Papers by Dragan Mihailovic
Nature Communications, Nov 2, 2023
Research Square (Research Square), Sep 5, 2023
Mirror symmetry plays a major role in determining the properties of matter and is of particular i... more Mirror symmetry plays a major role in determining the properties of matter and is of particular interest in condensed many-body systems undergoing symmetry breaking transitions under non-equilibrium conditions. Typically, in the aftermath of such transitions, one of the two possible broken symmetry states is emergent. However, synthetic systems and those formed under non-equilibrium conditions may exhibit metastable states comprising of both left (L) and right (R) handed symmetry. Here we explore the formation of chiral charge-density wave (CDW) domains after a laser quench in 1T-TaS2 with scanning tunneling microscopy. Typically, we observed transient domains of both chiralities, separated spatially from each other by domain walls with different structure. In addition, we observe transient density of states modulations consistent with interference of L and R-handed charge density waves within the surface monolayer. Theoretical modeling of the intertwined domain structures using a classical charged lattice gas model reproduces the experimental domain wall structures. The superposition (S) state cannot be understood classically within the correlated electron model but is found to be consistent with interferences of L and R-handed charge-density waves within domains, confined by surrounding domain walls, vividly revealing for the first time an interference of Fermi electrons with opposite chirality in charge density wave systems.
arXiv (Cornell University), Mar 12, 2021
Emergent metastability in non-equilibrium systems is a subject that touches everything from the o... more Emergent metastability in non-equilibrium systems is a subject that touches everything from the origins of life 1 to the quantum nature of the universe 2. In condensed quantum matter, a good topical example is the metastability of topologically inhibited self-organization of electronic domains in a correlated electronic crystal in the aftermath of a symmetry-breaking phase transition 3. Understanding the dynamics of such systems is crucial for developing new quantum technologies and exploring fundamental aspects of many-body non-equilibrium quantum mechanics. Here, a non-equilibrium state is set up by carrier injection in the quantum material (M), resulting in a domain structure, whose time-evolution is investigated by scanning tunneling microscopy. Demonstrating a new approach to modelling of emergent non-equilibrium quantum behavior, we use an array of 2008 qubits in a programmable noisy superconducting quantum simulator (NSQS) without error correction (P), in which mutual qubit interconnections correspond directly to the electronic interactions on the triangular lattice of the electronic crystal material. The success of the simulations critically depends on both the faithfulness of the model correspondence between the two systems and careful management of the decoherence pathways. Importantly, decoherence of both P and M is driven by noise with a characteristic / frequency spectrum. The simulations reveal how an emergent false vacuum state arises, describing the time evolution and temperature dependence of the observed electronic domain dynamics of M solely on the basis of microscopic electronic interactions. The parallel experiments demonstrate the potential of NSQSs for studying emergent non-equilibrium dynamics in complex many-body quantum systems.
Scientific Reports
Mirror symmetry plays a major role in determining the properties of matter and is of particular i... more Mirror symmetry plays a major role in determining the properties of matter and is of particular interest in condensed many-body systems undergoing symmetry breaking transitions under non-equilibrium conditions. Typically, in the aftermath of such transitions, one of the two possible broken symmetry states is emergent. However, synthetic systems and those formed under non-equilibrium conditions may exhibit metastable states comprising of both left (L) and right (R) handed symmetry. Here we explore the formation of chiral charge-density wave (CDW) domains after a laser quench in 1T-TaS2 with scanning tunneling microscopy. Typically, we observed transient domains of both chiralities, separated spatially from each other by domain walls with different structure. In addition, we observe transient density of states modulations consistent with interference of L and R-handed charge density waves within the surface monolayer. Theoretical modeling of the intertwined domain structures using a c...
