18 results on '"Blanco-Canosa, P."'
Search Results
2. Catalogue of Phonon Instabilities in Symmetry Group 191 Kagome MT$_6$Z$_6$ Materials
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Feng, X., Jiang, Y., Hu, H., Călugăru, D., Regnault, N., Vergniory, M. G., Felser, C., Blanco-Canosa, S., and Bernevig, B. Andrei
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Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
Kagome materials manifest rich physical properties due to the emergence of abundant electronic phases. Here, we carry out a high-throughput first-principles study of the kagome 1:6:6 family MT$_6$Z$_6$ materials in space group 191, focusing on their phonon instability and electronic flat bands. Different MT$_6$Z$_6$ kagome candidates reveal a remarkable variety of kagome flat bands ranging from unfilled, partially filled, to fully filled. Notably, the Mn/Fe-166 compounds exhibit partially filled flat bands with a pronounced sharp peak in the density of states near the Fermi level, leading to magnetic orders that polarize the bands and stabilize the otherwise unstable phonon. When the flat bands are located away from the Fermi level, we find a large number of phonon instabilities, which can be classified into three types, based on the phonon dispersion and vibrational modes. Type-I instabilities involve the in-plane distortion of kagome nets, while type-II and type-III present out-of-plane distortion of trigonal M and Z atoms. We take MgNi$_6$Ge$_6$ and HfNi$_6$In$_6$ as examples to illustrate the possible CDW structures derived from the emergent type-I and type-II instabilities. The type-I instability in MgNi$_6$Ge$_6$ suggests a nematic phase transition, governed by the local twisting of kagome nets. The type-II instability in HfNi$_6$In$_6$ may result in a hexagonal-to-orthorhombic transition, offering insight into the formation of MT$_6$Z$_6$ in other space groups. Additionally, the predicted ScNb$_6$Sn$_6$ is analyzed as an example of the type-III instability. Our predictions suggest a vast kagome family with rich properties induced by the flat bands, possible CDW transitions, and their interplay with magnetism., Comment: 14 pages, 7 figures, with 1000 pages of additional supplemental materials
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- 2024
3. Pressure induced quasi-long-range $\sqrt{3} \times \sqrt{3}$ charge density wave and competing orders in the kagome metal FeGe
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Korshunov, A., Kar, A., Lim, C. -Y., Subires, D., Deng, J., Jiang, Y., Hu, H., Călugăru, D., Yi, C., Roychowdhury, S., Shekhar, C., Garbarino, G., Törmä, P., Felser, C., Bernevig, B. Andrei, and Blanco-Canosa, S.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
Electronic ordering is prevalent in correlated systems, which commonly exhibit competing interactions. Here, we use x-ray diffraction to show that the charge density wave transition temperature of FeGe increases with pressure and evolves towards a $\sqrt{3}\times\sqrt{3}$ periodic lattice modulation, $\mathbf{q}$$^*$=$\left(\frac{1}{3}\ \frac{1}{3}\ \frac{1}{2}\right)$. In the pressure interval between 4$<$$p$$<$12 GPa both orders coexist and the spatial extent of the $\sqrt{3}\times\sqrt{3}$ order at high pressure becomes nearly long-range, $\sim$30 unit cells, while the correlation length of the 2$\times$2 phase remains shorter-ranged. The $\sqrt{3}\times\sqrt{3}$ phase is the ground state above 15 GPa, consistent with harmonic DFT calculations that predict a dimerization induced $\sqrt{3}\times\sqrt{3}$ order without phonon softening. The pressure dependence of the integrated intensities of $\mathbf{q}$$_\mathrm{CDW}=\left(\frac{1}{2}\ 0\ \frac{1}{2}\right)$ and $\mathbf{q}$$^*$ indicates a competition between the 2$\times$2 and $\sqrt{3}\times\sqrt{3}$ and demonstrates that the ground state of FeGe is characterized by a rich landscape of metastable/fragile phases. We discuss possible scenarios based on an order-disorder transformation and the formation of Friedel oscillations.
