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Papers by Devashibhai Adroja

Research paper thumbnail of Magneto-Elastic Coupling in a Sinusoidal Modulated Magnet Cr2GaN

Chinese Physics Letters

We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr2GaN... more We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr2GaN. A magnetic phase transition is identified at T ≈ 170 K, whereas no trace of structural transition is observed down to 6 K. Combining Rietveld refinement with irreducible representations, the spin configuration of Cr ions in Cr2GaN is depicted as an incommensurate sinusoidal modulated structure characterized by a propagating vector k = (0.365, 0.365, 0). Upon warming up to the paramagnetic state, the magnetic order parameter closely resembles to the temperature dependence of c-axis lattice parameter, suggesting strong magneto-elastic coupling in this compound. Therefore, Cr2GaN provides a potential platform for exploration of magnetically tuned properties such as magnetoelectric, magnetostrictive and magnetocaloric effects, as well as their applications.

Research paper thumbnail of Crystalline Electric Field as a Probe for Long-Range Antiferromagnetic Order and Superconducting State ofCeFeAsO1−xFx

Physical Review Letters, 2008

We use inelastic neutron scattering to study the crystalline electric field (CEF) excitations of ... more We use inelastic neutron scattering to study the crystalline electric field (CEF) excitations of Ce 3þ in CeFeAsO 1Àx F x (x ¼ 0, 0.16). For nonsuperconducting CeFeAsO, the Ce CEF levels have three magnetic doublets in the paramagnetic state, but these doublets split into six singlets when the Fe ions order antiferromagnetically. For superconducting CeFeAsO 0:84 F 0:16 (T c ¼ 41 K), where the static antiferromagnetic order is suppressed, the Ce CEF levels have three magnetic doublets at @! ¼ 0, 18.7, 58.4 meV at all temperatures. Careful measurements of the intrinsic linewidth À and the peak position of the 18.7 meV mode reveal a clear anomaly at T c , consistent with a strong enhancement of local magnetic susceptibility 00 ð@!Þ below T c. These results suggest that CEF excitations in the rare-earth oxypnictides can be used as a probe of spin dynamics in the nearby FeAs planes.

Research paper thumbnail of Spin-glass order induced by dynamic frustration

Research paper thumbnail of Vibrational Dynamics of Filled Skutterudites La T 4 X 12 ( T = Fe, Ru, Os, X = As, Sb)

Journal of the Physical Society of Japan, 2013

We report on the vibrational properties of the lanthanum filled skutterudite compounds LaRu 4 Sb ... more We report on the vibrational properties of the lanthanum filled skutterudite compounds LaRu 4 Sb 12 , LaOs 4 Sb 12 , and LaOs 4 As 12 studied by inelastic neutron scattering. The experimental data are backed up by ab initio lattice dynamics calculations of the complete series of lanthanum filled skutterudites LaT 4 X 12 with T = Fe, Ru, Os and X = As, Sb. We present details of their structural properties, phonon dispersion relations, vibrational densities of states Zð!Þ and specific heats C V ðT Þ calculated from Zð!Þ within the harmonic approximation. Powder averaged lattice dynamics (PALD) technique is applied to approximate the experimental signal presented as the generalized density of states Gð!Þ with high accuracy. Furthermore, the PALD approach is exploited to compute average transverse v PALD t and longitudinal v PALD l sound velocities, elastic constants c PALD 11 , c PALD 44 , bulk moduli B PALD , and Debye temperatures  PALD D. The PALD results are compared with data computed from ab initio lattice dynamics calculations. All calculated properties are in very good agreement with literature data.

Research paper thumbnail of Antiferromagnetic Correlations in Strongly Valence Fluctuating CeIrSn

Physical Review Letters, 2021

CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuati... more CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of TK ∼ 480 K. We report a negative in-plane thermal expansion α/T below 2 K, which passes through a broad minimum near 0.75 K. Volume and a-axis magnetostriction for B a are markedly negative at low fields and change sign before a sharp metamagnetic anomaly at 6 T. These behaviors are unexpected for Ce-based intermediate valence systems, which should feature positive expansivity. Rather they point towards antiferromagnetic correlations at very low temperatures. This is supported by muon spin relaxation measurements down to 0.1 K, which provide microscopic evidence for a broad distribution of internal magnetic fields. Comparison with isostructural CeRhSn suggests that these antiferromagnetic correlations emerging at T TK result from geometrical frustration.

