arXiv subjects

T. Mertelj

Publications and source records attributed to T. Mertelj.

At least 19 recordsLinked to original sources

arXiv2025

Critical photoinduced reflectivity relaxation dynamics in single-layer Bi-based cuprates near the pseudogap end point

A comprehensive study of photoinduced transient reflectivity dynamics in heavily overdoped single-layer cuprate (Bi,Pb)$_{2}$Sr$_{2}$CuO$_{6+\delta}$ (Pb-Bi-2201) across the end points of the pseudogap and superconducting phases was conducted using optical ultrafast time-resolved pump-probe spectroscopy. In the Pb-Bi-2201 near the proposed pseudogap end-point doping, the transient reflectivity dynamics above $T_{{\rm c}}$ resemble the pseudogap response observed in the optimally doped La-Bi-2201. With decreasing temperature, however, the relaxation time exhibits a power-law divergence, $\tau\sim10\hbar/k_{\mathrm{B}}T$, consistent with quantum critical behavior near the proposed pseudogap end-point doping. A similar power-law increase in relaxation time is also observed at a slightly more overdoped composition, though it is less pronounced.

cond-mat.supr-con↗

arXiv2024

Anomalous hardening of spin waves in cobalt/molecular-semiconductor heterostructures reveals strongly anisotropic spinterface magnetism

The interface between a ferromagnetic metal and an organic molecular semiconductor, commonly referred to as a spinterface, is an important component for advancing spintronic technologies. Hybridization of the ferromagnetic-metal surface d orbitals with the molecular-semiconductor p orbitals induces profound modifications not only in the interfacial molecular layer, but also in the surface ferromagnetic-metal atomic layer. These effects are particularly pronounced at low temperatures, manifesting as substantial modifications in the magnetic properties of thin-film magnetic-metal/organic heterostructures. Despite extensive research and interest, the magnetic-ordering and magnetic-properties of the spinterface remain poorly understood. Using ultrafast time-resolved magneto-optical spectroscopy, to investigate the magnetic dynamics in such heterostructures, we unveil the unique spinterface-magnetism and its universality for a broad variety of cobalt/molecular-semiconductor interfaces. In particular, our findings demonstrate the presence of highly anisotropic low-temperature superparamagnetism at the cobalt/molecular-semiconductor spinterface. This anisotropic interfacial superparamagnetism is likely driven by strong chemical modifications in the cobalt interfacial layer caused by the chemisorbed molecular layer. These results highlight the pivotal role of molecular chemisorption in tuning the magnetic properties at spinterfaces, paving the way for future spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Ultrafast optical polarimetry in magnetic phases of Kondo semi metal CeSb

We investigated photoinduced ultrafast transient dynamics in different magnetic phases in CeSb by means of the time resolved magneto-optical spectroscopy. We observe a distinctive coherent oscillations in the ground-state antiferromagnetic (AF) phase and the high-magnetic field ferromagnetic (F) phase. While the AF-phase oscillations frequencies match the recent Raman scattering findings the F-phase oscillation frequency does not correspond to the previously observed magnetic excitation. The large spectroscopic factor, g=3.94, and optical polarization properties suggest that it corresponds to a previously undetected Ce^{3+} coherent crystal-field state excitation. The AF-phase oscillations show no magnetic field dependence so their lattice origin cannot be entirely excluded. The non-oscillatory part of the transients is qualitatively similar in all investigated magnetic phases with a faster sub-picosecond dynamics in the ferromagnetic and ferro-para-magnetic phases and is attributed to differences in the electronic structure, which affect the photo-excited quasiparticle energy relaxation kinetics.

cond-mat.str-el↗

arXiv2022

First-order kinetics bottleneck during photoinduced ultrafast insulator-metal transition in 3D orbitally-driven Peierls insulator CuIr$_{2}$S$_{4}$