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- 2024
4. Frustrated charge density wave and quasi-long-range bond-orientational order in the magnetic kagome FeGe
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Subires, D., Kar, A., Korshunov, A., Fuller, C. A., Jiang, Y., Hu, H., Călugăru, Dumitru, McMonagle, C., Yi, C., Roychowdhury, S., Shekhar, C., Strempfer, J., Jana, A., Vobornik, I., Dai, J., Tallarida, M., Chernyshov, D., Bosak, A., Felser, C., Bernevig, B. Andrei, and Blanco-Canosa, S.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
The intrinsic frustrated nature of a kagome lattice is amenable to the realization of exotic phases of matter, such as quantum spin liquids or spin ices, and more recently the multiple-$\mathrm{\textbf{q}}$ charge density waves (CDW) in the kagome metals. Despite intense efforts to understand the mechanism driving the electronic modulations, its origin is still unknown and hindered by competing interactions and intertwined orders. Here, we identify a dimerization-driven 2D hexagonal charge-diffuse precursor in the antiferromagnetic kagome metal FeGe and demonstrate that the fraction of dimerized/undimerized states is the relevant order parameter of the multiple-$\mathrm{\textbf{q}}$ CDW of a continuous phase transition. The pretransitional charge fluctuations with propagation vector $\mathrm{\textbf{q}=\textbf{q}_M}$ at T$_{\mathrm{CDW}}$$<$T$<$T$^*$(125 K) are anisotropic, hence holding a quasi-long-range bond-orientational order. The broken translational symmetry emerges from the anisotropic diffuse precursor, akin to the Ising scenario of antiferromagnetic triangular lattices. The temperature and momentum dependence of the critical scattering show parallels to the stacked hexatic $\mathrm{B}$-phases reported in liquid crystals and transient states of CDWs and highlight the key role of the topological defect-mediated melting of the CDW in FeGe.
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- 2024
5. Self-stacked 1$\mathrm{T}$-1$\mathrm{H}$ layers in 6$\mathrm{R}$-NbSeTe and the emergence of charge and magnetic correlations due to ligand disorder
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Mahatha, S. K., Phillips, J., Corral-Sertal, J., Subires, D., Korshsunov, A., Kar, A., Buck, J., Diekmann, F., Ivanov, Y. P., Chuvilin, A., Mondal, D., Vobornik, I., Bosak, A., Rossnagel, K., Pardo, V., Fumega, Adolfo O., and Blanco-Canosa, S.
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Strongly Correlated Electrons - Abstract
The emergence of correlated phenomena arising from the combination of 1$\mathrm{T}$ and 1$\mathrm{H}$ van der Waals layers is the focus of intense research. Here, we synthesize a novel self-stacked 6$\mathrm{R}$ phase in NbSeTe, showing a perfect alternating 1T and 1H layers that grow coherently along the c-direction, as revealed by scanning transmission electron microscopy. Angle resolved photoemission spectroscopy shows a mixed contribution of the trigonal and octahedral Nb bands to the Fermi level. Diffuse scattering reveals temperature-independent short-range charge fluctuations with propagation vector $\mathrm{q_{CO}}$=(0.25,0), derived from the condensation of a longitudinal mode in the 1T layer. We observe that ligand disorder quenches the formation of a charge density wave. Magnetization measurements suggest the presence of an inhomogeneous, short-range magnetic order, further supported by the absence of a clear phase transition in the specific heat. These experimental analyses in combination with \textit{ab initio} calculations indicate that the ground state of 6$\mathrm{R}$-NbSeTe is described by a statistical distribution of short-range charge-modulated and spin-correlated regions driven by ligand disorder. Our results devise a route to synthesize 1$\mathrm{T}$-1$\mathrm{H}$ self-stacked bulk heterostructures to study emergent phases of matter., Comment: 12 pages, including Supplementary Information. 4 figures + 6 supplementary figures
