23 research outputs found
Intense terahertz radiation via the transverse thermoelectric effect
Terahertz (THz) radiation is a powerful tool with widespread applications
ranging from imaging, sensing, and broadband communications to spectroscopy and
nonlinear control of materials. Future progress in THz technology depends on
the development of efficient, structurally simple THz emitters that can be
implemented in advanced miniaturized devices. Here we show how the natural
electronic anisotropy of layered conducting transition metal oxides enables the
generation of intense terahertz radiation via the transverse thermoelectric
effect. In thin films grown on offcut substrates, femtosecond laser pulses
generate ultrafast out-of-plane temperature gradients, which in turn launch
in-plane thermoelectric currents, thus allowing efficient emission of the
resulting THz field out of the film structure. We demonstrate this scheme in
experiments on thin films of the layered metals PdCoO2 and La1.84Sr0.16CuO4,
and present model calculations that elucidate the influence of the material
parameters on the intensity and spectral characteristics of the emitted THz
field. Due to its simplicity, the method opens up a promising avenue for the
development of highly versatile THz sources and integrable emitter elements.Comment: 27 pages, 11 figure
Transparent EuTiO3 films : a possible two-dimensional magneto-optical device
The magneto-optical activity of high quality transparent thin films of insulating EuTiO3 (ETO) deposited on a thin SrTiO3 (STO) substrate, both being non-magnetic materials, are demonstrated to be a versatile tool for light modulation. The operating temperature is close to room temperature and allows for multiple device engineering. By using small magnetic fields birefringence of the samples can be switched off and on. Similarly, rotation of the sample in the field can modify its birefringence În. In addition, În can be increased by a factor of 4 in very modest fields with simultaneously enhancing the operating temperature by almost 100 K
Fano interference of the Higgs mode in cuprate high-Tc superconductors
Despite decades of search for the pairing boson in cuprate high-Tc
superconductors, its identity still remains debated to date. For this reason,
spectroscopic signatures of electron-boson interactions in cuprates have always
been a center of attention. For example, the kinks in the quasiparticle
dispersion observed by angle-resolved photoemission spectroscopy (ARPES)
studies have motivated a decade-long investigation of electron-phonon as well
as electron-paramagnon interactions in cuprates. On the other hand, the overlap
between the charge-order correlations and the pseudogap in the cuprate phase
diagram has also generated discussions about the potential link between them.
In the present study, we provide a fresh perspective on these intertwined
interactions using the novel approach of Higgs spectroscopy, i.e. an
investigation of the amplitude oscillations of the superconducting order
parameter driven by a terahertz radiation. Uniquely for cuprates, we observe a
Fano interference of its dynamically driven Higgs mode with another collective
mode, which we reveal to be charge density wave fluctuations from an extensive
doping- and magnetic field-dependent study. This finding is further
corroborated by a mean field model in which we describe the microscopic
mechanism underlying the interaction between the two orders. Our work
demonstrates Higgs spectroscopy as a novel and powerful technique for
investigating intertwined orders and microscopic processes in unconventional
superconductors
Precise control of atoms with MBE: from semiconductors to complex oxides
Molecular Beam Epitaxy (MBE) is a high-vacuum technique with atomic-layer control and precision. It is based on the chemical reaction of the atoms, molecules, or atomic clusters vaporized from the specific evaporation sources on the substrates. The molecular beam defines a unidirectional ballistic flow of atoms and/or molecules without any collisions amongst. In the late 1960s, MBE was initially developed for the growth of GaAs and (Al, Ga)As systems[1,2] due to the unprecedented capabilities and then was applied to study other material systems. MBE growth is conventionally performed in vacuum and ultra-high vacuum (UHV) (10-8â10-12 mbar) conditions
Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy
In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE) which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2âxSrxNiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control
The Superconducting Dome in Artificial High-<i>T<sub>c</sub></i> Superlattices Tuned at the FanoâFeshbach Resonance by Quantum Design
While the search for new high-temperature superconductors had been driven by the empirical âtrials and errorsâ method for decades, we now report the synthesis of Artificial High-Tc Superlattices (AHTS) designed by quantum mechanics theory at the nanoscale. This discovery paves the way for engineering a new class of high-temperature superconductors, following the predictions of the Bianconi Perali Valletta (BPV) theory recently implemented in 2022 by Mazziotti et al. including Rashba spin-orbit coupling to create nanoscale AHTS composed of quantum wells. The high-Tc superconducting properties within these superlattices are controlled by a conformational parameter of the superlattice geometry, specifically, the ratio L/d which represents the thickness of La2CuO4 layers (L) relative to the superlattice period (d). Using molecular beam epitaxy, we have successfully grown numerous AHTS samples. These samples consist of initial layers of stoichiometric La2CuO4 units with a thickness L, doped by interface space charge, and intercalated with second layers of non-superconducting metallic material, La1.55Sr0.45CuO4 with thickness denoted as W = d â L. This configuration forms a quantum superlattice with periodicity d. The agreement observed between the experimental dependence Tc (the superconducting transition temperature) versus L/d ratio and the predictions of the BPV theory for AHTS in the form of the superconducting dome validates the hypothesis that the superconducting dome arises from the FanoâFeshbach or shape resonance in multigap superconductivity driven by quantum nanoscale confinement
Nonequilibrium Phase Transitions in Cuprates Observed by Ultrafast Electron Crystallography
Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable âstructural isosbesticâ point and a threshold effect for the dependence of c-axis expansion (Îc) on fluence (F), with Îc/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at âź0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity
Engineering interfaces in cuprate superconductors
International Conference on Strongly Correlated Electron Systems (SCES 2007), Houston, TX, MAY 13-18, 2007International audienceUsing an advanced molecular beam epitaxy system for atomic-layer engineering of complex oxides, we have fabricated a variety of superlattices with stacked layers of La2-xSrxCuO4 doped to different levels. In superlattices formed by stacking highly overdoped, metallic La1.5Sr0.5CuO4 and insulating La2CuO4 layers we have observed superconductivity at temperature as high as 30 K, even though neither of the building blocks was superconducting. Different possible mechanisms of this superconductivity are discussed. (C) 2007 Elsevier B.V. All rights reserved