Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements
We present low-temperature low-power intermodulation-distortion (IMD) measurements of high-quality MgB[subscript 2] thin films that are inconsistent with presumed s-wave symmetry of the order parameter. The measurements were carried out in a stripline resonator at approximately 2 GHz between 1.8 K a...
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| Format: | Article |
| Language: | en_US |
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American Physical Society
2010
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| Online Access: | http://hdl.handle.net/1721.1/52517 |
| _version_ | 1811096463329984512 |
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| author | Moeckly, B. H. Agassi, Y. D. Oates, Daniel E. |
| author2 | Lincoln Laboratory |
| author_facet | Lincoln Laboratory Moeckly, B. H. Agassi, Y. D. Oates, Daniel E. |
| author_sort | Moeckly, B. H. |
| collection | MIT |
| description | We present low-temperature low-power intermodulation-distortion (IMD) measurements of high-quality MgB[subscript 2] thin films that are inconsistent with presumed s-wave symmetry of the order parameter. The measurements were carried out in a stripline resonator at approximately 2 GHz between 1.8 K and T[subscript c]. The IMD arises from the nonlinear Meissner effect in which the penetration depth is dependent on the RF magnetic field. Specifically, the observed IMD vs temperature T for T≪T[subscript c]/2 varies as T[superscript −2], while for an s-wave gap symmetry in the clean limit, the low-temperature IMD decreases exponentially with decreasing temperature. We calculate the IMD from first principles for different order-parameter symmetries using a Green’s function approach and compare the results with the measured data. We propose that the observed upturn in the low-temperature IMD implies an admixture of an order parameter with nodal lines into the energy gaps of MgB[subscript 2]. Most likely, this admixture is prominent for the π gap. Within the constraints of the hexagonal crystal symmetry of MgB[subscript 2], the best fit with our IMD measurements is obtained with a gap Δ(ϕ,T)=Δ[subscript 0](T)sin(6ϕ), where ϕ is the azimuthal angle in the abˆ plane, and Δ[subscript 0](T) is the amplitude, weakly temperature dependent at low temperatures. This gap symmetry entails six nodal lines. We also present low-temperature penetration-depth measurements that are consistent with the proposed nodal gap symmetry. To relate our proposition with existing literature, we review other low-temperature probes of the order-parameter symmetry. The literature presents conflicting results, some of which are in direct support of the symmetry proposed here. |
| first_indexed | 2024-09-23T16:43:46Z |
| format | Article |
| id | mit-1721.1/52517 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T16:43:46Z |
| publishDate | 2010 |
| publisher | American Physical Society |
| record_format | dspace |
| spelling | mit-1721.1/525172022-10-03T07:53:29Z Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements Evidence for non-s-wave symmetry of the π gap in MgB[subscript 2] from intermodulation distortion measurements Moeckly, B. H. Agassi, Y. D. Oates, Daniel E. Lincoln Laboratory Oates, Daniel E. Oates, Daniel E. We present low-temperature low-power intermodulation-distortion (IMD) measurements of high-quality MgB[subscript 2] thin films that are inconsistent with presumed s-wave symmetry of the order parameter. The measurements were carried out in a stripline resonator at approximately 2 GHz between 1.8 K and T[subscript c]. The IMD arises from the nonlinear Meissner effect in which the penetration depth is dependent on the RF magnetic field. Specifically, the observed IMD vs temperature T for T≪T[subscript c]/2 varies as T[superscript −2], while for an s-wave gap symmetry in the clean limit, the low-temperature IMD decreases exponentially with decreasing temperature. We calculate the IMD from first principles for different order-parameter symmetries using a Green’s function approach and compare the results with the measured data. We propose that the observed upturn in the low-temperature IMD implies an admixture of an order parameter with nodal lines into the energy gaps of MgB[subscript 2]. Most likely, this admixture is prominent for the π gap. Within the constraints of the hexagonal crystal symmetry of MgB[subscript 2], the best fit with our IMD measurements is obtained with a gap Δ(ϕ,T)=Δ[subscript 0](T)sin(6ϕ), where ϕ is the azimuthal angle in the abˆ plane, and Δ[subscript 0](T) is the amplitude, weakly temperature dependent at low temperatures. This gap symmetry entails six nodal lines. We also present low-temperature penetration-depth measurements that are consistent with the proposed nodal gap symmetry. To relate our proposition with existing literature, we review other low-temperature probes of the order-parameter symmetry. The literature presents conflicting results, some of which are in direct support of the symmetry proposed here. United States Department of the Navy 2010-03-11T19:09:20Z 2010-03-11T19:09:20Z 2009-11 2009-09 Article http://purl.org/eprint/type/JournalArticle 1550-235X 1098-0121 http://hdl.handle.net/1721.1/52517 Agassi, Y. D., D. E. Oates, and B. H. Moeckly. “Evidence for non- s -wave symmetry of the pi gap in MgB2 from intermodulation distortion measurements.” Physical Review B 80.17 (2009): 174522. © 2009 The American Physical Society en_US http://dx.doi.org/10.1103/PhysRevB.80.174522 Physical Review B Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Physical Society APS |
| spellingShingle | Moeckly, B. H. Agassi, Y. D. Oates, Daniel E. Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements |
| title | Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements |
| title_full | Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements |
| title_fullStr | Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements |
| title_full_unstemmed | Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements |
| title_short | Evidence for non-s-wave symmetry of the pi gap in MgB[subscript 2] from intermodulation distortion measurements |
| title_sort | evidence for non s wave symmetry of the pi gap in mgb subscript 2 from intermodulation distortion measurements |
| url | http://hdl.handle.net/1721.1/52517 |
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