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- 2024
6. Kagome Materials II: SG 191: FeGe as a LEGO Building Block for the Entire 1:6:6 series: hidden d-orbital decoupling of flat band sectors, effective models and interaction Hamiltonians
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Jiang, Yi, Hu, Haoyu, Călugăru, Dumitru, Felser, Claudia, Blanco-Canosa, Santiago, Weng, Hongming, Xu, Yuanfeng, and Bernevig, B. Andrei
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
The electronic structure and interactions of kagome materials such as 1:1 (FeGe class) and 1:6:6 (MgFe$_6$Ge$_6$ class) are complicated and involve many orbitals and bands at the Fermi level. Current theoretical models treat the systems in an $s$-orbital kagome representation, unsuited and incorrect both quantitatively and qualitatively to the material realities. In this work, we lay the basis of a faithful framework of the electronic model for this large class of materials. We show that the complicated ``spaghetti" of electronic bands near the Fermi level can be decomposed into three groups of $d$-Fe orbitals coupled to specific Ge orbitals. Such decomposition allows for a clear analytical understanding (leading to different results than the simple $s$-orbital kagome models) of the flat bands in the system based on the $S$-matrix formalism of generalized bipartite lattices. Our three minimal Hamiltonians can reproduce the quasi-flat bands, van Hove singularities, topology, and Dirac points close to the Fermi level, which we prove by extensive ab initio studies. We also obtain the interacting Hamiltonian of $d$ orbitals in FeGe using the constraint random phase approximation (cRPA) method. We then use this as a fundamental ``LEGO"-like building block for a large family of 1:6:6 kagome materials, which can be obtained by doubling and perturbing the FeGe Hamiltonian. We applied the model to its kagome siblings FeSn and CoSn, and also MgFe$_6$Ge$_6$. Our work serves as the first complete framework for the study of the interacting phase diagram of kagome compounds., Comment: 5+50 pages, 3+16 figures, previously submitted. This is the second paper of a series on kagome materials. See also the first paper: arXiv:2305.15469
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- 2023
7. Temperature and thickness dependence of the thermal conductivity in 2D ferromagnet Fe$_3$GeTe$_2$
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Claro, Marcel S., Corral-Sertal, Javier, Fumega, Adolfo O., Blanco-Canosa, Santiago, Suárez-Rodríguez, Manuel, Hueso, Luis E., Pardo, Victor, and Rivadulla, Francisco
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Condensed Matter - Materials Science - Abstract
The emergence of symmetry-breaking orders such as ferromagnetism and the weak interlayer bonding in van der Waals materials, offers a unique platform to engineer novel heterostructures and tune transport properties like thermal conductivity. Here, we report the experimental and theoretical study of the cross-plane thermal conductivity, $\kappa_\perp$, of the van der Waals 2D ferromagnet Fe$_3$GeTe$_2$. We observe a non-monotonic increase of $\kappa_\perp$ with the thickness and a large suppression in artificially-stacked layers, indicating a diffusive transport regime with ballistic contributions. These results are supported by the theoretical analyses of the accumulated thermal conductivity, which show an important contribution of phonons with mean free paths between 10 and 200 nm. Moreover, our experiments show a reduction of the $\kappa_\perp$ in the low-temperature ferromagnetic phase occurring at the magnetic transition. The calculations show that this reduction in $\kappa_\perp$ is associated with a decrease in the group velocities of the acoustic phonons and an increase in the phonon-phonon scattering of the Raman modes that couple to the magnetic phase. These results demonstrate the potential of van der Waals ferromagnets for thermal transport engineering.
