Welcome to the vibrational spectroscopy group!

Research Interests

Design of sub-K heat exchangers used in Dilution Refrigerators, thermal contact resistance measurements at cryogenic temperatures
Ultrafast measurement of non-equilibrium heat transfer using optical and x-ray spectroscopy (femto-to-nanosecond time scale)
Ultrafast thermometry (a quite different principle than thermocouples, RTDs, Thermistors, IR pyrometers, or Thermal imaging cameras)
Ultrafast evolution of structural/magnetic/electrical phase transitions in ferroelectrics, multiferroics, thermoelectric, battery materials (superionic conductors), photovoltaics, and quantum materials (femto-to-nanosecond time scale)
Thermal transport and phase transition of nuclear materials
Thermodynamics of phase transitions
Irradiation damage evolution
Direct probing of atoms, electrons, electron spins and their dynamics using neutrons, x-rays, and optical spectroscopy

(see below for available experimental facilities in our research group)

RECENT NEWS

We report the effect of mode- and orbital-resolved spin-phonon coupling on both phonon and magnon energies and lifetimes – Jayakrishnan SS and D. Bansal*. “Effect of spin-phonon coupling on phonons and magnons in the antiferromagnet NiO.” Physical Review B, Vol. 111, 104306, 2025. Link

We provide a direct mapping of orbital fluctuations and how they strongly scatter phonons in Bi2Fe4O9 – A.P. Roy, M.K. Chattopadhyay, R. Mittal, S.N. Achary, A.K. Tyagi, M. Duc Le, and D. Bansal*. “Orbital fluctuations and spin-orbital-lattice coupling in Bi2Fe4O9.” Physical Review B, Vol. 111, 014310, 2025. Link arXiv

We report unprecedently strong KK interactions and spin-phonon coupling in CrVO4 – A.P. Roy, Jayakrishnan SS, V. Dwij, A. Khandelwal, M.K. Chattopadhyay, V. Sathe, R. Mittal, P.U. Sastry, S.N. Achary, A.K. Tyagi, P.D. Babu, M. Duc Le, and D. Bansal*. “Evidence of strong orbital-selective spin-orbital-phonon coupling in CrVO4.” Physical Review Letters, Vol. 132, 026701, 2024. Link

Preview Article – D. Bansal. “Aliovalence-doped thermoelectrics.” Joule, Vol. 7, Issue 10, 2203-2205, 2023. Link

A new paper on nonthermal bonding origin in SnSe using femtosecond x-ray diffuse scattering – Y. Huang, S. Teitelbaum, S. Yang, G.D. la Pena, T. Sato, M. Chollet, D. Zhu, J.L. Niedziela, D. Bansal, A. F. May, A.M. Lindenberg, O. Delaire, M. Trigo, and D.A. Reis. “Nonthermal bonding origin of a novel photoexcited lattice instability in SnSe.” Physical Review Letters, Vol. 131, 156902, 2023. Link

A new paper on nonlocal probing of amplitude mode dynamics using femtosecond x-ray diffraction – R. Rathore, H. Singhal, V. Dwij, M. Gupta, A. Pathak, J.A. Chakera, R. Mittal, A.P. Roy, A. Babu, R. Kulkarni, A. Thamizhavel, A.H. Said, and D. Bansal*. “Nonlocal probing of amplitude mode dynamics in charge-density-wave phase of EuTe4.” Ultrafast Science (AAAS), Vol. 3, Article ID: 0041, 2023. Link

A new paper experimentally characterizes the multiple charge density wave orders, amplitude mode, and multiple Kohn anomalies in EuTe4 – R. Rathore, A. Pathak, M. Gupta, R. Mittal, R. Kulkarni, A. Thamizhavel, H. Singhal, A.H. Said, and D. Bansal*. “Evolution of static charge density wave order, amplitude mode dynamics, and suppression of Kohn anomalies at the hysteretic transition in EuTe4.” Physical Review B, Vol. 107, 024101, 2023. Link

A new paper characterizing the phason thermal transport in the incommensurate phase of TlInTe2 – N. Bajaj, D. Chemate, H.P. Veeravenkata, A. Khandelwal, M.K. Chattopadhyay, M. Dutta, A.P. Roy, A. Sagdeo, A. Jain, S.S. Prabhu, K. Biswas, and D. Bansal*. “Sublinear temperature dependence of thermal conductivity in the incommensurate phase of TlInTe2.” Physical Review B, Vol. 106, 214101, 2022. Link

We demonstrate the role of linearly dispersing bands at the Fermi level in triggering charge density wave and multiple Kohn anomalies in EuTe4 – A. Pathak, M. Gupta, R. Mittal, and D. Bansal*. “Orbital- and atom-dependent linear dispersion across the Fermi level induces charge density wave instability in EuTe4.” Physical Review B, Vol. 105, 035120, 2022. Link

We demonstrate the role of anharmonic coupling between three phonon instabilities to drive ferroelectricity in SBNO – A.P. Roy, N. Bajaj, A. Gupta, V. Sathe, S.K. Mishra, R. Mittal, M. Duc Le, and D. Bansal*. “Strong trilinear coupling of phonon instabilities drives the avalanche-like hybrid improper ferroelectric transition in SrBi2Nb2O9.” Physical Review B, Vol. 103, 134111, 2021. Link

We developed a Monte Carlo solver for the Boltzmann transport equation for heat transfer at the nano to microscales – A. Pathak, A. Pawnday, A.P. Roy, A.J. Aref, G.F. Dargush, and D. Bansal*. “MCBTE: A variance-reduced Monte Carlo Solution of the linearized Boltzmann transport equation for phonons.” Computer Physics Communications, Vol. 265, 108003, 2021. Link arXiv code https://doi.org/10.1016/j.cpc.2021.108003

We demonstrate the role of Fermi and hidden nesting in driving charge density wave and Kohn anomalies in uranium – A.P. Roy, N. Bajaj, R. Mittal, P.D. Babu, and D. Bansal*. “Quasi-one-dimensional Fermi surface nesting and hidden nesting enable multiple Kohn anomalies in alpha-uranium.” Physical Review Letters, Vol. 126, 096401, 2021. Link Science Highlight 1 2 Appeared in campus diary (page 20) Appeared on the cover of PRL, Vol. 126 Issue 9

