Light and warm superconductors versus hole superconductors

  • NEST Seminar
Speaker
Jorge E. Hirsch
Affiliation
Department of Physics, University of California San Diego
Date
2023-07-04
Time
11:00
Venue
ONLY ONSITE: NEST meeting room
Host
Francesco Giazotto
Abstract:
The conventional (BCS) theory of superconductivity predicts that superconductivity is caused by the electron-phonon interaction, giving rise to high critical temperatures for materials with light ions. In particular, hydrogen-rich materials under high pressure are predicted to be high Tc superconductors, and during the last 8 years 15 different such hydrides have been claimed to be superconductors with Tc's exceeding those of the high Tc cuprates [1], up to and above room temperature [2]. Many other light-element compounds have been predicted to be high Tc superconductors by analogy with MgB2. However I will argue that the experimental evidence for these claims is faulty [3], and that in fact to date the experimental evidence that light elements favor high temperature superconductivity is non-existent [4]. If what I am arguing is true, it indicates that there is a fundamental flaw in the BCS assumption that the electron-phonon interaction causes superconductivity. I will discuss the alternative theory of hole superconductivity proposed to apply to all superconductors [5], that predicts that high temperature superconductivity results from holes conducting through closely spaced negatively charged anions, as is the case in the cuprates, pnictides, and MgB2, and that the ionic mass is irrelevant. It also explains the Meissner effect, which I claim BCS theory does not and cannot explain. I will discuss predictions of the theory that have been experimentally verified, predictions that have not yet been tested experimentally that would validate the theory if verified, and guidelines for the search for higher temperature superconducting materials arising from this theory.
[1] Warren Pickett and Mikhail Eremets, “The quest for room-temperature superconductivity in hydrides”, Physics Today 72, 52–58 (2019).
[2] N. Dasenbrock-Gammon et al, “Evidence of near-ambient superconductivity in a N-doped lutetium hydride”, Nature 615, 244–250 (2023).
[3] J. E. Hirsch, “Electrical resistance of hydrides under high pressure: evidence of superconductivity or confirmation bias?”, https://osf.io/g7hyc (2023) and references therein. 
[4] J. E. Hirsch, “Superconducting materials: Judge and jury of BCS-electron–phonon theory”, Appl. Phys. Lett. 121, 080501 (2022).
[5] References in https://jorge.physics.ucsd.edu/hole.html

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Istituto Nanoscienze Consiglio Nazionale delle Ricerche

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Pisa NEST

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56127 Pisa

phone +39 050 509525/418

fax +39 050 509550

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via Campi 213/A, I 

41125 Modena 7

phone +39 059 2055629

fax +39 059 2055651″