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- 2023
8. Kagome Materials I: SG 191, ScV$_6$Sn$_6$. Flat Phonon Soft Modes and Unconventional CDW Formation: Microscopic and Effective Theory
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Hu, Haoyu, Jiang, Yi, Călugăru, Dumitru, Feng, Xiaolong, Subires, David, Vergniory, Maia G., Felser, Claudia, Blanco-Canosa, Santiago, and Bernevig, B. Andrei
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
Kagome Materials with flat bands exhibit wildly different physical properties depending on symmetry group, and electron number. For the case of ScV$_6$Sn$_6$ in space group 191, we investigate the existence of a charge density wave (CDW) at vector $\bar{K}=(\frac{1}{3},\frac{1}{3},\frac{1}{3})$ and its relationship with the phonon behavior. The experimental findings reveal a $\sim$95K CDW without nesting/peaks in the electron susceptibility at $\bar{K}$. Notably, ScV$_6$Sn$_6$ exhibits a collapsed phonon mode at $H=(\frac{1}{3},\frac{1}{3},\frac{1}{2})$ and an imaginary flat phonon band in the vicinity of $H$. The soft phonon is attributed to triangular Sn ($Sn^T$) mirror-even vibrations along the $z$-direction. We develop a simple force constant model to describe the entire soft phonon dispersion. By employing a new (Gaussian) approximation of the hopping parameter, we demonstrate the renormalization of the phonon frequency and the consequent collapse of the $H$ phonon. Additionally, we propose an effective model with two order parameters (OPs) to explain the appearance of the CDW at $\bar{K}$, which competes with the collapsed phonon at $H$. Through comparisons with experimental data, we show that the $H$ OP undergoes a second-order phase transition while exhibiting substantial fluctuations, ultimately inducing the first-order transition of the $\bar{K}$ OP. Furthermore, we extend our analysis to the similar compound YV$_6$Sn$_6$, which lacks a CDW phase, attributing this difference to the participation of the heavier Y atom in the out-of-plane phonon behavior. Our comprehensive study not only elucidates the CDW in ScV$_6$Sn$_6$ but also presents a significant advancement in modeling complex electronic systems, fostering collaborations between ab-initio simulations and analytical approaches., Comment: 5+108 pages, 3+42 figures, previously submitted. See also the related experimental study arXiv:2304.09173
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- 2023
9. Softening of a flat phonon mode in the kagome ScV$_6$Sn$_6$
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Korshunov, A., Hu, H., Subires, D., Jiang, Y., Călugăru, D., Feng, X., Rajapitamahuni, A., Yi, C., Roychowdhury, S., Vergniory, M. G., Strempfer, J., Shekhar, C., Vescovo, E., Chernyshov, D., Said, A. H., Bosak, A., Felser, C., Bernevig, B. Andrei, and Blanco-Canosa, S.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science - Abstract
The long range electronic modulations recently discovered in the geometrically frustrated kagome lattice have opened new avenues to explore the effect of correlations in materials with topological electron flat bands. The observation of the lattice response to the emergent new phases of matter, a soft phonon mode, has remained elusive and the microscopic origin of charge density waves (CDWs) is still unknown. Here, we show, for the first time, a complete melting of the ScV$_ 6$Sn$_ 6$ (166) kagome lattice. The low energy phonon with propagation vector $\frac{1}{3} \frac{1}{3} \frac{1}{2}$ collapses at 98 K, without the emergence of long-range charge order, which sets in with a propagation vector $\frac{1}{3} \frac{1}{3} \frac{1}{3}$. The CDW is driven (but locks at a different vector) by the softening of an overdamped phonon flat plane at k$_z$=$\pi$. We observe broad phonon anomalies in momentum space, pointing to (1) the existence of approximately flat phonon bands which gain some dispersion due to electron renormalization, and (2) the effects of the momentum dependent electron-phonon interaction in the CDW formation. Ab initio and analytical calculations corroborate the experimental findings to indicate that the weak leading order phonon instability is located at the wave vector $\frac{1}{3} \frac{1}{3} \frac{1}{2}$ of a rather flat collapsed mode. We analytically compute the phonon frequency renormalization from high temperatures to the soft mode, and relate it to a peak in the orbital-resolved susceptibility, obtaining an excellent match with both ab initio and experimental results, and explaining the origin of the approximately flat phonon dispersion. Our data report the first example of the collapse of a softening of a flat phonon plane and promote the 166 compounds of the kagome family as primary candidates to explore correlated flat phonon-topological flat electron physics., Comment: 10 pages, 4 figures
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- 2023