JOURNAL PUBLICATIONS

† co-first authors * corresponding author

R. Rathore, H. Singhal, R. Kulkarni, A. Thamizhavel, D. Bansal, and J.A. Chakera. “Development of ultrashort intense broadband laser-plasma x-ray source for ultrafast Laue x-ray diffraction.” Review of Scientific Instruments, Vol. 96, pg. 074902, 2025. Link
Y. Murtunge, V. Patil, R. Puranik, U. Pandey, Jayakrishnan SS, D. Bansal, A. Maity, R. Venkatramani, A. Thamizhavel, S.B. Kulkarni, S.S. Prabhu. "Synthesis, Growth and Optical Characterization of Sodium Mesitylene Sulphonate (SMS) Crystals for THz Wave Generation.” Optical Materials, Vol. 166, 117175, 2025. Link
J. Ding, Md T. Rahman, C. Mao, J.L. Niedziela, D. Bansal, A.F. May, D.L. Abernathy, Y. Ren, A. Zewalkink, and O. Delaire. "Atomic dynamics in 𝑀⁢Cr⁢𝑋2 (𝑀=Ag,Cu;𝑋=S,Se) across magnetic and superionic transitions AgCrSe2.” Physical Review Materials, Vol. 9, 035402, 2025. Link
Jayakrishnan SS and D. Bansal*. “Effect of spin-phonon coupling on phonons and magnons in the antiferromagnet NiO.” Physical Review B, Vol. 111, 104306, 2025. Link
A.P. Roy, M.K. Chattopadhyay, R. Mittal, S.N. Achary, A.K. Tyagi, M. Duc Le, and D. Bansal*. “Orbital fluctuations and spin-orbital-lattice coupling in Bi2Fe4O9.” Physical Review B, Vol. 111, 014310, 2025. Link arXiv
T. Maran, A. Jain, M. Sundaramoorthy, A.P. Roy, B. Joseph, G. Lingannan, A. Mohan, D. Bansal, S.M. Yusuf, and A. Sonachalam. “Hydrostatic pressure effect on structural and transport properties of co-existing layered and disordered rock-salt phase of LixCoO2.” Physical Review Materials, Vol. 8, 125401, 2024. Link
V.B. Jayakrishnan, S.K. Mishra, A.B. Shinde, S. Wajhal, P.S.R. Krishna, P.U. Sastry, S.B. Phapale, A.P. Roy, D. Bansal. “Dielectric, structural and vibrational properties of (Na0.975Bi0.025)(Nb0.95Ti0.05)O3 at elevated temperature.” Journal of Applied Physics, Vol. 136, 094101, 2024. Link
V. Sharma*, S. Ramakrishnan*, Jayakrishnan SS, S.R. Kotla B. Maiti, C. Eisele, H. Agarwal, L. Noohinejad, M. Tolkiehn, D. Bansal*, S. van Smaalen*, and A. Thamizhavel*. “Room temperature charge density wave in a tetragonal polymorph of Gd2Os3Si5 and study of its origin in the RE2T3X5 (RE = Rare earth, T = transition metal, X = Si, Ge) series.” Chemistry of Materials, Vol. 36, 6888-6901, 2024. Link
A.P. Roy, Jayakrishnan SS, V. Dwij, A. Khandelwal, M.K. Chattopadhyay, V. Sathe, R. Mittal, P.U. Sastry, S.N. Achary, A.K. Tyagi, P.D. Babu, M. Duc Le, and D. Bansal*. “Evidence of strong orbital-selective spin-orbital-phonon coupling in CrVO4.” Physical Review Letters, Vol. 132, 026701, 2024. Link
S. Amanat, K. Gholami, R.R-Dehkharghani, and D. Bansal. “Modified non-dominated sorting genetic algorithm-II for the optimal design of soil-concrete periodic plane wave barriers.” Computers and Geotechnics, Vol. 165, 105947, 2024. Link
D. Bansal*. “Aliovalence-doped thermoelectrics.” Joule, Vol. 7, Issue 10, 2203-2205, 2023. Link
Y. Huang, S. Teitelbaum, S. Yang, G.D. la Pena, T. Sato, M. Chollet, D. Zhu, J.L. Niedziela, D. Bansal, A. F. May, A.M. Lindenberg, O. Delaire, M. Trigo, and D.A. Reis. “Nonthermal bonding origin of a novel photoexcited lattice instability in SnSe.” Physical Review Letters, Vol. 131, 156902, 2023. Link
P. Goel, M.K. Gupta, S. Kumar, R. Mittal, A.P. Roy, D. Bansal, M.D. Le, R. Shukla, S.N. Achary, S. Mukhopadhyay, A.K. Tyagi, and S.L. Chaplot. “Tuning of structure and host dynamics via yttrium doping in Bi2O3 to enhance oxygen ion diffusion.” Physical Review Materials, Vol. 7, 095402, 2023. Link
R. Rathore, H. Singhal, V. Dwij, M. Gupta, A. Pathak, J.A. Chakera, R. Mittal, A.P. Roy, A. Babu, R. Kulkarni, A. Thamizhavel, A.H. Said, and D. Bansal*. “Nonlocal probing of amplitude mode dynamics in charge-density-wave phase of EuTe4.” Ultrafast Science (AAAS), Vol. 3, Article ID: 0041, 2023. Link
R. Rathore, A. Pathak, M. Gupta, R. Mittal, R. Kulkarni, A. Thamizhavel, H. Singhal, A.H. Said, and D. Bansal*. “Evolution of static charge density wave order, amplitude mode dynamics, and suppression of Kohn anomalies at the hysteretic transition in EuTe4.” Physical Review B, Vol. 107, 024101, 2023. Link
N. Bajaj, D. Chemate, H.P. Veeravenkata, A. Khandelwal, M.K. Chattopadhyay, M. Dutta, A.P. Roy, A. Sagdeo, A. Jain, S.S. Prabhu, K. Biswas, and D. Bansal*. “Sublinear temperature dependence of thermal conductivity in the incommensurate phase of TlInTe2.” Physical Review B, Vol. 106, 214101, 2022. Link
