Abstract-Terahertz charge dynamics unveil fundamental transport anisotropy in charge-ordered Pr 0.5 Eu 0.5 NiO 3 nickelate thin films

Sarmistha Das, G. L. Prajapati, Anagha P, and D. S. Rana

https://journals.aps.org/prb/accepted/ad074O16Ea9E1c1763c31290edb7c0df04b9f8b35

Electrons, condensed in a collective mode and behaving as free charge carriers, are two important facets induced by complex intertwining of charge, spin, orbital and lattice degrees of freedom. Existence of these two electronic ground states in the same structural/chemical phase is as much desired as much is elusive in complex oxides. Using some unique attributes of terahertz (THz) spectroscopy, we show existence of two fundamentally different electronic phenomena in Pr0.5Eu0.5NiO3, member of contemporary rare-earth nickelates, in the same orthorhombic phase but along two different orthogonal in-plane axes [001] and [1-10] of thin films. While a collective response of charge manifests via charge-density-wave (CDW) excitation along [001] direction, an entirely different Drude-Smith type free carrier response manifests along the other in-plane orthogonal axis. This anisotropy, on one hand, unveils the strained engineered crystallographic preferences of the underlying charge-ordering phenomenon, on the other hand, the different conduction channels open up the possibilities of application of nickelates such as in THz transmission modulators.

Abstract-Coexistence of Kosmotropic and Chaotropic Impacts of Urea on Water As Revealed by Terahertz Spectroscopy

Keiichiro Shiraga , Yuichi Ogawa, Koichiro Tanaka, Takashi Arikawa, Naotaka Yoshikawa, Masahito Nakamura, Katsuhiro Ajito, Takuro Tajima,

http://pubs.acs.org/doi/10.1021/acs.jpcb.7b11839

Whether urea can serve as a kosmotrope or chaotrope has long been a topic of debate. In this study, broad-band THz spectroscopy (0.2–12 THz) of aqueous solutions of urea was used to characterize the hydration state and the hydrogen bond structure of water around urea. Three low-frequency vibration modes of urea were found around 2, 4, and above 12 THz. After eliminating the contribution of these modes, the “urea-vibration-free” complex dielectric constant was decomposed into the relaxation modes of bulk water and the oscillation modes of water. When hydration water is defined to be reorientationally retarded relative to bulk, our analysis revealed that the hydration number is 1.9 independent of urea concentrations up to 5 M, and this number is in close agreement with that of water constrained by strong acceptor hydrogen bonds of urea oxygen. Regarding the hydrogen bond structure, it was found that the tetrahedral-like water structure is mostly preserved (though the hydrogen bond lifetime is significantly shortened) but the population of non-hydrogen-bonded water molecules fragmented from the network is markedly increased, presumably due to urea’s NH2 inversion. These experimental results point to the coexistence of apparently two contradictory aspects of urea: dynamical retardation (the kosmotropic aspect) by the −CO group and slight structural disturbance (the chaotropic aspect) by the −NH2 group.

Abstract-Terahertz Spectroscopy and Global Analysis of the Rotational Spectrum of Doubly Deuterated Amidogen Radical ND2

Mattia Melosso, Claudio Degli Esposti,  Luca Dore,

http://iopscience.iop.org/article/10.3847/1538-4365/aa9220/meta

The deuteration mechanism of molecules in the interstellar medium is still being debated. Observations of deuterium-bearing species in several astronomical sources represent a powerful tool to improve our understanding of the interstellar chemistry. The doubly deuterated form of the astrophysically interesting amidogen radical could be a target of detection in space. In this work, the rotational spectrum of the ND2 radical in its ground vibrational and electronic  state has been investigated between 588 and 1131 GHz using a frequency modulation millimeter/submillimeter-wave spectrometer. The ND2 molecule has been produced in a free-space glass absorption cell by discharging a mixture of ND3 and Ar. Sixty-four new transition frequencies involving J values from 2 to 5 and K a values from 0 to 4 have been measured. A global analysis including all the previous field-free pure rotational data has been performed, allowing for a more precise determination of a very large number of spectroscopic parameters. Accurate predictions of rotational transition frequencies of ND2 are now available from a few gigahertz up to several terahertz.

Abstract-Experimental Observation of Bethe Strings

Zhe Wang, Jianda Wu, Wang Yang, Anup Kumar Bera, Dmytro Kamenskyi, A.T.M. Nazmul Islam, Shenglong Xu, Joseph Matthew Law, Bella Lake, Congjun Wu, Alois Loidl

(Submitted on 13 Jun 2017)

           https://arxiv.org/abs/1706.04181

Almost one century ago, string states - complex bound states (Wellenkomplexe) of magnetic excitations - have been predicted to exist in one-dimensional quantum magnets and since then become a subject of intensive theoretical study. However, experimental realization and identification of string states in condensed-matter systems remains an unsolved challenge up to date. Here we use high-resolution terahertz spectroscopy to identify string states in the antiferromagnetic Heisenberg-Ising chain SrCo2V2O8 in strong longitudinal magnetic fields. We observe complex bound states (strings) and fractional magnetic excitations (psinons and antipsinons) in the field-induced critical regime, which are precisely described by the Bethe ansatz. Our study reveals that two-string and three-string states govern the quantum spin dynamics close to the quantum criticality, while the fractional excitations are dominant at low energies, reflecting the antiferromagnetic quantum fluctuations.