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10. Spectroscopy of the frustrated quantum antiferromagnet Cs$_2$CuCl$_4$
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Fumega, Adolfo O., Wong, D., Schulz, C., Rodríguez, F., and Blanco-Canosa, S.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We investigate the electronic structure of Cs$_2$CuCl$_4$, a material discussed in the framework of a frustrated quantum antiferromagnet, by means of resonant inelastic x-ray scattering (RIXS) and Density Functional Theory (DFT). From the non-dispersive highly localized dd excitations, we resolve the crystal field splitting of the Cu$^{2+}$ ions in a strongly distorted tetrahedral coordination. This allows us to model the RIXS spectrum within the Crystal Field Theory (CFT), assign the dd orbital excitations and retrieve experimentally the values of the crystal field splitting parameters D$_q$, D$_s$ and D$_{\tau}$. The electronic structure obtained ab-initio agrees with the RIXS spectrum and modelled by CFT, highlighting the potential of combined spectroscopic, cluster and DFT calculations to determine the electronic ground state of complex materials., Comment: 7 pages, 4 figures
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- 2022
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11. Anharmonicity reveals the tunability of the charge density wave orders in monolayer VSe$_2$
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Fumega, Adolfo O., Diego, Josu, Pardo, V., Blanco-Canosa, S., and Errea, Ion
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Strongly Correlated Electrons - Abstract
VSe$_2$ is a layered compound that has attracted great attention due to its proximity to a ferromagnetic state that is quenched by the presence of a charge density wave (CDW) phase. In the monolayer limit, unrelated experiments have reported different CDW orders with transition temperatures in the range of 130 to 220 K, making this monolayer very controversial. Here we perform first-principles non-perturbative anharmonic phonon calculations in monolayer VSe$_2$ in order to estimate the CDW order and the corresponding transition temperature. Our analysis solves previous experimental contradictions as we reveal that monolayer VSe$_2$ develops two independent charge density wave orders associated to $\sqrt{3} \times \sqrt{7}$ and $4 \times 4$ modulations that compete as a function of strain. In fact, tiny variations of only 1.5% in the lattice parameter are enough to stabilize one order or the other, which underlines that the CDW order becomes substrate-dependent. The predicted CDW temperature is strain-dependent and has a value of around 220 K, in good agreement with experiments. Moreover, we analyze the impact of external Lennard-Jones interactions on the CDW. We show that these can act together with the anharmonicity to suppress the CDW orders. In the particular case of monolayer VSe$_2$, this may give rise to the emergence of a ferromagnetic order., Comment: 8 pages, 4 figures, and supplemental material
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- 2022
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12. Order-disorder Peierls instability in the kagome metal (Cs,Rb)V$_3$Sb$_5$
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Subires, D., Korshunov, A., Said, A. H., Sánchez, L., Ortiz, Brenden R., Wilson, Stephen D., Bosak, A., and Blanco-Canosa, S.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
The nature of the charge density wave phases in the kagome metal compound AV$_3$Sb$_5$ has raised many questions and their origin is still under debate. Here, we combine diffuse scattering (DS) and inelastic x-ray scattering (IXS) to identify a 3-dimensional (3D) precursor of the charge order with propagation vector (0.5 0 0.5), which condenses into a 3D-CDW through a first order phase transition. The quasi-elastic critical scattering indicates that the dominant contribution to the diffuse precursor is the elastic central peak without phonon softening. However, the inelastic spectra show a small broadening of the Einstein-type phonon mode on approaching the phase transition. Our results point to the situation where the Fermi surface instability at the \textit{L} point is of order-disorder type with a critical growth of quasi-static domains. The results go beyond the classical weak-coupling Peierls transition dynamics and are discussed within models including strong-electron phonon coupling and non-adiabaticity.
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- 2022
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13. Phonon collapse and van der Waals melting of the 3D charge density wave of VSe$_2$
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Diego, Josu, Said, A. H., Mahatha, S. K., Bianco, Raffaello, Monacelli, Lorenzo, Calandra, Matteo, Mauri, Francesco, Rossnagel, K., Errea, Ion, and Blanco-Canosa, S.
