arXiv subjects

Chloe Herrera

Publications and source records attributed to Chloe Herrera.

4 recordsLinked to original sources

arXiv2021

Scanning SQUID characterization of extremely overdoped $La_{2-x}Sr_{x}CuO_{4}$

Recently, advances in film synthesis methods have enabled a study of extremely overdoped $La_{2-x}Sr_{x}CuO_{4}$. This has revealed a surprising behavior of the superfluid density as a function of doping and temperature, the explanation of which is vividly debated. One popular class of models posits electronic phase separation, where the superconducting phase fraction decreases with doping, while some competing phase (e.g. ferromagnetic) progressively takes over. A problem with this scenario is that all the way up to the dome edge the superconducting transition remains sharp, according to mutual inductance measurements. However, the physically relevant scale is the Pearl penetration depth, $Λ_{P}$, and this technique probes the sample on a length scale $L$ that is much larger than $Λ_{P}$. In the present paper, we use local scanning SQUID measurements that probe the susceptibility of the sample on the scale $L << Λ_{P}$. Our SQUID maps show uniform landscapes of susceptibility and excellent overall agreement of the local penetration depth data with the bulk measurements. These results contribute an important piece to the puzzle of how high-temperature superconductivity vanishes on the overdoped side of the cuprates phase diagram.

cond-mat.supr-con↗

arXiv2019

A local maximum in the superconducting transition temperature of Nb-doped strontium titanate under uniaxial compressive stress

Superconducting strontium titanate (STO) is in the spotlight as a low carrier concentration semiconductor in proximity to polar order. Its superconducting pairing mechanism poses an open fundamental challenge, which may be resolved by controlling how strongly the superconducting and polar orders interact. Here, we show for the first time that non-monotonic superconducting transition temperature behavior in uniaxially compressed STO can occur, revealing a reduction followed by a peak in the superconducting transition temperature. The corresponding displacements in the lattice are extremely small, in the sub picometer range, indicating that this material approaches a singularity in electron-phonon coupling, consistent with STO transforming to the polar (ferroelectric) phase that influences the superconductivity.

cond-mat.supr-con↗

arXiv2019

Precision measurements of the AC field dependence of the superconducting transition in strontium titanate

Strontium titanate has resurfaced as a material prompting vigorous debate about the origin of its superconductivity in the extremely low carrier concentration regime. Here, we used simultaneous AC susceptibility and transport methods to explore the superconducting phase transition region in this material. We determined that strontium titanate is extremely sensitive to even small AC fields, which also influence the resistive transition; we suggest that extreme vortex sizes and mobilities contribute to this large effect. Our findings will be of importance for accurately determining transition temperature, informing the debate about the pairing mechanism in strontium titanate, for which even millikelvin errors may be critical.

cond-mat.supr-con↗

arXiv2019

Strain-engineered interaction of quantum polar and superconducting phases

Much of the focus of modern condensed matter physics concerns control of quantum phases with examples that include flat band superconductivity in graphene bilayers, the interplay of magnetism and ferroelectricity, and induction of topological transitions by strain. Here we report the first observation of a reproducible and strong enhancement of the superconducting critical temperature, $T_c$, in strontium titanate (SrTiO3) obtained through careful strain engineering of interacting superconducting phase and the polar quantum phase (quantum paraelectric). Our results show a nearly 50% increase in $T_c$ with indications that the increase could become several hundred percent. We have thus discovered a means to control the interaction of two quantum phases through application of strain, which may be important for quantum information science. Further, our work elucidates the enigmatic pseudogap-like and preformed electron pairs phenomena in low dimensional strontium titanate as potentially resulting from the local strain of jammed tetragonal domains.

cond-mat.supr-con↗