Research paper thumbnail of Muon-spin relaxation study of the layered kagome superconductor CsV$_3$Sb$_5$

The Z2 topological metals RV3Sb5 (R = K, Rb, Cs) with a layered kagome structure provide a unique... more The Z2 topological metals RV3Sb5 (R = K, Rb, Cs) with a layered kagome structure provide a unique opportunity to investigate the interplay between charge order, superconductivity and topology. Here, we report muon-spin relaxation/rotation (µSR) measurements performed on CsV3Sb5 across a broad temperature range, in order to uncover the nature of the charge-density wave order and superconductivity in this material. From zero-field µSR, we find that spontaneous magnetic fields appear below 50 K which is well below the charge-density wave transition (T * ∼ 93 K). We show that these spontaneous fields are dynamic in nature making it difficult to associate them with a hidden static order. The superconducting state of CsV3Sb5 is found to preserve time-reversal symmetry and the transverse-field µSR results are consistent with a superconducting state that has two fully open gaps.

Research paper thumbnail of Crystal field excitations across the isostructural transition in TbNiAl and TbPdAl

Solid State Communications, 2008

ABSTRACT We report on the inelastic neutron scattering study performed on TbNiAl and TbPdAl with ... more ABSTRACT We report on the inelastic neutron scattering study performed on TbNiAl and TbPdAl with special focus on the isostructural transition that occurs for both compounds around 110 K. The measured inelastic neutron spectra revealed crystal-field excitations below 15 meV. The corresponding scattering intensity shifts gradually to lower energies when increasing temperature from 4 to 140 K that corresponds to gradual population of the excited crystal-field states. We did not observe any significant deviation from this tendency around the temperature of the structural transition, which may indicate that the crystal field potential seen by the Tb ion has a very similar strength as well as local point symmetry above and below the structural phase transition.

Research paper thumbnail of Unconventional superconductivity in Y$_5$Rh$_6$Sn$_{18}$ probed by muon spin relaxation

arXiv: Superconductivity, 2015

Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissn... more Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high$-$temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor \yrhsn\ ($T_{\bf c}$ = 3.0 K). The electronic heat capacity of \yrhsn\ shows a T3T^3T3 dependence below TbfcT_{\bf c}Tbfc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu$_5$Rh$_6$Sn$_{18}$ which is a strong coupling s−s-s−wave superconductor. The temperature dependence of the deduced superfluid density \yrhsn\ is consistent with a BCS s−s-s−wave gap function, while the...

Research paper thumbnail of Phononic bandgap and phonon anomalies in HfN and HfN/ScN metal/semiconductor superlattices measured with inelastic x-ray scattering

Applied Physics Letters, 2020

Epitaxial metal/semiconductor superlattice heterostructures with lattice-matched abrupt interface... more Epitaxial metal/semiconductor superlattice heterostructures with lattice-matched abrupt interfaces and suitable Schottky barrier heights are attractive for thermionic energy conversion, hot electron-based solar energy conversion, and optical hyperbolic metamaterials. HfN/ScN is one of the earliest demonstrations of epitaxial single-crystalline metal/semiconductor heterostructures and has attracted significant interest in recent years to harness its excellent properties in device applications. Although the understanding of the mechanism of thermal transport in HfN/ScN superlattices is extremely important for their practical applications, not much attention has been devoted to measuring their phonon dispersion and related properties. In this Letter, we employ non-resonant meV-resolution inelastic x-ray scattering to determine the momentum-dependent phonon modes in epitaxial metallic HfN and lattice-matched HfN/ScN metal/semiconductor superlattices. HfN exhibits a large phononic bandga...

Research paper thumbnail of 2 6 Ju l 2 01 5 Unconventional superconductivity in Y 5 Rh 6 Sn 18 probed by muon spin relaxation

Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissn... more Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high−temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 (Tc = 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T 3 dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s−wave superconductor. The temperature dependence of the deduced superfluid density Y5Rh6Sn18 is consistent with a BCS s−wave gap function, while the zero-field muon spin relaxatio...

Research paper thumbnail of B 101 , 134408 ( 2020 ) Spin dynamics of a magnetic Weyl semimetal Sr

Zhengwei Cai,1,* Song Bao,1,* Wei Wang ,1,* Zhen Ma,1 Zhao-Yang Dong ,2 Yanyan Shangguan,1 Jinghu... more Zhengwei Cai,1,* Song Bao,1,* Wei Wang ,1,* Zhen Ma,1 Zhao-Yang Dong ,2 Yanyan Shangguan,1 Jinghui Wang,1 Kejing Ran,1 Shichao Li,1 Kazuya Kamazawa,3 Mitsutaka Nakamura,4 Devashibhai Adroja,5,6 Shun-Li Yu,1,7,† Jian-Xin Li,1,7,‡ and Jinsheng Wen 1,7,§ 1National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China 2Department of Applied Physics, Nanjing University of Science and Technology, Nanjing 210094, China 3Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Tokai, Ibaraki 319-1106, Japan 4J-PARC Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan 5ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom 6Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa 7Collaborative Innovation Center of Advanced Microstructures, Nanjing ...