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Condensed Matter - Materials Science - Abstract
Among transition metal dichalcogenides (TMDs), VSe$_2$ is considered to develop a purely 3-dimensional (3D) charge-density wave (CDW) at T$_{CDW}$=110 K. Here, by means of high resolution inelastic x-ray scattering (IXS), we show that the CDW transition is driven by the collapse of an acoustic mode at the critical wavevector \textit{q}$_{CDW}$= (2.25 0 0.7) r.l.u. and critical temperature T$_{CDW}$=110 K. The softening of this mode starts to be pronounced for temperatures below 2$\times$ T$_{CDW}$ and expands over a rather wide region of the Brillouin zone, suggesting a large contribution of the electron-phonon interaction to the CDW formation. This interpretation is supported by our first principles calculations that determine a large momentum-dependence of the electron-phonon interaction, peaking at the CDW wavevector, in the presence of nesting. Fully anharmonic {\it ab initio} calculations confirm the softening of one acoustic branch at \textit{q}$_{CDW}$ as responsible for the CDW formation and show that van der Waals interactions are crucial to melt the CDW. Our work also highlights the important role of out-of-plane interactions to describe 3D CDWs in TMDs.
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- 2020
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14. Electronic structure and magnetic exchange interactions of Cr-based van der Waals ferromagnets. A comparative study between CrBr3 and Cr2Ge2Te6
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Fumega, Adolfo O., Blanco-Canosa, S., Babu-Vasili, H., Zhou, Jian-Shi, Rivadulla, F., and Pardo, Victor
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Condensed Matter - Materials Science - Abstract
Low dimensional magnetism has been powerfully boosted as a promising candidate for numerous applications. The stability of the long-range magnetic order is directly dependent on the electronic structure and the relative strength of the competing magnetic exchange constants. Here, we report a comparative pressure-dependent theoretical and experimental study of the electronic structure and exchange interactions of two-dimensional ferromagnets CrBr3 and Cr2Ge2Te6 . While CrBr3 is found to be a Mott-Hubbard-like insulator, Cr2Ge2Te6 shows a charge-transfer character due to the broader character of the Te 5p bands at the Fermi level. This different electronic behaviour is responsible of the robust insulating state of CrBr3 , in which the magnetic exchange constants evolve monotonically with pressure, and the proximity to a metal-insulator transition predicted for Cr2Ge2Te6 , which causes a non-monotonic evolution of its magnetic ordering temperature. We provide a microscopic understanding for the pressure evolution of the magnetic properties of the two systems.
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- 2020
15. Absence of ferromagnetism in VSe$_2$ caused by its charge density wave phase
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Fumega, Adolfo O., Gobbi, M., Dreher, P., Wan, W., González-Orellana, C., Peña-Díaz, M., Rogero, C., Herrero-Martín, J., Gargiani, P., Ilyn, M., Ugeda, M. M., Pardo, Victor, and Blanco-Canosa, S.
