Dirk Wulferding's research works | Seoul National University and other places

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Field- and temperature-driven magnetic excitations in rouaite Cu 2 ( OH ) 3 NO 3

Article

February 2025

11 Reads

Physical Review B

[...]

Field-evolution of off-diagonal Raman tensor elements
a Integrated scattering intensity of the CDW amplitude mode at 9.1 meV in GdTe3 as a function of out-of-plane field strength and light polarization with ein⊥ eout. At small fields, domain poling effects contribute, while at higher fields the axialness of the Higgs mode increases linearly with B, as indicated by the arrow on the right. Crystallographic axes are indicated at the top. All data was acquired at T = 2 K. b Field-dependent Raman tensor element β extracted from fits to the integrated intensity plotted in panel (a). The standard deviation for each fitted value is within the size of the symbols. The data at B = 0 has been omitted due to ambiguity in fitting (see Supplementary Note 7 and Supplementary Figs. 8–11 for details). The dashed line is a guide to the eyes. The field regime dominated by field-poling effects is indicated by a shaded background. c–f Field- and polarization angle dependence of the Raman scattering intensity for four selected modes (10.8 meV, 12 meV, 15 meV, and 17 meV) measured with ein⊥ eout at T = 2 K.

Raman scattering process in the framework of single-particle spectral function involving field-tuned axial Higgs modes
a A gapless state at T > TCDW. b Below TCDW a charge-density wave gap (ΔCDW) opens around the region relevant for the Raman scattering process. The system is in its ground state. c The Raman scattering process probing the axial Higgs mode: An incident photon with energy hν (green arrow) excites an electron from the valence band to an unoccupied state across ΔCDW, which couples to an amplitudon (red and blue shaded areas around ΔCDW) in a second step. In the final step, the electron recombines with the hole and emits a photon with energy hν′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$h\nu {\prime}$$\end{document} (orange arrow) with a polarization orthogonal to that of the incident photon.

Magnetic field control over the axial character of Higgs modes in charge-density wave compounds

January 2025

7 Reads

Nature Communications

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Understanding how symmetry-breaking processes generate order out of disorder is among the most fundamental problems of nature. The scalar Higgs mode – a massive (quasi-) particle – is a key ingredient in these processes and emerges with the spontaneous breaking of a continuous symmetry. Its related exotic and elusive axial counterpart, a Boson with vector character, can be stabilized through the simultaneous breaking of multiple continuous symmetries. Here, we employ a magnetic field to tune the recently discovered axial Higgs-type charge-density wave amplitude modes in rare-earth tritellurides. We demonstrate a proportionality between the axial Higgs component and the applied field, and a 90° phase shift upon changing the direction of the magnetic field. This indicates that the axial character is directly related to magnetic degrees of freedom. Our approach opens up an in-situ control over the axial character of emergent Higgs modes.

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Magnetic field control over the axialness of Higgs modes in charge-density wave compounds

November 2024

6 Reads

[...]

Understanding how symmetry-breaking processes generate order out of disorder is among the most fundamental problems of nature. The scalar Higgs mode - a massive (quasi-) particle - is a key ingredient in these processes and emerges with the spontaneous breaking of a continuous symmetry. Its related exotic and elusive axial counterpart, a Boson with vector character, can be stabilized through the simultaneous breaking of multiple continuous symmetries. Here, we employ a magnetic field to tune the recently discovered axial Higgs-type charge-density wave amplitude modes in rare-earth tritellurides. We demonstrate a proportionality between the axial Higgs component and the applied field, and a 90 $^{\circ}$ phase shift upon changing the direction of the B-field. This indicates that the axial character is directly related to magnetic degrees of freedom. Our approach opens up an in-situ control over the axialness of emergent Higgs modes.

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Creation of a half vortex ring via a local dipole field
a, b Fluxoid quantization of thick and thin slabs. The thick slab accommodates the magnetic flux quantum (Φ0). The thin slab experiences field penetration, but no vortex exists. c, d Creation of a half vortex ring by a local dipole field of an MFM tip in thick slabs and thin slabs. Unquantized magnetic flux can be trapped in the thin slab geometry.

