Dirk Wulferding's research while affiliated with Seoul National University and other places
What is this page?
This page lists the scientific contributions of an author, who either does not have a ResearchGate profile, or has not yet added these contributions to their profile.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
It was automatically created by ResearchGate to create a record of this author's body of work. We create such pages to advance our goal of creating and maintaining the most comprehensive scientific repository possible. In doing so, we process publicly available (personal) data relating to the author as a member of the scientific community.
If you're a ResearchGate member, you can follow this page to keep up with this author's work.
If you are this author, and you don't want us to display this page anymore, please let us know.
Publications (105)
We present a temperature- and polarization-resolved phononic and electronic Raman scattering study in combination with the first-principles calculations on the kagome metal Ni3In with anisotropic transport properties and non-Fermi liquid behavior. At temperatures below 50 K and down to 2 K, several Raman phonon modes, including particularly an inte...
We present a systematic Raman spectroscopy study on a series of pyrochlore ruthenates, a system which is not yet clearly settled on its magnetic origin and structure. Apart from the Raman-active phonon modes, new peaks that appear in the energy range of 15–35 meV below the Néel temperature (TN) are assigned as one-magnon modes. The temperature evol...
The emergence of scalar Higgs-type amplitude modes in systems where symmetry is spontaneously broken has been a highly successful, paradigmatic description of phase transitions, with implications ranging from high-energy particle physics to low-energy condensed matter systems. Here, we uncover two successive high temperature phase transitions in th...
We present a systematic Raman spectroscopy study on a series of pyrochlore ruthenates, a system which is not yet clearly settled on its magnetic origin and structure. Apart from the Raman-active phonon modes, new peaks that appear in the energy range of 15 - 35 meV below the N\'{e}el temperature are assigned as one-magnon modes. The temperature evo...
RuX3 trihalides (X=halogen atoms) offer a prominent platform for exploring the Kitaev spin liquid. Using polarization-resolved Raman spectroscopy, we report a comparative study of lattice, magnetic, and electronic excitations on X=Cl and Br. Our phonon Raman spectra show that RuBr3 retains a three-layer honeycomb lattice without structural transiti...
Fermi-surface fluctuations and lattice instabilities in the two-dimensional metallic kagome superconductor CsV3Sb5 are elucidated via polarization-resolved Raman spectroscopy. The presence of a weak electronic continuum in high-quality samples marks the crossover into the charge-density-wave (CDW) ordered phase, while impurity-rich samples promote...
Magnetotransport properties of single- and double-rhombohedral trilayer graphene (TLG) are studied. Double TLG is obtained by folding single TLG, yielding a twist angle of 4°. Raman spectroscopic measurements confirm ABC stacking order and the presence of interlayer coupling. The Landau fan diagram exhibits independently superimposed features of ea...
We uncover a wide temperature regime of enhanced spin-lattice fluctuations in single crystals of the pyrochlore ruthenate Nd$_2$Ru$_2$O$_7$. These fluctuations, prominent in Raman spectroscopy, yet elusive to thermodynamic probes, emerge below the N\'{e}el temperature and culminate in a new low-energy amplitude excitation with an order-parameter-li...
The Shastry–Sutherland compound SrCu 2 (BO 3 ) 2 constituting orthogonally coupled dimers harbors an S = 0 singlet ground state. The confluence of strong interdimer interaction and frustration engenders a spectrum of low-energy excitations including localized triplons as well as singlet and triplet bound states. Their dynamics are controlled by an...
The Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$ constituting orthogonally coupled dimers harbors a $S=0$ singlet ground state. The confluence of strong interdimer interaction and frustration engenders a spectrum of low-energy excitations including localized triplons as well as singlet and triplet bound states. Their dynamics are controlled by...
Substitution effects of Os for Ru in {\alpha}-RuCl3 are investigated in a wide composition range of 0 =< x =< 0.67 in Ru1-xOsxCl3 by X-ray and electron diffraction, magnetic susceptibility, heat capacity, and Raman spectroscopy measurements. Apart from the Kitaev physics with antiferromagnetic interactions increasing with x, a rich phase diagram is...
We present an experimental study of the quasi-elastic Raman scattering (QES) of plane-wave and twisted light by liquid crystals. Depending on their temperature, these crystals can exhibit isotropic, nematic and chiral nematic phases. The question is addressed of how the phase of a crystal and the state of incident light can affect the quasi–elastic...
