Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W53: Invited Session: Discoveries in SrTiO3 |
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Sponsoring Units: DCMP Chair: Chris Leighton, University of Minnesota Room: Grand Ballroom C3 |
Thursday, March 5, 2015 2:30PM - 3:06PM |
W53.00001: Multiband superconductivity in n-doped SrTiO$_{3}$ Invited Speaker: Kamran Behnia The superconducting state of n-doped SrTiO$_{3}$ occupies a singular place in the history of superconductivity. Besides being the first oxide superconductor, it was one of the earliest ``semiconducting superconductors,'' the first experimentally-detected multi-gap superconductor and the first case of a superconducting dome. Half a century after its discovery, it remains the most dilute superconductor [1]. We present a systematic study of quantum oscillations and superconducting transition in doped SrTiO$_{3}$, over a wide range of carrier concentration from 10$^{17}$ to 10$^{20}$ cm$^{-3}$ [2]. Mobile carriers were introduced either by removing oxygen or by substituting Ti by Nb. Superconductivity was found to persists down to an exceptionally low concentration of mobile electrons (n$=$3 10$^{17}$ cm$^{-3}$ and T$_{c}=$34 mK). At this concentration range, with the Fermi temperature below 10 K, the narrowness of the relevant energy window severely restricts possible pairing scenarios. We identify two critical doping levels, which are the filling thresholds of the upper conduction bands. This clarifies the limits of single-band, two-band and three-band superconducting regimes. We find that the exceptionally-wide superconducting dome of SrTiO$_{3}$ has a structure with two distinct domes, each peaking near a critical doping level. Thermal conductivity measurements uncover the existence of multiple nodeless superconducting gaps at optimal doping [3]. \\[4pt] [1] X. Lin \textit{et al.,} Phys. Rev. X 3, 021002 (2013). \\[0pt] [2] X. Lin \textit{et al.,} Phys. Rev. Lett. \textbf{112}, 207002 (2014)\\[0pt] [3] X. Lin et al., Phys. Rev. B~\textbf{90}, 140508(R)~(2014). [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:42PM |
W53.00002: Doping and Hall effect in SrTiO$_{3}$ Invited Speaker: Susanne Stemmer Electron-doped SrTiO$_{3}$ has generated renewed interest because of reports of coexisting magnetism and superconductivity, and of superconducting transitions at extremely low carrier densities. In this talk, we will present new insights into doping and its electronic structure obtained using very high quality SrTiO$_{3}$ films grown by molecular beam epitaxy. We discuss the arrangements and imaging of individual La dopant atoms and clusters using quantitative scanning transmission electron microscopy. We present studies of the temperature dependence of the Hall coefficient, Hall mobility, and of Shubnikov-de Haas oscillations. We will particularly discuss the significance of the regime in which the resistance follows a $T^{2}$ temperature-dependence over a wide range of temperatures and doping. \\[4pt] This work was performed in collaboration with Evgeny Mikheev, Adam Kajdos, Jinwoo Hwang, Jack Zhang, and Jim Allen. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 4:18PM |
W53.00003: Optically-Induced Persistent Magnetization in Oxygen Deficient Strontium Titanate Invited Speaker: Scott Crooker Interest in electronics and spintronics based on complex oxide materials has exploded in recent years, fueled by the ability to grow atomically-precise heterostructures of various oxides [1]. A foundational material in this burgeoning field is strontium titanate, a (nominally) non-magnetic wide-bandgap semiconductor. Owing to its ubiquity in oxide materials science, studies of SrTiO$_3$'s interesting dielectric, lattice, and optical properties represent mature research areas. However, renewed interest in SrTiO$_3$ was recently sparked by observations of unexpected {\it spin and magnetization} phenomena at interfaces between SrTiO$_3$ and other nonmagnetic oxides [1]. The formation and distribution of oxygen vacancies ($V_O$) in SrTiO$_3$ are widely thought to play an essential but as-yet-incompletely understood role in these emergent phenomena. Here we demonstrate a surprising new aspect to the phenomenology of magnetism in SrTiO$_3$ by reporting the observation of an optically-induced and persistent magnetization in slightly oxygen-deficient SrTiO$_{3-\delta}$ bulk crystals, using magnetic circular dichroism spectroscopy and optically-coupled SQUID studies [2]. This magnetization appears below 18K, persists for hours below 10K, and is tunable via the polarization and wavelength of sub-bandgap (400-500 nm) light. As such, magnetic patterns can be ``written'' into SrTiO$_{3-\delta}$, and subsequently read out, using light alone. This magnetism occurs only in crystals containing $V_O$, and is consistent with a metastable spin polarization of $V_O$-related defect complexes. These data reveal a detailed interplay between magnetism, lattice defects, and light in an archetypal complex oxide material, which may yield new insights into the recent exciting spin physics observed at oxide interfaces. \\[4pt] [1] see, {\it e.g.}: H.Y. Hwang {\it et al.}, Nat. Mater. {\bf 11}, 103 (2012); J. Mannhart \& D.G. Schlom, Science {\bf 327}, 1607 (2010); MRS Bulletin {\bf 38}, 1017 (2013).\\[0pt] [2] W.D. Rice, P. Ambwani, M. Bombeck, J.D. Thompson, G. Haugstad, C. Leighton \& SC, Nat. Mater. {\bf 13}, 481 (2014); ibid, J.Vac. Sci. Tech. B {\bf 32}, 04E102 (2014). [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:54PM |
W53.00004: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 4:54PM - 5:30PM |
W53.00005: Spectroscopic findings in SrTiO$_{3}$ applications: LaAlO$_{3}$/SrTiO$_{3}$ and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$ heterostructures Invited Speaker: Jun-Sik Lee Recently, a number of transport and magnetization studies have shown signs of exotic functionalities in SrTiO$_{3}$ based heterostructures, which are totally unexpected properties with no bulk analog in the constituent materials. However, it is still early stage to understand such a functionality, which limits improving SrTiO$_{3}$ applications. For this reason, we performed spectroscopic studies on the SrTiO$_{3}$ based heterostructures, such as LaAlO$_{3}$/SrTiO$_{3}$ and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$ using element-specific techniques. For example, we found direct evidence for in-plane ferromagnetic order at the interface, with Ti$^{3+}$ character in the $d_{xy}$ orbital of the anisotropic $t_{2g}$ band in LaAlO$_{3}$/SrTiO$_{3}$ heterostructure. Also, we found that the unexpected metal to insulator transition in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$ is due to changes in Mn 3$d$-electron confinement. These findings establish a striking example of emergent phenomena at oxide interfaces. In this presentation, I will introduce more details of spectroscopic findings on those heterostructures. [Preview Abstract] |
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