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8 results on '"Namrata Gurung"'

1. Correlation between electronic and structural orders in 1T-TiSe_{2}

Author

Hiroki Ueda, Michael Porer, José R. L. Mardegan, Sergii Parchenko, Namrata Gurung, Federica Fabrizi, Mahesh Ramakrishnan, Larissa Boie, Martin Josef Neugebauer, Bulat Burganov, Max Burian, Steven Lee Johnson, Kai Rossnagel, and Urs Staub

Subjects
Physics, QC1-999
Abstract

The correlation between electronic and crystal structures of 1T-TiSe_{2} in the charge-density wave (CDW) state is studied by x-ray diffraction in order to clarify basic properties in the CDW state, transport properties, and chirality. Three families of reflections are used to probe atomic displacements and the orbital asymmetry in Se. Two distinct onset temperatures are found: T_{CDW} and a lower T^{*} indicative for an onset of Se out-of-plane atomic displacements. T^{*} coincides with a DC resistivity maximum and the onset of the proposed gyrotropic (chiral) electronic structure. However, no indication for chirality is found. The relation between the atomic displacements and the transport properties is discussed in terms of Ti 3d and Se 4p states that only weakly couple to the CDW order.

Published
2021
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2. Ultrafast electron localization in the EuNi_{2}(Si_{0.21}Ge_{0.79})_{2} correlated metal

Author

Jose R. L. Mardegan, Serhane Zerdane, Giulia Mancini, Vincent Esposito, Jérémy R. Rouxel, Roman Mankowsky, Cristian Svetina, Namrata Gurung, Sergii Parchenko, Michael Porer, Bulat Burganov, Yunpei Deng, Paul Beaud, Gerhard Ingold, Bill Pedrini, Christopher Arrell, Christian Erny, Andreas Dax, Henrik Lemke, Martin Decker, Nazaret Ortiz, Chris Milne, Grigory Smolentsev, Laura Maurel, Steven L. Johnson, Akihiro Mitsuda, Hirofumi Wada, Yuichi Yokoyama, Hiroki Wadati, and Urs Staub

Subjects
Physics, QC1-999
Abstract

Ultrafast electron delocalization induced by a femtosecond laser pulse is a well-known process in which electrons are ejected from the ions within the laser pulse duration. However, very little is known about the speed of electron localization out of an electron gas in correlated metals, i.e., the capture of an electron by an ion. Here, we demonstrate by means of pump-probe x-ray techniques across the Eu L_{3} absorption edge that an electron localization process in the EuNi_{2}(Si_{0.21}Ge_{0.79})_{2} intermetallic material occurs within a few hundred femtoseconds after the optical excitation. Spectroscopy and diffraction data collected simultaneously at low temperature and for various laser fluences show that the localization dynamics process is much faster than the thermal expansion of the unit cell along the c direction which occurs within picoseconds. Nevertheless, this latter process is still much slower than pure electronic effects, such as screening, and the subpicosecond timescale indicates an optical phonon driven origin. In addition, comparing the laser fluence dependence of the electronic response with that found in other intermediate 4f valence materials, we suggest that the electron localization process observed in this Eu-based correlated metal is mainly related to changes in the 4f hybridization. The observed ultrafast electron localization process sparks fundamental questions for our understanding of electron correlations and their coupling to the lattice.

Published
2021
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3. Structural involvement in the melting of the charge density wave in 1T-TiSe_{2}

Author

Max Burian, Michael Porer, Jose R. L. Mardegan, Vincent Esposito, Sergii Parchenko, Bulat Burganov, Namrata Gurung, Mahesh Ramakrishnan, Valerio Scagnoli, Hiroki Ueda, Sonia Francoual, Federica Fabrizi, Yoshikazu Tanaka, Tadashi Togashi, Yuya Kubota, Makina Yabashi, Kai Rossnagel, Steven L. Johnson, and Urs Staub

Subjects
Physics, QC1-999
Abstract

In this work, we use ultrafast pump-probe nonresonant and resonant x-ray diffraction to track the periodic lattice distortion and the electronic charge density wave in 1T-TiSe_{2} upon optical excitation. We observe a fluence regime in which the periodic lattice deformation is strongly suppressed but the charge density wave related Se 4p orbital order remains mostly intact. Complete melting of both structural and electronic order occurs four to five times faster than expected from a purely electronic charge-screening process, strongly suggesting a structurally assisted weakening of excitonic correlations. Our experimental data provide insight on the intricate coupling between structural and electronic order in stabilizing the periodic-lattice-distortion/charge-density-wave state in 1T-TiSe_{2}. The results further show that electron-phonon coupling can lead to different, energy dependent phase-transition pathways in condensed matter systems, opening different possibilities in the conception of nonequilibrium phenomena at the ultrafast scale.