Raman scattering phonon data of the quasi-two-dimensional quantum spin system (CuCl)LaNb2O7 are used to derive an effective structural model that may serve as a basis for its unconventional magnetic properties. Furthermore, a rich spectrum of magnetic excitations is observed, including quasielastic energy density fluctuations and finite energy boun...
The S=1 Haldane state is constructed from a product of local singlet dimers in the bulk and topological states at the edges of a chain. It is a fundamental representative of topological quantum matter. Its well-known archetype, the quasi-one-dimensional SrNi2V2O8 shows both conventional as well as unconventional magnetic Raman scattering. The forme...
The folding of Bernal-stacked bilayer graphene leads to electronic devices that can be understood as combinations of a twisted double-bilayer graphene and a fold. In magnetotransport experiments contributions of the two different parts can be identified. For the twisted double-bilayer graphene Landau fan diagrams with satellite fans depending on tw...
Chloromenite, Cu9O2(SeO3)4Cl6, is the product of volcanic activity. To conduct various physical studies both natural and synthetic samples of chloromenite were used which resulted in a long-standing controversy regarding its crystal structure. We carried out the temperature dependent single crystal X-ray diffraction study in the range 100 – 370 K a...
The variations of Raman and optic absorption
spectra of Co-Al layered double hydroxides (LDH) intercalated
with nitrate and carbonate anions have been studied as a
function of the Co2+/Al3+ ratio. It was revealed from the
comparative analysis of the hydrogen bond frequencies in
Raman spectra and the phonon repetition lines in optic
absorption...
Understanding the link between a charge density wave (CDW) instability and superconductivity is a central theme of the 2D metallic kagome compounds $A$V$_3$Sb$_5$ ($A$=K, Rb, and Cs). Using polarization-resolved electronic Raman spectroscopy, we shed light on Fermi surface fluctuations and electronic instabilities. We observe a quasielastic peak (Q...
We present an experimental study of the quasi-elastic Raman scattering (QES) of plane-wave and twisted light by liquid crystals. Depending on their temperature, these crystals can exhibit isotropic, nematic and chiral nematic phases. The question is addressed of how the phase of a crystal and the state of incident light can affect the quasi-elastic...
![(a) The 2H-structure of TaSe2\documentclass[12pt]{minimal}...](publication/352788621/figure/fig3/AS:1039911478104067@1624945625205/a-The-2H-structure-of-TaSe2documentclass12ptminimal-usepackageamsmath_Q320.jpg)
![In-plane resistivity ρ\documentclass[12pt]{minimal}...](publication/352788621/figure/fig5/AS:1039911478099991@1624945625510/In-plane-resistivity-rdocumentclass12ptminimal-usepackageamsmath_Q320.jpg)
In order to understand the superconducting gap nature of a 2H-Pd0.08TaSe2 single crystal with Tc=3.13K, in-plane thermal conductivity κ, in-plane London penetration depth λL, and the upper critical fields Hc2 have been investigated. At zero magnetic field, it is found that no residual linear term κ0/T exists and λL follows a power-law Tn (T: temper...
The $S=1$ Haldane state is constructed from a product of local singlet dimers in the bulk and topological states at the edges of a chain. It is a fundamental representative of topological quantum matter. Its well-known representative, the quasi-one-dimensional SrNi$_2$V$_2$O$_8$ shows both conventional as well as unconventional magnetic Raman scatt...
We have successfully grown single crystals of PbMn2Ni6Te3O18 and present a comprehensive study of their magnetic, thermodynamic, and Raman spectroscopic properties. PbMn2Ni6Te3O18 consists of a planar network of pairwise rotated NiO6 dimers coupled by corners. Similarities to Ni3TeO6 exist, which forms honeycomb layers. The magnetic susceptibility...
Using magnetic force microscopy operating at sub-Kelvin temperatures, we characterize the heavy fermion superconductor CeCoIn5. We pinpoint the absolute London penetration depth of λ ( 0 ) = 435 ± 20 nm and report its temperature dependence, which is closely linked to the symmetry of the superconducting gap. In addition, we directly measure the pin...
Using magnetic force microscopy operating at sub-Kelvin temperatures we characterize the heavy-fermion superconductor CeCoIn$_5$. We pinpoint the absolute London penetration depth $\lambda(0) = 435 \pm 20$ nm and report its temperature dependence, which is closely linked to the symmetry of the superconducting gap. In addition, we directly measure t...