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
How magnetism emerges in low-dimensional materials such as transition metal dichalcogenides at the monolayer limit is still an open question. Herein, we present a comprehensive study of the magnetic properties of single crystal and monolayer VSe$_{2}$, both experimentally and \emph{ab initio}. Magnetometry, X-ray magnetic circular dichrosim (XMCD) and \emph{ab initio} calculations demonstrate that the charge density wave in bulk stoichiometric VSe$_{2.0}$ causes a structural distortion with a strong reduction in the density of sates at the Fermi level, prompting the system towards a non-magnetic state but on the verge of a ferromagnetic instability. In the monolayer limit, the structural rearrangement induces a Peierls distortion with the opening of an energy gap at the Fermi level and the absence of magnetic order. Control experiments on defect-induced VSe$_{2-\delta}$ single crystals show a breakdown of magnetism, discarding vacancies as a possible origin of magnetic order in VSe$_{2}$., Comment: polished version, updated acknowledgments
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- 2019
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16. Synthetic antiferromagnetic coupling between ultra-thin insulating garnets
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Gomez-Perez, Juan M., Vélez, Saül, McKenzie-Sell, Lauren, Amado, Mario, Herrero-Martín, Javier, López-López, Josu, Blanco-Canosa, S., Hueso, Luis E., Chuvilin, Andrey, Robinson, Jason W. A., and Casanova, Fèlix
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
The use of magnetic insulators is attracting a lot of interest due to a rich variety of spin-dependent phenomena with potential applications to spintronic devices. Here we report ultra-thin yttrium iron garnet (YIG) / gadolinium iron garnet (GdIG) insulating bilayers on gadolinium iron garnet (GGG). From spin Hall magnetoresistance (SMR) and X-ray magnetic circular dichroism measurements, we show that the YIG and GdIG magnetically couple antiparallel even in moderate in-plane magnetic fields. The results demonstrate an all-insulating equivalent of a synthetic antiferromagnet in a garnet-based thin film heterostructure and could open new venues for insulators in magnetic devices. As an example, we demonstrate a memory element with orthogonal magnetization switching that can be read by SMR., Comment: 12 pages, 5 figures, Supplemental Material (3 pages)
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- 2018
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17. Orbital control of noncollinear magnetic order in nickelate heterostructures
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Frano, A., Schierle, E., Haverkort, M. W., Lu, Y., Wu, M., Blanco-Canosa, S., Nwankwo, U., Boris, A. V., Wochner, P., Cristiani, G., Habermeier, H. U., Logvenov, G., Hinkov, V., Benckiser, E., Weschke, E., and Keimer, B.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We have used resonant x-ray diffraction to develop a detailed description of antiferromagnetic ordering in epitaxial superlattices based on two-unit-cell thick layers of the strongly correlated metal LaNiO3. We also report reference experiments on thin films of PrNiO3 and NdNiO3. The resulting data indicate a spiral state whose polarization plane can be controlled by adjusting the Ni d-orbital occupation via two independent mechanisms: epitaxial strain and quantum confinement of the valence electrons. The data are discussed in the light of recent theoretical predictions., Comment: 5 pages, 3 figures
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- 2013
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18. Long-range transfer of electron-phonon coupling in oxide superlattices
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Driza, N., Blanco-Canosa, S., Bakr, M., Soltan, S., Khalid, M., Mustafa, L., Kawashima, K., Christiani, G., Habermeier, H. -U., Khaliullin, G., Ulrich, C., Tacon, M. Le, and Keimer, B.
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Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Condensed Matter - Superconductivity - Abstract
The electron-phonon interaction is of central importance for the electrical and thermal properties of solids, and its influence on superconductivity, colossal magnetoresistance, and other many-body phenomena in correlated-electron materials is currently the subject of intense research. However, the non-local nature of the interactions between valence electrons and lattice ions, often compounded by a plethora of vibrational modes, present formidable challenges for attempts to experimentally control and theoretically describe the physical properties of complex materials. Here we report a Raman scattering study of the lattice dynamics in superlattices of the high-temperature superconductor $\bf YBa_2 Cu_3 O_7$ and the colossal-magnetoresistance compound $\bf La_{2/3}Ca_{1/3}MnO_{3}$ that suggests a new approach to this problem. We find that a rotational mode of the MnO$_6$ octahedra in $\bf La_{2/3}Ca_{1/3}MnO_{3}$ experiences pronounced superconductivity-induced lineshape anomalies, which scale linearly with the thickness of the $\bf YBa_2 Cu_3 O_7$ layers over a remarkably long range of several tens of nanometers. The transfer of the electron-phonon coupling between superlattice layers can be understood as a consequence of long-range Coulomb forces in conjunction with an orbital reconstruction at the interface. The superlattice geometry thus provides new opportunities for controlled modification of the electron-phonon interaction in complex materials., Comment: 13 pages, 4 figures. Revised version to be published in Nature Materials
- Published
- 2012
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