Ultrafast dynamics across the photoinduced three-dimensional Peierls-like insulator-metal (IM) transition in CuIr$_{2}$S$_{4}$ was investigated by means of the all-optical ultrafast multi-pulse time-resolved spectroscopy. The structural coherence of the low-$T$ broken symmetry state is strongly suppressed on a sub-picosecond timescale above a threshold excitation fluence of $F_{\mathrm{c}}\approx3$ mJ/cm$^{2}$ (at 1.55-eV photon energy) resulting in a structurally inhomogeneous transient state which persists for several-tens of picoseconds before reverting to the original low-$T$ state. The electronic order shows a transient gap filling at a significantly lower fluence threshold of $\sim0.6$~mJ/cm$^{2}$. The data suggest that the photoinduced-transition structural dynamics to the high-$T$ metallic phase is governed by first-order-transition nucleation kinetics that prevents the complete structural transition into the high-$T$ phase even at excitation fluences significantly larger than $F_{\mathrm{c}}$. In contrast, the dynamically-decoupled electronic order is suppressed rather independently due to a photoinduced Mott transition.

cond-mat.str-el↗

arXiv2022

Lattice vibrational modes in changchengite from Raman spectroscopy and first principles electronic structure

We measured room-temperature phonon Raman spectra of changchengite (IrBiS) and compared the experimental phonon wavenumbers to the theoretical ones obtained by means of the \emph{ab initio} density-functional-theory calculations in the presence and absence of the spin-orbit coupling effects. Combining two different excitation photon energies all the symmetry predicted Raman modes are experimentally observed. The electronic properties of IrBiS are found to be similar to the recently studied isostructural compound IrBiSe showing a large Dresselhaus spin-orbit valence band splitting. A good agreement between the experimental and theoretically predicted Raman phonon wavenumbers is found only when the lattice parameter is constrained to the experimental value. The inclusion of the spin orbit coupling does not significantly affect the phonon wavenumbers.

cond-mat.mtrl-sci↗

arXiv2021

First-order kinetics bottleneck during photoinduced ultrafast insulator-metal transition in 3D orbitally-driven Peierls insulator CuIr$_{2}$S$_{4}$

The spinel-structure CuIr$_{2}$S$_{4}$ compound displays a rather unusual orbitally-driven three-dimensional Peierls-like insulator-metal transition. The low-T symmetry-broken insulating state is especially interesting due to the existence of a metastable irradiation-induced disordered weakly conducting state. Here we study intense femtosecond optical pulse irradiation effects by means of the all-optical ultrafast multi-pulse time-resolved spectroscopy. We show that the structural coherence of the low-T broken symmetry state is strongly suppressed on a sub-picosecond timescale above a threshold excitation fluence resulting in a structurally inhomogeneous transient state which persists for several-tens of picoseconds before reverting to the low-T disordered weakly conducting state. The electronic order shows a transient gap filling at a significantly lower fluence threshold. The data suggest that the photoinduced-transition dynamics to the high-T metallic phase is governed by first-order-transition nucleation kinetics that prevents the complete ultrafast structural transition even when the absorbed energy significantly exceeds the equilibrium enthalpy difference to the high-T metallic phase. In contrast, the dynamically-decoupled electronic order is transiently suppressed on a sub-picosecond timescale rather independently due to a photoinduced Mott transition.

cond-mat.str-el↗

arXiv2020

Orbitally-driven insulator-metal transition in CuIr$_2$S$_4$: Temperature dependent transient reflectivity study

Ultrafast transient reflectivity across the unusual three-dimensional Peierls-like insulator-metal (IM) transition in CuIr_{2}S_{4} was measured as a function of temperature. The low-temperature insulating-phase transient response is dominated by broken-symmetry-induced coherent lattice oscillations that abruptly vanish at the IM transition. The coherent mode spectra are consistent with Raman spectra reported in literature. The origin of the broken-symmetry-induced is also briefly discussed.

cond-mat.str-el↗

arXiv2018

Optical creation and temperature stability of the hidden charge density wave state in 1T-TaS_{2-x}Se_{x}

The femtosecond transinet optical spectroscopy is employed to study the relaxation dynamics of the equilibrium and hidden metastable charge-density-wave states in single crystals of 1$T$-TaS$_{2-x}$Se$_{x}$ as a function of the Se doping $x$. Similarly to pristine 1$T$-TaS$_{2}$, the transition to a hidden phase is observed at low temperature after a quench with a single 50~fs laser pulse, in the commensurate Mott phase up to $x=0.6$. The photo-induced hidden-phase formation is accompanied by a notable change in the coherent phonon spectra, and particularly the collective amplitude mode. While the stability of the hidden phase with increased temperatures is only slightly dependent of the Se content the hidden-phase creation-treshold fluence strongly increases with the Se content from 1 to $\sim4$ mJ/cm$^{2}$.