An osmium chloride with the chemical formula of OsxCl3 (x = 0.81) was synthesized and its crystal structure and thermodynamic properties were investigated. OsxCl3 crystallizes in a layered CdCl2-type structure with the triangular lattice partially occupied by Os ions on average. However, on microscopic length scales, the triangular lattice is compo...
We compare two crystallographic phases of the low-dimensional WP2 to better understand features of electron-electron and electron-phonon interactions in topological systems. The topological β phase, a Weyl semimetal with a giant magnetoresistance, shows a larger intensity of electronic Raman scattering compared to the topologically trivial α phase....
We compare two crystallographic phases of the low-dimensional WP$_2$ to better understand features of electron-electron and electron-phonon interactions in topological systems. The topological $\beta$-phase, a Weyl semimetal with a giant magneto-resistance, shows a larger intensity of electronic Raman scattering compared to the topologically trivia...
The pure Kitaev honeycomb model harbors a quantum spin liquid in zero magnetic fields, while applying finite magnetic fields induces a topological spin liquid with non-Abelian anyonic excitations. This latter phase has been much sought after in Kitaev candidate materials, such as α-RuCl3. Currently, two competing scenarios exist for the intermediat...
We present a novel route to tune and adapt the energy of surface plasmon resonances (SPR) of 3-dimensional (3D) Au nanowire arrays. Based on an annealing and defect management of anodic aluminum oxide (AAO) we demonstrate a tuning of the longitudinal resonance mode (L mode) of plasmons towards higher energies. Here we present an experimental fabric...
The development of bismuth based photocatalysts in response to emerging demand for solving the environmental problems has attracted immense interest over the last few years. This is owed to their low cost, non-toxicity and high stability. Here, we report the synthesis of a nanohybrid consisting of 3D flower-like BiOI microspheres decorated with pla...
The pure Kitaev honeycomb model harbors a quantum spin liquid in zero magnetic fields, while applying finite magnetic fields induces a topological spin liquid with non-Abelian anyonic excitations. This latter phase has been much sought after in Kitaev candidate materials, such as $\alpha$-RuCl$_3$. Currently, two competing scenarios exist for the i...
Quantum spin liquids are outstanding examples of highly quantum entangled phases of matter and serve as a testbed to gauge central concepts of strongly correlated materials. Enormous research efforts in the past few decades have brought an in-depth understanding of these novel phases, although their conundrums have not yet been solved completely. I...
We report a Raman scattering study of single-crystalline homometallic oxyborate Mn2OBO3, a compound realizing a one-dimensional ribbon-structure. Phonon excitations as a function of temperature and light polarization are compared to lattice dynamical calculations, giving evidence for a strong coupling between lattice and magnetic degrees of freedom...
We report on optical absorption and polarized light microscopy studies of nano-flakes of double layered hydroxides (LDHs), expressed by the general chemical formula [M 2+ 1-x M 3+ x (OH) 2 ] x+ (A y-) x/y ×mH 2 O (short version: M 2+ (n)M 3+-A), where divalent M 2+ and trivalent M 3+ cations are Co 2+ and Al 3+ , correspondingly. The layers of LDHs...
We present a systematic study of the interplay between lattice parameters and the energy of the optical phonons as well as the antiferromagnetic coupling strength, $J$, in the high-$T_{\text{c}}$ superconducting cuprate $R$Ba$_2$Cu$_3$O$_{6+\delta}$ (\mbox{R-123}, $R =$ Y, Dy, Gd, Sm, Nd) with hole-doping $p$ ($0.00<p \lesssim 0.04$). The energy of...
Multi-drug resistance (MDR) of bacteria is a major threat to public health globally and its unprecedented increase calls for immediate alternative medical strategies. Antimicrobial photodynamic therapy (aPDT) offers alternative modalities to combat the growing MDR typically by means of targeted cellular internalization of a photosensitizer (PS) cap...
Fe3+ S=5/2 ions form saw-tooth-like chains along the a axis of the oxoselenite Fe2O(SeO3)2 and an onset of long-range magnetic order is observed for temperatures below TC=105 K. This order leads to distinct fingerprints in phonon mode linewidths and energies as resolved by Raman scattering. In addition, new excitations with small linewidths emerge...
Fe$^{3+}$ $S = 5/2$ ions form saw-tooth like chains along the $a$ axis of the oxo-selenite Fe$_2$O(SeO$_3$)$_2$ and an onset of long-range magnetic order is observed for temperatures below $T_C = 105$ K. This order leads to distinct fingerprints in phonon mode linewidths and energies as resolved by Raman scattering. In addition, new excitations wit...
