Unusual superconducting isotope effect in the presence of a quantum criticality

Kedem, Yaron; Zhu, Jian‐Xin; Balatsky, Alexander V.

doi:10.1103/physrevb.93.184507

Cited by 20 publications

(27 citation statements)

References 32 publications

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“…[19], FE modes close to a quantum critical point (QCP) were suggested as the source of SC and used to explain the vanishing SC for increased levels of doping. An unusual isotope effect was proposed as a method to study the phenomenology of the critical behavior [20] and was experimentally observed [21], supporting the connection of SC to the QCP. The coexistence of FE and SC was observed [22] and strain was also proposed as a tuning parameter [23] and experimentally investigated [24].…”

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confidence: 86%

Novel pairing mechanism for superconductivity at a vanishing level of doping driven by critical ferroelectric modes

Kedem

2018

Phys. Rev. B

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Superconductivity (SC) occurring at low densities of mobile electrons is still a mystery since the standard theories do not apply in this regime. We address this problem by using a microscopic model for ferroelectric (FE) modes, which mediate an effective attraction between electrons. When the dispersion of modes, around zero momentum, is steep, forward scattering is the main pairing process and the self-consistent equation for the gap function can be solved analytically. The solutions exhibit unique features: Different momentum components of the gap function are decoupled, and at the critical regime of the FE modes, different frequency components are also decoupled. This leads to effects that can be observed experimentally: The gap function can be nonmonotonic in temperature and the critical temperature can be independent of the chemical potential. The model is applicable to lightly doped polar semiconductors, in particular, strontium titanate.

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confidence: 86%

Novel pairing mechanism for superconductivity at a vanishing level of doping driven by critical ferroelectric modes

Kedem

2018

Phys. Rev. B

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“…Electron-doped STO is one of the most dilute superconductors known [103,104], and most likely a non-BCS mechanism is necessary for its explanation More recently a gate-tunable insulatingsuperconducting transition has been observed in an STO weak link [105], again pointing to anomalous behavior in this material. The dependence of the superconducting T c on the percentage of 18 0 in the STO is an active topic of theoretical [106,107] and experimental [108] research. We will return to the question of superconductivity in STO in the "Open Questions" section.…”

Section: The Case Of Srt Io 3 To Datementioning

confidence: 99%

Prospects and applications near ferroelectric quantum phase transitions: a key issues review

et al. 2017

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The emergence of complex and fascinating states of quantum matter in the neighborhood of zero temperature phase transitions suggests that such quantum phenomena should be studied in a variety of settings. Advanced technologies of the future may be fabricated from materials where the cooperative behavior of charge, spin and current can be manipulated at cryogenic temperatures. The progagating lattice dynamics of displacive ferroelectrics make them appealing for the study of quantum critical phenomena that is characterized by both space- and time-dependent quantities. In this key issues article we aim to provide a self-contained overview of ferroelectrics near quantum phase transitions. Unlike most magnetic cases, the ferroelectric quantum critical point can be tuned experimentally to reside at, above or below its upper critical dimension; this feature allows for detailed interplay between experiment and theory using both scaling and self-consistent field models. Empirically the sensitivity of the ferroelectric T 's to external and to chemical pressure gives practical access to a broad range of temperature behavior over several hundreds of Kelvin. Additional degrees of freedom like charge and spin can be added and characterized systematically. Satellite memories, electrocaloric cooling and low-loss phased-array radar are among possible applications of low-temperature ferroelectrics. We end with open questions for future research that include textured polarization states and unusual forms of superconductivity that remain to be understood theoretically.

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“…For example, Raman scattering found that the hardening of the FE soft mode in the dilute metal is indistinguishably similar to what is seen in the insulator [21]. The anomaly in resistivity was found to terminate at a threshold carrier density (n * ), near which the superconducting transition temperature was enhanced [21] providing evidence for a link between superconducting pairing and ferroelectricity, a subject of present attention [22][23][24][25][26][27][28][29][30][31][32].…”

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confidence: 98%

Charge transport in a polar metal

et al. 2019

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The fate of electric dipoles inside a Fermi sea is an old issue, yet poorly-explored. Sr1−xCaxTiO3 hosts a robust but dilute ferroelectricity in a narrow (0.002 < x < 0.02) window of substitution. This insulator becomes metallic by removal of a tiny fraction of its oxygen atoms. Here, we present a detailed study of low-temperature charge transport in Sr1−xCaxTiO 3−δ , documenting the evolution of resistivity with increasing carrier concentration (n). Below a threshold carrier concentration, n * (x), the polar structural phase transition has a clear signature in resistivity and Ca substitution significantly reduces the 2 K mobility at a given carrier density. For three different Ca concentrations, we find that the phase transition fades away when one mobile electron is introduced for about 7.9±0.6 dipoles. This threshold corresponds to the expected peak in anti-ferroelectric coupling mediated by a diplolar counterpart of Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Our results imply that the transition is driven by dipole-dipole interaction, even in presence of a dilute Fermi sea. At higher carrier concentrations, our data resolves slight upturns in low-temperature resistivity in both Ca-free and Ca-substituted samples, reminiscent of Kondo effect and most probably due to oxygen vacancies.arXiv:1909.04278v1 [cond-mat.supr-con]

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Unusual superconducting isotope effect in the presence of a quantum criticality

Cited by 20 publications

References 32 publications

Novel pairing mechanism for superconductivity at a vanishing level of doping driven by critical ferroelectric modes

Novel pairing mechanism for superconductivity at a vanishing level of doping driven by critical ferroelectric modes

Prospects and applications near ferroelectric quantum phase transitions: a key issues review

Charge transport in a polar metal

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