Creation of a superconducting vortex‒antivortex pair via MFM
a Schematics illustrating the creation of superconducting vortex‒antivortex pairs (SVAPs) via an in-plane magnetized MFM tip. SVAPs (red dots) and trapped interstitial vortices (TIVs, green dots) are generated by the tip, whereas regular vortices (blue dots) are formed by the stray field of the system. b Illustration of the SVAP configuration created by the MFM tip. Antivortices (white dots) are induced by both the external stray field and the tip field, whereas SVAPs (red dots) and TIVs (dark green dots) represent confined vortices. The yellow arrow indicates the position of the MFM tip during the SVAP creation process. c, d MFM images obtained from two separate experiments with the same conditions and a shifted scan frame. The yellow arrow indicates the position of the MFM tip, which remains at a fixed tip‒sample distance of 600 nm during SVAP formation. The bright dots in the MFM image correspond to antivortices, whereas the dark dots represent vortices.

Thermally assisted depinning of SVAPs
The thermal evolution of the vortices in Fig. 1c and d are shown in a–d and e–h, respectively. After a thermal pulse with an amplitude of Tset, as denoted in the image, is applied, MFM images are obtained at 4.2 K. The inset curve in d provides a detailed time scale of the applied thermal pulse. The annihilation of each vortex‒antivortex pair is traced by the box‒circle link with a dotted colored line. i Schematic view of the creation of isolated vortices via out-of-plane magnetization. j‒l Thermal evolution of isolated vortices created according to the method described in i. The images demonstrate the isotropic behavior of the vortices during the thermal process. All MFM images were taken at 4.2 K with a tip-to-sample distance of 600 nm.

Pair annihilation of an elongated single SVAP
a–c Manipulation process of one end of an SVAP by an MFM tip. After moving the scan frame step by step via piezo walkers, a final vortex‒antivortex distance of 17 µm is achieved. d–f Thermally assisted depinning of both the vortex and the antivortex and pair annihilation as a result of successive heat pulses. Note that a confining interaction still exists between the antivortex and its previously manipulated counterpart because of the movement of the antivortex, as indicated by the white arrow, which is clearly visible in d and e. All MFM images were taken at 4.2 K with a tip‒sample distance of 600 nm.

Thermal evolution of the SVAPs in thinner Nb films
Thermally assisted depinning and pair annihilation of SVAPs in Nb films of a–d 100 nm, e–h 50 nm, and i–l 30 nm. Note that the superconducting transition temperatures (Tc) and magnetic penetration depths (λ) are different in various Nb films, ranging from ≈ 8.7 K to 8.3 K and from ≈ 90 nm to 145 nm, respectively. The annihilation of each vortex‒antivortex pair is traced by the box‒circle link with a dotted colored line.

Vortex confinement through an unquantized magnetic flux

September 2024

53 Reads

NPG Asia Materials

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Geometrically confined superconductors often experience a breakdown in the quantization of magnetic flux owing to the incomplete screening of the supercurrent against field penetration. In this study, we report that magnetic field confinement occurs regardless of the dimensionality of the system, even extending to 1D linear potential systems. By using a vector-field magnetic force microscope, we successfully create a vortex‒antivortex pair connected by a 1D unquantized magnetic flux in ultrathin superconducting films. Through an investigation of the manipulation and thermal behavior of the vortex pair, we uncover a long-range interaction mediated by the unquantized magnetic flux. These findings suggest a universal phenomenon of unquantized magnetic flux formation, independent of the geometry of the system. Our results present an experimental route for investigating the impact of confinement on superconducting properties and order parameters in unconventional superconductors characterized by extremely low dimensionality.

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Vortex confinement through an unquantized magnetic flux

Preprint

July 2024

16 Reads

[...]