Research paper thumbnail of Symmetry Origin of the Dzyaloshinskii–Moriya Interaction and Magnetization Reversal in YVO3

Inorganic Chemistry

We have investigated magneto-structural phase transitions in polycrystalline YVO3 using high-reso... more We have investigated magneto-structural phase transitions in polycrystalline YVO3 using high-resolution neutron powder diffraction toward understanding the phenomenon of magnetization reversal. Contrary to earlier reports, our study reveals that both C-type and G-type antiferromagnetic ordering, corresponding to G-type and C-type orbital ordered phases, respectively, occur at the same temperature (TN = 115 K) with the G-type antiferromagnetic phase growing at the expense of the C-type one on cooling. These processes cease at TS ∼ 77 K; however, a minor (∼4%) untransformed C-type phase remains unchanged down to 1.7 K. The symmetry analysis indicates different symmetry origins of the Dzyaloshinskii-Moriya interaction in each phase, which can explain the magnetization reversal observed between TN and TS. We discuss that magnetic phase separation and associated weak ferromagnetism may be the common mechanism underlying the magnetization reversal phenomenon observed in other RVO3 systems (R = rare earth).

Research paper thumbnail of Neutron scattering study of the Kondo insulators CeT 2Al10 (T = Fe, Ru, Os)

Acta Crystallographica Section A Foundations and Advances, Dec 1, 2017

The recent discovery of topological Kondo insulating behaviour in strongly correlated electron sy... more The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in the field of Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT2Al10 (T=Fe, Ru and Os), crystalizing in the orthorhombic crystal structure, possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu2Al10 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10 with a paramagnetic ground state down to 50 mK [1-3]. We are investigating this family of compounds using neutron diffraction, inelastic neutron scattering (INS) and muon spin rotation/relaxation (µSR) measurements to understand the role of anisotropic c-f hybridization on the anomalous magnetic structure, anisotropic magnetic exchanges, and spin gap formation as well as on their magnetic and transport properties. Our neutron diffraction studies on T=Ru and Os show that the magnetic ordering with propagation vector K=[1 0 0], but the direction of the moment is along the c-axis, which is not the easy axis of the magnetization. Further the ordered state moment is much smaller than that expected from the J=5/2 state of Ce3+ ion. We will show that the observed magnetic structure, direction and magnitude of the moment, is very sensitive to the electron and hole-doping in these compounds, but the crystal structure remains the orthorhombic.. We have observed a clear sign of a spin gap in all three compounds from INS study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our INS studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive gapped spin wave excitations below TN [3]. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy (CEF), which prefers the moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K [3]. We will discuss the origin of the anisotropic hybridization gap in CeFe2Al10 based on theoretical models of heavy-fermion semiconductors. Further the effect of electron-and hole-doping as well as chemical pressure effect on the magnetic and transport properties of CeT2All0 compounds will be discussed based on our INS and µSR results. Our µSR study reveals a long range magnetic ordering for electron doping in the Kondo insulator CeFe2Al10. We will compare the results of our INS study of CeT2Al10 with that of topological Kondo insulators, such as SmB6, CeNiSn and CeRu4Sn6.

Research paper thumbnail of Spin dynamics and Griffiths singularity in the random quantum Ising magnet PrTiNbO6

npj Quantum Materials

In crystalline magnets, interaction randomness is usually thought as a negative factor preventing... more In crystalline magnets, interaction randomness is usually thought as a negative factor preventing interesting quantum phenomena to occur. However, intriguing interplay between randomness and quantumness can also leads to unique phenomena in the strongly correlated materials. Among others, the random transverse-field Ising spin chain (RTIC) hosts a renowned quantum Griffiths phase. Although the RTIC model has been regarded as a toy model for long, here we materialize this model with the compound PrTiNbO6, which has a disordered ground state with pronounced quantum fluctuations and continuous spin excitations. The observed anomalous spin dynamics of PrTiNbO6 can be accounted by the RTIC model with a consistent set of parameters determined from fitting the thermodynamic data, and it is ascribed to the quantum Griffiths rare regions in the system. Our results provide a concrete example of quantum Griffiths magnet, and offer an ideal experimental platform for investigating the dynamical ...

