The study of phase transitions in real time under nonequilibrium conditions is of fundamental interest in many areas of physics. A special category of recent fundamental and practical interest are transitions to metastable hidden states which occur under conditions of particle-hole asymmetry. While such behavior has been invoked in cosmology to explain baryogenesis, it is not commonly observed elsewhere. In the quasi-two-dimensional dichalcogenide, 1T-TaS2, conditions for the formation of an electronically textured hidden “false vacuum” state are created by femtosecond laser photoexcitation and the resulting state is distinct from others states of the system in the equilibrium phase diagram. Femtosecond photoexcited low temperature scanning tunneling microscopy reveals long range order and a remarkable quantum duality of polaron behavior with a vivid real-space illustration of the interplay of Mott physics, Anderson disorder localization, orbital stacking order and collective polaron behaviour. The current system – and the concept of metastable states created by charge injection – are of practical interest for ultrafast low-energy low-temperature non-volatile memory devices with immediate applications in cryogenic computing.
COBISS.SI-ID: 30455335
Recent demonstrations of controlled switching between different ordered macroscopic states by impulsive electromagnetic perturbations in complex materials have opened some fundamental questions on the mechanisms responsible for such remarkable behavior. Here we experimentally address the question of whether two-dimensional (2D) Mott physics can be responsible for unusual switching between states of different electronic order in the layered dichalcogenide 1T-TaS2, or it is a result of subtle inter-layer orbitronic re-ordering of its helical stacking structure. We report on the switching properties both in-plane and perpendicular to the layers by current-pulse injection, the anisotropy of electronic transport in the commensurate ground state, and relaxation properties of the switched metastable state. Contrary to recent theoretical calculations, which predict a uni-directional metal perpendicular to the layers, we observe a large resistivity in this direction, with a temperature-dependent anisotropy. Remarkably, large resistance ratios are observed in the memristive switching both in-plane (IP) and out-of-plane (OP). The relaxation dynamics of the metastable state for both IP and OP electron transport are seemingly governed by the same mesoscopic quantum re-ordering process. We conclude that 1T-TaS2 shows resistance switching arising from an interplay of both IP and OP correlations.
COBISS.SI-ID: 30469415
Femtosecond pulse induced charge ordering studied by low-temperature 4-probe STM reveals a multitude of hidden states with different long range order, from a commensurate polaronic crystal order to a new type of polaron glass. The dynamical properties of these states are shown to be distinctly different, as revealed by the relaxation properties on intermediate timescales, while the photoinduced transition from one long range ordered state to another is shown to proceed within a few femtoseconds.
COBISS.SI-ID: 29901863
Transition metal dichalcogenides (TMDs) have a deceptively simple structure and chemical formula, but this family of binary layered crystal materials consists of members sporting very diverse properties; each member has several polytypes and each polytype a rich phase diagram. The capability of growing TMD monocrystals with a well-defined number of layers and a small number of defects is instrumental in producing samples tailored for specific purposes. Molecular beam epitaxy is a thin film growth method designed for slow but precise assembly of constituent atoms or molecules into a crystalline layer. We present the results of growing TaS2 thin films obtained with our MBE system equipped with a sulfur cracker source. The thin films have been characterized by AFM, Raman spectroscopy, XRD and TEM.
COBISS.SI-ID: 31274279
We present the results of growing TaS2 thin films obtained with our MBE system equipped with a sulfur cracker source. The thin films have been characterized by AFM, Raman spectroscopy, XRD and TEM.
COBISS.SI-ID: 30740519