S. Amanat, K. Gholami, R.R-Dehkharghani, and D. Bansal.“Plane waves mitigation in saturated porous media using optimal periodic wave barriers.” Applied Acoustics, Vol. 200, 109085, 2022. Link
M. Gupta, J. Ding, D. Bansal, D.L. Abernathy, G. Ehlers, N.C. Osti, W.G. Zeier, and O. Delaire. “Strongly Anharmonic Phonons and Their Role in Superionic Diffusion and Ultralow Thermal Conductivity of Cu7PSe6.” Advanced Energy Materials, Vol. 12, Issue 23, 2200596, 2022. Link
S. Amanat, R.R-Dehkharghani, M. Bitaraf, and D. Bansal. “Analytical and numerical investigation of finite and infinite periodic lattices for mitigation of seismic waves in layered grounds.” International Journal of Engineering Science, Vol. 173, 103655, 2022. Link
A. Pathak, M. Gupta, R. Mittal, and D. Bansal*. “Orbital- and atom-dependent linear dispersion across the Fermi level induces charge density wave instability in EuTe4.” Physical Review B, Vol. 105, 035120, 2022. Link
Y. Huang, S. Yang, S. Teitelbaum, G.D. la Pena, T. Sato, M. Chollet, D. Zhu, J.L. Niedziela, D. Bansal, A. F. May, A.M. Lindenberg, O. Delaire, D.A. Reis, M. Trigo. “Observation of a novel lattice instability in ultrafast photoexcited SnSe.” Physical Review X, Vol. 12, 011029, 2022. Link
A. Pathak, A. Pawnday, A.P. Roy, A.J. Aref, G.F. Dargush, and D. Bansal*. “MCBTE: A variance-reduced Monte Carlo Solution of the linearized Boltzmann transport equation for phonons.” Computer Physics Communications, Vol. 265, 108003, 2021. Link arXiv code https://doi.org/10.1016/j.cpc.2021.108003
A.P. Roy, N. Bajaj, A. Gupta, V. Sathe, S.K. Mishra, R. Mittal, M. Duc Le, and D. Bansal*. “Strong trilinear coupling of phonon instabilities drives the avalanche-like hybrid improper ferroelectric transition in SrBi2Nb2O9.” Physical Review B, Vol. 103, 134111, 2021. Link
A.P. Roy, N. Bajaj, R. Mittal, P.D. Babu, and D. Bansal*. “Quasi-one-dimensional Fermi surface nesting and hidden nesting enable multiple Kohn anomalies in alpha-uranium.” Physical Review Letters, Vol. 126, 096401, 2021. Link Science Highlight 1 2 Appeared in campus diary (page 20) Appeared on the cover of PRL, Vol. 126 Issue 9
N. Rana, A.P. Roy, D. Bansal* and G. Dixit*. “Four-dimensional imaging of lattice dynamics using ab-initio simulation.” npj Computational Materials, Vol. 7, Article No. 7, 2021. Link arXiv Science Highlight 1 2 3 4
N. Bajaj, A.P. Roy, A. Khandelwal, M.K. Chattopadhyay, V. Sathe, S.K. Mishra, R. Mittal, P.D. Babu, M. Duc Le, J.L. Niedziela*, and D. Bansal*. “Magnetoelastic coupling and spin contributions to entropy and thermal transport in biferroic yttrium orthochromite.” Journal of Physics: Condensed Matter, Vol. 33, pg. 125702, 2021. Link
J.L. Niedziela, D. Bansal, J. Ding, T. Lanigan-Atkins, C. Li, A. F. May, H. Wang, J. Y. Y. Lin, D. L. Abernathy, G. Ehlers, A. Huq, D. Parshall, J. W. Lynn, and O. Delaire. “Controlling phonon lifetimes via sublattice disordering in AgBiSe2.” Physical Review Materials, Vol. 4, 105402, 2020. Link Editor's suggestion
T. Lanigan-Atkins, S. Yang, J.L. Niedziela, D. Bansal, A. F. May, A. A. Puretzky, J. Y. Y. Lin, D. M. Pajerowski, T. Hong, S. Chi, G. Ehlers, and O. Delaire. “Extended anharmonic collapse of phonon dispersions in SnS and SnSe.” Nature Communications, Vol. 11, Article No. 4430, 2020. Link Science Highlight 1
D. Bansal*, J.L. Niedziela, S. Calder, T. Lanigan-Atkins, R. Rawl, A. Said, D.L. Abernathy, A.I. Kolesnikov, H. Zhou, and O. Delaire*. “Magnetically driven phonon instability enables the metal–insulator transition in h-FeS.” Nature Physics. Vol. 16, pg. 669-675, 2020. Link Science Highlight 1 2 3 4 5
X. He, D. Bansal, B. Winn, S. Chi, L. Boatner, and O. Delaire. “Anharmonic Eigenvectors and Acoustic Phonon Disappearance in Quantum Paraelectric SrTiO3.” Physical Review Letters, Vol. 124, 145901, 2020. Link
J. Ding, J.L. Niedziela, D. Bansal, J. Wang, X. He, A.F. May, G. Ehlers, D.L. Abernathy, A. Said, A. Alatas, Y. Ren, G. Arya, and O. Delaire. "Anharmonic lattice dynamics and superionic transition in AgCrSe2.” PNAS, Vol. 117, pg. 3930-3937, 2020. DOI: https://doi.org/10.1073/pnas.1913916117 Link
D. Bansal*, J.L. Niedziela, X. He, T. Lanigan Atkins, A. Said, A. Alatas, D.L. Abernathy, Y. Ren, B. Gao, S.-W. Cheong, and O. Delaire*. “Lattice dynamics of the hybrid improper ferroelectrics (Ca,Sr)3Ti2O7.” Physical Review B, Vol. 100, 214304, 2019. Link