In A3Cr2O8, where A = Sr or Ba, the Cr5+ ions surrounded by oxygen ions in a tetrahedral coordination are Jahn-Teller active. The Jahn-Teller distortion leads to a structural transition and a related emergence of three twinned monoclinic domains below the structural phase transition. This transition is highly dynamic over an extended temperature ra...
In A3Cr2O8, where A = Sr or Ba, the Cr5+ ions surrounded by oxygen ions in a tetrahedral coordination are Jahn-Teller active. The Jahn-Teller distortion leads to a structural transition and a related emergence of three twinned monoclinic domains below the structural phase transition. This transition is highly dynamic over an extended temperature ra...
In $A_{3}$Cr$_{2}$O$_{8}$, where $A$ = Sr or Ba, the Cr$^{5+}$ ions surrounded by oxygen ions in a tetrahedral coordination are Jahn-Teller active. The Jahn-Teller distortion leads to a structural transition and a related emergence of three twinned monoclinic domains below the structural phase transition. This transition is highly dynamic over an e...
BaNa2Fe[VO4]2 contains a Jahn-Teller active ion (FeII, 3d6, high-spin) in an octahedral coordination. On the basis of a combination of temperature-dependent X-ray diffraction and Mössbauer and Raman spectroscopies, we demonstrate the coupling of lattice dynamics with the electronic ground state of FeII. We identify three lattice modes combined to a...
Raman spectroscopy is employed to probe directly the soft rotation and tilting modes, which are two primary order parameters predicted in the hybrid improper ferroelectric material Ca$_3$Mn$_2$O$_7$. We observe a giant softening of the 107-cm$^{-1}$ octahedron tilting mode by 26~cm$^{-1}$, on heating through the structural transition from a ferroel...
In search of novel, improved materials for magnetic data storage and spintronic devices, compounds that allow a tailoring of magnetic domain shapes and sizes are essential. Good candidates are materials with intrinsic anisotropies or competing interactions, as they are prone to host various domain phases that can be easily and precisely selected by...
In VO$_2$, the explicit origin of the insulator-to-metal transition is still disputable between Peierls and Mott insulators. Along with the controversy, its second monoclinic (M2) phase has received considerable attention due to the presence of electron correlation in undimerized vanadium ions. However, the origin of the M2 phase is still obscure....
We report Raman light scattering in the phase separated superconducting single crystal Rb0.77Fe1.61Se2 with Tc = 32 K. The spectra have been measured in a wide temperature range 3K -500K. The observed phonon lines from the majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN= 525 K demonstrate modest anomalies in frequency, inte...
We constructed a $^3$He magnetic force microscope operating at the base
temperature of 300 mK under a vector magnetic field of 2-2-9 T in the $x-y-z$
direction. Fiber optic interferometry as a detection scheme is employed in
which two home-built fiber walkers are used for the alignment between the
cantilever and the optical fiber. The noise level o...
We report a magnetic force microscopy study of the magnetic domain evolution
in the layered manganite La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ (with $x=0.32$).
This strongly correlated electron compound is known to exhibit a wide range of
magnetic phases, including a recently uncovered biskyrmion phase. We observe a
continuous transition from dendritic to...
We present a local probe study of the magnetic superconductor,
ErNi$_2$B$_2$C, using magnetic force microscopy at sub-Kelvin temperatures.
ErNi$_2$B$_2$C is an ideal system to explore the effects of concomitant
superconductivity and ferromagnetism. At 500 mK, far below the transition to a
weakly ferromagnetic state, we directly observe a structured...
In the giant Rashba semiconductor BiTeI electronic surface scattering with
Lorentzian linewidth is observed that shows a strong dependence on surface
termination and surface potential shifts. A comparison with the topological
insulator Bi2Se3 evidences that surface confined quantum well states are the
origin of these processes. We notice an enhance...
In the giant Rashba semiconductor BiTeI electronic surface scattering with Lorentzian linewidth is observed that shows a strong dependence on surface termination and surface potential shifts. A comparison with the topological insulator Bi2Se3 evidences that surface confined quantum well states are the origin of these processes. We notice an enhance...
We present a Raman spectroscopic investigation of charge compensated
antiferromagnetic
(Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_{3}$O$_{y}$ single
crystals. In this system $x$ controls the interactions and $y$ the doping. We
determine the two-magnon Raman peak position $E_{max}$. In the absence of
doping $E_{max}$ is directly proportiona...