Research paper thumbnail of Intermultiplet transitions and magnetic long-range order in Sm-based pyrochlores

Physical Review B

We present bulk and neutron scattering measurements performed on the isotopically enriched 154 Sm... more We present bulk and neutron scattering measurements performed on the isotopically enriched 154 Sm2Ti2O7 and 154 Sm2Sn2O7 samples. Both compounds display sharp heat capacity anomalies, at 350 mK and 440 mK, respectively. Inelastic neutron scattering measurements are employed to determine the crystalline electric field (CEF) level scheme, which includes transitions between the ground-state and first excited J multiplets of the Sm 3+ ion. To further validate those results, the single-ion magnetic susceptibility of the compounds is calculated and compared with the experimental DC-susceptibility measured in low applied magnetic fields. It is demonstrated that the inclusion of intermultiplet transitions in the CEF analysis is fundamental to the understanding of the intermediate and, more importantly, low temperature magnetic behaviour of the Sm-based pyrochlores. Finally, the heat capacity anomaly is shown to correspond to the onset of an all-in-all-out long-range order in the stannate sample, while in the titanate a dipolar long-range order can be only indirectly inferred.

Research paper thumbnail of Neutron Scattering Studies of the Breathing Pyrochlore Antiferromagnet LiGaCr4O8

Physical Review Letters

We report neutron scattering measurements of the spinel oxide LiGaCr 4 O 8 , in which magnetic io... more We report neutron scattering measurements of the spinel oxide LiGaCr 4 O 8 , in which magnetic ions Cr 3þ form a breathing pyrochlore lattice. Our experiments reveal the coexistence of a nearly dispersionless resonance mode and dispersive spin-wave excitations in the magnetically ordered state, which can be quantitatively described by a quantum spin model of hexagonal loops and linear spin-wave theory with the same set of exchange parameters, respectively. Comparison to other Cr spinel oxides reveals a linear relationship between the resonance energy and lattice constant across all these materials, which is in agreement with our hexagonal loop calculations. Our results suggest a unified picture for spin resonances in Cr spinel oxides.

Research paper thumbnail of Spin dynamics of a magnetic Weyl semimetal Sr1−xMn1−ySb2

Research paper thumbnail of Gapless spin-liquid state in the structurally disorder-free triangular antiferromagnet NaYbO2

Physical Review B

We present the structural characterization and low-temperature magnetism of the triangular-lattic... more We present the structural characterization and low-temperature magnetism of the triangular-lattice delafossite NaYbO 2. Synchrotron x-ray diffraction and neutron scattering exclude both structural disorder and crystalelectric-field randomness, whereas heat-capacity measurements and muon spectroscopy reveal the absence of magnetic order and persistent spin dynamics down to at least 70 mK. Continuous magnetic excitations with the low-energy spectral weight accumulating at the K-point of the Brillouin zone indicate the formation of a novel spin-liquid phase in a triangular antiferromagnet. This phase is gapless and shows a non-trivial evolution of the low-temperature specific heat. Our work demonstrates that NaYbO 2 practically gives the most direct experimental access to the spin-liquid physics of triangular antiferromagnets.

Research paper thumbnail of Interplay between hybridisation gaps and unusual magnetic orders in Kondo semiconductors CeT2Al10 (T = Ru and Os)

Research paper thumbnail of Partial vibrational density of states for amorphous solids from inelastic neutron scattering

Physical Review B

We introduce coherent inelastic neutron scattering with isotope substitution as a technique for m... more We introduce coherent inelastic neutron scattering with isotope substitution as a technique for measuring site-specific information on the vibrational dynamics of amorphous solids. The technique is used to extract experimentally the partial vibrational density of states G α (E) for both Ge and Se in the prototypical networkforming glass GeSe 2 , where α specifies the chemical species and E denotes the energy. The efficacy of the approximations used in interpreting the experimental data is validated by using a first-principles model, for which the set of true partial vibrational density of states is directly accessible. Our approach offers an opportunity for exploring accurately the vibrational dynamics of disordered materials.