J.L. Niedziela*†, D. Bansal*† , A. May, J. Ding, T. Lanigan-Atkins, G. Ehlers, D.L. Abernathy, A. Said, and O. Delaire*. “Selective breakdown of phonon quasiparticles across superionic transition in CuCrSe2.” Nature Physics. Vol. 15, pg. 73-78, 2019. († co-first authors) Link Science Highlights 1 2 3 4 5 6 7 8 9
S. Muy, J.C. Bachman, L. Giordano, H.-H. Chang, D.L. Abernathy, D. Bansal, O. Delaire, S. Hori, R. Kanno, F. Maglia, S. Lupart, P. Lamp, and Y.S.-Horn. “Tuning Mobility and Stability of Lithium Ion Conductors based on Lattice Dynamics.” Energy & Environmental Science. Vol. 11, pg. 850-859, 2018. DOI: 10.1039/C7EE03364H Link
P. Jain, D. Bansal, G. Sharma, A. Bhattacharya, B. Ingale, O. Delaire, R. Chatterjee. “Observation of low-temperature metastable states in complex CaMn7O12.” Journal of Physics: Condensed Matter. Vol. 30, pg. 075801, 2018. Link
D. Bansal*, J.L. Niedziela, R. Sinclair, V. Ovidiu Garlea, D.L. Abernathy, S. Chi, Y. Ren, H. Zhou, and O. Delaire*. “Momentum-resolved observations of the phonon instability driving geometric improper ferroelectricity in yttrium manganite.” Nature Communications, Vol. 9, Article No. 15, 2018. Link Science Highlights 1 2 3 4 5 6 7
C. Luo, D. Bansal, J. Li, D. Viehland, B. Winn, Y. Ren, X. Li, H. Luo, and O. Delaire. “Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in (Na,Bi)TiO3- xBaTiO3 single crystals near the morphotropic phase boundary.” Physical Review B, Vol. 96, 174108, 2017. Link
S. Mukhopadhyay, D. Bansal, O. Delaire, D. Perrodin, E. Bourret-Courchesne, D.J. Singh, and L. Lindsay. “Curious case of cuprous chloride: Giant thermal resistance and anharmonic quasiparticle spectra driven by dispersion nesting.” Physical Review B, Vol. 96, 100301(R), 2017. Link
R.R-Dehkharghani, D. Bansal, A. Aref, and G. Dargush. “Analysis and optimal design of stress wave intensity attenuation in layered structures.” International Journal of Structural Stability and Dynamics, Vol. 18, pg. 1850015, 2018. Link
D. Bansal*, J.L. Niedziela, A.F. May, A. Said, G. Ehlers, D.L. Abernathy, A. Huq, M. Kirkham, H. Zhou, and O. Delaire*. “Lattice dynamics and thermal transport in multiferroic CuCrO2.” Physical Review B, Vol. 95, 054306, 2017. Link
F. Bao, R. Archibald, J. Niedziela, D. Bansal, and O. Delaire. “Complex optimization for big computational and experimental neutron datasets.” Nanotechnology, Vol. 27, pg. 484002, 2016. Link
X. Chen, D. Bansal, S. Sullivan, D.L. Abernathy, A.A. Aczel, J. Zhou, O. Delaire, and L. Shi. “Weak coupling of acoustic-like phonons and magnon dynamics in incommensurate spin ladder compound Sr14Cu24O41.” Physical Review B, Vol. 94, 134309, 2016. (Editors’ suggestion) Link
D. Bansal*, J. Hong, C.W. Li, A.F. May, W. Porter, M.Y. Hu, D.L. Abernathy, and O. Delaire*. “Phonon anharmonicity and negative thermal expansion in SnSe.” Physical Review B, Vol. 94, 054307, 2016. Link
D. Bansal*, A. Aref, G. Dargush, and O. Delaire*. “Modeling non-harmonic behavior of materials from experimental inelastic neutron scattering and thermal expansion measurements.” Journal of Physics: Condensed Matter, Vol. 28, pg. 385201, 2016. Link
F. Bao, R. Archibald, D. Bansal, and O. Delaire. “Hierarchical optimization for neutron scattering problems.” Journal of Computational Physics, Vol. 315, pg. 39-51, 2016. Link
D. Bansal*, C.W. Li, A.H. Said, D.L. Abernathy, J-Q. Yan, and O. Delaire*. “Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7-xTex.” Physical Review B, Vol. 92, 214301, 2015. Link
C.W. Li, J. Hong, A. May, D. Bansal, S. Chi, T. Hong, G. Ehlers, and O. Delaire. “Orbitally- driven giant phonon anharmonicity in SnSe.”Nature Physics, Vol. 11, No. 12, pg. 1063-1069, 2015. Link
R.R-Dehkharghani, D. Bansal, A. Aref, and G. Dargush. “Interface profile optimization for stress wave attenuation in bi-layered plates.” Composites Part B: Engineering, Vol. 82, No. 1, pg. 129-142, 2015. Link
D.C. Rai, S.K. Jain, C.V.R. Murty, and D. Bansal. “Large capacity reaction floor-wall assembly for pseudo-dynamic testing at IIT Kanpur and its load rating.” Current Science, Vol. 106, No. 1, pg. 93-100, 2014. Link
D. Bansal*, G. Dargush, A. Aref, and A.R. Hadjesfandiari. “Cubic Single Crystal Representations in Classical and Size-dependent Couple Stress Elasticity.” arXiv:1510.06048. Link

