QM2 - Quantum Matter and Materials | November 20, 14:30
The interplay between the electronic and lattice degrees of freedom in Density Waves probed with femtosecond real-time probes
In many of the advanced solids exhibiting macroscopic quantum phenomena (e.g. superconductivity) their functional properties arise from a delicate balance between interactions among different degrees of freedom (electrons, phonons, spins). An example of such is the appearance of Charge Density Wave (CDW) ground state in several quasi one- or two-dimensional metals. According to the standard Peierls’ scenario the appearance of the CDW phase is driven by the divergent static electronic susceptibility at a wave vector q=2kF. This classical description has been challenged [1], arguing that the appearance of CDWs, in particular in the transition-metal dichalcogenides, is due to strong (q-dependent) electron-phonon coupling [1]. I will review some recent studies where some of the open questions were addressed utilizing femtosecond time-resolved optical [2] and structural probes [3-5]. Using femtosecond electron diffraction we were able to directly follow the photo-triggered dynamics of the periodic lattice distortion (order parameter) in dichalcogenides [3,4], point out the importance of three-dimensionality for the existence of CDWs in these quasi-2D systems [4], and to track the different stages of the photo-induced phase transition between different CDW phases [5]. [1] e.g. M. Johannes and I. Mazin, Phys. Rev. B 77 (2008); L. Gor'kov, Phys. Rev. B 85, 165142 (2012); H-M. Eiter, PNAS 110, 64 (2013). [2] H. Schäfer, et al., Phys. Rev. Lett. 105, 066402 (2010); H. Schäfer, et al., EPJ-ST 222, 1005 (2013). [3] M. Eichberger, et al., Nature 468, 799 (2010). [4] N. Erasmus, et al., Phys. Rev. Lett. 109, 167402 (2012); E. Eichberger, et al., APL 102, 121106 (2013). [5] K. Haupt, et al., in preparation.
Jure Demsar, Ilmenau University of Technology
Seminar Room, Institute of Physics II
Contact: Paul H.M. van Loosdrecht