Strongly correlated electron systems; Quantum materials; Intense single-cycle THz radiation; Pump-probe experiments; X-ray free-electron laser; Low-temperature x-ray diffraction
Ingold Gerhard, Abela Rafael, Arrell Christopher, Beaud Paul, Böhler Pirmin, Cammarata Marco, Deng Yunpei, Erny Christian, Esposito Vincent, Flechsig Uwe, Follath Rolf, Hauri Christoph, Johnson Steven, Juranic Pavle, Mancini Giulia Fulvia, Mankowsky Roman, Mozzanica Aldo, Oggenfuss Roland Alex, Patterson Bruce D., Patthey Luc, Pedrini Bill, Rittmann Jochen, Sala Leonardo, Savoini Matteo, et al. (2019), Experimental station Bernina at SwissFEL: condensed matter physics on femtosecond time scales investigated by X-ray diffraction and spectroscopic methods, in Journal of Synchrotron Radiation
, 26(3), 874-886.
Ultrashort electromagnetic pulses with frequencies in the THz range have recently become a focus of research, in particular of strongly correlated materials. The fundamental reason is that the energy scale of low-temperature quantum phases, such as charge, spin or orbital order and also superconductivity, is in the meV range and, thus, corresponds to THz frequencies.An important objective is the development of broadband THz sources that deliver pulses with a single field-oscillation at high peak power. Such radiation is ideally suited for initiation and control of ultrafast processes by either non-resonant broadband excitation, or by selectively accessing THz active bands, e.g., lattice modes (phonons) or magnetic resonances (magnons) in crystalline structures and vibrational or rotational modes in molecules.Access to such modes by strong THz fields allows unprecedented control over transient states of matter on ultrafast time scales. Recent examples using intense THz radiation to influence ground states of quantum materials include: Ultrafast control of magnetism via the ferroelectric polarization in multiferroic compounds or driving and detecting the so-called Higgs mode in superconductors. In addition to the knowledge gained in basic research, this development is also expected to lead to advances in more applied fields, such as faster data storage technology and more efficient catalysts.However, many applications require significantly higher THz field strength than currently available. Thus, one of the bottlenecks of THz generation is the limited pulse energy (< 50 µJ) and field strength (a few MV/cm at maximum). Here we propose to overcome this limitation by use of a Cr:forsterite laser system to efficiently pump organic crystals that emit THz radiation. This approach will yield: i). THz fields up to E = 150 MV/cm (B = 50 T) and a pulse energy of 1.5 mJ, ii). polarization control using photo-elastic modulators, iii). narrow bandwidth option using metamaterial filters.The high-field THz source proposed here will enable pump-probe experiments at SwissFEL to directly study THz-driven effects at the inherent time and length scale of atoms by time-resolved femtosecond x-ray scattering. Intense single-cycle THz radiation will be used to pump the specimen, which is, thereafter, probed by hard x-ray pulses from the ARAMIS beamline. The project is unique due to the combination of the dedicated THz source, ultrashort and ultrabright x-ray pulses from SwissFEL, and the low-temperature capabilities (sub-5 K) of the ESB endstation.