Physical Review B, 2012
We systematically investigate the photoexcited (PE) quasi-particle (QP) relaxation and lowenergy ... more We systematically investigate the photoexcited (PE) quasi-particle (QP) relaxation and lowenergy electronic structure in electron doped Ba(Fe1−xCox)2As2 single crystals as a function of Co doping, 0 ≤ x ≤ 0.11. The evolution of the photoinduced reflectivity transients with x proceeds with no abrupt changes. In the orthorhombic spin-density-wave (SDW) state a bottleneck associated with a partial charge-gap opening is detected, similar to previous results in different SDW iron-pnictides. The relative charge gap magnitude 2∆(0)/kBTs decreases with increasing x. In the superconducting (SC) state an additional relaxational component appears due to a partial (or complete) destruction of the SC state proceeding on a sub-0.5-picosecond timescale. From the SC component saturation behavior the optical SC-state destruction energy, Up/kB = 0.3 K/Fe, is determined near the optimal doping. The subsequent relatively slow recovery of the SC state indicates clean SC gaps. The T-dependence of the transient reflectivity amplitude in the normal state is consistent with the presence of a pseudogap in the QP density of states. The polarization anisotropy of the transients suggests that the pseudogap-like behavior might be associated with a broken 4-fold rotational symmetry resulting from nematic electronic fluctuations persisting up to T ≃ 200 K at any x. The second moment of the Eliashberg function, obtained from the relaxation rate in the metallic state at higher temperatures, indicates a moderate electron phonon coupling, λ 0.3, that decreases with increasing doping.
Physical Review B, 2013
We investigate temperature and fluence dependent dynamics of the photoexcited quasi-particle rela... more We investigate temperature and fluence dependent dynamics of the photoexcited quasi-particle relaxation and low-energy electronic structure in electron-doped 1111-structure Sm(Fe0.93Co0.07)AsO single crystal. We find that the behavior is qualitatively identical to the 122-structure Ba(Fe,Co)2As2 including the presence of a normal state pseudogap and a marked 2-fold symmetry breaking in the tetragonal phase that we relate to the electronic nematicity. The 2-fold symmetry breaking appears to be a general feature of the electron doped iron pnictides.
Journal of Superconductivity and Novel Magnetism, 2009
We investigate the quasiparticle relaxation and low-energy electronic structure in a near-optimal... more We investigate the quasiparticle relaxation and low-energy electronic structure in a near-optimally doped pnictide superconductor with T c = 49.5 K by means of femtosecond spectroscopy. Multiple relaxation processes are evident, with distinct superconducting state dynamics and a clear "pseudogap"-like feature with an onset above 180 K indicating the existence of a temperature-independent gap of magnitude Δ PG = 61 ± 9 meV above and below T c. The fluence and temperature dependence of the superconducting state dynamics shows similar behaviour to the cuprate superconductors with the superconducting-condensate vaporization energy of E va /k B ≈ 1.5 K per Fe ion.
Physical Review B, 2007
Magnetic properties of high purity stoichiometric La2CuO4 nanoparticles are systematically invest... more Magnetic properties of high purity stoichiometric La2CuO4 nanoparticles are systematically investigated as a function of particle size. Ferromagnetic single-domain spin clusters are shown to spontaneously form at the surface of fine grains as well as paramagnetic defects. Hysteresis loops and thermomagnetic irreversibility are observed in a wide temperature range 5 − 350 K with the remnant moment and coercivity gradually decreasing with increasing temperature. Possible origins of the spontaneous surface ferromagnetic clusters and the relation of our data to the appearance of unusual magnetic phenomena and phase separation of doped cuprates are discussed.
Anali PAZU
V članku so predstavljeni rezultati meritev fluenčne odvisnosti tranziente reflektivnosti vzbujen... more V članku so predstavljeni rezultati meritev fluenčne odvisnosti tranziente reflektivnosti vzbujene z ultrakratkimi laserskimi pulzi v kristalih η-Mo4O11. Rezultati meritev kažejo, da lahko v kristalih pri nizkih temperaturah z dovolj veliko fluenco induciramo fazni prehod, ki ni znan iz temperaturnega faznega diagrama.
Applied Physics Letters
Progress in high-performance computing demands significant advances in memory technology. Among n... more Progress in high-performance computing demands significant advances in memory technology. Among novel memory technologies that promise efficient device operation on a sub-ns timescale, resistance switching between charge ordered phases of 1 T-TaS2 has shown to be potentially useful for development of high-speed, energy efficient nonvolatile memory devices. Measurement of the electrical operation of such devices in the picosecond regime is technically challenging and hitherto still largely unexplored. Here, we use an optoelectronic “laboratory-on-a-chip” experiment for measurement of ultrafast memory switching, enabling accurate measurement of electrical switching parameters with 100 fs temporal resolution. Photoexcitation and electro-optic sampling on a (Cd,Mn)Te substrate are used to generate and, subsequently, measure electrical pulse propagation with intra-band excitation and sub-gap probing, respectively. We demonstrate high contrast nonvolatile resistance switching from high to...
