ABSTRACT
The high-field superconducting state in CeCoIn(5) has been studied by transverse field muon spin rotation measurements with an applied field parallel to the crystallographic c axis close to the upper critical field mu(0)H(c2) = 4.97 T. At magnetic fields mu(0)H > or = 4.8 T the muon Knight shift is enhanced and the superconducting transition changes from second order towards first order as predicted for Pauli-limited superconductors. The field and temperature dependence of the transverse muon spin relaxation rate sigma reveal paramagnetic spin fluctuations in the field regime from 2 T < or = mu(0)H < 4.8 T. In the normal state close to H(c2) correlated spin fluctuations as described by the self-consistent renormalization theory are observed. The results support the formation of a mode-coupled superconducting and antiferromagnetically ordered phase in CeCoIn(5) for H directed parallel to the c axis.
ABSTRACT
The detailed dynamics of the positively charged muonium (Mu+) in heavily doped p-type Si:B is reported. Below 200 K, Mu+ is static and isolated, and is located in a stretched Si-Si bond. Above approximately 200 K, Mu+ diffuses incoherently. At temperatures higher than 300 K, the Mu+-B- complex is formed while above 520 K, it starts to dissociate. There is significant enhancement of the diffusion of Mu+ in Si compared to H+ and D+-this is attributed to its smaller mass.
ABSTRACT
We determine the local structure of isolated positively charged muonium (Mu+) in heavily doped p-type GaAs based on muon level crossing resonance and zero applied field muon spin depolarization data. These measurements provide the first direct experimental confirmation that Mu+, and by analogy H+, is located within a stretched Ga-As bond. The distances between Mu+ and the nearest neighbor Ga and As atoms are estimated to be 1.83 +/- 0.10 A; and 1.76 +/- 0.10 A, respectively. These results are compared to existing theoretical calculations on the structure of hydrogen in GaAs and additionally provide data on the induced electric field gradients.
ABSTRACT
A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the <0001> direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c axis. Its small ionization energy (
ABSTRACT
We report direct detection of the formation and subsequent breakup of a complex containing positively charged muonium ( Mu+) and a substitutional Zn(Ga) acceptor in heavily doped p-type GaAs:Zn. Mu+ diffuses above 200 K with a hop rate nu = nu(0)e(-E(nu)/k(B)T) where nu(0) = (7.7+/-2.0)x10(8) s(-1) and E(nu) = 0.15(4) eV. Above 350 K, it forms the complex with a trapping radius of 500+/-200 A. The Mu-Zn complex breaks up above 550 K with a dissociation energy of 0.88(7) eV and prefactor of (5+/-4)x10(12) s(-1). Above 750 K, the cyclic reaction Mu+<--> Mu0 takes place.
ABSTRACT
Bond-centered muonium ( Mu(0)(BC)) has been observed in very heavily doped n-type Si:P. It exhibits a Curie-like electronic spin susceptibility which leads to a giant negative shift in the muon spin precession frequency. At high dopant levels, the Mu(0)(BC) hyperfine parameters, deduced from a model involving spin exchange with free carriers, are significantly reduced from those in intrinsic Si. This indicates that the spin density distribution for Mu(0)(BC) in metallic Si:P is altered significantly by charge screening effects, likely a general phenomenon for deep impurities in materials with high carrier concentrations.