Conference proceedings/presentations

Discussions

M. Romo, E. Morales, H. Bonifaz, J. Haro, and D. Bansal. "Some lessons on soil liquefaction under the Mw 7.8 Muisne earthquake in 2016 in Ecuador." 12th National Conference on Earthquake Engineering, Salt Lake City, Utah, USA, June 27–July 1, 2022. Article
"Time-resolved diffraction: general discussion." Time-resolved imaging of photo-induced dynamic - Faraday Discussion, Virtual (online mode), UK, February 1 – February 4, 2021. Article
"Mechanical Engineering | Ed-Conclave." IIT Bombay, Mumbai, MH, India, June 10, 2023. (Discussion/Info session with prospective B.Tech. students; Prof. Dipanshu Bansal and Prof. Avinash Bhardwaj) Video Link

Student presentations

Kumar Bharti, and D. Bansal. "Investigating multiple charge-density-wave instabilities in NbTe4", 2025 Spring Meeting, European Materials Research Society (E-MRS), Strasbourg, France, May 26-30, 2025.
V. Dwij, R. Puranik, U. Pandey, Jayakrishnan SS, D. Bansal, and S.S. Prabhu. “Seeing is Believing: Imaging Ultrafast Ferroelectric Domain Dynamics.” Ultrafast Sciences (UFS-2024), NISER Bhubaneswar, Odisha, India, November 28-30, 2024.
S.S. Jayakrishnan, and D. Bansal. "Phonon-Driven Spin Wave Modulation in Nickel Oxide." International Conference on Electronic structure theory of emergent spin orbit driven phenomenon (ESTESODP 2024), IIT Bombay, MH, India, November 13-15, 2024.
Kumar Bharti, and D. Bansal. "Origin of room temperature incommensurate charge-density-wave in NbTe4." International Conference on Electronic structure theory of emergent spin orbit driven phenomenon (ESTESODP 2024), IIT Bombay, MH, India, November 13-15, 2024.
Arun Babu, Mukund Kumar, Himanshu Singhal, Ajmal Ansari, Suddhasatta Mahapatra, Juzer A. Chakera and D. Bansal. "Precision fabrication and thermal transport in nano heaters using EUV diffraction." IITB - IoE - SCPP Theme Meeting: Ultrafast Processes: Nanosecond to Attosecond Dynamics, IIT Bombay, MH, India, November 7, 2024.
V. Dwij, R. Puranik, U. Pandey, Jayakrishnan SS, D. Bansal, and S.S. Prabhu. “Light-induced polarization switching dynamics in ferroelectrics.” IITB - IoE - SCPP Theme Meeting: Ultrafast Processes: Nanosecond to Attosecond Dynamics, IIT Bombay, MH, India, November 7, 2024.
R. Rathore, H. Singhal, D. Bansal, R. Kulkarni, A. Thamizhavel, and J.A. Chakera. “Development of novel Laue X-ray diffraction setup using fs laser plasma X-ray source.” National Laser Symposium (NLS-32), Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, MP, India, January 29–February 1, 2024.
S.S. Jayakrishnan, A.P. Roy, and D. Bansal. "Importance of V in the Magnetic Interactions in CrVO4." 67th DAE Solid State Physics Symposium (DAE-SSPS), Gandhi Institute of Technology and Management (GITAM), Visakhapatnam, Andhra Pradesh, India, December 20 – 24, 2023. (Best poster award)
R. Rathore, H. Singhal, V. Dwij, M. Gupta, A. Pathak, J.A. Chakera, R. Mittal, A.P. Roy, A. Babu, R. Kulkarni, A. Thamizhavel, A.H. Said, and D. Bansal. “Nonlocal probing of amplitude mode dynamics in charge-density-wave phase of EuTe4.” TIFR Condensed-Matter Physics Conference, Hyderabad, Telangana, India, December 14 - 16, 2023.
A.P. Roy, N. Bajaj, R. Mittal, and D. Bansal. “Role of Fermi Surface Nesting and Hidden Nesting in controlling Kohn Anomalies in α-Uranium.” Materials Research Society Fall Meeting (MRS-2023 Fall), Boston, MA, USA, November 26 - December 1, 2023.
A.P. Roy, N. Bajaj, A. Gupta, V. Sathe, S.K. Mishra, R. Mittal, M.D. Le, and D. Bansal. “Strong trilinear coupling of phonon instabilities drives the avalanche-like hybrid improper ferroelectric transition in SrBi2Nb2O9.” Materials Research Society Fall Meeting (MRS-2023 Fall), Boston, MA, USA, November 26 - December 1, 2023.
A.P. Roy, N. Bajaj, R. Mittal, and D. Bansal. “Quasi-One-Dimensional Fermi Surface Nesting and Hidden Nesting Enable Multiple Kohn Anomalies in α-Uranium.” Third International Conference on Physics of Materials and Nanotechnology (ICPN-2023), Mangalore University, Mangalore, Karnataka, India, September 21 - 23, 2023.
A. P. Roy, Jayakrishnan SS, V. Dwij, A. Khandelwal, M. K. Chattopadhyay, V. Sathe, R. Mittal, S. K. Mishra, M. D. Le, and D. Bansal. "Evidence of strong orbital-selective spin-orbital-phonon coupling in CrVO4." Third International Conference on Physics of Materials and Nanotechnology (ICPN-2023), Mangalore University, Mangalore, Karnataka, India, September 21 - 23, 2023. (Best poster award)
A.P. Roy, V. Dwij, A. Khandelwal, M. K. Chattopadhyay, V. Sathe, R. Mittal, P. U. Sastry, S.N. Achary, A. K. Tyagi, M. D. Le, and D. Bansal. "Deciphering the spin-phonon coupling in chromium orthovanadate." IX International Conference on Perspectives in Vibrational Spectroscopy (ICOPVS-2022), UGC Indore, Madhya Pradesh, India, December 13 – 17, 2022. Abstract Booklet (see No. A-P 9)
A.P. Roy, N. Bajaj, A. Gupta, V. Sathe, S.K. Mishra, R. Mittal, M. Duc Le, and D. Bansal. “Strong trilinear coupling of phonon instabilities drives the avalanche-like hybrid improper ferroelectric transition in SrBi2Nb2O9.” IX International Conference on Perspectives in Vibrational Spectroscopy (ICOPVS-2022), UGC Indore, Madhya Pradesh, India, December 13 – 17, 2022.
S.S. Jayakrishnan, A.P. Roy, and D. Bansal. "Calculation of Susceptibility and exchange constants from first principles." IX International Conference on Perspectives in Vibrational Spectroscopy (ICOPVS 2022), UGC Indore, Madhya Pradesh, India, December 13 – 17, 2022.
N. Bajaj, A. Khandelwal, M.K. Chattopadhyay, S. K. Mishra, R. Mittal, and D. Bansal. “Investigating phonon dynamics across magnetic transition in multiferroic YCrO3” 47th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2022), Delft, The Netherlands, August 28 – September 2, 2022. Article
N. Bajaj, D. Chemate, M.Dutta, S. S. Prabhu, K. Biswas, and D. Bansal. “Probing Tl sublattice dynamics in ultralow thermal conductivity TlInTe2” 47th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2022), Delft, The Netherlands, August 28 – September 2, 2022. Article
A.P. Roy, N. Bajaj, R. Mittal, and D. Bansal. “Electron and phonon properties of alpha-Uranium from first-principles simulations.” 65th DAE Solid State Physics Symposium (DAE-SSPS), Bhabha Atomic Research Center (BARC), Mumbai, MH, India, December 15–19, 2021.
A.P. Roy, N. Bajaj, A. Gupta, V. Sathe, S.K. Mishra, R. Mittal, M. Duc Le, and D. Bansal. “Strong trilinear coupling of phonon instabilities drives the avalanche-like hybrid improper ferroelectric transition in SrBi2Nb2O9.” 7th Conference on Neutron Scattering (CNS), Bhabha Atomic Research Center (BARC), Mumbai, MH, India, November 25–27, 2021. Poster (see EG13)
A. Pathak, A. Pawnday, A.P. Roy, A.J. Aref, G.F. Dargush, and D. Bansal. “Linearized Peierls Boltzmann Transport Solution of Heat Accumulation at Interfaces.” Materials Research Society Spring Meeting and Exhibit 2021, Virtual (online mode), USA, April 17 – April 23, 2021.

