arXiv subjects

Cedomir Petrovic

Publications and source records attributed to Cedomir Petrovic.

At least 37 records · Page 2Linked to original sources

arXiv2023

Coupling of magnetism and Dirac fermions in YbMnSb2

We report inelastic neutron scattering measurements of magnetic excitations in YbMnSb2, a low-carrier-density Dirac semimetal in which the antiferromagnetic Mn layers are interleaved with Sb layers that host Dirac fermions. We observe a considerable broadening of spin waves, which is consistent with substantial spin fermion coupling. The spin wave damping, $γ$, in YbMnSb2 is roughly twice larger compared to that in a sister material, YbMnBi2, where an indication of a small damping consistent with theoretical analysis of the spin-fermion coupling was reported. The inter-plane interaction between the Mn layers in YbMnSb2 is also much stronger, suggesting that the interaction mechanism is rooted in the same spin-fermion coupling. Our results establish the systematics of spin-fermion interactions in layered magnetic Dirac materials.

cond-mat.str-el↗

arXiv2023

Pressure-induced magnetic properties of quasi-2D Cr2Si2Te6 and Mn3Si2Te6

Recently, the pressure has been used as external stimuli to induce structural and magnetic phase transitions in many layered quantum materials whose layers are linked by van der Waals forces. Such materials with weakly held layers allow relatively easy manipulation of the superexchange mechanism and lead to novel magnetic behavior. Using the hydrostatic pressure as a disorderless means to manipulate the interlayer coupling, we applied pressure on two quasi-2D sister compounds, namely, Cr2Si2Te6 (CST) and Mn3Si2Te6 (MST), up to ~1 GPa. Magnetic property measurements with the application of pressure revealed that the ferromagnetic transition temperature decreases in CST while the opposite trend occurs for the ferrimagnet MST. In MST, the magnetization decreases with the increase in the pressure, and such trend is not clearly noticed in CST, within the pressure range studied. Theoretical calculations showed the overall pressure effect on layer separation, bond angle, and exchange coupling, strongly influencing the change in subsequent magnetic characteristics. Exchange coupling in Mn3Si2Te6 is strongly frustrated and the first nearest neighbor interaction is the most dominant of the components with the strongest pressure dependence. Whereas, in Cr2Si2Te6, the exchange coupling parameters exhibit very little dependence on the pressure. This combined experimental and theoretical work has the potential to expand to other relevant quantum materials.

cond-mat.mtrl-sci↗

arXiv2022

Spin-phonon interaction and short range order in $\mathrm{Mn_3Si_{2}Te_6}$

The vibrational properties of ferrimagnetic $\mathrm{Mn_3Si_{2}Te_6}$ single crystals are investigated using Raman spectroscopy and density functional theory calculations. Eighteen Raman-active modes are identified, fourteen of which are assigned according to with the trigonal symmetry. Four additional peaks, obeying the $A_{1g}$ selection rules, are attributed to the overtones. The unconventional temperature evolution of the $A_{1g}^5$ mode self-energy suggests a competition between different short-range magnetic correlations that significantly impact the spin-phonon interaction in $\mathrm{Mn_3Si_{2}Te_6}$. The research provides a comprehensive insight to the lattice properties, studies their temperature dependence and shows the arguments for existence of competing short-range magnetic phases in $\mathrm{Mn_3Si_{2}Te_6}$.

cond-mat.mtrl-sci↗

arXiv2022

Suppression of Superconductivity and Nematic Order in Fe$_{1-y}$Se$_{1-x}$S$_x$ (0$\leq$$x$$\leq$1, $y$$\leq$0.1) Crystals by Anion Height Disorder

Connections between crystal chemistry and critical temperature $T_c$ have been in the focus of superconductivity, one of the most widely studied phenomena in physics, chemistry and materials science alike. In most Fe-based superconductors, materials chemistry and physics conspire so that $T_c$ correlates with the average anion height above the Fe plane, i. e. with the geometry of the FeAs4 or FeCh4 (Ch = Te, Se, or S) tetrahedron. By synthesizing Fe$_{1-y}$Se$_{1-x}$S$_x$ (0$\leq$$x$$\leq$1, $y$$\leq$0.1), we find that in alloyed crystals $T_c$ is not correlated with the anion height like it is for most other Fe superconductors. Instead, changes in $T_c$($x$) and tetragonal-to-orthorombic (nematic) transition $T_s$($x$) upon cooling are correlated with disorder in Fe vibrations in the direction orthogonal to Fe planes, along the crystallographic c-axis. The disorder stems from the random nature of S substitution, causing deformed Fe(Se,S)4 tetrahedra with different Fe-Se and Fe-S bond distances. Our results provide evidence of $T_c$ and $T_s$ suppression by disorder in anion height. The connection to local crystal chemistry may be exploited in computational prediction of new superconducting materials with Fe/S building blocks.

