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Chronister A, Pustogow A, Kikugawa N, Sokolov DA, Jerzembeck F, Hicks CW, Mackenzie AP, Bauer ED, Brown SE. Evidence for even parity unconventional superconductivity in Sr 2RuO 4. Proc Natl Acad Sci U S A 2021; 118:e2025313118. [PMID: 34161272 PMCID: PMC8237678 DOI: 10.1073/pnas.2025313118] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Unambiguous identification of the superconducting order parameter symmetry in [Formula: see text] has remained elusive for more than a quarter century. While a chiral p-wave ground state analogue to superfluid 3He-A was ruled out only very recently, other proposed triplet-pairing scenarios are still viable. Establishing the condensate magnetic susceptibility reveals a sharp distinction between even-parity (singlet) and odd-parity (triplet) pairing since the superconducting condensate is magnetically polarizable only in the latter case. Here field-dependent 17O Knight shift measurements, being sensitive to the spin polarization, are compared to previously reported specific heat measurements for the purpose of distinguishing the condensate contribution from that due to quasiparticles. We conclude that the shift results can be accounted for entirely by the expected field-induced quasiparticle response. An upper bound for the condensate magnetic response of <10% of the normal state susceptibility is sufficient to exclude all purely odd-parity candidates.
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Affiliation(s)
- Aaron Chronister
- Department of Physics & Astronomy, University of California, Los Angeles, CA 90095;
| | - Andrej Pustogow
- Department of Physics & Astronomy, University of California, Los Angeles, CA 90095;
| | - Naoki Kikugawa
- Cryogenic Center for Liquid Hydrogen and Materials Science, National Institute for Materials Science, Tsukuba 305-0003, Japan
| | - Dmitry A Sokolov
- Physics of Quantum Materials Department, Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
| | - Fabian Jerzembeck
- Physics of Quantum Materials Department, Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
| | - Clifford W Hicks
- Physics of Quantum Materials Department, Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
- School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom
| | - Andrew P Mackenzie
- Physics of Quantum Materials Department, Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
- Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, United Kingdom
| | - Eric D Bauer
- Materials Physics and Applications, Los Alamos National Laboratory, Los Alamos, NM 87545
| | - Stuart E Brown
- Department of Physics & Astronomy, University of California, Los Angeles, CA 90095;
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Kaur M, Lewis CM, Chronister A, Phun GS, Mueller LJ. Non-Uniform Sampling in NMR Spectroscopy and the Preservation of Spectral Knowledge in the Time and Frequency Domains. J Phys Chem A 2020; 124:5474-5486. [PMID: 32496067 DOI: 10.1021/acs.jpca.0c02930] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The increased sensitivity under weighted non-uniform sampling (NUS) is demonstrated and quantified using Monte Carlo simulations of nuclear magnetic resonance (NMR) time- and frequency-domain signals. The concept of spectral knowledge is introduced and shown to be superior to the frequency-domain signal-to-noise ratio for assessing the quality of NMR data. Two methods for rigorously preserving spectral knowledge and the time-domain NUS knowledge enhancement upon transformation to the frequency domain are demonstrated, both theoretically and numerically. The first, non-uniform weighted sampling using consistent root-mean-square noise, is applicable to data sampled on the Nyquist grid, whereas the second, the block Fourier transform using consistent root-mean-square noise, can be used to transform time-domain data acquired with arbitrary, off-grid NUS.
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Affiliation(s)
- Manpreet Kaur
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Callie M Lewis
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Aaron Chronister
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Gabriel S Phun
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Leonard J Mueller
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
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Pustogow A, Luo Y, Chronister A, Su YS, Sokolov DA, Jerzembeck F, Mackenzie AP, Hicks CW, Kikugawa N, Raghu S, Bauer ED, Brown SE. Constraints on the superconducting order parameter in Sr 2RuO 4 from oxygen-17 nuclear magnetic resonance. Nature 2019; 574:72-75. [PMID: 31548658 DOI: 10.1038/s41586-019-1596-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Accepted: 07/15/2019] [Indexed: 11/09/2022]
Abstract
Phases of matter are usually identified through spontaneous symmetry breaking, especially regarding unconventional superconductivity and the interactions from which it originates. In that context, the superconducting state of the quasi-two-dimensional and strongly correlated perovskite Sr2RuO4 is considered to be the only solid-state analogue to the superfluid 3He-A phase1,2, with an odd-parity order parameter that is unidirectional in spin space for all electron momenta and breaks time-reversal symmetry. This characterization was recently called into question by a search for an expected 'split' transition in a Sr2RuO4 crystal under in-plane uniaxial pressure, which failed to find any such evidence; instead, a dramatic rise and a peak in a single-transition temperature were observed3,4. Here we use nuclear magnetic resonance (NMR) spectroscopy of oxygen-17, which is directly sensitive to the order parameter via hyperfine coupling to the electronic spin degrees of freedom, to probe the nature of superconductivity in Sr2RuO4 and its evolution under strain. A reduction of the Knight shift is observed for all strain values and at temperatures below the critical temperature, consistent with a drop in spin polarization in the superconducting state. In unstrained samples, our results contradict a body of previous NMR work reporting no change in the Knight shift5 and the most prevalent theoretical interpretation of the order parameter as a chiral p-wave state. Sr2RuO4 is an extremely clean layered perovskite and its superconductivity emerges from a strongly correlated Fermi liquid, and our work imposes tight constraints on the order parameter symmetry of this archetypal system.
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Affiliation(s)
- A Pustogow
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA.
| | - Yongkang Luo
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA. .,Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan, China.
| | - A Chronister
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA
| | - Y-S Su
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA
| | - D A Sokolov
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - F Jerzembeck
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - A P Mackenzie
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.,School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - C W Hicks
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - N Kikugawa
- National Institute for Materials Science, Tsukuba, Japan
| | - S Raghu
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, USA
| | - E D Bauer
- Los Alamos National Laboratory, Los Alamos, New Mexico, USA
| | - S E Brown
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA.
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