skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Searching for signatures of E 6

Publication Date:
Sponsoring Org.:
OSTI Identifier:
Grant/Contract Number:
DE FG02 13ER41958; SC0011095
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review D
Additional Journal Information:
Journal Volume: 96; Journal Issue: 1; Related Information: CHORUS Timestamp: 2017-07-24 22:16:53; Journal ID: ISSN 2470-0010
American Physical Society
Country of Publication:
United States

Citation Formats

Joglekar, Aniket, and Rosner, Jonathan L. Searching for signatures of E 6. United States: N. p., 2017. Web. doi:10.1103/PhysRevD.96.015026.
Joglekar, Aniket, & Rosner, Jonathan L. Searching for signatures of E 6. United States. doi:10.1103/PhysRevD.96.015026.
Joglekar, Aniket, and Rosner, Jonathan L. Mon . "Searching for signatures of E 6". United States. doi:10.1103/PhysRevD.96.015026.
title = {Searching for signatures of E 6},
author = {Joglekar, Aniket and Rosner, Jonathan L.},
abstractNote = {},
doi = {10.1103/PhysRevD.96.015026},
journal = {Physical Review D},
number = 1,
volume = 96,
place = {United States},
year = {Mon Jul 24 00:00:00 EDT 2017},
month = {Mon Jul 24 00:00:00 EDT 2017}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on July 24, 2018
Publisher's Accepted Manuscript

Save / Share:
  • We report comprehensive 77 Se NMR measurements on a single crystalline sample of the recently discovered FeSe-based high-temperature superconductor K x Fe 2 - y Se 2 ( T c = 33 K) in a broad temperature range up to 290 K. Despite deviations from the stoichiometric KFe 2 Se 2 composition, we observed 77 Se NMR line shapes as narrow as 4.5 kHz under a magnetic field applied along the crystal c axis, and found no evidence for co-existence of magnetic order with superconductivity. On the other hand, the 77 Se NMR line shape splits into two peaks withmore » equal intensities at all temperatures when we apply the magnetic field along the ab plane. This suggests that K vacancies may have a superstructure and that the local symmetry of the Se sites is lower than the tetragonal fourfold symmetry of the average structure. This effect might be a prerequisite for stabilizing the s ± symmetry of superconductivity in the absence of the hole bands at the Brillouin zone center. From the increase of NMR linewidth below T c induced by the Abrikosov lattice of superconducting vortices, we estimate the in-plane penetration depth λ ab ~ 290 nm and the carrier concentration n e ~ 1 × 10 + 21 cm - 3 . Our Knight shift 77 K data indicate that the uniform spin susceptibility decreases progressively with temperature, in analogy with the case of FeSe ( T c ~ 9 K) as well as other FeAs high- T c systems. The strong suppression of 77 K observed immediately below T c for all crystal orientations is consistent with a singlet pairing of Cooper pairs. We do not however observe the Hebel-Slichter coherence peak of the nuclear spin-lattice relaxation rate 1 / T 1 immediately below T c , expected for conventional BCS s-wave superconductors. In contrast with the case of FeSe, we do not observe evidence for an enhancement of low-frequency antiferromagnetic spin fluctuations near T c in 1 / T 1 T . Instead, 1 / T 1 T exhibits qualitatively the same behavior as overdoped non-superconducting Ba(Fe 1 - x Co x ) 2 As 2 with x ~ 0 . 14 or greater, where hole bands are missing in the Brillouin zone center. We will discuss the implications of our results on the unknown mechanism of high-temperature superconductivity in FeSe and FeAs systems.« less
  • Cited by 67
  • Cited by 20
  • The Ho2Ti2O7, Er2Ti2O7 and Yb2Ti2O7 pyrochlores were studied by synchrotron X-ray diffraction to determine whether the (002) peak, forbidden in the pyrochlore space group Fd-3m but observed in single crystal neutron scattering measurements, is present due to a deviation of their pyrochlore structure from Fd-3m symmetry. Synchrotron diffraction measurements on precisely synthesized stoichiometric and non-stoichiometric powders and a crushed floating zone crystal of Ho2Ti2O7 revealed that the (002) reflection is absent in all cases to a sensitivity of approximately one part in 30,000 of the strongest X-ray diffraction peak. This indicates to high sensitivity that the structural space group ofmore » these rare earth titanate pyrochlores is Fd-3m, and that thus the (002) peak observed in the neutron scattering experiments has a non-structural origin. The cell parameters and internal strain for lightly stuffed Ho2+xTi2-xO7 are also presented.« less