arXiv subjects

Terence M. Bretz-Sullivan

Publications and source records attributed to Terence M. Bretz-Sullivan.

3 recordsLinked to original sources

arXiv2020

Fermi surface topology and non-trivial Berry phase in the flat-band semimetal Pd$_3$Pb

A study of the Fermi surface of the putative topological semimetal Pd$_3$Pb has been carried out using Shubnikov-de Haas (SdH) oscillations measured in fields of up to 60 T. Pd$_3$Pb has garnered attention in the community due to a peculiar Fermi surface that has been proposed theoretically by Ahn, Pickett, and Lee, [Phys. Rev. B 98, 035130 (2018)] to host a dispersion-less band along $X-Γ$ as well as multiple triply-degenerate band crossings that, under the influence of spin-orbit coupling, lead to ten four-fold degenerate Dirac points. Analysis of the SdH oscillation data verifies the calculated multi-sheet Fermi surface, revealing a $Γ$ centered spheroid that had not been resolved experimentally in prior studies. A comprehensive, angle-dependent analysis of the phase of the SdH oscillations convincingly demonstrates a non-trivial Berry phase for two bands along $Γ-R$, supporting the theoretical predictions, while simultaneously evidencing interference between extremal orbits that mimics a trivial Berry phase at intermediate angles.

cond-mat.str-el↗

arXiv2020

Discovery of two-dimensional anisotropic superconductivity at KTaO$_3$ (111) interfaces

The unique electronic structure found at interfaces between materials can allow unconventional quantum states to emerge. Here we observe superconductivity in electron gases formed at interfaces between (111) oriented KTaO$_3$ and insulating overlayers of either EuO or LaAlO$_3$. The superconducting transition temperature, approaching 2.2 K, is about one order of magnitude higher than that of the LaAlO$_3$/SrTiO$_3$ system. Strikingly, similar electron gases at (001) KTaO$_3$ interfaces remain normal down to 25 mK. The critical field and current-voltage measurements indicate that the superconductivity is two dimensional. Higher mobility EuO/KTaO$_3$ (111) samples show a large in-plane anisotropy in transport properties at low temperatures prior to onset of superconductivity, suggesting the emergence of a stripe like phase where the superconductivity is nearly homogeneous in one direction, but strongly modulated in the other.

cond-mat.supr-con↗

arXiv2019

Superconductivity in the dilute single band limit in reduced Strontium Titanate

We report on superconductivity in single crystals of SrTiO$_{3-δ}$ with carrier densities $\textit{n} < 1.4 \times10^{18}cm^{-3}$, where only a single band is occupied. For all samples in this regime, the resistive transition occurs at $T_{c} \approx 65 \pm 25 \ mK$. We observe a zero resistance state for $\textit{n}$ as low as $1.03 \times10^{17}cm^{-3}$, and a partial resistive transition for $\textit{n} = 3.85 \times10^{16}cm^{-3}$. We observe low critical current densities, relatively high and isotropic upper critical fields, and an absence of diamagnetic screening in these samples. Our findings suggest an inhomogeneous superconducting state, embedded within a homogeneous high-mobility 3-dimensional electron gas. $T_{c}$ does not vary appreciably when $\textit{n}$ changes by more than an order of magnitude, inconsistent with conventional superconductivity.

cond-mat.supr-con↗