Own presentations

D. Bansal. "Non-Fourier Heat Transfer in Semiconductor Chips." Seminar at Navrachana University, Vadodara, Gujarat, India, April 9, 2025. (General invited academic seminar talk to students and faculty)
D. Bansal. "RADAR stealth at high frequencies (up to 80 GHz)." Brainstorming Workshop on Infrared Signature and Stealth Technologies for Aircraft, IIT Bombay, MH, India, March 25, 2025. (Invited talk)
A. Verma, M.D. Atrey, and D. Bansal. "Design and Analysis of Continuous Heat Exchanger for Dilution Refrigerators." IITB - IoE - SCPP Workshop on Cryogenics Engineering, IIT Bombay, MH, India, March 6, 2025. (Invited talk)
D. Bansal. "Fundamental & applications of FTIR & LRIS." Workshop on Applications of Advanced Analytical Techniques in Research & Industry, IIT Bombay, MH, India, February 18-19, 2025. (Invited workshop talk to students and industry)
D. Bansal. "Strong orbital-selective spin-orbital-phonon coupling in CrVO4." DAE-BRNS 10th Interdisciplinary Symposium on Materials Chemistry (ISMC-2024), Bhabha Atomic Research Center (BARC), Mumbai, MH, India, December 4–7, 2024. (Invited talk)
A. Babu, M. Kumar, H. Singhal, A. Ansari, S. Mahapatra, J.A. Chakera and D. Bansal. "Tracking the heat transfer from nano heaters in the non-Fourier regime." Ultrafast Sciences (UFS), NISER Bhubaneswar, Bhubaneswar, India, November 28-30, 2024. (Invited talk)
A. Verma, M.D. Atrey, and D. Bansal. "Design and Analysis of Continuous Heat Exchanger for Dilution Refrigerators." National Conference on Cryogenics and Superconductivity (NCCS-29), Inter-University Accelerator Centre (IUAC), Delhi, India, November 27-29, 2024.
D. Bansal. "Tutorials on Inelastic Neutron Scattering Techniques and Applications." 13th Asia-Oceania Neutron Scattering Association (AONSA) Neutron School, Bhabha Atomic Research Center (BARC), Mumbai, MH, India, November 24–28, 2024. (Invited lecture to existing and prospective neutron scattering users)
D. Bansal. "Stimulated Raman Scattering." National Workshop on Fluorescence and Raman Spectroscopy (FCS XV), IIT Bombay, MH, India, November 16-18, 2024. (Invited workshop talk to students)
D. Bansal. "Strong orbital-selective spin-orbital-phonon coupling in CrVO4." International Conference on Electronic structure theory of emergent spin orbit driven phenomenon (ESTESODP 2024), IIT Bombay, MH, India, November 13-15, 2024. (Invited talk)
D. Bansal. "Probing lattice instabilities, electron-phonon coupling, and spin-phonon coupling using spectroscopy techniques." International Workshop on Advanced Generation and Usage of THz and X-rays (AGTaX2024), Inter-University Accelerator Centre (IUAC), Delhi, India, October 07-09, 2024. (Invited talk)
D. Bansal. "Probing lattice instabilities, thermal transport, and spin-phonon coupling using X-ray free-electron lasers, THz, and IR spectroscopy." Theme meeting on Science with Free Electron Lasers and High Power IR-THz Sources, Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, MP, India, August 20-21, 2024. (Plenary talk)
D. Bansal, A. Babu, M. Kumar, H. Singhal, A. Ansari, S. Mahapatra, and J.A. Chakera. "Thermal contact resistance using time-resolved EUV diffraction -- a novel technique to study conduction-cooled superconducting RF cavity", 29th International Cryogenic Engineering Conference (ICEC), Geneva, Switzerland, July 22-26, 2024.
D. Bansal. "Probing electron-phonon and spin-orbital-phonon coupling using neutron and optical spectroscopy." I-MAT24 (Conference on Innovations in Materials Science and Workshop on Characterization Techniques), IIT Roorkee, Uttarakhand, India, April 24-27, 2024. (Invited) Link
D. Bansal. "Phonon measurement using inelastic neutron scattering and their application to superionic conductors." Workshop on Neutron Scattering and Muon Spectroscopy, IIT Guwahati, Assam, India, February 16-17, 2024. (Invited)
D. Bansal. "Origin of charge-density-wave instability in α-Uranium and rare-earth telluride EuTe4." X-ray Spectroscopy Special Interest Group, Argonne National Laboratory, Lemont, Illinois, USA, September 27, 2023. (Invited) Schedule
D. Bansal. "Introduction to crystallography and phase transitions." XIX School on Neutron as Probes of Condensed Matter (NPCM-2022), Bhabha Atomic Research Center (BARC), Mumbai, MH, India, November 14–19, 2022. (Lecture to university lecturers and Ph.D. students)
D. Bansal. "Origin of charge-density-wave instability in rare-earth telluride EuTe4." Ultrafast Sciences (UFS), IISER Thiruvananthapuram, Thiruvananthapuram, India, November 3-5, 2022. (Invited)
D. Bansal. "Real-time mapping of energy carriers." IIT Bombay's Institute Award Lecture Series 2022, IIT Bombay, MH, India, November 2-3, 2022. (Invited)
D. Bansal. "Real-time mapping of energy carriers and their role in phase transitions and heat transport." The National Academy of Sciences India, Prayagraj, UP, India, September 21, 2022. (Online, Invited)
D. Bansal. "A paradigm shift in thermometry for application in defense, health, and manufacturing." IIT Bombay's Annual CSR Conclave 2022, IIT Bombay, MH, India, July 6, 2022.
D. Bansal. "Real-time mapping of energy carriers and their role in phase transitions and heat transport." Indian National Science Academy (INSA), New Delhi, India, May 18, 2022. (Online, Invited)
D. Bansal. "A look into physical phenomenon from the atomic vibrations perspective." Research Seminar, IIT Bombay, MH, India, April 18, 2022.
D. Bansal. "Investigating quasi-particle coupling in momentum-energy and space-time domain." 65th DAE Solid State Physics Symposium (DAE-SSPS), Bhabha Atomic Research Center (BARC), Mumbai, MH, India, December 15–19, 2021.
D. Bansal. “Tuning anharmonic phonon coupling using magnetism in magnetoelectric h-FeS.” Materials Research Society Fall Meeting 2021 (Virtual), Boston, MA, USA, December 6–8, 2021.
D. Bansal. "Probing quasi-particle coupling of energy materials using inelastic neutron scattering and first-principles simulations." 7th Conference on Neutron Scattering (CNS), Bhabha Atomic Research Center (BARC), Mumbai, MH, India, November 25-27, 2021. Talk (see between 6:21:05.1 and 6:38:26.6)
D. Bansal. "Phase transitions -- A look from the atomic vibration perspective." IISc Banglore, India, September 11, 2020. (Invited) Talk
D. Bansal. "Probing geometric improper ferroelectric transition using neutron/x-ray scattering and first-principles simulations" 64th DAE Solid State Physics Symposium (DAE-SSPS), IIT Jodhpur, Jodhpur, Rajasthan, India, December 18-22, 2019. (Invited)
D. Bansal. "Probing Lattice Instabilities in Thermoelectric SnSe using Spectroscopic Studies." Ultrafast Sciences (UFS), IIT Bombay, Mumbai, India, November 7-9, 2019. (Invited)
D. Bansal. "Probing lattice instabilities through neutron, x-ray, and free-electron laser sources." Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, MP, India, August 29, 2019. (Invited - Materials & Advanced Accelerator Sciences Division and FEL utilization laboratory)
D. Bansal. “Improper ferroelectric and superionic crystals: A lattice dynamics perspective on instabilities and thermal transport .” Materials Research Society of India (MRSI) Colloquium, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, TN, India, May 16, 2019. (Invited talk)
