Engineering topics

Jeong, Hanbyeol

Publications and source records attributed to Jeong, Hanbyeol.

6 records

DOE OSTI2024

Coexistence of antiferrodistortive and polar order in a superconducting SrTi⁢O 3 film

Strontium titanate (SrTiO 3 ) can exhibit multiple orders, including superconductivity, an antiferrodistortive instability and ferroelectricity. The cooperation or competition between these orders in samples that undergo all three transitions is of great fundamental interest. Here we report scanning transmission electron microscopy imaging of the antiferrodistortive and ferroelectric structural distortions in a compressively strained SrTiO 3 film that was previously shown to become superconducting at ~ 410 mK. The experiments are complemented by first-principles simulations. Unlike the polar ferroelectric phase, which is suppressed by dopants, the antiferrodistortive order is insensitive to the presence of the free carriers. The single domain nature of the antiferrodistortive phase excludes any role of antiferrodistortive domain walls in the superconductivity. Furthermore, a previously reported low temperature resistance anomaly is associated with the ferroelectric transition, not the antiferrodistortive transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Anomalous superconducting diode effect in a polar superconductor

A superconductor with broken time-reversal and inversion symmetry may exhibit nonreciprocal charge transport, including a nonreciprocal critical current, also known as superconducting diode effect. Here, we report an intrinsic superconducting diode effect in a polar strontium titanate film. Differential resistance measurements reveal a superconducting state whose depairing current is polarity dependent. There is, however, no measurable deviation from Ohmic behavior, implying that this state does not arise from a bulk magnetochiral anisotropy. In the entire measurement range, the only deviation from linearity in the differential resistance is on the edge of the superconducting transition at high magnetic fields, likely due to the motion of flux vortices. Furthermore, the magnitude of the effect is preserved even when the in-plane magnetic field is oriented parallel to the current, indicating that this effect truly does not originate from a bulk magnetochiral anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Ferroelectricity and superconductivity in strained Eu x Sr 1 – x TiO 3 films

The superconducting transition of SrTiO 3 can be influenced by tuning its ferroelectric transition, but the underlying reasons remain poorly understood. Here, we investigate compressively strained, Sm-doped films of Eu x Sr 1-x TiO 3 that were grown by molecular beam epitaxy to determine the effect of alloying with Eu on both superconductivity and ferroelectricity, both of which are present in strained SrTiO 3 films. Remarkably, superconductivity survives up to x = 0.14. Films at the lowest alloy concentration studied here, x = 0.09, exhibit no suppression of their superconducting transition temperature, but a strong reduction of the upper critical field (H c2 ), compared to non-alloyed, strained SrTiO 3 films. In addition, these films lack the sharp ferroelectric transition that appears in films without Eu in second harmonic generation measurements. Here, we postulate that Eu-alloying causes a crossover from a globally ordered ferroelectric state to one with only short-range polar order. We discuss the connection between the loss of global polar order and the change in the superconducting properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Similarity in the critical thicknesses for superconductivity and ferroelectricity in strained SrTiO 3 films

The possible connection between superconductivity and polar order in SrTiO 3 has been discussed extensively in the recent literature. Here, the thickness dependence of the superconducting and ferroelectric transitions in strained, epitaxial films of SrTiO 3 films is studied. Both superconductivity and ferroelectricity are absent in thinner films (25 nm and below). Here, we discuss the possible origins of the thickness dependence of both phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Role of locally polar regions in the superconductivity of SrTiO 3

Understanding the interaction between polar and superconducting order parameters may hold the key to several classes of superconductors that remain poorly understood, including SrTiO 3 and several tellurides. Here we show that doped, strained SrTiO 3 films can exhibit both global or local polar order, respectively, depending on the amount of epitaxial mismatch strain, thereby providing a platform to understand how inversion symmetry breaking affects superconductivity. We find that the superconducting critical temperature correlates with the length scale of polar order. In particular, the transition temperature is enhanced when polar nanodomains are sufficiently large or, in the extreme limit, films are globally ferroelectric. In these cases, the Cooper pairs reside in a noncentrosymmetric environment. Conversely, low transition temperatures are found when the nanodomains are small. The findings point to the length scale of polar nanodomains and spin-orbit coupling as important parameters controlling the superconductivity of SrTiO 3 . Furthermore, the ability to control the size of the polar domains opens up new opportunities to design and control the nature of superconductivity in a wide range of materials.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Superconductivity in magnetically doped SrTiO 3

Doped SrTiO 3 is a superconductor whose pairing mechanism is still not fully understood. The response of a superconductor to impurities has long been used to obtain insights into the nature of the superconducting state. In this work, we investigate the superconductivity of SrTiO 3 films that are doped or alloyed with different rare earth ions, which carry a magnetic moment.. It is shown that large concentrations (up to a few percent) of rare earth ions with unpaired f-electrons, such as Sm and Eu, do not reduce the superconducting critical temperature and critical fields. The finding is independent of whether the rare earth ion acts as a dopant or is an isovalent impurity. The interactions between the superconducting condensate and the magnetic dopants that could result in the observed insensitivity to magnetic impurities are discussed.

36 MATERIALS SCIENCE↗