arXiv subjects

S. Carr

Publications and source records attributed to S. Carr.

4 recordsLinked to original sources

arXiv2013

Microscopic coexistence of a two-component incommensurate spin density wave with superconductivity in underdoped NaFe$_{0.983}$Co$_{0.017}$As

We have performed $^{75}$As and $^{23}$Na nuclear magnetic resonance (NMR) measurements on a single crystal of NaFe$_{0.9835}$Co$_{0.0165}$As and found microscopic coexistence of superconductivity with a two-component spin density wave (SDW). Using $^{23}$Na NMR we measured the spatial distribution of local magnetic fields. The SDW was found to be incommensurate with a major component having magnetic moment ($\sim0.2\,μ_B$/Fe) and a smaller component with magnetic moment ($\sim0.02\,μ_B$/Fe). Spin lattice relaxation experiments reveal that this coexistence occurs at a microscopic level.

cond-mat.supr-con↗

arXiv2013

Spin-pairing and penetration depth measurements from nuclear magnetic resonance in NaFe$_{0.975}$Co$_{0.025}$As

We have performed $^{75}$As nuclear magnetic resonance (NMR) Knight shift measurements on single crystals of NaFe$_{0.975}$Co$_{0.025}$As to show that its superconductivity is a spin-paired, singlet state consistent with predictions of the weak-coupling BCS theory. We use a spectator nucleus, $^{23}$Na, uncoupled from the superconducting condensate, to determine the diamagnetic magnetization and to correct for its effect on the $^{75}$As NMR spectra. The resulting temperature dependence of the spin susceptibility follows the Yosida function as predicted by BCS for an isotropic, single-valued energy gap. Additionally, we have analyzed the $^{23}$Na spectra that become significantly broadened by vortices to obtain the superconducting penetration depth as a function of temperature with $λ_{ab}(0) = 5,327 \pm$ 78$\,Å$.

cond-mat.supr-con↗

arXiv2012

Direct observation of the proliferation of ferroelectric loop domains and vortex-antivortex pairs

We discovered "stripe" patterns of trimerization-ferroelectric domains in hexagonal REMnO3 (RE=Ho, ---, Lu) crystals (grown below ferroelectric transition temperatures (Tc), reaching up to 1435 oC), in contrast with the vortex patterns in YMnO3. These stripe patterns roughen with the appearance of numerous loop domains through thermal annealing just below Tc, but the stripe domain patterns turn to vortex-antivortex domain patterns through a freezing process when crystals cross Tc even though the phase transition appears not to be Kosterlitz-Thouless-type. The experimental systematics are compared with the results of our six-state clock model simulation and also the Kibble-Zurek Mechanism for trapped topological defects.

cond-mat.mtrl-sci↗

arXiv2008

Challenge of polarized beams at future colliders

A short overview about the potential of polarized beams at future colliders is given. In particular the baseline design for polarized beams at the ILC is presented and the physics case for polarized $e^-$ and $e^+$ is discussed. In order to fulfil the precision requirements spin tracking from the source to the interaction point is needed. Updates concerning the theoretical calculations as well as their implementation in simulation codes are reported.

hep-ph↗