Geometrically confined superconductors often experience a breakdown in the quantization of magnetic flux owing to the incomplete screening of the supercurrent against the field penetration. In this study, we report that the confinement of a magnetic field occurs regardless of the dimensionality of the system, extending even to 1D linear potential systems. By utilizing a vector-field magnetic force microscope, we successfully create a vortex-antivortex pair connected by a 1D unquantized magnetic flux in ultra-thin superconducting films. Through an investigation of the manipulation and thermal behavior of the vortex pair, we uncover a long-range interaction mediated by the unquantized magnetic flux. These findings suggest a universal phenomenon of unquantized magnetic flux formation, independent of the geometry of the system. Our results present an experimental route for probing the impact of confinement on superconducting properties and order parameters in unconventional superconductors characterized by extremely low dimensionality.

Origin of Distinct Insulating Domains in the Layered Charge Density Wave Material 1T-TaS2

June 2024

25 Reads

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Vertical charge order shapes the electronic properties in layered charge density wave (CDW) materials. Various stacking orders inevitably create nanoscale domains with distinct electronic structures inaccessible to bulk probes. Here, the stacking characteristics of bulk 1T-TaS2 are analyzed using scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. It is observed that Mott-insulating domains undergo a transition to band-insulating domains restoring vertical dimerization of the CDWs. Furthermore, STS measurements covering a wide terrace reveal two distinct band insulating domains differentiated by band edge broadening. These DFT calculations reveal that the Mott insulating layers preferably reside on the subsurface, forming broader band edges in the neighboring band insulating layers. Ultimately, buried Mott insulating layers believed to harbor the quantum spin liquid phase are identified. These results resolve persistent issues regarding vertical charge order in 1T-TaS2, providing a new perspective for investigating emergent quantum phenomena in layered CDW materials.

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Charge-ordered phases in the hole-doped triangular Mott insulator 4 Hb - TaS 2

Article

May 2024

12 Reads

4 Citations

[...]

4Hb-TaS2 has been proposed to possess unconventional superconductivity with broken time-reversal symmetry due to distinctive layered structure, featuring a heterojunction between a 2D triangular Mott insulator and a charge-density wave metal. However, since a frustrated spin state in the correlated insulating layer is susceptible to charge ordering with carrier doping, it is required to investigate the charge distribution driven by interlayer charge transfer to understand its superconductivity. Here, we use scanning-tunneling microscopy and spectroscopy (STM/S) to investigate the charge-ordered phases of 1T−TaS2 layers within 4Hb-TaS2, explicitly focusing on the non-half-filled regime. Our STS results show an energy gap which exhibits an out-of-phase relation with the charge density. We ascribe the competition between onsite and nonlocal Coulomb repulsion as the driving force for the charge-ordered insulating phase of a doped triangular Mott insulator. In addition, we discuss the role of the insulating layer in the enhanced superconductivity of 4Hb-TaS2.

Insulating commensurate CDW phase of 1T‐TaS2. a) A schematic representation of the atomic structure of 1T‐TaS2 with the SD superstructure. The black and red arrows correspond to the unit vectors of the 1 × 1 and the 13×13$\sqrt {13}\times \sqrt {13}$ lattices, respectively. b) An STM image of the commensurate CDW phase in 1T‐TaS2 (Vset = −400 mV, Iset = 50 pA). Each bright protrusion represents an SD (inset). c) The representative dI/dV spectrum acquired on the surface of a Type‐I domain (Vset = −400 mV, Iset = 50 pA, Vmod = 5 mV). The bandgap, ≈0.39 eV, is marked by a black arrow. Our spectrum exhibits enhanced band edge features marked by red arrows.