D. Bansal. "Lattice instabilities and thermal transport in improper ferroelectric and superionic crystals." Bhabha Atomic Research Center (BARC), Mumbai, MH, India, April 4, 2019. (Invited)
D. Bansal, J.L. Niedziela, X. He, T. Lanigan-Atkins, A. Said, A. Alatas, D.L. Abernathy, Y. Ren, B. Gao, S.-W. Cheong, and O. Delaire."Lattice dynamics of hybrid improper ferroelectric (Ca,Sr)3Ti2O7." APS March Meeting 2019, Boston, MA, USA, March 4-8, 2019.
D. Bansal. "Vibrational Spectroscopy of Conventional Superconductor Niobium at Cryogenic Temperatures." 27th National Symposium on Cryogenics and Superconductivity, IIT Bombay, MH, India, January 16-18, 2019.
D. Bansal. "Lattice instabilities and thermal transport in improper ferroelectric and superionic crystals." Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, MP, India, December 13, 2018. (Invited)
D. Bansal, J.L. Niedziela, R. Sinclair, V.O. Garlea, D.L. Abernathy, S. Chi, Y. Ren, H. Zhou, and O. Delaire. “Direct evidence of phonon instability driving geometric improper ferroelectricity in multiferroic YMnO3.” ACNS 2018 – American Conference on Neutron Scattering, College Park, MD, USA, June 24-29, 2018.
D. Bansal, J.L. Niedziela, R. Sinclair, V.O. Garlea, D.L. Abernathy, S. Chi, Y. Ren, H. Zhou, and O. Delaire. “Direct evidence of phonon instability driving geometric improper ferroelectricity in multiferroic YMnO3.” APS March Meeting 2018, Los Angeles, CA, USA, March 5-9, 2018.
D. Bansal, J.L. Niedziela, R. Sinclair, V.O. Garlea, D.L. Abernathy, S. Chi, Y. Ren, H. Zhou, and O. Delaire. “Experimental and theoretical determination of anharmonic soft phonons in the improper ferroelectric YMnO3.” The 14th International Meeting on Ferroelectrics, San Antonio, TX, USA, September 4-8, 2017.
D. Bansal, J.L. Niedziela, A. May, V.O. Garlea, G. Ehlers, A. Huq, M. Kirkham, D.L. Abernathy, S. Chi, A.H. Said, Y. Ren, R. Sinclair, H. Zhou, and O. Delaire. “Role of lattice dynamics in the emergence of polarization in Type-I and Type-II multiferroics.” 2017 Joint Nanoscience and Neutron Scattering User Meeting, Oak Ridge National Laboratory, Oak Ridge, TN, USA, August 1-2, 2017. (Invited)
D. Bansal. “Quasiparticle coupling and thermal transport in thermoelectric SnSe and Mo3Sb7.” European Synchrotron Radiation Facility (ESRF), Grenoble, France, May 16, 2017. (Invited)
D. Bansal, J.L. Niedziela, A. May, A.H. Said, G. Ehlers, D.L. Abernathy, A. Huq, M. Kirkham, H. Zhou, and O. Delaire. “Lattice dynamics and thermal transport in multiferroic CuCrO2.” APS User Meeting 2017, Argonne National Laboratory, Argonne, IL, USA, May 8-11, 2017. (Invited)
D. Bansal, J.L. Niedziela, A. May, A.H. Said, G. Ehlers, D.L. Abernathy, A. Huq, M. Kirkham, H. Zhou, and O. Delaire. “Spin-lattice coupling and thermal transport in multiferroic CuCrO2.” APS March Meeting 2017, New Orleans, LA, USA, March 13-17, 2017.
D. Bansal, J.L. Niedziela, C.W. Li, J. Hong, and O. Delaire. “Phonon Dynamics and First Principles Simulations: Leveraging Big Data to Gain New Insights into Material Properties.” Shull-Wollan Science Symposium, Oak Ridge National Laboratory, Oak Ridge, TN, USA, September 22, 2016. (Invited – Joint with J.L. Niedziela)
D. Bansal, J.L. Niedziela, F. Bao, J. Hong, C.W. Li, I.I. Al-Qasir, V. Lynch, D.L. Abernathy, R. Archibald, E. Lingerfelt, and O. Delaire. “Modeling of time-of-flight INS intensity and phonons in single-crystals.” Math and Neutrons Seminar Series – Shull-Wollan Center, Oak Ridge National Laboratory, Oak Ridge, TN, USA, August 30, 2016. (Invited – Joint with J.L. Niedziela)
D. Bansal, J.L. Niedziela, A.H. Said, G. Ehlers, D.L. Abernathy, A. Huq, M. Kirkham, H. Zhou, and O. Delaire. “Spin-phonon coupling in triangular lattice antiferromagnetic multiferroic CuCrO2.” CNMS User Meeting, Oak Ridge National Laboratory, Oak Ridge, TN, USA, August 9-12, 2016.
D. Bansal, J.L. Niedziela, A.H. Said, G. Ehlers, D.L. Abernathy, A. Huq, M. Kirkham, H. Zhou, and O. Delaire. “Spin-phonon coupling in geometrically frustrated antiferromagnetic multiferroic CuCrO2.” 4th Annual Postdoctoral Research Symposium, Oak Ridge National Laboratory, Oak Ridge, TN, USA, August 8, 2016.
D. Bansal, J.L. Niedziela, F. Bao, J. Hong, C.W. Li, I.I. Al-Qasir, V. Lynch, D.L. Abernathy, R. Archibald, and O. Delaire. “Modeling of time-of-flight INS intensity and phonons in single- crystals.” ACNS 2016 – American Conference on Neutron Scattering, Long Beach, CA, USA, July 10-14, 2016.
D. Bansal, J.L. Niedziela, A.H. Said, G. Ehlers, D.L. Abernathy, A. Huq, M. Kirkham, H. Zhou, and O. Delaire. “Spin-phonon coupling in multiferroic CuCrO2.” ACNS 2016 – American Conference on Neutron Scattering, Long Beach, CA, USA, July 10-14, 2016.
D. Bansal, C.W. Li, A.H. Said, D.L. Abernathy, J-Q. Yan, and O. Delaire. “Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7-xTex.” APS March Meeting 2016, Baltimore, MD, USA, March 14-18, 2016.
D. Bansal. “Probing atomic vibrations using inelastic neutron and x-ray scattering.” Indian Institute of Technology, Gandhinagar, Gujrat, India, January 13, 2016. (Invited)
D. Bansal, C.W. Li, J. Hong, A.F. May, S. Chi, T. Hong, G. Ehlers, A.H. Said, D.L. Abernathy, J-Q. Yan, and O. Delaire. “Phonon Anharmonicity and Electron-Phonon Coupling in Thermoelectric Compounds SnSe and Mo3Sb7-xTex.” Materials Research Society Fall Meeting 2015, Boston, MA, USA, November 30 – December 4, 2015.
D. Bansal, J.L. Niedziela, J. Hong, C.W. Li, I.I. Al-Qasir, V. Lynch, D.L. Abernathy, and O. Delaire. “Modeling of time-of-flight inelastic neutron scattering from phonons in single- crystals.” SNS-HFIR User Group (SHUG) Meeting, Oak Ridge National Laboratory, Oak Ridge, TN, USA, October 26-27, 2015.
D. Bansal, C.W. Li, A.H. Said, D.L. Abernathy, J-Q. Yan, and O. Delaire. “Investigating the effect of electron-phonon coupling on thermoelectric properties in Mo3Sb7-xTex.” 3rd Annual Postdoctoral Research Symposium, Oak Ridge National Laboratory, Oak Ridge, TN, USA, July 30, 2015.
D. Bansal. “Modeling, quantifying, and understanding anharmonicity in Nb, SnSe/SnS, and Mo3Sb7-xTex.” Material Science and Technology Division, Physical Science Directorate, Oak Ridge National Laboratory, Oak Ridge, TN, USA, May 1, 2015.
D. Bansal. “Materials by Design based upon quantification and understanding of anharmonicity in real and reciprocal space.” University at Buffalo – State University of New York, Buffalo, NY, USA, April 20, 2015.
D. Bansal, G. Dargush, A. Aref, A.R. Hadjesfandiari, and P. Singla. “Multi-scale characterization of cubic single crystals.” EMI 2014 – Engineering Mechanics Institute Conference, McMaster University, Hamilton, Ontario, Canada, August 5-8, 2014.
D. Bansal, A. Aref, and G. Dargush. “High fidelity physics based constitutive model for metals and alloys at high temperature and pressure.” ICNS 2013 – International Conference on Neutron Scattering, Edinburgh, UK, July 8-12, 2013.
D. Bansal, A. Aref, and G. Dargush. “Self-consistent calculation of the thermal expansion coefficient and compressibility from the inelastic neutron scattering data.” ICNS 2013 – International Conference on Neutron Scattering, Edinburgh, UK, July 8-12, 2013.

