Enhancing superconductivity in SrTiO
            <sub>3</sub>
            films with strain

Ahadi, Kaveh; Galletti, Luca; Li, Yuntian; Salmani-Rezaie, Salva; Wu, Wangzhou; Stemmer, Susanne

doi:10.1126/sciadv.aaw0120

Cited by 163 publications

(149 citation statements)

References 46 publications

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“…The T C values [ Fig. 1(a)] are in agreement with values previously reported for strained, doped films on LSAT [28]. Enhanced T C values (up to 600 mK) near the peak of the superconducting dome relative to unstrained, doped SrTiO 3 are directly connected to the ferroelectric normal state, as shown elsewhere [28,29].…”

supporting

confidence: 89%

Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 films

et al. 2020

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Superconductors that possess both broken spatial inversion symmetry and spin-orbit interactions exhibit a mix of spin singlet and triplet pairing. Here, we report on measurements of the superconducting properties of electron-doped, strained SrTiO 3 films. These films have an enhanced superconducting transition temperature and were previously shown to undergo a transition to a polar phase prior to becoming superconducting. We show that some films show signatures of an unusual superconducting state, such as an in-plane critical field that is higher than both the paramagnetic and orbital pair breaking limits. Moreover, nonreciprocal transport, which reflects the ratio of odd vs. even pairing interaction, is observed. Together, these characteristics indicate that these films provide a tunable platform for investigations of unconventional superconductivity.

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confidence: 89%

Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 films

et al. 2020

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“…The superconducting critical temperatures, measured in Ref. 17, are for the same films studied in this work. The phase diagram shows the well-known superconducting "dome" [1] in close proximity to the quantum critical point of the spontaneous ferroelectric order.…”

Section: Interplay Between Ferroelectricity and Superconductivitymentioning

confidence: 93%

“…Further details of film growth and transport measurements are described in Ref. 17. Optical SHG experiments were performed using an ultrafast laser supplying 40-fs pulses at a 10-kHz repetition rate and a center wavelength of 800 nm.…”

Section: Samarium-dopedmentioning

confidence: 99%

“…In thin films, epitaxial * These authors contributed equally to this work. † Corresponding author: harter@ucsb.edu strain is also known to stabilize ferroelectricity [13][14][15][16], and a striking recent study has shown that in-plane compressive strain can enhance the superconducting critical temperature by up to a factor of two [17]. To establish a clear link between this superconducting enhancement and ferroelectricity, here we directly measure the ferroelectric order parameter of compressively strained films of electron-doped SrTiO 3 .…”

Section: Introductionmentioning

confidence: 99%

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Ferroelectric enhancement of superconductivity in compressively strained SrTiO3 films

Russell

Ratcliff

Ahadi

et al. 2019

Phys. Rev. Materials

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SrTiO3 is an incipient ferroelectric on the verge of a polar instability, which is avoided at low temperatures by quantum fluctuations. Within this unusual quantum paraelectric phase, superconductivity persists despite extremely dilute carrier densities. Ferroelectric fluctuations have been suspected to play a role in the origin of superconductivity by contributing to electron pairing. To investigate this possibility, we used optical second harmonic generation to measure the doping and temperature dependence of the ferroelectric order parameter in compressively strained SrTiO3 thin films. At low temperatures, we uncover a spontaneous out-of-plane ferroelectric polarization with an onset that correlates perfectly with normal-state electrical resistivity anomalies. These anomalies have previously been associated with an enhancement of the superconducting critical temperature in doped SrTiO3 films, directly linking the ferroelectric and superconducting phases. We develop a long-range mean-field Ising model of the ferroelectric phase transition to interpret the data and extract the relevant energy scales in the system. Our results support a long-suspected connection between ferroelectricity and superconductivity in SrTiO3, but call into question the role played by ferroelectric fluctuations.

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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].…”

Section: Introductionmentioning

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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Enhancing superconductivity in SrTiO ₃ films with strain

Cited by 163 publications

References 46 publications

Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 films

Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 films

Ferroelectric enhancement of superconductivity in compressively strained SrTiO3 films

Charge transport in a polar metal

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Enhancing superconductivity in SrTiO 3 films with strain

Cited by 163 publications

References 46 publications

Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 films

Possible signatures of mixed-parity superconductivity in doped polar SrTiO3 films

Ferroelectric enhancement of superconductivity in compressively strained SrTiO3 films

Charge transport in a polar metal

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Enhancing superconductivity in SrTiO ₃ films with strain