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  1. Article ; Online: Absolute calibration of the latent heat of transition using differential thermal analysis.

    Bar, Tapas / Bansal, Bhavtosh

    The Review of scientific instruments

    2021  Volume 92, Issue 7, Page(s) 75106

    Abstract: We describe a simple and accurate differential thermal analysis setup to measure the latent heat of solid state materials undergoing abrupt phase transitions in the temperature range from 77 K to above room temperature. We report a numerical technique ... ...

    Abstract We describe a simple and accurate differential thermal analysis setup to measure the latent heat of solid state materials undergoing abrupt phase transitions in the temperature range from 77 K to above room temperature. We report a numerical technique for the absolute calibration of the latent heat of transition without the need for a reference sample. The technique is applied to three different samples-vanadium sesquioxide undergoing the Mott transition, bismuth barium ruthenate undergoing a magnetoelastic transition, and an intermetallic Heusler compound. In each case, the inferred latent heat value agrees with the literature value within its error margins. To further demonstrate the importance of absolute calibration, we show that the changes in the latent heat of the Mott transition in vanadium sesquioxide (V
    Language English
    Publishing date 2021-08-03
    Publishing country United States
    Document type Journal Article
    ZDB-ID 209865-9
    ISSN 1089-7623 ; 0034-6748
    ISSN (online) 1089-7623
    ISSN 0034-6748
    DOI 10.1063/5.0056857
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  2. Article ; Online: Dynamic hysteresis at a noisy saddle node shows power-law scaling but nonuniversal exponent.

    Kundu, Satyaki / Patel, Ranjan Kumar / Middey, Srimanta / Bansal, Bhavtosh

    Physical review. E

    2023  Volume 108, Issue 2-1, Page(s) 24101

    Abstract: Dynamic hysteresis, viz., delay in switching of a bistable system on account of the finite sweep rate of the drive, has been extensively studied in dynamical and thermodynamic systems. Dynamic hysteresis results from slowing of the response around a ... ...

    Abstract Dynamic hysteresis, viz., delay in switching of a bistable system on account of the finite sweep rate of the drive, has been extensively studied in dynamical and thermodynamic systems. Dynamic hysteresis results from slowing of the response around a saddle-node bifurcation. As a consequence, the hysteresis area increases with the sweep rate. Mean-field theory, relevant for noise-free situations, predicts power-law scaling with the area scaling exponent of 2/3. We have experimentally investigated the dynamic hysteresis for a thermally driven metal-insulator transition in a high-quality NdNiO_{3} thin film and found the scaling exponent to be about 1/3, far less than the mean-field value. To understand this, we have numerically studied Langevin dynamics of the order parameter and found that noise, which can be thought to parallel finite temperature effects, influences the character of dynamic hysteresis by systematically lowering the dynamical exponent to as small as 0.2. The power-law scaling character, on the other hand, is unaffected in the range of chosen parameters. This work rationalizes the ubiquitous power-law scaling of the dynamic hysteresis as well as the wide variation in the scaling exponent between 0.66 and 0.2 observed in different systems over the last 30 years.
    Language English
    Publishing date 2023-09-18
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2844562-4
    ISSN 2470-0053 ; 2470-0045
    ISSN (online) 2470-0053
    ISSN 2470-0045
    DOI 10.1103/PhysRevE.108.024101
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  3. Book ; Online: Absolute calibration of the latent heat of transition using differential thermal analysis

    Bar, Tapas / Bansal, Bhavtosh

    2021  

    Abstract: We describe a simple and accurate differential thermal analysis set up to measure the latent heat of solid state materials undergoing abrupt phase transitions in the temperature range from 77 K to above room temperature. We report a numerical technique ... ...

    Abstract We describe a simple and accurate differential thermal analysis set up to measure the latent heat of solid state materials undergoing abrupt phase transitions in the temperature range from 77 K to above room temperature. We report a numerical technique for the absolute calibration of the latent heat of the transition, without the need of a reference sample. The technique is applied to three different samples -- vanadium sesquioxide undergoing the Mott transition, bismuth barium ruthenate undergoing a magnetoelastic transition, and an intermetallic Heusler compound. In each case, the inferred latent heat value agrees with the literature value to within its error margins. To further demonstrate the importance of absolute calibration, we show that the changes in the latent heat of the Mott transition in vanadium sesquioxide (V$_2$O$_3$) stays constant to within 2% even as the depth of supersaturation changes by about 10 K, in non-equilibrium dynamic hysteresis measurements. We also apply this technique for the measurement of the temperature-dependent specific heat.

    Comment: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments (volume 92, Issue 7) and may be found at this link (https://doi.org/10.1063/5.0056857)
    Keywords Condensed Matter - Statistical Mechanics
    Subject code 612
    Publishing date 2021-10-11
    Publishing country us
    Document type Book ; Online
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  4. Article ; Online: Experimental determination of the bare energy gap of GaAs without the zero-point renormalization.