cond-mat.str-el↗

arXiv2018

Ultrafast destruction and recovery of the spin density wave order in iron based pnictides: a multi-pulse optical study

We report on systematic excitation-density dependent all-optical femtosecond time resolved study of the spin-density wave state in iron-based superconductors. The destruction and recovery dynamics are measured by means of the standard and a multi-pulse pump-probe technique. The experimental data are analyzed and interpreted in the framework of an extended three temperature model. The analysis suggests that the optical-phonons energy-relaxation plays an important role in the recovery of almost exclusively electronically driven spin density wave order.

cond-mat.str-el↗

arXiv2017

Dynamics of the superconducting order parameter through ultrafast normal-to-superconducting phase transition in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ from multi-pulse polarization-resolved transient optical reflectivity

A systematic temperature dependent study of the femtosecond optical superconducting (SC) state destruction and recovery in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ cuprate superconductor by means of the all-optical polarization-sensitive multi-pulse spectroscopy is presented. At low temperatures and a partial SC state suppression an anisotropic SC-gap recovery-timescale is suggested by the data. The SC state destruction and recovery dynamics are compared to the recent TR-ARPES-inferred SC-gap dynamics and a qualitative agreement is found. Using a phenomenological response function the experimental data are also compared to time dependent Ginzburg-Landau model simulations.

cond-mat.supr-con↗

arXiv2017

Evolution of coherent collective modes through consecutive CDW transitions in (PO$_{2}$)$_{4}$(WO$_{3}$)$_{12}$ mono-phosphate tungsten bronze

All optical femtosecond relaxation dynamics in a single crystal of mono-phosphate tungsten bronze (PO$_{2}$)$_{4}$(WO$_{3}$)$_{2m}$ with alternate stacking m=6 of WO$_{3}$ layers was studied through the three consequent charge density wave (CDW) transitions. Several transient coherent collective modes associated to the different CDW transitions were observed and analyzed in the framework of the time dependent Ginzburg-Landau theory. Remarkably, the interference of the modes leads to an apparent rectification effect in the transient reflectivity response. A saturation of the coherent-mode amplitudes with increasing pump fluence well below the CDWs destruction threshold fluence indicates a decoupling of the electronic and lattice parts of the order parameter under strong optical drive.

cond-mat.str-el↗

arXiv2016

Fluence dependent femtosecond quasi-particle and Eu^{2+} -spin relaxation dynamics in EuFe_{2}(As,P)_{2}

We investigated temperature and fluence dependent dynamics of the time resolved optical reflectivity in undoped spin-density-wave (SDW) and doped superconducting (SC) EuFe$_{2}$(As,P)$_{2}$ with emphasis on the ordered Eu$^{2+}$-spin temperature region. The data indicate that the SDW order coexists at low temperature with the SC and Eu$^{2+}$-ferromagnetic order. Increasing the excitation fluence leads to a thermal suppression of the Eu$^{2+}$-spin order due to the crystal-lattice heating while the SDW order is suppressed nonthermally at a higher fluence.

cond-mat.supr-con↗

arXiv2016

Real time measurement of the emergence of superconducting order in a high temperature superconductor

Systems which rapidly evolve through symmetry-breaking transitions on timescales comparable to the fluctuation timescale of the single-particle excitations may behave very differently than under controlled near-ergodic conditions. A real-time investigation with high temporal resolution may reveal new insights into the ordering through the transition that are not available in static experiments. We present an investigation of the system trajectory through a normal-to-superconductor transition in a prototype high-temperature superconducting cuprate in which such a situation occurs. Using a multiple pulse femtosecond spectroscopy technique we measure the system trajectory and time-evolution of the single-particle excitations through the transition in La$_{1.9}$Sr$_{0.1}$CuO$_{4}$ and compare the data to a simulation based on time-dependent Ginzburg-Landau theory, using laser excitation fluence as an adjustable parameter controlling the quench conditions in both experiment and theory. The comparison reveals the presence of significant superconducting fluctuations which precede the transition on short timescales. By including superconducting fluctuations as a seed for the growth of superconducting order we can obtain a satisfactory agreement of the theory with the experiment. Remarkably, the pseudogap excitations apparently play no role in this process.

cond-mat.supr-con↗

arXiv2015

Superconducting gap in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ from temperature dependent transient optical reflectivity