cond-mat.supr-con↗

arXiv2022

Role of Local Ru Hexamers in Superconductivity of Ruthenium Phosphide

Superconductivity in binary ruthenium pnictides occurs proximal to and upon suppression of a mysterious non-magnetic ground state, preceded by a pseudogap phase associated with Fermi surface instability, and its critical temperature, T$_{c}$, is maximized around the pseudogap quantum critical point. By analogy with isoelectronic iron based counterparts, antiferromagnetic fluctuations became "usual suspects" as putative mediators of superconducting pairing. Here we report on a high temperature local symmetry breaking in RuP, the parent of the maximum-Tc branch of these novel superconductors, revealed by combined nanostructure-sensitive powder and single crystal X-ray total scattering experiments. Large local Ru$_{6}$ hexamer distortions associated with orbital-charge trimerization form above the two-stage electronic transition in RuP. While hexamer ordering enables the nonmagnetic ground state and presumed complex oligomerization, the relevance of pseudogap fluctuations for superconductivity emerges as a distinct prospect. As a transition metal system in which partial d-manifold filling combined with high crystal symmetry promotes electronic instabilities, this represents a further example of local electronic precursors underpinning the macroscopic collective behavior of quantum materials.

cond-mat.supr-con↗

arXiv2022

Giant thermoelectric power factor anisotropy in PtSb$_{1.4}$Sn$_{0.6}$

We report giant anisotropy in thermoelectric power factor ($S^2σ$) of marcasite structure-type PtSb$_{1.4}$Sn$_{0.6}$. PtSb$_{1.4}$Sn$_{0.6}$, synthesized using ambient pressure flux growth method upon mixing Sb and Sn on the same atomic site, is a new phase different from both PtSb$_2$ and PtSn$_2$ that crystallize in the cubic $Pa\bar{3}$ pyrite and $Fm\bar{3}m$ fluorite unit cell symmetry, respectively. Giant difference in $S^2σ$ for heat flow applied along different principal directions of the orthorhombic unit cell mostly stems from anisotropic Seebeck coefficients.

cond-mat.mtrl-sci↗

arXiv2022

Short-range Crystalline Order-Tuned Conductivity in Cr$_2$Si$_2$Te$_6$ van der Waals Magnetic Crystals

Two-dimensional magnetic materials (2DMM) are significant for studies on the nature of 2D long range magnetic order but also for future spintronic devices. Of particular interest are 2DMM where spins can be manipulated by electrical conduction. Whereas Cr$_2$Si$_2$Te$_6$ exhibits magnetic order in few-layer crystals, its large band gap inhibits electronic conduction. Here we show that the defect-induced short-range crystal order in Cr$_2$Si$_2$Te$_6$ on the length scale below 0.6 nm induces substantially reduced band gap and robust semiconducting behavior down to 2 K that turns to metallic above 10 GPa. Our results will be helpful to design conducting state in 2DMM and call for spin-resolved measurement of the electronic structure in exfoliated ultrathin crystals.

cond-mat.str-el↗

arXiv2021

Photoinduced anisotropic lattice dynamic response and domain formation in thermoelectric SnSe

Identifying and understanding the mechanisms behind strong phonon-phonon scattering in condensed matter systems is critical to maximizing the efficiency of thermoelectric devices. To date, the leading method to address this has been to meticulously survey the full phonon dispersion of the material in order to isolate modes with anomalously large linewidth and temperature-dependence. Here we combine quantitative MeV ultrafast electron diffraction (UED) analysis with Monte Carlo based dynamic diffraction simulation and first-principles calculations to directly unveil the soft, anharmonic lattice distortions of model thermoelectric material SnSe. A small single-crystal sample is photoexcited with ultrafast optical pulses and the soft, anharmonic lattice distortions are isolated using MeV-UED as those associated with long relaxation time and large displacements. We reveal that these modes have interlayer shear strain character, induced mainly by c-axis atomic displacements, resulting in domain formation in the transient state. These findings provide an innovative approach to identify mechanisms for ultralow and anisotropic thermal conductivity and a promising route to optimizing thermoelectric devices.

