Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A45: Quantum Criticality, Superconductivity and Topology in Ferroelectric MetalsInvited Live Streamed
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Avraham Klein, Ariel University Room: McCormick Place W-375D |
Monday, March 14, 2022 8:00AM - 8:36AM |
A45.00001: Theory of superconductivity mediated by soft polar modes in incipient ferroelectrics Invited Speaker: Maria Navarro Gastiasoro Experimental evidence suggests that superconductivity in SrTiO3 is mediated by a soft transverse ferroelectric mode which, according to conventional theories, has negligible coupling with electrons. A phenomenological Rashba type coupling has been proposed on symmetry arguments but a microscopic derivation is lacking. Here we fill this gap and obtain a linear coupling directly from a minimal microscopic model of the electronic structure. We find that the effective electron-electron pairing interaction has a strong momentum dependence. This yields an unusual situation in which the leading s-wave channel is followed by a sub-leading p-wave state which shows a stronger pairing instability than the d-wave state. The bare Rashba coupling constant is estimated for the lowest band of doped SrTiO3 with the aid of first-principles computations and found to be much larger than previously thought. We argue that although for a uniform system the BCS coupling λ is small, it can produce the right order of magnitude for Tc in the presence of structural inhomogeneities. Finally, following an analogous method, we discuss the relevance of the quadratic coupling to the soft polar mode in this system. |
Monday, March 14, 2022 8:36AM - 9:12AM |
A45.00002: Polar Order and Superconductivity in SrTiO3 Invited Speaker: Susanne Stemmer Currently, there exist many different theoretical proposals that link ferroelectricity and superconductivity in SrTiO3. This talk will focus on our experiments on strained SrTiO3 films, which can undergo successive ferroelectric and superconducting transitions, resulting in a factor of two enhancement of the superconducting transition temperature. The ferroelectric transition is an order-disorder transition and local polar order persists to temperatures far above the ferroelectric transition and exist even in unstrained SrTiO3. We show that these local polar regions, along with superconductivity, are suppressed in the over-doped regime. We show that local polar order is key to the enhanced superconducting transition temperature. We also discuss recent insights into the nature of the superconducting state, including its surprising robustness against alloying with large concentrations of magnetic elements. |
Monday, March 14, 2022 9:12AM - 9:48AM |
A45.00003: Theory of superconductivity due to quadratic coupling to near-critical transverse phonons. Invited Speaker: Mikhail V Feigelman Superconductivity near the quantum ferroelectric critical point is the subject of active research due to both conceptual interest in systems with competing order parameters, and practical need to understand peculiar superconductivity in very diluted metal Strontium Titanate (STO) , which keeps being superconducting down to tiny concentrations ~ 10^17 electrons per cubic centimeters. Fermi energy is much below Debye energy in so much diluted metal, rendering classical Migdal-Eliashberg approach to phonon-induced superconductivity inapplicable. Surprisingly enough, the first microscopic theory of superconductivity, developed by Bardeen, Cooper and Schrieffer, is strongly relevant to this case. I will show that interaction of electron density with a pair of two (virtual) soft transverse optical phonons [1] leads to static attractive potential between electrons whose decay length scales inversely with soft optical gap. in pristine STO this length is close to 3 nm, thus dilute metal with concentration below 10^18 can be considered as a Fermi-gas with local attraction, those superconductivity was treated in details in Ref.[2]. The proposed model leads to the dependence of critical temperature in electron concentration in agreement with experimental data [3] for low doping. In addition, I will show that suppression of Tc by hydrostatic pressure [4] and strong increase of Tc due to isotopic substitution 16 O →18 O observed in [5] are both explained within the same theory. The talk is based upon the results published in [6]. |
Monday, March 14, 2022 9:48AM - 10:24AM |
A45.00004: Tuning from ferroelectric topological insulator to superconductor in (Pb,Sn,In)Te Invited Speaker: John M Tranquada At low temperature, SnTe is both a ferroelectric and a topological crystalline insulator. One can tune both the bulk insulating (and conducting surface) character and achieve a superconducting state, with a transition as high as 4.7 K, by partial substitution of Pb and In for Sn. Our neutron scattering measurements confirm the soft zone-center transverse-optical phonon in superconducting (Pb,Sn,In)Te, making it similar to the case of doped SrTiO3. Intriguingly, in the case of Pb0.5Sn0.5Te, superconductivity is only observed when sufficient In is substituted to push the system into an electron-doped regime, where the normal-state resistivity is non-metallic and larger than that for SrTiO3 when doped into its regime of superconductivity. This unexpected combination of features is in need of an explanation. |
Monday, March 14, 2022 10:24AM - 11:00AM |
A45.00005: Superconductivity in low-density Dirac materials Invited Speaker: Vladyslav Kozii The experimental observation of superconductivity in doped semimetals and semiconductors, where the Fermi energy is comparable to or smaller than the characteristic phonon frequencies, is not captured by the standard lore. I present a mechanism for superconductivity in low-density three-dimensional Dirac materials that are close to a ferroelectric quantum critical point. I show that while the Coulomb repulsion between electrons is strongly screened by the lattice polarization near the critical point, the electron-phonon coupling is significantly increased by critical fluctuations, even in the case of vanishing carrier density. Applying these results to low-density systems, I show that the superconducting transition temperature is strongly enhanced upon approaching the quantum critical point. Furthermore, I will demonstrate that at vanishing electron density the ferroelectric transition is preempted by a new ferroelectric density wave order, which breaks translational symmetry in addition to inversion. This new quantum critical point significantly enhances soft phonon fluctuations, resulting in a strong pairing interaction that can drive a superconducting instability even at vanishing carrier density. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700