Research paper thumbnail of Magneto-Elastic Coupling in a Sinusoidal Modulated Magnet Cr2GaN

Chinese Physics Letters

We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr2GaN... more We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr2GaN. A magnetic phase transition is identified at T ≈ 170 K, whereas no trace of structural transition is observed down to 6 K. Combining Rietveld refinement with irreducible representations, the spin configuration of Cr ions in Cr2GaN is depicted as an incommensurate sinusoidal modulated structure characterized by a propagating vector k = (0.365, 0.365, 0). Upon warming up to the paramagnetic state, the magnetic order parameter closely resembles to the temperature dependence of c-axis lattice parameter, suggesting strong magneto-elastic coupling in this compound. Therefore, Cr2GaN provides a potential platform for exploration of magnetically tuned properties such as magnetoelectric, magnetostrictive and magnetocaloric effects, as well as their applications.

Research paper thumbnail of Crystalline Electric Field as a Probe for Long-Range Antiferromagnetic Order and Superconducting State ofCeFeAsO1−xFx

Physical Review Letters, 2008

We use inelastic neutron scattering to study the crystalline electric field (CEF) excitations of ... more We use inelastic neutron scattering to study the crystalline electric field (CEF) excitations of Ce 3þ in CeFeAsO 1Àx F x (x ¼ 0, 0.16). For nonsuperconducting CeFeAsO, the Ce CEF levels have three magnetic doublets in the paramagnetic state, but these doublets split into six singlets when the Fe ions order antiferromagnetically. For superconducting CeFeAsO 0:84 F 0:16 (T c ¼ 41 K), where the static antiferromagnetic order is suppressed, the Ce CEF levels have three magnetic doublets at @! ¼ 0, 18.7, 58.4 meV at all temperatures. Careful measurements of the intrinsic linewidth À and the peak position of the 18.7 meV mode reveal a clear anomaly at T c , consistent with a strong enhancement of local magnetic susceptibility 00 ð@!Þ below T c. These results suggest that CEF excitations in the rare-earth oxypnictides can be used as a probe of spin dynamics in the nearby FeAs planes.

Research paper thumbnail of Spin-glass order induced by dynamic frustration

Research paper thumbnail of Vibrational Dynamics of Filled Skutterudites La T 4 X 12 ( T = Fe, Ru, Os, X = As, Sb)

Journal of the Physical Society of Japan, 2013

We report on the vibrational properties of the lanthanum filled skutterudite compounds LaRu 4 Sb ... more We report on the vibrational properties of the lanthanum filled skutterudite compounds LaRu 4 Sb 12 , LaOs 4 Sb 12 , and LaOs 4 As 12 studied by inelastic neutron scattering. The experimental data are backed up by ab initio lattice dynamics calculations of the complete series of lanthanum filled skutterudites LaT 4 X 12 with T = Fe, Ru, Os and X = As, Sb. We present details of their structural properties, phonon dispersion relations, vibrational densities of states Zð!Þ and specific heats C V ðT Þ calculated from Zð!Þ within the harmonic approximation. Powder averaged lattice dynamics (PALD) technique is applied to approximate the experimental signal presented as the generalized density of states Gð!Þ with high accuracy. Furthermore, the PALD approach is exploited to compute average transverse v PALD t and longitudinal v PALD l sound velocities, elastic constants c PALD 11 , c PALD 44 , bulk moduli B PALD , and Debye temperatures  PALD D. The PALD results are compared with data computed from ab initio lattice dynamics calculations. All calculated properties are in very good agreement with literature data.

Research paper thumbnail of Antiferromagnetic Correlations in Strongly Valence Fluctuating CeIrSn

Physical Review Letters, 2021

CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuati... more CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of TK ∼ 480 K. We report a negative in-plane thermal expansion α/T below 2 K, which passes through a broad minimum near 0.75 K. Volume and a-axis magnetostriction for B a are markedly negative at low fields and change sign before a sharp metamagnetic anomaly at 6 T. These behaviors are unexpected for Ce-based intermediate valence systems, which should feature positive expansivity. Rather they point towards antiferromagnetic correlations at very low temperatures. This is supported by muon spin relaxation measurements down to 0.1 K, which provide microscopic evidence for a broad distribution of internal magnetic fields. Comparison with isostructural CeRhSn suggests that these antiferromagnetic correlations emerging at T TK result from geometrical frustration.