    Roy, Basabendra / Mukhuti, Kingshuk / Bansal, Bhavtosh

    Journal of physics. Condensed matter : an Institute of Physics journal

    2019  Volume 32, Issue 10, Page(s) 10LT01

    Abstract: The energy gap of simple band insulators like GaAs is a strong function of temperature due to the electron-phonon interactions. Interestingly, the perturbation from zero-point phonons is also predicted to cause significant (a few percent) renormalization ...

    Abstract The energy gap of simple band insulators like GaAs is a strong function of temperature due to the electron-phonon interactions. Interestingly, the perturbation from zero-point phonons is also predicted to cause significant (a few percent) renormalization of the energy gap at absolute zero temperature but its value has been difficult to estimate both theoretically and, of course, experimentally. Given the experimental evidence (Bhattacharya et al 2015 Phys. Rev. Lett. 114 047402) that strongly supports that the exponential broadening (Urbach tail) of the excitonic absorption edge at low temperatures is the manifestation of this zero temperature electron-phonon scattering, we argue that the location of the Urbach focus is the zero temperature unrenormalized gap. Experiments on GaAs yield the zero temperature bare energy gap to be 1.581 eV and thus the renormalization is estimated to be 66 meV.
    Language English
    Publishing date 2019-11-19
    Publishing country England
    Document type Journal Article
    ZDB-ID 1472968-4
    ISSN 1361-648X ; 0953-8984
    ISSN (online) 1361-648X
    ISSN 0953-8984
    DOI 10.1088/1361-648X/ab58f8
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Critical Slowing Down at the Abrupt Mott Transition: When the First-Order Phase Transition Becomes Zeroth Order and Looks Like Second Order.

    Kundu, Satyaki / Bar, Tapas / Nayak, Rajesh Kumble / Bansal, Bhavtosh

    Physical review letters

    2020  Volume 124, Issue 9, Page(s) 95703

    Abstract: We report that the thermally induced Mott transition in vanadium sesquioxide shows critical slowing down and enhanced variance ("critical opalescence") of the order parameter fluctuations measured through low-frequency resistance-noise spectroscopy. ... ...

    Abstract We report that the thermally induced Mott transition in vanadium sesquioxide shows critical slowing down and enhanced variance ("critical opalescence") of the order parameter fluctuations measured through low-frequency resistance-noise spectroscopy. Coupled with the observed increase of the phase-ordering time, these features suggest that the strong abrupt transition is controlled by a critical-like singularity in the hysteretic metastable phase. The singularity is identified with the spinodal point and is a likely consequence of the strain-induced long-range interaction.
    Language English
    Publishing date 2020-03-23
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.124.095703
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  6. Article ; Online: How pump-probe differential reflectivity at negative delay yields the perturbed-free-induction-decay: theory of the experiment and its verification.

    Mondal, Richarj / Roy, Basabendra / Pal, Bipul / Bansal, Bhavtosh

    Journal of physics. Condensed matter : an Institute of Physics journal

    2018  Volume 30, Issue 50, Page(s) 505902

    Abstract: We present a simple but mathematically complete first-principles theory for the pump-probe differential reflectivity experiment at negative delay (probe preceding the pump) to show how it gives information about the perturbed-free-induction-decay of ... ...

    Abstract We present a simple but mathematically complete first-principles theory for the pump-probe differential reflectivity experiment at negative delay (probe preceding the pump) to show how it gives information about the perturbed-free-induction-decay of coherent polarization. The calculation, involving the optical Bloch equations to describe the induced polarization and the Ewald-Oseen idea to calculate the reflected signal as a consequence of the free oscillations of perturbed dipoles, also explicitly includes the process of lock-in detection of a double-chopped signal after it has passed through a monochromator. The theory giving a closed form expression for the measured signal in both time and spectal domains is compared with experiments on high quality GaAs quantum well sample. The dephasing time inferred experimentally at 4 K compares remarkably well with the inverse of the absorption linewidth of the continuous-wave photoluminescence excitation spectrum. Spectrally-resolved signal at negative delay calculated from our theoretical expression nicely reproduces the coherent spectral oscillations observed in our experiments, although exact fitting of the experimental spectra with the theoretical expression is difficult on account of multiple resonances.
    Language English
    Publishing date 2018-12-19
    Publishing country England
    Document type Journal Article
    ZDB-ID 1472968-4
    ISSN 1361-648X ; 0953-8984
    ISSN (online) 1361-648X
    ISSN 0953-8984
    DOI 10.1088/1361-648X/aaed79
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  7. Article ; Online: Distinguishing quantum dot-like localized states from quantum well-like extended states across the exciton emission line in a quantum well.

    Bhuyan, Sumi / Mondal, Richarj / Pal, Bipul / Bansal, Bhavtosh

    Journal of physics. Condensed matter : an Institute of Physics journal

    2018  Volume 30, Issue 10, Page(s) 105402

    Abstract: We have closely examined the emission spectrum at the heavy-hole exciton resonance in a high-quality GaAs multi-quantum well sample using picosecond excitation-correlation photoluminescence (ECPL) spectroscopy. Dynamics of the ECPL signal at low and high ...