Coexistence of dimerized (Type‐I) and undimerized (Type‐II) layer terminations on the upper terrace of a step edge. a,b) STM images of the surface of bulk 1T‐TaS2 with the upper and lower terraces separated by a monolayer step obtained at different bias voltages (a Vset = −400 mV, Iset = 100 pA and b Vset = +170 mV, Iset = 100 pA, Vmod = 5 mV). c) The dI/dV map was acquired simultaneously with the STM image shown in b (See Experimental Section). d) Line dI/dV spectra acquired along the line marked by the arrow shown in (c). e) Averaged dI/dV spectra of the Type‐I (black) and Type‐II (red) domains acquired from defect‐free areas (Vset = −400 mV, Iset = 200 pA, Vmod = 5 mV).

Three different Type‐I insulator domains on a flat surface. a,b) Three different domains are shown by both the a) STM image and b) the dI/dV map (Vset = +170 mV, Iset = 50 pA, Vmod = 5 mV). c) dI/dV spectra of the three domains (α, α*, and β) indicated in b averaged over areas not affected by local defects (Vset = −400 mV, Iset = 50 pA, Vmod = 5 mV). Each spectrum is vertically shifted with equal spacing for clarity. The vertical dashed line indicates the energy for the maps shown in (a) and (b). The higher dI/dV intensity in the tunneling spectra corresponds to the lower contrast in b) the dI/dV map, which is simultaneously acquired with the topographic image (a) (see Experimental Section) For comparison, the spectrum of domain‐α is superimposed as a faint gray line. There is an upward band shift for domain‐α* and a band edge broadening (marked by red arrows) for domain‐β.

Formation energies and electronic structures of the various stacking configurations. a) A schematic representation of the SD supercell with 13 Ta atoms, each labeled in line with previous studies which have identified L, I, and H (identical by threefold rotational symmetry, shaded in gray) as the most stable sliding configurations among the 12 possibilities (B‐M).[¹⁹] b) Direct comparison of the formation energies of two different types of stacking configurations and their variations: fully dimerized (black), subsurface undimerized (blue), and surface undimerized configurations (red). Formation energies of other possible stacking configurations, marked by short gray lines, and their corresponding PDOS spectra are presented in Figure S7 (Supporting Information). c) A visual representation of four distinct stacking configurations discussed in (b). Each object denotes the position of the supercell center on individual layers, with the shaded regions (gray) indicating dimerization between adjacent layers. d) The calculated PDOS spectra of the four different Type‐I stacking configurations identified in (b). Each spectrum is vertically shifted with equal spacing, in order of their formation energies, with the lowest at the bottom. The red arrows point to the wider band edges caused by undimerized subsurface layers.

Origin of Distinct Insulating Domains in the Layered Charge Density Wave Material 1T‐TaS2

May 2024

68 Reads

5 Citations

[...]

Vertical charge order shapes the electronic properties in layered charge density wave (CDW) materials. Various stacking orders inevitably create nanoscale domains with distinct electronic structures inaccessible to bulk probes. Here, the stacking characteristics of bulk 1T‐TaS2 are analyzed using scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. It is observed that Mott‐insulating domains undergo a transition to band‐insulating domains restoring vertical dimerization of the CDWs. Furthermore, STS measurements covering a wide terrace reveal two distinct band insulating domains differentiated by band edge broadening. These DFT calculations reveal that the Mott insulating layers preferably reside on the subsurface, forming broader band edges in the neighboring band insulating layers. Ultimately, buried Mott insulating layers believed to harbor the quantum spin liquid phase are identified. These results resolve persistent issues regarding vertical charge order in 1T‐TaS2, providing a new perspective for investigating emergent quantum phenomena in layered CDW materials.