cond-mat.mtrl-sci↗

arXiv2021

On single crystal total scattering data reduction and correction protocols for analysis in direct space

We explore data reduction and correction steps and processed data reproducibility in the emerging single crystal total scattering based technique of three-dimensional differential atomic pair distribution function (3D-$Δ$PDF) analysis. All steps from sample measurement to data-processing are outlined in detail using a CuIr$_2$S$_4$ example crystal studied in a setup equipped with a high-energy x-ray beam and a flat panel area detector. Computational overhead as it pertains to data-sampling and the associated data processing steps is also discussed. Various aspects of the final 3D-$Δ$PDF reproducibility are explicitly tested by varying data-processing order and included steps, and by carrying out a crystal-to-crystal data comparison. We identify situations in which the 3D-$Δ$PDF is robust, and caution against a few particular cases which can lead to inconsistent 3D-$Δ$PDFs. Although not all the approaches applied here-in will be valid across all systems, and a more in-depth analysis of some of the effects of the data processing steps may still needed, the methods collected here-in represent the start of a more systematic discussion about data processing and corrections in this field.

cond-mat.mtrl-sci↗

arXiv2020

Magnetic, superconducting, and topological surface states on Fe$_{1+y}$Te$_{1-x}$Se$_{x}$

The idea of employing non-Abelian statistics for error-free quantum computing ignited interest in recent reports of topological surface superconductivity and Majorana zero modes (MZMs) in FeTe$_{0.55}$Se$_{0.45}$. An associated puzzle is that the topological features and superconducting properties are not observed uniformly across the sample surface. Understanding and practical control of these electronic inhomogeneities present a prominent challenge for potential applications. Here, we combine neutron scattering, scanning angle-resolved photoemission spectroscopy (ARPES), and microprobe composition and resistivity measurements to characterize the electronic state of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$. We establish a phase diagram in which the superconductivity is observed only at sufficiently low Fe concentration, in association with distinct antiferromagnetic correlations, while the coexisting topological surface state occurs only at sufficiently high Te concentration. We find that FeTe$_{0.55}$Se$_{0.45}$ is located very close to both phase boundaries, which explains the inhomogeneity of superconducting and topological states. Our results demonstrate the compositional control required for use of topological MZMs in practical applications.

cond-mat.supr-con↗

arXiv2020

The electric pulses induced multi-resistance states in the hysteresis temperature range of 1T-TaS2 and 1T-TaS1.6Se0.4

The electric pulse-induced responses of 1T-TaS2 and 1T-TaS1.6Se0.4 crystals in the commensurate charge-density-wave (CCDW) phase in the hysteresis temperature range have been investigated. We observed that abrupt multiple steps of the resistance are excited by electric pulses at a fixed temperature forming multi metastable like states. We propose that the response of the system corresponds to the rearrangements of the textures of CCDW domains and the multi-resistance states or the nonvolatile resistance properties excited simply by electric pulses have profound significance for the exploration of solid-state devices.

cond-mat.mtrl-sci↗

arXiv2020

Vacancy defect control of colossal thermopower in FeSb2

Iron diantimonide is a material with the highest known thermoelectric power. By combining scanning transmission electron microscope study with electronic transport neutron, X-ray scattering and first principle calculation we identify atomic defects that control colossal thermopower magnitude and nanoprecipitate clusters with Sb vacancy ordering which induce additional phonon scattering and substantially reduce thermal conductivity. Defects are found to cause rather weak but important monoclinic distortion of the unit cell Pnnm to Pm. The absence of Sb along [010] for high defect concentration forms conducting path due to Fe d orbital overlap. The connection between atomic defect anisotropy and colossal thermopower in FeSb2 paves the way for the understanding and tailoring of giant thermopower in related materials.

cond-mat.mtrl-sci↗

arXiv2020

Room-Temperature Skyrmion Thermopower in Fe3Sn2

We present first room-temperature thermoelectric signature of the skyrmion lattice. This was observed in Fe3Sn2, a Kagome Dirac crystal with massive Dirac fermions that features high-temperature skyrmion phase. The room-temperature skyrmion lattice shows magnetic-field dependence of the wavevector whereas thermopower is dominated by the electronic diffusion mechanism, allowing for the skyrmionic bubble lattice detection. Our results pave the way for the future skyrmion-based devices based on the manipulation of the thermal gradient.