Published
2021
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4. Melting of magnetic order in NaOsO3 by femtosecond laser pulses

Author

Flavio Giorgianni, Max Burian, Namrata Gurung, Martin Kubli, Vincent Esposito, Urs Staub, Paul Beaud, Steven L. Johnson, Yoav William Windsor, Laurenz Rettig, Dmitry Ozerov, Henrik Lemke, Susmita Saha, Federico Pressacco, Stephen Patrick Collins, Tadashi Togashi, Tetsuo Katayama, Shigeki Owada, Makina Yabashi, Kazunari Yamaura, Yoshikazu Tanaka, and V. Scagnoli

Abstract

NaOsO3 has recently attracted significant attention for the strong coupling between its electronic band structure and magnetic ordering. Here, we used time-resolved magnetic x-ray diffraction to determine the timescale of the photoinduced antiferromagnetic dynamics in NaOsO3. Our measurements are consistent with a sub-100 fs melting of the antiferromagnetic long-range order that occurs significantly faster than the lattice dynamics as monitored by the transient change in intensity of selected Bragg structural reflections, which instead show a decrease of intensity on a timescale of several ps.

Published
2022
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5. Structural involvement in the melting of the charge density wave in 1T−TiSe2

Author

Urs Staub, Steven L. Johnson, Yoshikazu Tanaka, Valerio Scagnoli, Max Burian, Bulat Burganov, Yuya Kubota, Kai Rossnagel, J. R. L. Mardegan, Mahesh Ramakrishnan, Federica Fabrizi, Sergii Parchenko, Vincent Esposito, Michael Porer, Namrata Gurung, Tadashi Togashi, Sonia Francoual, Hiroki Ueda, and Makina Yabashi

Subjects
Materials science, Condensed matter physics, Distortion, 0103 physical sciences, 02 engineering and technology, Electronic structure, 021001 nanoscience & nanotechnology, 010306 general physics, 0210 nano-technology, 01 natural sciences, Ultrashort pulse, Charge density wave
Abstract

The authors find that the structural distortion and the underlying electronic structure of the charge density wave in TiSe${}_{2}$ show different energetics at ultrafast timescales.

Published
2021
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6. Probing spin fluctuations in NaOsO3 by muon spin rotation and NMR spectroscopy

Author

Chennan Wang, Nicholas S. Bingham, Kazunari Yamaura, Hubertus Luetkens, Paola Caterina Forino, Valerio Scagnoli, Giuseppe Allodi, Namrata Gurung, Joel A. T. Verezhak, S. Sanna, Gurung N., Wang C., Bingham N.S., Verezhak J.A.T., Yamaura K., Allodi G., Forino P.C., Sanna S., Luetkens H., and Scagnoli V.

Subjects
Physics, Metal-insulator transition, Muon, Condensed matter physics, Magnetic moment, Magnetism, Relaxation (NMR), Muon spin spectroscopy, 02 engineering and technology, 021001 nanoscience & nanotechnology, Condensed Matter Physics, 01 natural sciences, Magnetic field, Nuclear magnetic resonance, 0103 physical sciences, General Materials Science, 010306 general physics, 0210 nano-technology, Spin (physics), Néel temperature, Phase transition
Abstract

We have used muon spin rotation and relaxation (μSR) and 23Na nuclear magnetic resonance (NMR) spectroscopic methods in the NaOsO3 antiferromagnetic phase to determine the temperature evolution of the magnetic order parameter and the role of the magnetic fluctuations at the Néel temperature. Additionally, we performed muon spin relaxation measurements in the vicinity of TA = 30 K, where the appearance of an anomaly in the electrical resistivity was suggested to be due to a progressive reduction of the Os magnetic moment associated with spin fluctuation. Our measurements suggest the absence of prominent change in the spin fluctuations frequency at TA, within the muon probing time scale and the absence of a reduction of the localized Os magnetic moment reflected by the stability within few permille of the local magnetic field strength sensed by the muons below 50 K.

