Temperature dependence of the average electron-hole pair creation energy in Al0.8Ga0.2As

The temperature dependence of the average energy consumed in the creation of an electron-hole pair in the wide bandgap compound semiconductor Al 0.8Ga0.2As is reported following X-ray measurements made using an Al0.8Ga0.2As photodiode diode coupled to a low-noise charge-sensitive preamplifier operating in spectroscopic photon counting mode. The temperature dependence is reported over the range of 261 K-342 K and is found to be best represented by the equation ε AlGaAs 7.327-0.0077 T, where εAlGaAs is the average electron-hole pair creation energy in eV and T is the temperature in K. © 2013 © 2013 Author(s)

DichroMatch: a website for similarity searching of circular dichroism spectra

Circular dichroism (CD) spectroscopy is a widely used method for examining the structure, folding and conformational changes of proteins. A new online CD analysis server (DichroMatch) has been developed for identifying proteins with similar spectral characteristics by detecting possible structurally and functionally related proteins and homologues. DichroMatch includes six different methods for determining the spectral nearest neighbours to a query protein spectrum and provides metrics of how similar these spectra are and, if corresponding crystal structures are available for the closest matched proteins, information on their secondary structures and fold classifications. By default, DichroMatch uses all the entries in the Protein Circular Dichroism Data Bank (PCDDB) for its comparison set, providing the broadest range of publicly available protein spectra to match with the unknown protein. Alternatively, users can download or create their own specialized data sets, thereby enabling comparisons between the structures of related proteins such as wild-type versus mutants or homologues or a series of spectra of the same protein under different conditions. The DichroMatch server is freely available at http://dichromatch.cryst.bbk.ac.uk

Studies of the superconducting properties of Sn1-xInxTe (x=0.38 to 0.45) using muon-spin spectroscopy

The superconducting properties of Sn1-xInxTe (x = 0.38 to 0.45) have been studied using magnetization and muon-spin rotation or relaxation (muSR) measurements. These measurements show that the superconducting critical temperature Tc of Sn1-xInxTe increases with increasing x, reaching a maximum at around 4.8 K for x = 0.45. Zero-field muSR results indicate that time-reversal symmetry is preserved in this material. Transverse-field muon-spin rotation has been used to study the temperature dependence of the magnetic penetration depth lambda(T) in the mixed state. For all the compositions studied, lambda(T) can be well described using a single-gap s-wave BCS model. The magnetic penetration depth at zero temperature lambda(0) ranges from 500 to 580 nm. Both the superconducting gap Delta(0) at 0 K and the gap ratio Delta(0)/kBTc indicate that Sn1-xInxTe (x = 0.38 to 0.45) should be considered as a superconductor with intermediate to strong coupling.Comment: 7 pages, 6 figures, 3 table

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, $\mu_{0}H_{\mathrm{c1}} = \left(10.3 \pm 0.1\right)$ mT. The Werthamer-Helfand-Hohenberg model is used to approximate the upper critical field $\mu_{0}H_{\mathrm{c2}} = \left(11.2 \pm 0.2\right)$ 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.Comment: 11 pages, 7 figures, 2 table

Probing the superconducting ground state of the noncentrosymmetric superconductors CaTSi3 (T = Ir, Pt) using muon-spin relaxation and rotation

The superconducting properties of CaTSi3 (where T = Pt and Ir) have been investigated using muon spectroscopy. Our muon-spin relaxation results suggest that in both these superconductors time-reversal symmetry is preserved, while muon-spin rotation data show that the temperature dependence of the superfluid density is consistent with an isotropic s-wave gap. The magnetic penetration depths and upper critical fields determined from our transverse-field muon-spin rotation spectra are found to be 448(6) and 170(6) nm, and 3800(500) and 1700(300) G, for CaPtSi3 and CaIrSi3 respectively. The superconducting coherence lengths of the two materials have also been determined and are 29(2) nm for CaPtSi3 and 44(4) nm for CaIrSi3.Comment: 6 pages, 7 figure

Comparative study of the centrosymmetric and non-centrosymmetric superconducting phases of Re3W using muon-spin spectroscopy and heat capacity measurements

We compare the low-temperature electronic properties of the centrosymmetric (CS) and non-centrosymmetric (NCS) phases of Re3W using muon-spin spectroscopy and heat capacity measurements. The zero-field muSR results indicate that time-reversal symmetry is preserved for both structures of Re3W. Transverse-field muon spin rotation has been used to study the temperature dependence of the penetration depth lambda(T) in the mixed state. For both phases of Re3W, lambda(T) can be explained using a single-gap s-wave BCS model. The magnetic penetration depth at zero temperature, lambda(0), is 164(7) and 418(6) nm for the centrosymmetric and the non-centrosymmetric phases of Re3W respectively. Low-temperature specific heat data also provide evidence for an s-wave gap-symmetry for the two phases of Re3W. Both the muSR and heat capacity data show that the CS material has a higher Tc and a larger superconducting gap Delta(0) at 0 K than the NCS compound. The ratio Delta(0)/kBTc indicates that both phases of Re3W should be considered as strong-coupling superconductors.Comment: 7 pages, to appear in Physical Review

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

Limits on τ lepton-flavor violating decays into three charged leptons

A search for the neutrinoless, lepton-flavor violating decay of the τ lepton into three charged leptons has been performed using an integrated luminosity of 468  fb^(-1) collected with the BABAR detector at the PEP-II collider. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (1.8–3.3)×10^(-8) at 90% confidence level

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