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Excitation of coherent phonons has the potential to dramatically alter the electronic structure of Dirac and Weyl semimetals, enabling sub-picosecond control of their optical and electronic properties. The Dirac semimetal SrMnSb2 is a candidate for such control, with a coherent-phonon mode that is predicted to close and reopen a gap at the Dirac node. Here, through a series of ultrafast pump-probe experiments, we establish suitable samples and conditions for driving the coherent phonon to high amplitude and attempting to observe the gap’s closure. Films of SrMnSb2 grown by molecular-beam epitaxy are shown to have phononic properties matching those of bulk crystals. We find that the phonon can be strongly excited by pump pulses with wavelength near 1500 nm, which will excite a 30-nm film almost uniformly and will penetrate the arsenic capping layers that protect the films. We find that samples withstand pump pulses of fluence up to 20 mJ/cm2, and we demonstrate the potential for sequences of pulses to amplify the oscillation while suppressing other phonon modes. Armed with our new knowledge of the conditions for exciting the desired coherent phonon, future experiments will be well prepared to measure its motion and to observe phononic control of the Dirac-point gap. 

Abstract Access to synchrotron X-ray facilities has become an important aspect for many disciplines in experimental Earth science. This is especially important for studies that rely on probing samples in situ under natural conditions different from the ones found at the surface of the Earth. The non-ambient condition Earth science program at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, offers a variety of tools utilizing the infra-red and hard X-ray spectrum that allow Earth scientists to probe Earth and environmental materials at variable conditions of pressure, stress, temperature, atmospheric composition, and humidity. These facilities are important tools for the user community in that they offer not only considerable capacity (non-ambient condition diffraction) but also complementary (IR spectroscopy, microtomography), and in some cases unique (Laue microdiffraction) instruments. The availability of the ALS’ in situ probes to the Earth science community grows especially critical during the ongoing dark time of the Advanced Photon Source in Chicago, which massively reduces available in situ synchrotron user time in North America. 

Abstract Phonon polaritons (PhPs), excitations arising from the coupling of light with lattice vibrations, enable light confinement and local field enhancement, which is essential for various photonic and thermal applications. To date, PhPs with high confinement and low loss are mainly observed in the mid‐infrared regime and mostly in manually exfoliated flakes of van der Waals (vdW) materials. In this work, the existence of low‐loss, thickness‐tunable phonon polaritons in the far‐infrared regime within transferable freestanding SrTiO₃membranes synthesized through a scalable approach, achieving high figures of merit is demonstrated, which are comparable to the previous record values from the vdW materials. Leveraging atomic precision in thickness control, large dimensions, and compatibility with mature oxide electronics, functional oxide membranes present a promising large‐scale 2D platform alternative to vdW materials for on‐chip polaritonic technologies in the infrared regime. 

Abstract The competing and non‐equilibrium phase transitions, involving dynamic tunability of cooperative electronic and magnetic states in strongly correlated materials, show great promise in quantum sensing and information technology. To date, the stabilization of transient states is still in the preliminary stage, particularly with respect to molecular electronic solids. Here, a dynamic and cooperative phase in potassium‐7,7,8,8‐tetracyanoquinodimethane (K‐TCNQ) with the control of pulsed electromagnetic excitation is demonstrated. Simultaneous dynamic and coherent lattice perturbation with 8 ns pulsed laser (532 nm, 15 MW cm⁻², 10 Hz) in such a molecular electronic crystal initiates a stable long‐lived (over 400 days) conducting paramagnetic state (≈42 Ωcm), showing the charge–spin bistability over a broad temperature range from 2 to 360 K. Comprehensive noise spectroscopy, in situ high‐pressure measurements, electron spin resonance (ESR), theoretical model, and scanning tunneling microscopy/spectroscopy (STM/STS) studies provide further evidence that such a transition is cooperative, requiring a dedicated charge–spin–lattice decoupling to activate and subsequently stabilize nonequilibrium phase. The cooperativity triggered by ultrahigh‐strain‐rate (above 10⁶s⁻¹) pulsed excitation offers a collective control toward the generation and stabilization of strongly correlated electronic and magnetic orders in molecular electronic solids and offers unique electro‐magnetic phases with technological promises.