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Magnetic specific heat and thermal conductivity of YCu3(OD)6.5Br2.5
a, Semi-log plot of the magnetic specific heat (Cm; open circles) versus temperature T obtained after subtracting the lattice contribution. The pink line and green triangles represent numerical calculations of Cm for an ideal kagome antiferromagnet³⁹. The two vertical arrows denote two characteristic temperatures at 0.1J and 0.67J, and T* represents a weak specific anomaly. b, Magnetic entropy Sm versus T calculated by integrating Cm(T)/T. In the high-temperature limit, the full R ln 2 spin entropy (horizontal dashed line) is recovered. c, The very low-temperature Cm in a log–log scale. The solid line indicates a power-law behaviour Cm ∝ T². d, Plot of thermal conductivity κ versus T to a log–log scale. e, Semi-log plot of κ/T versus T. f, Temperature dependence of κ/T in the range T = 0.2–1.25 K. The solid red line represents a linear fit of κ/T. The thermal conductivity was measured three times at each temperature and the data points were subsequently averaged. The error bars in d–f indicate the standard deviation of the data points.
Source data

Spinon continuum and dynamic Raman susceptibility of YCu3(OD)6.5Br2.5
a, Temperature dependence of the magnetic Raman spectra obtained after subtracting phonon peaks in the Eg channel. b,c, Representative Raman susceptibility χ″(ω)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\chi {\prime\prime} (\omega )$$\end{document} (open circles) in the Eg channel at T = 2 K (b) and in the A1g channel at T = 7 K (c). The magnetic excitation is decomposed into three components: 1P (turquoise shading) and 2P (salmon) spinon–antispinon excitations with an additional low-energy excitation (RS; brown). The red solid lines represent the sum of three Gaussian line profiles. d,e, Colour plots of the Raman intensity IEgω\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${I}_{{E}_\mathrm{g}}\left(\omega \right)$$\end{document} (d) and χ″Eg(ω,T)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\chi {\prime\prime} }_{{E}_\mathrm{g}}(\omega,T)$$\end{document} (e) in the T–ω plane. The horizontal dashed lines indicate the temperature scale of the antiferromagnetic exchange strength J = 63 K determined from the specific heat. f, Temperature dependence of the dynamic Raman susceptibilities χEg dynT\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\chi }_{{E}_\mathrm{g}}^{\rm{dyn}}\left(T\right)$$\end{document} (pink circles) and χA1g dynT\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\chi }_{{A}_\mathrm{1g}}^{\rm{dyn}}\left(T\right)$$\end{document} (cyan squares) deduced from χ″(ω)s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\chi {\prime\prime} (\omega )s$$\end{document} through the Kramers–Kronig relation plotted together with the theoretical static magnetic susceptibility (KAFM, blue solid line) for a perfect kagome lattice. a.u., arbitrary units.
Source data

Power-law analysis of magnetic Raman susceptibility
a–d, Low-frequency Raman susceptibilities at selected temperatures in the Eg channel for T = 2–20 K (a) and T = 30–300 K (b) and in the Eg + A1g channel for T = 2–30 K (c) and T = 90–300 K (d). The vertical dashed lines mark two energy regimes: 1–5 and 5–10 meV. The solid lines are power-law fittings to χ″(ω)∝ωα\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\chi {\prime\prime} (\omega )\propto {\omega }^{\alpha }$$\end{document}. e,f, Temperature dependence of the extracted exponent α in the Eg and Eg + A1g channels and the two different energy windows: 1–5 meV (e) and 5–10 meV (f). The horizontal dashed line denotes α = 1.
Source data

High-field magnetization and 1/9 magnetization plateau
a, The pulsed-field magnetization m(H) of YCu3 (magenta circles) and its field derivative dm/dH (grey squares) measured at T = 2 K with a non-destructive pulse magnet up to 60 T. The blue solid line represents the calculated magnetization for the spin-1/2 KHAF, taken from ref. ²⁶. The pulsed-field data are calibrated to the low-field SQUID data (yellow triangles). b, Comparison of the in-plane (orange circles) and out-of-plane (azure squares) magnetization measured at T = 0.5 K, along with the calculated curve²⁸ (solid line). The vertical arrows in the dm/dH data (violet and coral lines) indicate the lower and upper critical fields of the 1/9 magnetization plateau. The horizontal dashed lines denote the theoretical 1/9 and 3/9 magnetization plateaus.
Source data

