47 research outputs found
NbS: A unique quasi one-dimensional conductor with three charge density wave transitions
Through transport, compositional and structural studies, we review the
features of the charge-density wave (CDW) conductor of NbS (phase II). We
highlight three central results: 1) In addition to the previously reported CDW
transitions at = 360\,K and = 150\,K, another CDW transition
occurs at a much higher temperature = 620-650\,K; evidence for the
non-linear conductivity of this CDW is presented. 2) We show that CDW
associated with the - transition arises from S vacancies acting as
donors. Such a CDW transition has not been observed before. 3) We show
exceptional coherence of the -CDW at room-temperature. Additionally, we
report on the effects of uniaxial strain on the CDW transition temperatures and
transport.Comment: 16 pages, 18 figure
Charge density wave ordering in NbSe3: possible models and the experimental evidence
Charge density wave (CDW) ordering in the prototypical low-dimensional
compound NbSe3 is reconsidered. We show that the widely accepted CDW model with
two incommensurate modulations, q1 = (0,0.241,0) and q2 = (0.5,0.260,0.5),
localized on type-III and type-I bi-capped trigonal prismatic (BCTP) columns,
does not explain some details, revealed by various microscopic methods. The
suggested alternative explanation is in a better accord with the entire
experimental evidence, including low-temperature (LT) scanning tunneling
microscopy (STM) results. It is based on the existence of modulated layered
nano-domains formed below both CDW onset temperatures. According to this model,
two of the three slightly different BCTP types of columns are modulated by the
same wave vector, either q1 or q2, which can easily switch over in a domain as
a whole. This approach explains the presence of the q2 modulation in the STM
images recorded above the T2 CDW transition and the absence of the q2
satellites in the corresponding diffraction patterns. The long periodic
modulation, detected by LT STM is attributed to a beating between the two CDWs,
centered on adjacent columns of the same type. These pairs of columns, both
either of type-III or type-I, modulated by the two alternative CDWs, represent
the basic modulation units, ordered into nano-domains
Nb S3: A unique quasi-one-dimensional conductor with three charge density wave transitions
© 2017 American Physical Society.We review the features of the charge density wave (CDW) conductor NbS3 (phase II) and include several additional results from transport, compositional, and structural studies. Particularly, we highlight three central results: (1) In addition to the previously reported CDW transitions at TP1=360K and TP2=150K, a third CDW transition occurs at a much higher temperature TP0≈620-650K; evidence for the nonlinear conductivity of this CDW is presented. (2) We show that the CDW associated with the TP2 transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. (3) We demonstrate the exceptional coherence of the TP1 CDW at room temperature. The effects of uniaxial strain on the CDW transition temperature and transport are reported
Ego sum Dominus Deus tuus fortis zelotes visitans iniquitatem patrum in filiis in tertiam et quartam generationem eorum... De straf van God voor het nageslacht in de christelijke receptie van Exodus 20,5 met name in de late scholastiek
The role of executive processes in prospective memory tasks
Prospective remembering refers to remembering and acting on behavioural intentions. Three experiments tested the hypothesis that prospective remembering requires the availability of executive processes. It was expected that this is more important when intentions are stated in categorical terms. Type of instruction (specific versus categorical), typicality of the cue in relation to the category specified, and executive load were manipulated. Results showed a general benefit of specific instructions. Furthermore, with categorical instructions, performance was better with typical cues. Although the data suggested that executive processes are responsible for the processing of cues, the load manipulation had no significant effect on the prospective memory measure. Thus, no evidence was found for the hypothesis that prospective remembering requires the availability of executive processes. It is argued that it is a matter of strategic choice whether executive processes are deployed: One does not need to monitor for cues but can choose to rely on bottom-up processes. Monitoring may be sufficient, but not necessary for successful prospective remembering