title: Detection of time-reversal symmetry breaking in the noncentrosymmetric superconductor Re6Zr using muon-spin spectroscopy.
abstract: We have investigated the superconducting state of the noncentrosymmetric compound Re6Zr using magnetization, heat capacity, and muon-spin relaxation or rotation (μSR) measurements. Re6Zr has a superconducting transition temperature, Tc=6.75±0.05  K. Transverse-field μSR experiments, used to probe the superfluid density, suggest an s-wave character for the superconducting gap. However, zero and longitudinal-field μSR data reveal the presence of spontaneous static magnetic fields below Tc indicating that time-reversal symmetry is broken in the superconducting state and an unconventional pairing mechanism. An analysis of the pairing symmetries identifies the ground states compatible with time-reversal symmetry breaking.
authors.affiliation: Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: R P
authors.initials: RP
authors.lastname: Singh
authors.affiliation: ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire OX11 0QX, United Kingdom.
authors.forename: A D
authors.initials: AD
authors.lastname: Hillier
authors.affiliation: ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire OX11 0QX, United Kingdom and H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.
authors.forename: B
authors.initials: B
authors.lastname: Mazidian
authors.affiliation: ISIS facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Oxfordshire OX11 0QX, United Kingdom and SEPnet and Hubbard Theory Consortium, School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom.
authors.forename: J
authors.initials: J
authors.lastname: Quintanilla
authors.affiliation: H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.
authors.forename: J F
authors.initials: JF
authors.lastname: Annett
authors.affiliation: Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: D McK
authors.initials: DM
authors.lastname: Paul
authors.affiliation: Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Balakrishnan
authors.affiliation: Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom.
authors.forename: M R
authors.initials: MR
authors.lastname: Lees