Events

Strong excitations of correlated quantum materials give rise to various non-thermal phases which are not present in their equilibrium counterpart. Recently, it was shown that the one-dimensional Fermi Hubbard Model features charge density wave and η-pairing phases upon photo-doping. In this study, we explore the non-equilibrium behavior of the Fermi Hubbard ladder and employ the Schrieffer-Wolff transformation to map it to a simplified t-J-like model, providing an effective equilibrium description of the photo-doped states. Our investigation highlights the significance of applying an electric field along the rung to the hopping term. This floquet manipulation allows to increase the spin and η-exchange coupling along the rung independent of the hopping term. Moreover, the magnitude of hopping decreases as a result of the drive. These combined effect tends to localize the excitons close to each other and thus enhance its binding energy. To characterize the ground state of the system, we employ relevant correlators and make notable observations. We show that at certain drive frequencies, the ground state encompasses a strongly bound holon-holon/doublon-holon pair along the rung, alongside inter-chain singlets. Additionally, we propose experimental setups to test our theory.

We investigated by means of the ultrafast time-resolved magneto-optical Kerr effect (MOKE) spectroscopy the effect of the interface between organic molecular semiconductors and cobalt on the magnetic anisotropy of polycrystalline Co thin films. Comparison of the effect was measured on interfaces of Co with: nonmagnetic metal (Al), metalorganic complexes tris(8-hydroxyquinoline)gallium (Gaq3) and M-phthalocyanines (M=Cu, Co) as well as Buckminster-fullerene (C60) molecules.In general, the transient MOKE signals were found to exhibit damped coherent spin wave oscillations (CSWO) with frequencies up to several tens of GHz. Detailed analysis of the spin-wave temperature and magnetic field dependences allowed us to compare the influence of different molecular interfaces.

In this talk, I will present a renormalization group analysis of the problem of Anderson localization on Regular Random Graphs (RRGs). I will first review and extend the finite-dimensional analysis of Abrahams, Anderson, Licciardello, and Ramakrishnan in terms of spectral observables, and discuss how to take the large-d limit. I will then motivate that the infinite-dimensional case, relevant also in the context of Many-Body Localization, recovers the Anderson model on RRGs. In this case, the renormalization group β-function necessarily involves two parameters, but the one-parameter scaling hypothesis is recovered for sufficiently large system sizes. I will also discuss how to understand this change in behavior in terms of the geometrical properties of the graphs. The talk will be based on arXiv:2306.14965 and ongoing work

While the eigenstate thermalization hypothesis (ETH) is well established for quantum-chaotic interacting systems, its validity for other classes of systems remains a matter of intense debate. Focusing on quadratic fermionic Hamiltonians, we here argue that the weak ETH is satisfied for few-body observables in many-body eigenstates of quantum-chaotic quadratic (QCQ) Hamiltonians. In contrast, the weak ETH is violated in two cases: (a) for sums of few-body observables in all quadratic Hamiltonians, and (b) for few-body observables in localized quadratic Hamiltonians. We argue that these properties can be traced back to the validity of single-particle eigenstate thermalization, and we highlight the subtle role of normalization of operators. Our results suggest that the difference between weak and no ETH in many-body eigenstates allows for a distinction between single-particle quantum chaos and localization. We test to which degree this phenomenology holds true for integrable systems such as the XYZ and XXZ models.

To improve the field of superconducting computer systems, a low-power, fast and durable memory device that is compatible with the single-flux-quantum (SFQ) logic is needed. Here we report on recent progress in the development of a so-called parallelotron (pTron) device that comprises a superconducting three-terminal amplifying nanowire cryotron (nTron) and a charge configuration memristor (CCM) based on 1T-TaS2. Besides the current-voltage characteristics and read operation, we also record switching of the device in real time when the switching pulse is applied to the control terminal. Measured results show great matching to model predictions, demonstrating the validity of the model and its potential usefulness for future optimization of the device’s parameters. We briefly discuss the effect of noise on the switching capabilities of the pTron device.

By combining time and angle-resolved photoemission spectroscopy (tr-ARPES) and broadband time-resolved optical spectroscopy (TR-OS) we investigate the effect of an optical excitation on the electronic and structural properties of the charge-density wave (CDW) system VTe2. Recently, the modification of the material’s electronic structure induced by CDW formation has been discussed because the strongly orbital-dependent changes may give rise to a topological change in specific bands.In our contribution, we show by means of TR-OS measurements the possibility to optically excite the amplitude mode (AM) of the CDW phase and therefore couple to the CDW condensate. Moreover, by studying the partial closing of the CDW gap our tr-ARPES experiments unveil a major role played by the lattice degrees of freedom in the stabilization of the CDW phase in VTe2.

Integrable systems offer rare examples of solvable many-body problems in the quantum world. Due to the fine-tuned structure, their realization in nature and experiment is never completely accurate, therefore effects of integrability are observed only transiently. One way to surpass that is to couple nearly integrable systems to baths and driving: these will stabilize integrable effects up to arbitrary time, as encoded in the time dependent, and eventually, the stationary state of form of a generalized Gibbs ensemble. However, the description of such driven dissipative nearly integrable models is challenging and no exact analytical methods have been proposed so far. Here we develop an iterative scheme in which integrability breaking perturbations (baths) determine the most necessary conserved quantities to be added into a truncated generalized Gibbs ensemble description. Our scheme significantly reduces the complexity of the problem, paving the way for thermodynamic results.

The transition metal dichalcogenide 1T-TaS2 is a layered compound that exhibits a series of increasingly commensurate charge density wave phases with decreasing temperature, including a low-temperature insulating phase. For a single 1T-TaS2 layer, with an odd number of electrons per Star-of-David cluster, the insulating behaviour may be attributed to Mott localisation. However, the stacking arrangement of multiple layers can lead to doubling of the unit cell, where the nature of the insulating state is ambiguous. Furthermore, the various possible stacking terminations lead to surface states with non-trivial interplay between band-insulating and Mott-insulating behaviour.