Journal of Superconductivity and Novel Magnetism, 2022
In cuprate superconductors, a pronounced maximum of superconducting ! "#$ is observed in compound... more In cuprate superconductors, a pronounced maximum of superconducting ! "#$ is observed in compounds that have an in-plane Cu-O distance %&'(close to ~1.92 Angstroms. On the other hand, direct measurements of the electron-phonon coupling ⟨) ⟩ as a function of %&'(show a clear linear correlation, implying that ! "#$ is a strongly non-linear function of ⟨) ⟩. Conventional superconductivity theories based on the electron-phonon interaction predict a monotonic dependence of ! "#$ on ⟨) ⟩, which makes them incompatible with the observed behavior. The observed cross-over behavior as a function of ⟨) ⟩ suggests that ! "#$ occurs at the cross-over from weak to strong coupling, which is also associated with the onset of carrier localization. A coexistence, with a dynamical exchange of localized and itinerant carriers in a two-component superconductivity scenario are in agreement with the observed anomalous behavior and are suggested to be the key to understanding the mechanism for achieving high ! "#$ .
arXiv: Strongly Correlated Electrons, 2017
The fundamental idea that many body systems in complex materials may self-organise into long rang... more The fundamental idea that many body systems in complex materials may self-organise into long range order under highly non-equilibrium conditions leads to the notion that entirely new emergent states with new and unexpected functionalities might be created. In this paper we show for the first time that a complex metastable state with long range order can be created through a non-equilibrium topological transformation in a transition metal dichalcogenide. Combining ultrafast optical pulse excitation with orbitally-resolved large-area scanning tunnelling microscopy we find subtle, but unambiguous evidence for long range electronic order which is different from all other known states in the system, and whose complex domain structure is not random, but is described by harmonics of the underlying charge density wave order. We show that the structure of the state is topologically distinct from the ground state, elucidating the origins of its remarkable metastability. These fundamental insi...
Nano Energy, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Science advances, 2018
Optical control of states exhibiting macroscopic phase coherence in condensed matter systems open... more Optical control of states exhibiting macroscopic phase coherence in condensed matter systems opens intriguing possibilities for materials and device engineering, including optically controlled qubits and photoinduced superconductivity. Metastable states, which in bulk materials are often associated with the formation of topological defects, are of more practical interest. Scaling to nanosize leads to reduced dimensionality, fundamentally changing the system's properties. In one-dimensional superconducting nanowires, vortices that are present in three-dimensional systems are replaced by fluctuating topological defects of the phase. These drastically change the dynamical behavior of the superconductor and introduce dynamical periodic long-range ordered states when the current is driven through the wire. We report the control and manipulation of transitions between different dynamically stable states in superconducting δ-MoN nanowire circuits by ultrashort laser pulses. Not only ca...
Physical Review Letters, 2003
We report on the very peculiar magnetic properties of an ensemble of very weakly coupled lithiumd... more We report on the very peculiar magnetic properties of an ensemble of very weakly coupled lithiumdoped MoS 2 nanotubes. The magnetic susceptibility of the system is nearly 3 orders of magnitude greater than in typical Pauli metals, yet there is no evidence for any instability which would alleviate this highly frustrated state. Instead, the material exhibits peculiar paramagnetic stability down to very low temperatures, with no evidence of a quantum critical point as T ! 0 in spite of clear evidence for strongly correlated electron behavior. The exceptionally weak intertube interactions appear to lead to a realization of a near-ideal one-dimensional state in which fluctuations prevent the system from reordering magnetically or structurally.
Science, 2001
We report on the synthesis, structure, and self-assembly of single-wall subnanometer-diameter mol... more We report on the synthesis, structure, and self-assembly of single-wall subnanometer-diameter molybdenum disulfide tubes. The nanotubes are up to hundreds of micrometers long and display diverse self-assembly properties on different length scales, ranging from twisted bundles to regularly shaped “furry” forms. The bundles, which contain interstitial iodine, can be readily disassembled into individual molybdenum disulfide nanotubes. The synthesis was performed using a novel type of catalyzed transport reaction including C 60 as a growth promoter.
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Papers by Dragan Mihailovic