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Collective lattice dynamics determine essential aspects of condensed matter, such as elastic and thermal properties. These exhibit strong dependence on the length-scale, reflecting the marked wavevector dependence of lattice excitations. The extreme ultraviolet transient grating (EUV TG) approach has demonstrated the potential of accessing a wavevector range corresponding to the 10s of nm length-scale, representing a spatial scale of the highest relevance for fundamental physics and forefront technology, previously inaccessible by optical TG and other inelastic scattering methods. In this manuscript we report on the capabilities of this technique in the context of probing thermoelastic properties of matter, both in the bulk and at the surface, as well as discussing future developments and practical considerations.

We utilize coherent femtosecond extreme ultraviolet (EUV) pulses derived from a free electron laser (FEL) to generate transient periodic magnetization patterns with periods as short as 44 nm. Combining spatially periodic excitation with resonant probing at the dichroic M-edge of cobalt allows us to create and probe transient gratings of electronic and magnetic excitations in a CoGd alloy. In a demagnetized sample, we observe an electronic excitation with 50 fs rise time close to the FEL pulse duration and ~0.5 ps decay time within the range for the electron-phonon relaxation in metals. When the experiment is performed on a sample magnetized to saturation in an external field, we observe a magnetization grating, which appears on a sub-picosecond time scale as the sample is demagnetized at the maxima of the EUV intensity and then decays on the time scale of tens of picoseconds via thermal diffusion. The described approach opens prospects for studying dynamics of ultrafast magnetic phenomena on nanometer length scales.

We use time-resolved x-ray resonant magnetic scattering (tr-XRMS) at the Co M$_{2,3}$- and Tb O$_1$-edges to study ultrafast demagnetization in an amorphous Co$_{88}$Tb$_{12}$ alloy with stripe domains. Combining the femtosecond temporal with nanometer spatial resolution of our experiment, we demonstrate that the equilibrium spin texture of the thin film remains unaltered by the optical pump-pulse on ultrashort timescales ($<$1 ps). However, after $\simeq$ 4 ps, we observe the onset of a significant domain wall broadening, which we attribute to a reduction of the uniaxial magnetic anisotropy of the system, due to energy transfer to the lattice. Static temperature dependent magnetometry measurements combined with analytical modeling of the magnetic structure of the thin film corroborate this interpretation.

We have investigated the infrared transmission of a two-dimensional (2DEG) electron gas confined in a $Al_{0.25}In_{0.75}As/Ga_{0.25}In_{0.75}As$ single quantum well in order to study the electron optical phonon interaction in a two phonon mode system. Infrared transmission experiments have been performed in both the perpendicular Faraday (PF) and tilted Faraday (TF) configurations for which the growth axis of the sample is tilted with respect to the incident light propagation direction and to the magnetic field direction. The experimental results lead to question the validity of the concept of polaron mass in a real material., Comment: 7 pages, 3 figures

We report tilted-field transport measurements in the quantum-Hall regime in an InAs/In_0.75Ga_0.25As/In_0.75Al_0.25As quantum well. We observe anti-crossings of spin-split Landau levels, which suggest a mixing of spin states at Landau level coincidence. We propose that the level repulsion is due to the presence of spin-orbit and of band-non-parabolicity terms which are relevant in narrow-gap systems. Furthermore, electron-electron interaction is significant in our structure, as demonstrated by the large values of the interaction-induced enhancement of the electronic g-factor., Comment: 4 pages, 3 figures

We report on the achievement of a two-dimensional electron gas in completely undoped In[0.75]Al[0.25]As/In[0.75]Ga[0.25]As metamorphic quantum wells. Using these structures we were able to reduce the carrier density, with respect to reported values in similar modulation-doped structures. We found experimentally that the electronic charge in the quantum well is likely due to a deep-level donor state in the In[0.75]Al[0.25]As barrier band gap, whose energy lies within the In[0.75]Ga[0.25]As/In[0.75]Al[0.25]As conduction band discontinuity. This result is further confirmed through a Poisson-Schroedinger simulation of the two-dimensional electron gas structure., Comment: 17 pages, 6 figures, to be published in J. Vac. Sci. Technol. B

We report magneto-transport measurements on high-mobility two-dimensional electron systems (2DESs) confined in In_0.75Ga_0.25As/In_0.75Al_0.25As single quantum wells. Several quantum Hall states are observed in a wide range of temperatures and electron densities, the latter controlled by a gate voltage down to values of 1.10^11 cm^-2. A tilted-field configuration is used to induce Landau level crossings and magnetic transitions between quantum Hall states with different spin polarizations. A large filling factor dependent effective electronic g-factor is determined by the coincidence method and cyclotron resonance measurements. From these measurements the change in exchange-correlation energy at the magnetic transition is deduced. These results demonstrate the impact of many-body effects in tilted-field magneto-transport of high-mobility 2DESs confined in In_0.75Ga_0.25As/In_0.75Al_0.25As quantum wells. The large tunability of electron density and effective g-factor, in addition, make this material system a promising candidate for the observation of a large variety of spin-related phenomena., Comment: 7 pages, 5 figures