Abstract
Magnetic monopoles are hypothesised elementary particles connected by Dirac strings that behave like infinitely thin solenoids (Dirac 1931 Proc. R. Soc. A 133 60). Despite decades of searching, free magnetic monopoles and their Dirac strings have eluded experimental detection, although there is substantial evidence for deconfined magnetic monopole quasiparticles in spin ice materials (Castelnovo et al 2008 Nature 326 411). Here we report the detection of a hierarchy of unequally-spaced magnetic excitations via high resolution inelastic neutron spectroscopic measurements on the quantum spin ice candidate . These excitations are well-described by a simple model of monopole pairs bound by a linear potential (Coldea et al Science 327 177) with an effective tension of 0.642(8) K at 1.65 K. The success of the linear potential model suggests that these low energy magnetic excitations are direct spectroscopic evidence for the confinement of magnetic monopole quasiparticles in the quantum spin ice candidate.
| Original language | English |
|---|---|
| Article number | 45LT01 |
| Journal | Journal of Physics Condensed Matter |
| Volume | 29 |
| Issue number | 45 |
| DOIs | |
| State | Published - Oct 20 2017 |
Funding
We would like to acknowledge K H Hong, A J Browne, G M McNally, D Le and S E Maytham for helpful comments and discussions. This work was supported by NSERC, ACS, PRF, CFI, NSF, STFC and EPSRC. PMS acknowledges the University of Edinburgh for funding through the Global Research and Principal’s Career Development Scholarships and the Canadian Centennial Scholarship Fund. CRW acknowledges financial support from the CRC (Tier II) program, PRF, CIFAR and NSERC. JWH and CM acknowledges financial support from NSERC. JPA and CS acknowledges financial support from the STFC, EPSRC and the ERC. Concerning previously obtained data from the DCS, CRW and HDZ acknowledge financial support from the NSF, the EIEG program (FSU) and the state of Florida. We acknowledge the support of the National Institute of Standards and Technology, US Department of Commerce, in providing the neutron research facilities used in this work. A portion of this research at Oak Ridge National Laboratory’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. Finally, the authors thank the Carnegie Trust for the Universities of Scotland for providing facilities and equipment for chemical synthesis.
| Funders | Funder number |
|---|---|
| Office of Basic Energy Sciences | |
| Scientific User Facilities Division | |
| US Department of Energy | |
| National Science Foundation | |
| National Institute of Standards and Technology | |
| U.S. Department of Commerce | |
| Parkinson Research Foundation | |
| American Chemical Society | |
| Oak Ridge National Laboratory | |
| CRC Health Group | |
| Canadian Institute for Advanced Research | |
| Fayetteville State University | |
| Natural Sciences and Engineering Research Council of Canada | |
| Canada Foundation for Innovation | |
| Engineering and Physical Sciences Research Council | EP/G030332/1 |
| Science and Technology Facilities Council | |
| European Research Council | |
| University of Edinburgh |
Keywords
- geometrically frustrated magnetism
- magnetic monopoles
- neutron scattering
- quantum spin ice
- spin ice