Thermodynamic properties of tantalum diselentde over a wide temperature range

Bolgar, A. S.; Trofimova, Zh. A.; Blinder, A. V.; Yanaki, A.A.

doi:10.1007/bf00793441

Powder Metall Met Ceram

1992

DOI: 10.1007/bf00793441

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Thermodynamic properties of tantalum diselentde over a wide temperature range

A. S. Bolgar

Zh. A. Trofimova

A. V. Blinder

et al.

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2012

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“…Thus, the photoinduced phase transition seems not to be purely electronically driven. Further support for the importance of strong e-ph coupling comes from the fact that the optically delivered energy required to fully drive the C-IC phase transition corresponds well to the energy required to heat up the sample to T c = 410 K. Using the measured absorbed energy and the specific heat of c p = 85.7 J/(mole K) [32] we indeed obtain a temperature increase of ∼ 110 K at the critical fluence F c = 2.5 mJ/cm 2 , see Fig. 3.…”

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Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

et al. 2012

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The dynamics of the photoinduced commensurate to incommensurate charge density wave (CDW) phase transition in 4H b -TaSe2 are investigated by femtosecond electron diffraction. In the perturbative regime the CDW reforms on a 150 ps timescale, which is two orders of magnitude slower than in other transition-metal dichalcogenides. We attribute this to a weak coupling between the CDW carrying T layers and thus demonstrate the importance of three-dimensionality for the existence of CDWs. With increasing optical excitation the phase transition is achieved showing a second order character in contrast to the first order behavior in thermal equilibrium.Reduced dimensionality seems to be a decisive property governing phenomena like high temperature superconductivity and charge density wave (CDW) formation. The latter is typical for quasi one-or two-dimensional metals where, in the ground state, the crystal displays a static periodic modulation of the conduction electron density accompanied by a periodic lattice displacement (PLD), both characterized by the wave vector q CDW [1]. The standard theory that describes the appearance of this macroscopic quantum state was formulated by Peierls [2]. By considering a one dimensional metal he has shown that the divergent static electronic susceptibility at a wave vector q = 2k F gives rise to an instability of the electronic system against perturbations at this wave vector. This so called Fermi surface nesting lowers the frequencies of q = 2k F phonons, which will eventually evolve into a static lattice displacement. From that band gaps at ± k F result, which reduce the total electronic energy. If the elastic energy cost to modulate atomic positions is lower than the electronic energy gain, the CDW state is the preferred ground state. Recently, this classical picture has been challenged [3][4][5], since (a) the nesting condition derived from the topology of the Fermi surface (2k F ) and the observed CDW modulation vectors (q CDW ) are not generally equal, and (b) the diverging susceptibility at q = 2k F is exceedingly fragile with respect to temperature, scattering or imperfect nesting [3]. Contrasting the standard Fermi surface nesting scenario the transition from the metallic into a CDW state was argued to occur due to strong qdependent electron-phonon coupling [3], particularly in transition-metal dichalcogenides [4].Only the concerted interplay of electronic and lattice degrees of freedom make the CDW formation possible. The two modulations can be individually examined by scanning tunneling microscopy [6], angular resolved photoemission spectroscopy [5] and electron, x-ray or neutron diffraction techniques [7]. In thermal equilibrium, the gap in the electronic spectrum and the atomic displacement amplitude (A) present different projections of the same order parameter [1]. Adding femtosecond temporal resolution to the experiment enables investigation of their dynamical behavior. Since the electronic system can be perturbed on timescales much faster than the characteristic lattic...

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Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

et al. 2012

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Thermodynamic properties of tantalum diselentde over a wide temperature range

Cited by 1 publication

References 7 publications

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

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