Research paper thumbnail of Muon-spin relaxation study of the layered kagome superconductor CsV$_3$Sb$_5$

The Z2 topological metals RV3Sb5 (R = K, Rb, Cs) with a layered kagome structure provide a unique... more The Z2 topological metals RV3Sb5 (R = K, Rb, Cs) with a layered kagome structure provide a unique opportunity to investigate the interplay between charge order, superconductivity and topology. Here, we report muon-spin relaxation/rotation (µSR) measurements performed on CsV3Sb5 across a broad temperature range, in order to uncover the nature of the charge-density wave order and superconductivity in this material. From zero-field µSR, we find that spontaneous magnetic fields appear below 50 K which is well below the charge-density wave transition (T * ∼ 93 K). We show that these spontaneous fields are dynamic in nature making it difficult to associate them with a hidden static order. The superconducting state of CsV3Sb5 is found to preserve time-reversal symmetry and the transverse-field µSR results are consistent with a superconducting state that has two fully open gaps.

Research paper thumbnail of Crystal field excitations across the isostructural transition in TbNiAl and TbPdAl

Solid State Communications, 2008

ABSTRACT We report on the inelastic neutron scattering study performed on TbNiAl and TbPdAl with ... more ABSTRACT We report on the inelastic neutron scattering study performed on TbNiAl and TbPdAl with special focus on the isostructural transition that occurs for both compounds around 110 K. The measured inelastic neutron spectra revealed crystal-field excitations below 15 meV. The corresponding scattering intensity shifts gradually to lower energies when increasing temperature from 4 to 140 K that corresponds to gradual population of the excited crystal-field states. We did not observe any significant deviation from this tendency around the temperature of the structural transition, which may indicate that the crystal field potential seen by the Tb ion has a very similar strength as well as local point symmetry above and below the structural phase transition.

Research paper thumbnail of Unconventional superconductivity in Y$_5$Rh$_6$Sn$_{18}$ probed by muon spin relaxation

arXiv: Superconductivity, 2015

Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissn... more Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high$-$temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor \yrhsn\ ($T_{\bf c}$ = 3.0 K). The electronic heat capacity of \yrhsn\ shows a T3T^3T3 dependence below TbfcT_{\bf c}Tbfc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu$_5$Rh$_6$Sn$_{18}$ which is a strong coupling s−s-s−wave superconductor. The temperature dependence of the deduced superfluid density \yrhsn\ is consistent with a BCS s−s-s−wave gap function, while the...

Research paper thumbnail of Phononic bandgap and phonon anomalies in HfN and HfN/ScN metal/semiconductor superlattices measured with inelastic x-ray scattering

Applied Physics Letters, 2020

Epitaxial metal/semiconductor superlattice heterostructures with lattice-matched abrupt interface... more Epitaxial metal/semiconductor superlattice heterostructures with lattice-matched abrupt interfaces and suitable Schottky barrier heights are attractive for thermionic energy conversion, hot electron-based solar energy conversion, and optical hyperbolic metamaterials. HfN/ScN is one of the earliest demonstrations of epitaxial single-crystalline metal/semiconductor heterostructures and has attracted significant interest in recent years to harness its excellent properties in device applications. Although the understanding of the mechanism of thermal transport in HfN/ScN superlattices is extremely important for their practical applications, not much attention has been devoted to measuring their phonon dispersion and related properties. In this Letter, we employ non-resonant meV-resolution inelastic x-ray scattering to determine the momentum-dependent phonon modes in epitaxial metallic HfN and lattice-matched HfN/ScN metal/semiconductor superlattices. HfN exhibits a large phononic bandga...

Research paper thumbnail of 2 6 Ju l 2 01 5 Unconventional superconductivity in Y 5 Rh 6 Sn 18 probed by muon spin relaxation

Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissn... more Conventional superconductors are robust diamagnets that expels magnetic fields through the Meissner effect. It would therefore be unexpected if a superconducting ground state would support spontaneous magnetics fields. Such broken time-reversal symmetry states have been suggested for the high−temperature superconductors, but their identification remains experimentally controversial. We present magnetization, heat capacity, zero field and transverse field muon spin relaxation experiments on the recently discovered caged type superconductor Y5Rh6Sn18 (Tc = 3.0 K). The electronic heat capacity of Y5Rh6Sn18 shows a T 3 dependence below Tc indicating an anisotropic superconducting gap with a point node. This result is in sharp contrast to that observed in the isostructural Lu5Rh6Sn18 which is a strong coupling s−wave superconductor. The temperature dependence of the deduced superfluid density Y5Rh6Sn18 is consistent with a BCS s−wave gap function, while the zero-field muon spin relaxatio...

