Perovskite-Oxide Based Hyperbolic Metamaterials

Abstract

We show that conducting LaxSr1-xTiO3 (LSTO) presents excellent plasmonic properties in the near-to mid-infrared region, and that these properties can be tuned with unrivalled flexibility by controlling the La composition. Taking advantage of this outstanding plasmonic response, we demonstrate a new class of hyperbolic metamaterials (HMMs) composed of LSTO/SrTiO3 (STO) epitaxial superlattices showing a high figure of merit in a spectral range not currently available with other known HMMs. The epitaxial nature of these HMMs combined with the tunability of the LSTO plasmonic response provides ultimate control on their dielectric properties, including their hyperbolic wavelength range. The epitaxial coherency and atomic level abruptness of the LSTO/STO interfaces supporting the plasmon resonances contribute to their low absorption losses. These HMMs involve individual layers with very low thicknesses (few nanometers), and can be combined by epitaxy to the many members of the functional oxide family, opening perspectives 2 for their very compact integration in multifunctional heterostructures. They can also be epitaxially grown on Si and GaAs technological platforms by epitaxy using SrTiO3/Si and SrTiO3/GaAs templates, making them perfectly suited for versatile integration in nanophotonic devices

Sensitive RHEED signature of Ti-excess enabling enhanced cationic composition control during the molecular beam epitaxy of SrTiO3 based solid solutions

“…Excellent fit of the ellipsometry data was obtained with p = 1.38 eV (2.094 x 10 15 rad.s -1 , see supplementary material). The free electron mass in LSTO is about 2.2 × m0, 42,57 where m0 = 9.11×10 -31 kg is the electronic mass, leading to a free electron concentration N of about 3.03x10 21 cm -3 (Eq.2). As every La atom delivers one free electron to the structure, 51 this corresponds to a La atomic concentration of about 18.2%, for a unit-cell volume of 59.71 Å 3 (= 3.905 2 x 3.916 Å 3 ).…”

Freestanding complex-oxide membranes

“…Surface PhPs have been recently observed in SrTiO 3 [248] in a wide range of frequencies from THz to mid-infrared. Moreover, the artificial TMO superlattices exhibit hyperbolic properties [249] which can serve as a precursor for the confined PhPs.…”

Giant Tuning of Electronic and Thermoelectric Properties by Epitaxial Strain in p-Type Sr-Doped LaCrO3 Transparent Thin Films

“…Among others, both thermoelectric oxides (TEO) and transparent conducting oxides (TCO) have attracted rising attention in the last decades because of their potential use as coolers or thermal energy harvesters which can power autonomous wireless sensor networks 1,2,3 , and/or as transparent conductors in numerous optoelectronic devices 4,5,6,7 . In the broad perovskite-oxide family of general chemical formula ABO3, in which the chemical and the resulting physical properties can be widely tuned, TCO and TEO properties can be adjusted and even both optimized in a single material, as in wellstudied titanates such as n-type La-doped SrTiO3 that can exhibit both transparency in the visibleinfrared range (more than 60%) together with high electrical conductivity and large thermoelectric power factor at room temperature (around 40 μW cm -1 K -2 ) 8,9,10,11,12,13 . These last few years, advanced n-type TCO have been intensively investigated, e.g.…”

“…Crystalline transition-metal oxides, so-called functional oxides, represent an important class of materials since they exhibit a wide range of remarkable properties useful for advanced applications such as nonvolatile memories, smart sensors, actuators, and energy harvesters. Among others, both thermoelectric oxides (TEO) and transparent conducting oxides (TCO) have attracted increasing attention in the last decades because of their potential use as coolers or thermal energy harvesters, which can power autonomous wireless sensor networks, − and/or as transparent conductors in numerous optoelectronic devices. − In the broad perovskite oxide family of general chemical formula ABO 3 , in which the chemical and the resulting physical properties can be widely tuned, the TCO and TEO properties can be adjusted and even optimized in a single material, as in well-studied titanates such as n-type La-doped SrTiO 3 that can exhibit both transparency in the visible-infrared range (more than 60%) together with high electrical conductivity and a large thermoelectric power factor at room temperature (around 40 μW cm –1 K –2 ). − In the last few years, advanced n-type TCO have been intensively investigated, e.g ., high-mobility stannates such as La-doped BaSnO 3 , whose electrical conductivity and thermoelectric properties can be tuned by aliovalent cationic substitution, − vanadates such as SrVO 3 , ,, and more recently molybdates such as SrMoO 3 . , In contrast, effective p-type TCO or transparent TEO are still to be found, which is a crucial issue for the continued development of oxide-based thermoelectric and optoelectronic devices. Sr-doped LaCrO 3 (La 1– x Sr x CrO 3 solid solutions) has shown for more than 40 years both p-type conduction and thermoelectricity, and more recently rather good optical transparency in the visible and near-infrared range .…”