Dielectric properties of single crystals of Al/sub 2/O/sub 3/, LaAlO/sub 3/, NdGaO/sub 3/, SrTiO/sub 3/, and MgO at cryogenic temperatures

Křupka, J.; Geyer, Richard G.; Kuhn, Manuela; Hinken, J.H.

doi:10.1109/22.320769

Cited by 219 publications

(90 citation statements)

References 8 publications

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“…Two bands are plotted, the colored one uses a range in C, the striped one a range in α and (see appendix). The bulk dielectric constant of LAO is about 24 26 . It may be substantially different for a strained ultra-thin film (see ref.…”

Section: Discussionmentioning

confidence: 99%

Surface defects and conduction in polar oxide heterostructures

2011

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The polar interface between LaAlO3 and SrTiO3 has shown promise as a field effect transistor, with reduced (nanoscale) feature sizes and potentially added functionality over conventional semiconductor systems. However, the mobility of the interfacial two-dimensional electron gas (2DEG) is lower than desirable. Therefore to progress, the highly debated origin of the 2DEG must be understood. Here we present a case for surface redox reactions as the origin of the 2DEG, in particular surface O vacancies, using a model supported by first principles calculations that describes the redox formation. In agreement with recent spectroscopic and transport measurements, we predict a stabilization of such redox processes (and hence Ti 3d occupation) with film thickness beyond a critical value, which can be smaller than the critical thickness for 2D electronic conduction, since the surface defects generate trapping potentials that will affect the interface electron mobility. Several other recent experimental results, such as lack of core level broadening and shifts, find natural explanation. Pristine systems will likely require changed growth conditions or modified materials with a higher vacancy free energy.

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Section: Discussionmentioning

confidence: 99%

Surface defects and conduction in polar oxide heterostructures

2011

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“…We conclude that R tot is dominated by power dissipation in the dielectric and the superconductor at low and high power, respectively, which is in accordance with the linear and quadratic frequency dependences of R tot measured in the two power ranges. Using R s ∼2 µΩ, which is typical for YBCO at 2.3 GHz and 1.7 K [5], and R tot ∼20 µΩ , we derive tanδ ∼3×10 −5 , which is 1-2 orders of magnitude higher than expected for MgO at 20 K [46,47]. GHz.…”

Section: The Nonlinear Surface Impedance Of Superconductors On Mgomentioning

confidence: 99%

Recent developments in the characterization of superconducting films by microwaves

Hein

Getta

Kreiskott

et al. 2002

Physica C: Superconductivity

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We describe and analyze selected surface impedance data recently obtained by different groups on cuprate, ruthenate and diboride superconducting films on metallic and dielectric substrates for fundamental studies and microwave applications. The discussion includes a first review of microwave data on MgB 2 , the weak-link behaviour of RABiTS-type YBa 2 Cu 3 O 7-δ tapes, and the observation of a strong anomalous powerdependence of the microwave losses in MgO at low temperatures. We demonstrate how microwave measurements can be used to investigate electronic, magnetic, and dielectric dissipation and relaxation in the films and substrates. The impact of such studies reaches from the extraction of microscopic information to the engineering of materials and further on to applications in power systems and communication technology.Keywords: Surface impedance, superconducting films, microwave dissipation, relaxation.Address: Dr. Matthias Hein, Dept. of Physics, Univ. of Wuppertal, D-42097 Wuppertal, Germany. Tel. +49(202) 439-2747, Fax +49(202) Email: mhein@venus.physik.uni-wuppertal.de M. Hein et al., EUCAS 2001, invited paper B3-01, page 2 of 19 Microwave measurements in condensed matter physics Theoretical backgroundThis paper illustrates the relevance of microwave measurements for the investigation of electronic and magnetic transport and ordering in condensed matter. While most work has been done on solids, the described techniques could also be adapted to soft matter or liquids.The presentation is based on a selection of examples and does not attempt to provide a complete description of activities in this field.The complex-valued surface impedance Z s =R s +iX s at a microwave frequency ω=2πf is related to the permeability and conductivity of a material, µ and σ, in the local limit by ) (where R s and X s are the surface resistance and reactance [1]. The material parameters µ and σ are complex-valued and frequency dependent, e.g., via electronic, magnetic, or dielectric relaxation. The generalized conductivity σ characterizes electrical conduction through transport and displacement currents.The electrodynamic response of metallic materials provides information on the electronic properties within a surface layer of the order of the London penetration depth ~200 nm, and on a variable time scale ∼1/ω. Such information is complementary to thermodynamic bulk properties and low-frequency transport data. The high frequencies also help to derive Fermi surface properties, which would require strong magnetic fields at very low temperatures otherwise [2]. We will focus in the following on superconductors, for which Z s bears information on the density of states and quasiparticle excitations above and below the transition temperature T c [3]. It is also related to the phase purity, grain connectivity and interface effects of technical materials, which cannot readily be studied at similar resolution by At present at least 50 renowned academic and industrial groups study superconductors at microwave frequencies, to ...

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“…Below 20K, R eff (T) decreases at the higher power and approaches 2µΩ. Expecting R s ≥1µΩ for high-quality epitaxial YBCO films [17], R eff (20K) yields an upper-limit for the loss tangent of ≈10 -6 , as expected for MgO at 20K and 2.3GHz [18,19]. However, at low power, R eff (T) increases and becomes dominated by dielectric losses.…”

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confidence: 99%

“…, with ε r ∼9.8 and ε ∞ ∼3 the permittivities for MgO at low and optical frequencies [18,25]. The relaxation time τ d increases for decreasing temperatures, leading to an increase of tanδ in the range ωτ d <1.…”

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confidence: 99%