One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet

January 2024

287 Reads

19 Citations

Nature Physics

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The spin-1/2 antiferromagnetic Heisenberg model on a kagome lattice is geometrically frustrated, which is expected to promote the formation of many-body quantum entangled states. The most sought-after among these is the quantum spin-liquid phase, but magnetic analogues of liquid, solid and supersolid phases may also occur, producing fractional plateaus in the magnetization. Here, we investigate the experimental realization of these predicted phases in the kagome material YCu3(OD)6+xBr3−x (x ≈ 0.5). By combining thermodynamic and Raman spectroscopic techniques, we provide evidence for fractionalized spinon excitations and observe the emergence of a 1/9 magnetization plateau. These observations establish YCu3(OD)6+xBr3−x as a model material for exploring the 1/9 plateau phase.

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Melting of Unidirectional Charge Density Waves across Twin Domain Boundaries in GdTe 3

Article

November 2023

28 Reads

5 Citations

Nano Letters

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... Moreover, we note that similar pseudogaps are present along theΓK direction in 4H b -TaS 2 as recently reported in Ref. [56]. This indicates the coexistence of multiple CDW orders in this compound (besides the √ 13 × √ 13 in the 1T layer), as measured in a very recent STM experiment [57] where a 3 × 3 modulation is revealed by the STM map which can be ascribed to the 1H layer. ...
Reference:
Darkness in interlayer and charge density wave states of 2H-TaS2

Charge-ordered phases in the hole-doped triangular Mott insulator 4 Hb - TaS 2

Citing Article
May 2024

[...]

... The second scenario, involving a decrease in the interlayer distance, seems to contradict the classical behavior of thermal expansion. However, in 1T -TaS 2 , the interlayer distance of the surface Mott layer (approximately 7Å) is significantly larger than that of the bulk layers (around 6Å) [39,79,80], which deviates from the typical surface contraction due to surface tension. Hence, the temperature dependence of the interlayer distance in the surface Mott layer is expected to be complex. ...
Reference:
Interlayer Hopping between Surface Mott Insulator and Bulk Band Insulator in layered 1T-TaS_{2}

Origin of Distinct Insulating Domains in the Layered Charge Density Wave Material 1T‐TaS2

Citing Article
Full-text available
May 2024

[...]

... [20] Inelastic neutron scattering also exhibits a low-energy conical continuum, [21] which can reproduce the specific-heat results expected of a U(1) Dirac QSL. [11] Notably, a one-ninth magnetization plateau and quantum oscillations at high fields have been observed in this system, [22][23][24][25] further suggesting that the YCu3-Br system is an exciting platform for studying physics in KHAs. However, the positions of the low-energy spin excitations deviate from those predicted by the typical KHA model, [7] likely due to the unique structure of this system. ...
Reference:
Antiferromagnetic Order and Possible Quantum Spin Liquid in Kagome Antiferromagnet LuCu3(OH)6Br2[Brx(OH)1–x]

One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet

Citing Article
Publisher preview available
January 2024

Nature Physics

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... Shadow and folded bands resulting from the CDW transition were clearly observed (Supplementary Note 1). The experimentally obtained CDW wave vector q CDW is about 0.43Å −1 (≈ 2/7 c * ), consistent with previous reports [35][36][37]. ...
Reference:
Identification of metastable lattice distortion free charge density wave at photoinduced interface via TRARPES

Melting of Unidirectional Charge Density Waves across Twin Domain Boundaries in GdTe 3

Citing Article
November 2023

Nano Letters

[...]

... The enhanced Kadowaki-Woods ratio and Sommerfeld coefficient [11] suggest stronger interactions among the charge carriers. Raman spectroscopy measurements further show fingerprints of Kondo coherence [34]. All these indicate that Ni 3 In is located close to a quantum critical point (Fig. 1d). ...
Reference:
Resolving the Kagome Origin of the Strange Metallicity in Ni$_3$In

Fingerprints for anisotropic Kondo lattice behavior in the quasiparticle dynamics of the kagome metal Ni 3 In

Citing Article
September 2023

[...]

