Several insulating materials can be switched by laser pulses into transient metal states with apparently nonthermal properties. Often, this has been interpreted as a nonthermal closing of a Mott gap. An alternative mechanism is the generation of in-gap states by the nonthermal population of multiplets (e. g. singlet-triplet excitations in dimerized systems), or the nonthermal reshuffling of charge between orbitals. I will present recent nonequilibrium dynamical mean field theory studies of model systems, which provide insights into the nature of photo-induced nonthermal metal states in 1T-TaS2 and rare earth nickelates, and realistic simulations of the photo-induced dynamics in VO2, which clarify the excitation and charge reshuffling processes leading to the nonthermal monoclinic metal phase.
Understanding the dynamics of complex, strongly interacting many-body systems is crucial in the field of quantum science and engineering. Recent advancements in controlling programmable many-body systems have provided insights into nonequilibrium states, often inaccessible to classical simulations. This talk explores the concept of dynamical resonances, which are radically distinct magnetization dynamics occurring only within a very narrow parameter regime, in the transverse field Ising model realized on a quantum annealer. One example that emerges in such a resonant regime are quantum many-body scars, which are rare, non-thermalizing eigenstates that challenge our understanding of quantum thermalization and ergodicity.
Quantum materials exhibit remarkable non-equilibrium phenomena when driven by the strong fields in femtosecond laser pulses. Recent years have seen a surge of interest in using ultrafast light-matter interaction to create and manipulate photon-dressed Floquet-Bloch states as a strategy for controlling material properties. This excitement is fueled by the predictive power of Floquet theory, which has been used, for example, to correctly predict the formation of topological edge modes in periodically-driven systems that exhibit no topological properties in equilibrium. Many of these proposals have been verified in quantum simulation settings, but are only just beginning to be explored in solids.In this talk, I will present results on the electrical transport properties of quantum materials driven by mid-infrared laser pulses, probed using an ultrafast optoelectronic device architecture. The talk will primarily focus on recent results obtained on the Weyl semimetal Td-MoTe2, where a rectified, helicity-dependent injection current that scales linearly with the applied laser field was observed. This scaling violates the perturbative description of nonlinear optics/transport, which demands a quadratic field scaling for current rectification to occur. The results can be explained using Floquet theory, which predicts that the observed linear scaling arises from the stimulated emission that accompanies the hybridization of Floquet-Bloch states.
Strong light-matter interaction constitutes the bedrock of all photonic applications, empowering material elements to create and mediate interactions of light with light. Among others, phononamplified interactions were shown to bring a specific twist into this, in the infrared (IR) frequency range. Thus, phono-magnetic effects are the low-frequency analogues of inverse Faraday and Cotton-Mouton effects where phonons, not electrons, mediate the interaction between light and spins. In this case, light couples to the spins indirectly by exciting coherent vibrations of the crystal lattice (phonons) that transfer angular momentum to the magnetic ions. The optically driven chiral phonons in materials with strong spin-orbit coupling were shown to produce giant effective magnetic fields that exceed those previously seen by several orders of magnitude. The mechanism allows for bidirectional control of the induced magnetization through phonon chirality that in turn can be controlled by the polarization of the laser pulse.
This seminar will focus on the potential of cavity electrodynamics in shaping material properties, opened by on our recent investigation into cavity-mediated thermal control of the metal-to-insulator transition in 1T-TaS2, which demonstrated the feasibility of reversible cavity manipulation of a phase transition in a correlated solid-state material.By immersing the charge density wave material 1T-TaS2 into cryogenic tunable terahertz cavities, we unveil a remarkable shift between conductive states. This transition, triggered by a substantial alteration in sample temperature, is controlled by mechanical adjustments of the distance between cavity mirrors and their alignment.
Enhancing the light-matter coupling in cavities provides an intriguing avenue to control properties of matter, from chemical reactions to transport and thermodynamic phase transitions. In this talk, I discuss two mechanisms in which quantum light can influence extended condensed matter systems, in particular strongly correlated electron systems: (i) The hybridization of light and matter can affect first-order metal insulator transitions, because light selectively modifies the free energy of the metallic phase . This mechanism has been discussed in relation to the cavity-controlled metalinsulator transition in 1T-TaS2. While it most likely is not the relevant mechanism in this case, we discuss other situations where it can be decisive. (ii) We discuss the possibility to induce photon mediated long-range interactions between spin and orbital degrees of freedom, which rely on the nonlinear light matter interaction (Raman scattering or two-photon absorption and emission).
Advances in time-resolved pump-probe spectroscopies have enabled us to follow the microscopic dynamics of quantum materials on femtosecond time scales. This gives us a glimpse into the inner workings of how complex, emergent functionalities of quantum many-body systems develop on ultrafast time scales or react to external forces. The ultimate dream of the community is to use light as a tuning parameter to create new states of matter on demand with designed properties and new functionalities, perhaps not achievable by other means. In this talk I will discuss recent progress in controlling and engineering properties of quantum materials through light-matter interaction. I will highlight work on Floquet engineering — the creation of effective Hamiltonians by time-periodic drives — on sub-cycle time scales combining theory and pump-probe experiments at the limits of energy and time resolution. I will then showcase recent theories on inducing superconductivity with light by employing enhanced light-matter interaction in the near-field involving polaritonic excitations.
J. Demsar1 1Institute of Physics, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, 55128 Mainz, Germany
T. Prosen1 1Faculty of mathematics and physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
The A2Mo3As3 (A = K, Rb, Cs) compounds are built of assembled Mo3As3 chains and are thus the potential realisations of quasi-one-dimensional metals. Various experiments on these materials hint to the Tomonaga-Luttinger liquid (TLL) physics from which superconductivity with a relatively high critical temperatures of Tc ≈ 10.5 K emerges. However, TLL and its relevance to emerging superconductivity are not yet resolved for A2Mo3As3 due to their multiband nature.Here we report a combined 75As nuclear quadrupole resonance (NQR), 87Rb and 133Cs nuclear magnetic resonance (NMR) and muon spin relaxation (mSR) study of Rb2Mo3As3 and Cs2Mo3As3 powders. The alkali metal spin-lattice relaxation rates show a characteristic power-law temperature dependence over a broad temperature range, which is a hallmark of the TLL dynamics dominated by the two-quasi-one-dimensional bands. Detailed analysis reveals that these compounds may be in an unusual state of effective attractive interactions, which opens up intriguing possibilities for the unconventional pairing symmetries of the superconducting state. To address the superconducting state we, in addition to 75As and alkali metal relaxation rate studies, employ also the ,transverse-field mSR. The temperature dependence of the muon relaxation rate, s, is in the superconducting state due to the field distribution created by the vortex lattice and is compared against s-, p- , and d-wave scenarios. The penetration depth l = 669 nm and the coherence length z = 3.4 nm are also determined.