cond-mat.mtrl-sci↗

arXiv2019

Topological magnetic-spin textures in two-dimensional van der Waals Cr2Ge2Te6

Two-dimensional (2D) van der Waals (vdW) materials show a range of profound physical properties that can be tailored through their incorporation in heterostructures and manipulated with external forces. The recent discovery of long-range ferromagnetic order down to atomic layers provides an additional degree of freedom in engineering 2D materials and their heterostructure devices for spintronics, valleytronics and magnetic tunnel junction switches. Here, using direct imaging by cryo-Lorentz transmission electron microscopy we show that topologically nontrivial magnetic-spin states, skyrmionic bubbles, can be realized in exfoliated insulating 2D vdW Cr2Ge2Te6. Due to the competition between dipolar interactions and uniaxial magnetic anisotropy, hexagonally-packed nanoscale bubble lattices emerge by field cooling with magnetic field applied along the out-of-plane direction. Despite a range of topological spin textures in stripe domains arising due to pair formation and annihilation of Bloch lines, bubble lattices with single chirality are prevalent. Our observation of topologically-nontrivial homochiral skyrmionic bubbles in exfoliated vdW materials provides a new avenue for novel quantum states in atomically-thin insulators for magneto-electronic and quantum devices.

cond-mat.mtrl-sci↗

arXiv2019

Magnetic-field control of topological electronic response near room temperature in correlated Kagome magnets

Strongly correlated Kagome magnets are promising candidates for achieving controllable topological devices owing to the rich interplay between inherent Dirac fermions and correlation-driven magnetism. Here we report tunable local magnetism and its intriguing control of topological electronic response near room temperature in the Kagome magnet Fe3Sn2 using small angle neutron scattering, muon spin rotation, and magnetoresistivity measurement techniques. The average bulk spin direction and magnetic domain texture can be tuned effectively by small magnetic fields. Magnetoresistivity, in response, exhibits a measurable degree of anisotropic weak localization behavior, which allows the direct control of Dirac fermions with strong electron correlations. Our work points to a novel platform for manipulating emergent phenomena in strongly-correlated topological materials relevant to future applications.

cond-mat.mtrl-sci↗

arXiv2017

Local corrugation and persistent charge density wave in ZrTe3 with Ni intercalation

The mechanism of emergent bulk superconductivity in transition metal intercalated ZrTe3 is investigated by studying the effect of Ni doping on the band structure and charge density wave (CDW). The study reports theoretical and experimental results in the range of Ni0.01ZrTe3 to Ni0.05ZrTe3. In the highest doped samples bulk superconductivity with Tc < TCDW is observed, while TCDW is strongly reduced. Relativistic ab-initio calculations reveal Ni incorporation occurs preferentially through intercalation in the van-der-Waals gap. Analysis of the structural and elec- tronic effects of intercalation, indicate buckling of the Te-sheets adjacent to the Ni site akin to a locally stabilised CDW-like lattice distortion. Experiments by low temperature x-ray diffraction, angle-resolved-photoemission spectroscopy (ARPES) as well as temperature dependent resistivity reveal the nearly unchanged persistence of the CDW into the regime of bulk superconductivity. The CDW gap is found to be unchanged in its extent in momentum space, with the gap size also unchanged or possibly slightly reduced on Ni intercalation. Both experimental observations suggest that superconductivity coexists with the CDW in NixZrTe3.

cond-mat.supr-con↗

arXiv2017

Disorder quenching of the Charge Density Wave in ZrTe3

The charge density wave (CDW) in ZrTe3 is quenched in samples with small amount of Te iso-electronically substituted by Se. Using angle-resolved photoemission spectroscopy we observe subtle changes in the electronic band dispersions and Fermi surfaces on Se substitution. The scattering rates are substantially increased, in particular for the large three-dimensional Fermi surface sheet. The quasi-one-dimensional band is unaffected by the substitution and still shows a gap at low temperature, which starts to open from room temperature. The detailed temperature dependence reveals that the long-range order is absent in the electronic states as in the periodic lattice distortion. The competition between superconductivity and CDW is thus linked to the suppression of long-range order of the CDW.

cond-mat.supr-con↗

arXiv2016

Polarized neutron scattering on HYSPEC: the HYbrid SPECtrometer at SNS

We describe some of the first polarized neutron scattering measurements performed at HYSPEC spectrometer at the Spallation Neutron Source, Oak Ridge National Laboratory. We discuss details of the instrument setup and the experimental procedures in the mode with full polarization analysis. Examples of polarized neutron diffraction and polarized inelastic neutron data obtained on single crystal samples are presented.

cond-mat.str-el↗