Transient states in polar semiconductors
MPSD Seminar
- Date: Nov 14, 2024
- Time: 11:00 AM - 12:00 PM (Local Time Germany)
- Speaker: Claude Monney
- University of Fribourg
- Location: MPSD Bldg. 900
- Room: Seminar Room EG.136
α-GeTe(111) is a polar semiconductor that exhibits the largest known Rashba-type spin splitting of so-far known materials. Moreover, due to its ferroelectric properties, it is possible to reversibly manipulate the spin polarization of its low-energy electronic structure by an external electric field [1], a promising behavior for spintronics applications. A natural question is to investigate whether it is possible to coherently modify the ferroelectric properties of GeTe with light pulses.
In the first part of my talk, I will show how we can use infrared light pulses to transiently enhance the polar distortion of GeTe [2]. Using time-resolved angle-resolved photoemission spectroscopy (ARPES), we reveal that the Rashba splitting of its bulk states is enhanced 200 fs after photoexcitation. I will explain how a surface photovoltage induced by the charge carrier excitation is at the origin of this counter-intuitive effect.
In the second part of my talk, I will switch to the isostructural compound SnTe. This material undergoes a polar structural distortion at about 100 K. At room temperature, it has been proposed to be a topological crystalline insulator in the undistorted phase [3]. However, the presence of topological surface states is intimately linked to the occurrence of the polar distortion.
First, I will show how static ARPES data acquired as a function temperature allow us to follow the evolution of the Rashba splitting induced by the structural distortion in the bulk bands, revealing substantial deviations from a mean-field-like transition [4].
Then, I will elaborate on the implications of our results for the topological nature of the surface states in SnTe. Using time-resolved ARPES data, I will show how tailored light pulses can be used to photoinduce a transient topological state in SnTe in the absence of any structural change. I will argue that a strong light-matter interaction is the relevant mechanism.
[1] J. Krempasky, S. Muff, J. Minár, N. Pilet, M. Fanciulli, A.P. Weber, E.B. Guedes, M. Caputo, E. Müller, V.V. Volobuev, M. Gmitra, C.A.F. Vaz, V. Scagnoli, G. Springholz, and J.H. Dil, Phys. Rev. X 8, 021067 (2018).
[2] G. Kremer, J. Maklar, L. Nicolaï, C.W. Nicholson, C. Yue, C. Silva, P. Werner, J.H. Dil, J. Krempasky, G. Springholz, R. Ernstorfer, J. Minár, L. Rettig and C. Monney, Nature Commun. 13:6396 (2022).
[3] E. Plekhanov, P. Barone, D. Di Sante and S. Picozzi, Phys. Rev. B 90, 161108(R) (2014).
[4] F. Chassot, A. Pulkkinen, G. Kremer, T. Zakusylo, G. Krizman, M. Hajlaoui, J. H. Dil, J. Krempasky, J. Minar, G. Springholz and C. Monney, Nano Letters 24, 82 (2024).
In the first part of my talk, I will show how we can use infrared light pulses to transiently enhance the polar distortion of GeTe [2]. Using time-resolved angle-resolved photoemission spectroscopy (ARPES), we reveal that the Rashba splitting of its bulk states is enhanced 200 fs after photoexcitation. I will explain how a surface photovoltage induced by the charge carrier excitation is at the origin of this counter-intuitive effect.
In the second part of my talk, I will switch to the isostructural compound SnTe. This material undergoes a polar structural distortion at about 100 K. At room temperature, it has been proposed to be a topological crystalline insulator in the undistorted phase [3]. However, the presence of topological surface states is intimately linked to the occurrence of the polar distortion.
First, I will show how static ARPES data acquired as a function temperature allow us to follow the evolution of the Rashba splitting induced by the structural distortion in the bulk bands, revealing substantial deviations from a mean-field-like transition [4].
Then, I will elaborate on the implications of our results for the topological nature of the surface states in SnTe. Using time-resolved ARPES data, I will show how tailored light pulses can be used to photoinduce a transient topological state in SnTe in the absence of any structural change. I will argue that a strong light-matter interaction is the relevant mechanism.
[1] J. Krempasky, S. Muff, J. Minár, N. Pilet, M. Fanciulli, A.P. Weber, E.B. Guedes, M. Caputo, E. Müller, V.V. Volobuev, M. Gmitra, C.A.F. Vaz, V. Scagnoli, G. Springholz, and J.H. Dil, Phys. Rev. X 8, 021067 (2018).
[2] G. Kremer, J. Maklar, L. Nicolaï, C.W. Nicholson, C. Yue, C. Silva, P. Werner, J.H. Dil, J. Krempasky, G. Springholz, R. Ernstorfer, J. Minár, L. Rettig and C. Monney, Nature Commun. 13:6396 (2022).
[3] E. Plekhanov, P. Barone, D. Di Sante and S. Picozzi, Phys. Rev. B 90, 161108(R) (2014).
[4] F. Chassot, A. Pulkkinen, G. Kremer, T. Zakusylo, G. Krizman, M. Hajlaoui, J. H. Dil, J. Krempasky, J. Minar, G. Springholz and C. Monney, Nano Letters 24, 82 (2024).
If you would like to meet with Claude during his visit, please contact Michael Fechner.