Thursday, September 3, 2015

Abstract-Band Structure and Terahertz Optical Conductivity of Transition Metal Oxides: Theory and Application to [Math Processing Error]

Hung T. Dang, Jernej Mravlje, Antoine Georges, and Andrew J. Millis

Phys. Rev. Lett. 115, 107003 – Published 3 September 2015

Density functional plus dynamical mean field calculations are used to show that in transition metal oxides, rotational and tilting ([Math Processing Error]-type) distortions of the ideal cubic perovskite structure produce a multiplicity of low-energy optical transitions which affect the conductivity down to frequencies of the order of 1 or 2 mV (terahertz regime), mimicking non-Fermi-liquid effects even in systems with a strictly Fermi-liquid self-energy. For [Math Processing Error], a material whose measured electromagnetic response in the terahertz frequency regime has been interpreted as evidence for non-Fermi-liquid physics, the combination of these band structure effects and a renormalized Fermi-liquid self-energy accounts for the low frequency optical response which had previously been regarded as a signature of exotic physics. Signatures of deviations from Fermi-liquid behavior at higher frequencies ([Math Processing Error]) are discussed.
  • Figure
  • Figure
  • Figure
  • Figure

Terahertz Probing, Characterization to be Featured at EuMW by Lake Shore

Lake Shore probe stations offer options for DC, RF and microwave probing of nanoscale devices and materials on full and partial wafers at variable temperatures.

"There is an increasing need for non-destructive RF/microwave measurements as a function of low temperature, as well as field, in a controlled environment."
Lake Shore Cryotronics, a leading innovator in solutions for measurement over a wide range of temperature and magnetic field conditions, will be exhibiting high-frequency material and device measurement solutions, including a prototype for a terahertz (THz) on-wafer cryogenic probing arm, during European Microwave Week (EuMW), September 8–10, in Paris.
The probe arm, which the company plans to introduce later this year, is designed to enable precise probing of millimeter-wave devices and materials at THz frequencies (75 GHz and up) in a Lake Shore CPX, CPX-VF, CRX-4K or CRX-VF probe station. By using the arm with a cryogenically rated probe and compatible VNAs installed on a probe station, researchers will be able to perform calibrated S-parameter and other high-frequency electrical measurements at cryogenic temperatures and in high magnetic fields.
Lake Shore will have the probe arm prototype at their EuMW stand (#131) and, in a related event, Lake Shore Application Scientist Dr. David Daughton will be sharing preliminary probe arm measurement results during Tuesday’s EuMC18-03 Reflectometers and Millimeterwave Characterization session.
Also at EuMW, Lake Shore will be discussing the value of cryogenic probe stations for characterizing new microwave devices, such as MMICs, LNAs, MEMS or superconducting circuits. For many of these applications, there is an increasing need for non-destructive RF/microwave measurements as a function of low temperature, as well as field, in a controlled environment. Lake Shore probe stations provide this environment and can be ordered with 40- or 67-GHz GSG style probes designed to ensure optimal microwave measurement performance at the very low temperatures.
Separate from probe station-based measurements, Lake Shore will also be answering questions about its Model 8501, a fully integrated, continuous wave (CW) THz based system for non-contact characterization of research-scale materials. The system enables measurements at 200 GHz to 1.5 THz frequencies with spectral resolution of better than 500 MHz, and features a high-field cryostat and superconducting magnet for measuring material responses across a range of temperatures and field strengths.
CW-THz spectroscopy can reveal properties that other techniques miss because many phenomena have been found to align with these frequencies, and it offers particular potential for characterizing dielectric materials for high-frequency and waveguiding applications.
For more information, visit
About Lake Shore Cryotronics, Inc. 
Supporting advanced research since 1968, Lake Shore Cryotronics ( is a leading innovator in measurement and control solutions for materials characterization under variable temperature and magnetic field conditions. High-performance product solutions from Lake Shore include cryogenic temperature sensors and instrumentation, magnetic test and measurement systems, probe stations, and precision materials characterizations systems that explore the electronic and magnetic properties of next-generation materials. Lake Shore serves an international base of research customers at leading university, government, aerospace, and commercial research institutions, and is supported by a global network of sales and service facilities.

Abstract-Terahertz Spectroscopy Applied For Investigation of Water Structure

J. Phys. Chem. B, Just Accepted Manuscript
DOI: 10.1021/acs.jpcb.5b06622
Publication Date (Web): September 3, 2015
Copyright © 2015 American Chemical Society

The absorption spectra of liquid water and different aqueous solutions were analyzed in a terahertz frequency domain (from 6 to 200 cm–1) which characterize the collective dynamics of water molecules. The particular attention was paid to the relaxation process in the range of ~6–80 cm-1. The physical essence of this process on the molecular level is still unclear. We found that the amplitude of this relaxation process correlates with the degree of destruction of water structure. The obtained data allowed us to interpret this process as a monomolecular relaxation of free water molecules. Based on a consideration of the water polarization in the electric field we proposed a method of calculation of the amount of free water molecules in solution.

Abstract-Time-domain numerical modeling of terahertz receivers based on photoconductive antennas

E. Moreno, Z. Hemmat, J. B. Roldán, M. F. Pantoja, A. R. Bretones, and S. G. García

We present here a simulator that solves the main semiconductor charge and transport equations coupled to Maxwell equations to study receivers based on photoconductive antennas (R-PCAs). Making use of this tool we were able to correctly characterize the operation of these antennas. In doing so, we compared simulations with the results of the semi-empirical expression ��THz(��)����(��)*��THz(��) employed to evaluate the detected photocurrent by means of the convolution between the photoconductivity in the receiver and the electric field linked to the emitter antenna. We were able to accurately reproduce experimental data with our simulation tool. These kinds of tools are essential to model photoconductive antennas, a fundamental step needed for the development of terahertz time-domain spectroscopy applications based on PCAs.
© 2015 Optical Society of America
Full Article  |  PDF Article