    Abstract We have closely examined the emission spectrum at the heavy-hole exciton resonance in a high-quality GaAs multi-quantum well sample using picosecond excitation-correlation photoluminescence (ECPL) spectroscopy. Dynamics of the ECPL signal at low and high energy sides of the excitonic photoluminescence (PL) peak show complementary behavior. The ECPL signal is positive (negative) below (above) the PL peak and it changes sign within a narrow band of energy lying between the excitonic absorption and emission peaks. The energy at which this sign change takes place is interpreted as the excitonic mobility edge as it separates localized excitons in quantum dot-like states from mobile excitons in quantum well-like states.
    Language English
    Publishing date 2018--14
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1472968-4
    ISSN 1361-648X ; 0953-8984
    ISSN (online) 1361-648X
    ISSN 0953-8984
    DOI 10.1088/1361-648X/aaab25
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  8. Book ; Online: Dissipation-induced symmetry breaking

    Mukhuti, Kingshuk / Sinha, Sudip / Sinha, Subhasis / Bansal, Bhavtosh

    Emphanitic transitions in lead- and tin-containing chalcogenides and halide perovskites

    2020  

    Abstract: Lead and tin-based chalcogenide semiconductors like PbTe or SnSe have long been known to exhibit an unusually low thermal conductivity that makes them very attractive thermoelectric materials. An apparently unrelated fact is that the excitonic bandgap in ...

    Abstract Lead and tin-based chalcogenide semiconductors like PbTe or SnSe have long been known to exhibit an unusually low thermal conductivity that makes them very attractive thermoelectric materials. An apparently unrelated fact is that the excitonic bandgap in these materials increases with temperature, whereas for most semiconductors one observes the opposite trend. These two anomalous features are also seen in a very different class of photovoltaic materials, namely the halide-perovskites such as CsPbBr3. It has been previously proposed that emphanisis, a local symmetry-breaking phenomenon, is the one common origin of these unusual features. Discovered a decade ago, emphanisis is the name given to the observed displacement of the lead or the tin ions from their cubic symmetry ground state to a locally distorted phase at high temperature. This phenomenon has been puzzling because it is unusual for the high-temperature state to be of a lower symmetry than the degenerate ground state. Motivated by the celebrated vibration-inversion resonance of the ammonia molecule, we propose a quantum tunneling-based model for emphanisis where decoherence is responsible for the local symmetry breaking with increasing temperature. From the analytic expression of the temperature dependence of the tunnel splitting (which serves as an order parameter), we provide three-parameter fitting formulae which capture the observed temperature dependence of the ionic displacements as well as the anomalous increase of the excitonic bandgap in all the relevant materials.

    Comment: The following article has been submitted to Applied Physics Letters
    Keywords Condensed Matter - Materials Science ; Quantum Physics
    Subject code 541
    Publishing date 2020-12-10
    Publishing country us
    Document type Book ; Online
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  9. Article ; Online: Classification of Transitions in Upconversion Luminescence of Lanthanides by Two-Dimensional Correlation Analysis.

    Mukhuti, Kingshuk / Adusumalli, Venkata N K B / Mahalingam, Venkataramanan / Bansal, Bhavtosh

    The journal of physical chemistry. A

    2019  Volume 123, Issue 12, Page(s) 2457–2461

    Abstract: Upconversion luminescence bands from ... ...

    Abstract Upconversion luminescence bands from Yb
    Language English
    Publishing date 2019-03-11
    Publishing country United States
    Document type Journal Article
    ISSN 1520-5215
    ISSN (online) 1520-5215
    DOI 10.1021/acs.jpca.8b11052
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Article ; Online: Highly Sensitive Upconverting Nanoplatform for Luminescent Thermometry from Ambient to Cryogenic Temperature.

    Mukhuti, Kingshuk / Adusumalli, V N K B / Koppisetti, Heramba V S R M / Bansal, Bhavtosh / Mahalingam, Venkataramanan

    Chemphyschem : a European journal of chemical physics and physical chemistry

    2020  Volume 21, Issue 15, Page(s) 1731–1736

    Abstract: Precise assessment of temperature is crucial in many physical, technological, and biological applications where optical thermometry has attracted considerable attention primarily due to fast response, contactless measurement route, and electromagnetic ... ...

    Abstract Precise assessment of temperature is crucial in many physical, technological, and biological applications where optical thermometry has attracted considerable attention primarily due to fast response, contactless measurement route, and electromagnetic passivity. Rare-earth-doped thermographic phosphors that rely on ratiometric sensing are very efficient near and above room temperature. However, being dependent on the thermally-assisted migration of carriers to higher excited states, they are largely limited by the quenching of the activation mechanism at low temperatures. In this paper, we demonstrate a strategy to pass through this bottleneck by designing a linear colorimetric thermometer by which we could estimate down to 4 K. The change in perceptual color fidelity metric provides an accurate measure for the sensitivity of the thermometer that attains a maximum value of 0.86 K
    Language English
    Publishing date 2020-07-10
    Publishing country Germany
    Document type Journal Article
    ISSN 1439-7641
    ISSN (online) 1439-7641
    DOI 10.1002/cphc.202000198
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