Experimental FACILITIES

Ultrafast Vibrational Spectroscopy

We have a custom-designed Ultrafast Vibrational Spectroscopy setup capable of measuring electron, electron spin, and atomic vibrations at a sub-picosecond time and sub-micron spatial resolution. The setup is suitable for studying (thermal) energy transport in both metallic and insulating samples and allows measurements in both frequency (femtosecond stimulated Raman scattering) and time (transient absorption and impulsive vibrational spectroscopy) domains.

Oscillator: VITARA-S (>300 mW, 80 MHz, pulse duration ~15 fs, > 70 nm spectral bandwidth)

Amplifier: Astrella V-USP-1K (>5 mJ, 1 kHz, pulse duration < 35 fs, ~30 nm spectral bandwidth)

Spectrometer and Monochromator

We have a multipurpose 300 mm focal length Czerny-Turner spectrometer equipped with a linear CCD array available within our laboratory, capable of measuring wavelengths ranging from 200 to 1100 nm. The spectral resolution of the spectrometer is better than 0.05 nm. The spectrometer can be used in a monochromator mode using a manual variable slit on one of the output ports.

We also have transmission-grating VIS and NIR spectrometers covering the range from 320 to 2200 nm.

Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA)

We have DSC and TGA instruments available within our laboratory, capable of measuring from room temperature to 1500 C in both nitrogen (N2) and argon (Ar) environments. The instrument allows us to probe heat flow across structural, electrical, and magnetic phase transitions.