In the s = 1/2 antiferromagnetic spin chain material TiPO4 the formation of a
spin gap takes place in a two step process with two characteristic
temperatures, T*=111 K and TSP=74 K. We observe an unusual lattice dynamics
over a large temperature regime as well as evidence for an orbital instability
preceding the spin-Peierls transition. We relate d...
We have grown epitaxial thin films of magnetite on MgO and
Al2O3 substrates with sharp and distinct
signatures of the Verwey transition in resistivity and magnetization. We
have used Raman scattering to separate the footprint of purely
structural changes from the effect of additional charge and orbital
order. Raman modes related to the structural p...
Lattice vibrations as well as magnetic excitations are investigated using Raman scattering to understand the high-Tc multiferroic properties of CuO. We observe a flat, broad spinon continuum extending to 2800 cm−1, being superimposed by magnon excitations with energies below 1350 cm−1. This allows us to estimate an exchange coupling constant of J=1...
Lattice vibrations as well as electronic excitations are used to investigate LuFe2O4, which is intensively discussed in the context of electronic multiferroics. All phonon modes and an electronic continuum show drastic changes through a series of magnetic, structural, and charge ordering temperatures. In particular, the 634 cm−1 Ag mode, correspond...
In the giant Rashba, polar semiconductor BiTeI phonons as well as spin
split bulk and surface states are probed using Raman scattering. The
observed bulk states are in good agreement with symmetry considerations
and photoemission data of spin splitting. A very large enhancement of
the Raman scattering cross section is observed if the laser energy i...
In the spin ladder compound BiCu$_2$PO$_6$ there exists a decisive dynamics
of spin excitations that we classify and characterize using inelastic light
scattering. We observe low-energy singlets and a broad triplon continuum
extending from 36 cm$^{-1}$ to 700 cm$^{-1}$ in ($aa$), ($bb$), and ($cc$)
light scattering polarizations. Though isolated sp...
Polarized Raman-scattering spectra of superconducting, single-crystalline
FeSe evidence pronounced phonon anomalies with temperature reduction. A large
6.5% hardening of the B_1g(Fe) phonon mode is attributed to the suppression of
local fluctuations of the iron spin state with the gradual decrease of the iron
paramagnetic moment. The ab-initio latt...
The spin dynamics and magnetic excitations of the slightly distorted triangular s = 3/2 system α-CaCr (2)O (4) are investigated by means of Raman spectroscopy and electron spin resonance (ESR) to elucidate its peculiar magnetic properties. Two-magnon excitations in circular RL symmetry show a multi-maximum structure with a dominant spectral weight...
We report the successful growth of a large (Cax
La1−x
)(Ba1.75−x
La0.25+x
)Cu3Oy
(CLBLCO) single crystal. In this material, x controls the maximum of T
c
(\(T_{c}^{\max }\)), with minimal structural changes. Therefore, it allows a search for correlations between material properties and \(T_{c}^{\max }\). We demonstrate that the crystals are good en...
Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5-150 nm which are often used to host photoactive n...
We present a comparative study of the low-dimensional compounds α- and β-TeVO4. Our data clearly show that the change in the local coordination geometry of V4+ ions between α- and β-TeVO4 leads to drastic differences in their magnetic properties. Despite sharing the same crystal structure, the two compounds manifest different magnetic exchange topo...
We present a comparative study of the low-dimensional compounds α- and β-TeVO 4. Our data clearly show that the change in the local coordination geometry of V 4+ ions comparing α- and β-TeVO 4 leads to a drastic differences in the magnetic properties. Despite sharing the same crystal structure, the two compounds realize different magnetic exchange...
Defects influence the optical and electronic properties of nanostructured materials that may be relevant for applications. In self-organized anodic aluminum oxide (AAO) templates we have investigated the effect of annealing, doping and nanoscale metal deposition. Optical absorption spectroscopy has been used as a sensitive probe for the defect dens...
We report the successful growth of a large
(Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_{3}$O$_{y}$ (CLBLCO) single
crystal. In this material, $x$ controls the maximum of Tc ($T_{c}^{\max}$),
with minimal structural changes. Therefore, it allows a search for correlations
between material properties and $T_{c}^{\max}$. We demonstrate that the...
The Raman-active phonons and magnetic excitations in the orbitally ordered, quasi one-dimensional Heisenberg antiferromagnet KCuF3 are studied as a function of temperature in the range between 3 and 290 K in different scattering configurations. The low-energy Eg and B1g phonon modes show an anomalous softening (∼25% and ∼13%, respectively) between...