are dominated by the $4d$-orbitals of transition metal Zr, with substantially lesser weight from the $5d$-orbitals of the Ir-atoms.Comment: 6 pages, 4 figure

Investigation of Superconducting Gap Structure in HfIrSi using muon spin relaxation/rotation

Appearance of strong spin-orbit coupling (SOC) is apparent in ternary equiatomic compounds with 5$d$-electrons due to the large atomic radii of transition metals. SOC plays a significant role in the emergence of unconventional superconductivity. Here we examined the superconducting state of HfIrSi using magnetization, specific heat, zero and transverse-field (ZF/TF) muon spin relaxation/rotation ($\mu$SR) measurements. Superconductivity is observed at $T_\mathrm{C}$ = 3.6 K as revealed by specific heat and magnetization measurements. From the TF$-\mu$SR analysis it is clear that superfluid density well described by an isotropic BCS type $s$-wave gap structure. Furthermore, from TF$-\mu$SR data we have also estimated the superconducting carrier density $n_\mathrm{s}$ = 6.6 $\times$10$^{26}$m$^{-3}$, London penetration depth $\lambda_{L}(0)$ = 259.59 nm and effective mass $m^{*}$ = 1.57 $m_{e}$. Our zero-field muon spin relaxation data indicate no clear sign of spontaneous internal field below $T_\mathrm{C}$, which implies that the time-reversal symmetry is preserved in HfIrSi. Theoretical investigation suggests Hf and Ir atoms hybridize strongly along the $c$-axis of the lattice, which is responsible for the strong three-dimensionality of this system which screens the Coulomb interaction. As a result despite the presence of correlated $d$-electrons in this system, the correlation effect is weakened, promoting electron-phonon coupling to gain importance.Comment: 8 pages, 4 figure

Evidence of Nodal Line in the Superconducting Gap Symmetry of Noncentrosymmetric ThCoC2_{2}

The newly discovered noncentrosymmetric superconductor ThCoC$_{2}$ exhibits numerous unconventional behavior in the field dependent heat capacity data. Here we present the first measurement of the gap symmetry of ThCoC$_{2}$ by muon spin rotation/relaxation $(\mu$SR) measurements. Temperature dependence of the magnetic penetration depth measured using the transverse field $\mu$SR measurement reveal the evidence of nodal pairing symmetry. To understand these findings, we carry out the calculations of superconducting pairing eigenvalue and eigenfunction symmetry due to the spin-fluctuation mechanism, by directly implemented the {\it ab-initio} band structures. We find that the system possesses a single Fermi surface with considerable three-dimensionality, and hence a strong nesting along the $k_z$-direction. Such a nesting promotes a superconducting pairing with a $\cos{k_z}$-like symmetry with a prominent nodal line on the $k_z=\pm\pi/2$ plane. The result agrees well with the experimental data.Comment: 3 pages, 5 figure

Evaluating PCR-Based Detection of Salmonella Typhi and Paratyphi A in the Environment as an Enteric Fever Surveillance Tool.

With prequalification of a typhoid conjugate vaccine by the World Health Organization, countries are deciding whether and at what geographic scale to provide the vaccine. Optimal local data to clarify typhoid risk are expensive and often unavailable. To determine whether quantitative polymerase chain reaction (qPCR) can be used as a tool to detect typhoidal Salmonella DNA in the environment and approximate the burden of enteric fever, we tested water samples from urban Dhaka, where enteric fever burden is high, and rural Mirzapur, where enteric fever burden is low and sporadic. Sixty-six percent (38/59) of the water sources of Dhaka were contaminated with typhoidal Salmonella DNA, in contrast to none of 33 samples of Mirzapur. If these results can be replicated in larger scale in Bangladesh and other enteric fever endemic areas, drinking water testing could become a low-cost approach to determine the presence of typhoidal Salmonella in the environment that can, in turn, guide informed-design of blood culture-based surveillance and thus assist policy decisions on investing to control typhoid

Mass azithromycin administration: considerations in an increasingly resistant world

No abstract available