... However, a relatively broad peak centered at ω = 159 cm -1 emerges below 150 K. In the absence of any structural phase transitions within this temperature range, the peak may be associated with a magnon (M) mode, which is often observed at temperatures well above the long-range magnetic ordering temperatures [45][46][47][48]. Moreover, a relatively large blueshift (Δω ~ 6 cm -1 ) of the suspected magnon peak in Ni2ScSbO6 is observed as T is decreased from 150 to 10 K, as shown in the SM, Fig. S6. ...
Reference:
Highly Entangled Magnetodielectric and Magnetostriction effects, and Spin-Phonon coupling in the Antiferromagnetic Ni$_2$ScSbO$_6

Linear scaling relationship of Néel temperature and dominant magnons in pyrochlore ruthenates

Citing Article
August 2023

[...]

... The peak positions of all phonon modes shift to higher wavenumbers, their resonance linewidths narrow, and their intensities increase with a decrease in temperature. A diffusive Raman-scattering response below 200 cm −1 in the temperature-dependent Raman spectra may indicate signatures of spin excitations [23,52,53]. However, detailed polarized Raman measurements as a function of temperature are necessary to verify the nature of the magnetic continuum. ...
Reference:
Experimental and Theoretical Evidence of Weak Spin-Lattice Coupling in the Double Perovskite Sr2YRuO6

Magnetic and spin-orbit exciton excitations in the honeycomb lattice compound RuBr 3

Citing Article
November 2022

[...]

... This group of materials host a unique phase transition into charge-density wave (CDW) order with T CDW = 78-102 K followed by superconductivity at low temperatures with T c = 0.9-2.5 K [1][2][3][4]. The CDW order sets the stage for a cascade of intertwined symmetry breaking orders developing concomitantly or subsequently with the CDW transition, including a possible orbital flux phase [5][6][7][8][9][10][11][12][13][14][15][16][17], electronic nematicity [18][19][20][21][22][23][24], and superconductivity. Therefore, determining the exact microscopic configuration and symmetry of the CDW order is of top significance to establish the foundation of understanding these unconventional many-body effects. ...
Reference:
Revealing Rotational Symmetry Breaking Charge-density Wave Order in Kagome Superconductor (Rb, K)V$_3$Sb$_5$ by Ultrafast Pump-probe Experiments

Emergent nematicity and intrinsic versus extrinsic electronic scattering processes in the kagome metal CsV 3 Sb 5

Citing Article
Full-text available
June 2022

Physical Review Research

[...]

... Also, the vertical stacks of a few graphene layers have awaken the scientific and technological interest. Bi-or trilayer graphene shows outstanding physical properties, suggesting its application in electronics and optoelectronics [24,25]. Moreover, the electronic properties of these layered materials may be tuned by varying the relative twisting angle between layers [26], even predicting superconductivity for specific misalignment angles [27]. ...
Reference:
Vacancies and Stone–Wales defects in twisted bilayer graphene – A comparative theoretical study

Twisted double ABC-stacked trilayer graphene with weak interlayer coupling

Citing Article
May 2022

[...]

... NQR measurements were performed with a phase-coherent Tecmag Apollo NMR spectrometer at room temperature. The 35 Cl spectrum of CrCl 3 has been measured with a standard Hahn spinecho method (π/2−τ−π pulse sequence) at a fixed frequency of 12.915 MHz and is published elsewhere. 16 The other NQR spectra have been recorded by a frequency sweep method, where the frequency is increased step by step and all individual Fourier transforms are summed up at the end. ...
Reference:
Structural and Magnetic Transitions Caused by Dimer Formation in the CrCl3–MoCl3 Solid Solution

Dimer Crystallization Induced by Elemental Substitution in the Honeycomb Lattice of Ru 1− x Os x Cl 3

Citing Article
January 2022

Journal of the Physical Society of Japan

[...]

Dirk Wulferding’s research while affiliated with Seoul National University and other places

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