Research paper thumbnail of B 101 , 134408 ( 2020 ) Spin dynamics of a magnetic Weyl semimetal Sr

Zhengwei Cai,1,* Song Bao,1,* Wei Wang ,1,* Zhen Ma,1 Zhao-Yang Dong ,2 Yanyan Shangguan,1 Jinghu... more Zhengwei Cai,1,* Song Bao,1,* Wei Wang ,1,* Zhen Ma,1 Zhao-Yang Dong ,2 Yanyan Shangguan,1 Jinghui Wang,1 Kejing Ran,1 Shichao Li,1 Kazuya Kamazawa,3 Mitsutaka Nakamura,4 Devashibhai Adroja,5,6 Shun-Li Yu,1,7,† Jian-Xin Li,1,7,‡ and Jinsheng Wen 1,7,§ 1National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China 2Department of Applied Physics, Nanjing University of Science and Technology, Nanjing 210094, China 3Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Tokai, Ibaraki 319-1106, Japan 4J-PARC Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan 5ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom 6Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa 7Collaborative Innovation Center of Advanced Microstructures, Nanjing ...

Research paper thumbnail of Symmetry Origin of the Dzyaloshinskii–Moriya Interaction and Magnetization Reversal in YVO3

Inorganic Chemistry

We have investigated magneto-structural phase transitions in polycrystalline YVO3 using high-reso... more We have investigated magneto-structural phase transitions in polycrystalline YVO3 using high-resolution neutron powder diffraction toward understanding the phenomenon of magnetization reversal. Contrary to earlier reports, our study reveals that both C-type and G-type antiferromagnetic ordering, corresponding to G-type and C-type orbital ordered phases, respectively, occur at the same temperature (TN = 115 K) with the G-type antiferromagnetic phase growing at the expense of the C-type one on cooling. These processes cease at TS ∼ 77 K; however, a minor (∼4%) untransformed C-type phase remains unchanged down to 1.7 K. The symmetry analysis indicates different symmetry origins of the Dzyaloshinskii-Moriya interaction in each phase, which can explain the magnetization reversal observed between TN and TS. We discuss that magnetic phase separation and associated weak ferromagnetism may be the common mechanism underlying the magnetization reversal phenomenon observed in other RVO3 systems (R = rare earth).

Research paper thumbnail of Neutron scattering study of the Kondo insulators CeT 2Al10 (T = Fe, Ru, Os)

Acta Crystallographica Section A Foundations and Advances, Dec 1, 2017

The recent discovery of topological Kondo insulating behaviour in strongly correlated electron sy... more The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in the field of Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT2Al10 (T=Fe, Ru and Os), crystalizing in the orthorhombic crystal structure, possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu2Al10 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10 with a paramagnetic ground state down to 50 mK [1-3]. We are investigating this family of compounds using neutron diffraction, inelastic neutron scattering (INS) and muon spin rotation/relaxation (µSR) measurements to understand the role of anisotropic c-f hybridization on the anomalous magnetic structure, anisotropic magnetic exchanges, and spin gap formation as well as on their magnetic and transport properties. Our neutron diffraction studies on T=Ru and Os show that the magnetic ordering with propagation vector K=[1 0 0], but the direction of the moment is along the c-axis, which is not the easy axis of the magnetization. Further the ordered state moment is much smaller than that expected from the J=5/2 state of Ce3+ ion. We will show that the observed magnetic structure, direction and magnitude of the moment, is very sensitive to the electron and hole-doping in these compounds, but the crystal structure remains the orthorhombic.. We have observed a clear sign of a spin gap in all three compounds from INS study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our INS studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive gapped spin wave excitations below TN [3]. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy (CEF), which prefers the moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K [3]. We will discuss the origin of the anisotropic hybridization gap in CeFe2Al10 based on theoretical models of heavy-fermion semiconductors. Further the effect of electron-and hole-doping as well as chemical pressure effect on the magnetic and transport properties of CeT2All0 compounds will be discussed based on our INS and µSR results. Our µSR study reveals a long range magnetic ordering for electron doping in the Kondo insulator CeFe2Al10. We will compare the results of our INS study of CeT2Al10 with that of topological Kondo insulators, such as SmB6, CeNiSn and CeRu4Sn6.

Research paper thumbnail of Spin dynamics and Griffiths singularity in the random quantum Ising magnet PrTiNbO6

npj Quantum Materials

In crystalline magnets, interaction randomness is usually thought as a negative factor preventing... more In crystalline magnets, interaction randomness is usually thought as a negative factor preventing interesting quantum phenomena to occur. However, intriguing interplay between randomness and quantumness can also leads to unique phenomena in the strongly correlated materials. Among others, the random transverse-field Ising spin chain (RTIC) hosts a renowned quantum Griffiths phase. Although the RTIC model has been regarded as a toy model for long, here we materialize this model with the compound PrTiNbO6, which has a disordered ground state with pronounced quantum fluctuations and continuous spin excitations. The observed anomalous spin dynamics of PrTiNbO6 can be accounted by the RTIC model with a consistent set of parameters determined from fitting the thermodynamic data, and it is ascribed to the quantum Griffiths rare regions in the system. Our results provide a concrete example of quantum Griffiths magnet, and offer an ideal experimental platform for investigating the dynamical ...