Published
2021

7. Field-induced double spin spiral in a frustrated chiral magnet

Author

Mahesh Ramakrishnan, Evan Constable, Andres Cano, Maxim Mostovoy, Jonathan S. White, Namrata Gurung, Enrico Schierle, Sophie de Brion, Claire V. Colin, Frederic Gay, Pascal Lejay, Eric Ressouche, Eugen Weschke, Valerio Scagnoli, Rafik Ballou, Virginie Simonet, Urs Staub, Theory of Condensed Matter, Solid State Materials for Electronics, The Swiss Light Source (SLS) (SLS-PSI), Paul Scherrer Institute (PSI), Magnétisme et Supraconductivité (NEEL - MagSup), Institut Néel (NEEL), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Vienna University of Technology (TU Wien), Théorie de la Matière Condensée (NEEL - TMC), Zernike Institute of Advanced Materials, University of Groningen [Groningen], Department of Materials [ETH Zürich] (D-MATL), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich), Helmoltz-Zentrum Berlin für Materialien und Energie (GmbH), Matériaux, Rayonnements, Structure (NEEL - MRS), Automatisation & caractérisation (NEEL - AUTOCARAC), Croissance Cristalline et MicroAnalyse (NEEL - C2MA), Magnétisme et Diffusion Neutronique (MDN), Modélisation et Exploration des Matériaux (MEM), Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Magnétisme et Supraconductivité (MagSup ), Théorie de la Matière Condensée (TMC ), Matériaux, Rayonnements, Structure (MRS), Automatisation et Caractérisation (AUTOCARAC ), Cristaux Massifs (CrisMass), Institut de Recherche Interdisciplinaire de Grenoble (IRIG), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])

Subjects
Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), MIXED-STATE, lcsh:TA401-492, FOS: Physical sciences, lcsh:Materials of engineering and construction. Mechanics of materials, PHASE-TRANSITIONS, [PHYS.COND.CM-SCE]Physics [physics]/Condensed Matter [cond-mat]/Strongly Correlated Electrons [cond-mat.str-el], lcsh:Atomic physics. Constitution and properties of matter, ComputingMilieux_MISCELLANEOUS, lcsh:QC170-197
Abstract

Magnetic ground states with peculiar spin textures, such as magnetic skyrmions and multifunctional domains are of enormous interest for the fundamental physics governing their origin as well as potential applications in emerging technologies. Of particular interest are multiferroics, where sophisticated interactions between electric and magnetic phenomena can be used to tailor several functionalities. We report the direct observation of a magnetic field induced long-wavelength spin spiral modulation in the chiral compound Ba3TaFe3Si2O14, which emerges out of a helical ground state, and is hallmarked by the onset of a unique chirality-dependent contribution to the bulk electric polarization. The periodicity of the field-induced modulation, several hundreds of nm depending on the field value, is comparable to the length scales of mesoscopic topological defects such as skyrmions, merons, and solitons. The phase transition and observed threshold behavior are consistent with a phenomenology based on the allowed Lifshitz invariants for the chiral symmetry of langasite, which intriguingly contain all the essential ingredients for the realization of topologically stable antiferromagnetic skyrmions. Our findings open up new directions to explore topological correlations of antiferromagnetic spintronic systems based on non-collinear magnetic systems with additional ferroic functionalities., npj Quantum Materials, 4 (1), ISSN:2397-4648

Published
2019
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8. Correlation between electronic and structural orders in 1 T − Ti Se 2

Author

J. R. L. Mardegan, Federica Fabrizi, Martin J. Neugebauer, Hiroki Ueda, Namrata Gurung, Urs Staub, Larissa Boie, Steven L. Johnson, Sergii Parchenko, Kai Rossnagel, Michael Porer, Max Burian, Bulat Burganov, and Mahesh Ramakrishnan

Subjects
Materials science, Strongly Correlated Electrons (cond-mat.str-el), Condensed matter physics, FOS: Physical sciences, 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, 3. Good health, Out of plane, Correlation, Condensed Matter - Strongly Correlated Electrons, Phase (matter), charge density waves, crystal symmetry, electrical conductivity, structural order parameter, transition-metal dichalcogenide, resonant elastic x-ray scattering, x-ray diffraction, 0103 physical sciences, ddc:530, sense organs, skin and connective tissue diseases, 010306 general physics, 0210 nano-technology, Charge density wave, Electronic properties
Abstract

The correlation between electronic and crystal structures of 1T-TiSe2 in the charge density wave (CDW) state is studied by x-ray diffraction. Three families of reflections are used to probe atomic displacements and the orbital asymmetry in Se. Two distinct onset temperatures are found, TCDW and a lower T* indicative for an onset of Se out-of-plane atomic displacements. T* coincides with a DC resistivity maximum and the onset of the proposed gyrotropic electronic structure. However, no indication for chirality is found. The relation between the atomic displacements and the transport properties is discussed in terms of Ti 3d and Se 4p states that only weakly couple to the CDW order., Comment: 16 pages, 4 figures + 13 pages supplementary info

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