Temperature and fluence dependence of the 1.55-eV optical transient reflectivity in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ was measured and analysed in the low and high excitation density limit. The effective magnitude of the superconducting gap of $\sim 5$ meV obtained from the low-fluence-data bottleneck model fit is consistent with the ARPES results for the $γ$-hole Fermi surface. The superconducting-state nonthermal optical destruction energy was determined from the fluence dependent data. The in-plane optical destruction energy scales well with T$_{\mathrm{c}}^{2}$ and is found to be similar in a number of different layered superconductors.

cond-mat.supr-con↗

arXiv2014

Coexistence of ferromagnetism and superconductivity in iron based pnictides: a time resolved magnetooptical study

Ferromagnetism and superconductivity are antagonistic phenomena. Their coexistence implies either a modulated ferromagnetic order parameter on a lengthscale shorter than the superconducting coherence length or a weak exchange coupling between the itinerant superconducting electrons and the localized ordered spins. In some iron based pnictide superconductors the coexistence of ferromagnetism and superconductivity has been clearly demonstrated. The nature of the coexistence, however, remains elusive since no clear understanding of the spin structure in the superconducting state has been reached and the reports on the coupling strength are controversial. We show, by a direct optical pump-probe experiment, that the coupling is weak, since the transfer of the excess energy from the itinerant electrons to ordered localized spins is much slower than the electron-phonon relaxation, implying the coexistence without the short-lengthscale ferromagnetic order parameter modulation. Remarkably, the polarization analysis of the coherently excited spin wave response points towards a simple ferromagnetic ordering of spins with two distinct types of ferromagnetic domains.

cond-mat.supr-con↗

arXiv2014

Multichannel photodiode detector for ultrafast optical spectroscopy

Construction and characterization of a multichannel photodiode detector based on commercially available components with high signal to noise of $\sim10^{6}$ and a rapid frame rate, suitable for time resolved femtosecond spectroscopy with high repetition femtosecond sources, is presented.

physics.optics↗

arXiv2014

Fast non-thermal switching between macroscopic charge-ordered quantum states induced by charge injection

The functionality of logic and memory elements in current electronics is based on multi-stability, driven either by manipulating local concentrations of electrons in transistors, or by switching between equivalent states of a material with a degener- ate ground state in magnetic or ferroelectric materials. Another possibility is offered by phase transitions with switching between metallic and insulating phases, but classical phase transitions are limited in speed by slow nucleation, proliferation of domains and hysteresis. We can in principle avoid these problems by using quantum states for switching, but microscopic systems suffer from decoherence which prohibits their use in everyday devices. Macroscopic quantum states, such as the superconducting ground state have the advantage that on a fundamental level they do not suffer from decoherence plaguing microscopic systems. Here we demonstrate for the first time ultrafast non-thermal switching between different metastable electronically ordered states by pulsed electrical charge injection. The macroscopic nature of the many-body quantum states(1-4) - which are not part of the equilibrium phase diagram - gives rise to unprecedented stability and remarka- bly sharp switching thresholds. Fast sub-50 ps switching, large associated re- sistance changes, 2-terminal operation and demonstrable high fidelity of bi-stability control suggest new opportunities for the use of macroscopic quantum states in electronics, particularly for an ultrafast non-volatile quantum charge-order resistive random access memory (QCOR-RAM).

cond-mat.mes-hall↗

arXiv2014

Ultrafast switching to a stable hidden topologically protected quantum state in an electronic crystal

Hidden states of matter with novel and unusual properties may be created if a system out of equilibrium can be induced to follow a trajectory to a state which is inaccessible or does not even exist under normal equilibrium conditions. Here we report on the discovery of a hidden (H) topologically protected electronic state in a layered dichalcogenide 1T-TaS2 crystal reached as a result of a quench caused by a single 35 fs laser pulse. The properties of the H state are markedly different from any other state of the system: it exhibits a large drop of electrical resistance, strongly modified single particle and collective mode spectra and a marked change of optical reflectivity. Particularly important and unusual, the H state is stable for an arbitrarily long time until a laser pulse, electrical current or thermal erase procedure is applied, causing it to revert to the thermodynamic ground state. Major observed events can be reproduced by a kinetic model describing the conversion of photo excited electrons and holes into an electronically ordered crystal, thus converting a Mott insulator to a conducting H state. Its long-time stability follows from the topological protection of the number of periods in the electronic crystal.

cond-mat.str-el↗