Research paper thumbnail of Intermultiplet transitions and magnetic long-range order in Sm-based pyrochlores

Physical Review B

We present bulk and neutron scattering measurements performed on the isotopically enriched 154 Sm... more We present bulk and neutron scattering measurements performed on the isotopically enriched 154 Sm2Ti2O7 and 154 Sm2Sn2O7 samples. Both compounds display sharp heat capacity anomalies, at 350 mK and 440 mK, respectively. Inelastic neutron scattering measurements are employed to determine the crystalline electric field (CEF) level scheme, which includes transitions between the ground-state and first excited J multiplets of the Sm 3+ ion. To further validate those results, the single-ion magnetic susceptibility of the compounds is calculated and compared with the experimental DC-susceptibility measured in low applied magnetic fields. It is demonstrated that the inclusion of intermultiplet transitions in the CEF analysis is fundamental to the understanding of the intermediate and, more importantly, low temperature magnetic behaviour of the Sm-based pyrochlores. Finally, the heat capacity anomaly is shown to correspond to the onset of an all-in-all-out long-range order in the stannate sample, while in the titanate a dipolar long-range order can be only indirectly inferred.

Research paper thumbnail of Neutron Scattering Studies of the Breathing Pyrochlore Antiferromagnet LiGaCr4O8

Physical Review Letters

We report neutron scattering measurements of the spinel oxide LiGaCr 4 O 8 , in which magnetic io... more We report neutron scattering measurements of the spinel oxide LiGaCr 4 O 8 , in which magnetic ions Cr 3þ form a breathing pyrochlore lattice. Our experiments reveal the coexistence of a nearly dispersionless resonance mode and dispersive spin-wave excitations in the magnetically ordered state, which can be quantitatively described by a quantum spin model of hexagonal loops and linear spin-wave theory with the same set of exchange parameters, respectively. Comparison to other Cr spinel oxides reveals a linear relationship between the resonance energy and lattice constant across all these materials, which is in agreement with our hexagonal loop calculations. Our results suggest a unified picture for spin resonances in Cr spinel oxides.

Research paper thumbnail of Spin dynamics of a magnetic Weyl semimetal Sr1−xMn1−ySb2

Research paper thumbnail of Gapless spin-liquid state in the structurally disorder-free triangular antiferromagnet NaYbO2

Physical Review B

We present the structural characterization and low-temperature magnetism of the triangular-lattic... more We present the structural characterization and low-temperature magnetism of the triangular-lattice delafossite NaYbO 2. Synchrotron x-ray diffraction and neutron scattering exclude both structural disorder and crystalelectric-field randomness, whereas heat-capacity measurements and muon spectroscopy reveal the absence of magnetic order and persistent spin dynamics down to at least 70 mK. Continuous magnetic excitations with the low-energy spectral weight accumulating at the K-point of the Brillouin zone indicate the formation of a novel spin-liquid phase in a triangular antiferromagnet. This phase is gapless and shows a non-trivial evolution of the low-temperature specific heat. Our work demonstrates that NaYbO 2 practically gives the most direct experimental access to the spin-liquid physics of triangular antiferromagnets.

Research paper thumbnail of Interplay between hybridisation gaps and unusual magnetic orders in Kondo semiconductors CeT2Al10 (T = Ru and Os)

Research paper thumbnail of Partial vibrational density of states for amorphous solids from inelastic neutron scattering

Physical Review B

We introduce coherent inelastic neutron scattering with isotope substitution as a technique for m... more We introduce coherent inelastic neutron scattering with isotope substitution as a technique for measuring site-specific information on the vibrational dynamics of amorphous solids. The technique is used to extract experimentally the partial vibrational density of states G α (E) for both Ge and Se in the prototypical networkforming glass GeSe 2 , where α specifies the chemical species and E denotes the energy. The efficacy of the approximations used in interpreting the experimental data is validated by using a first-principles model, for which the set of true partial vibrational density of states is directly accessible. Our approach offers an opportunity for exploring accurately the vibrational dynamics of disordered materials.