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Jyoti Saini

Publications and source records attributed to Jyoti Saini.

10 recordsLinked to original sources
arXiv2026

Contrasting anisotropic electron-phonon-spin coupling in Fe$_{3}$GeTe$_{2}$ and Fe$_{5}$GeTe$_{2}$: A helicity-resolved Raman study

Two-dimensional van der Waals ferromagnets Fe$_3$GeTe$ _2$ (F3GT) and Fe$_5$GeTe$_2$ (F5GT) exhibit pronounced magneto-optical responses, which open promising platforms for investigating the interplay among lattice, electronic, and magnetic degrees of freedom. Here, we present a comparative study of optical resonance-induced anisotropic electron-phonon coupling and its association with magnetic ordering in these systems using wavelength- and temperature-dependent helicity-resolved Raman spectroscopy. By resolving the doubly degenerate E modes under left- and right-circularly polarized excitations, we demonstrate that the temperature evolution of the chiral mode splitting ($Δf$) does not track the magnetization behavior, indicating that the helicity-dependent Raman response arises not solely from time-reversal symmetry breaking due to magnetic order, but also from spin-orbit-coupled electronic interactions. Notably, in F3GT, the out-of-plane magnetization indirectly governs the in-plane anisotropic electron-phonon coupling under optical resonance, whereas F5GT exhibits static anisotropic interactions. The Fano asymmetry parameter $1/q$ reveals mode- and temperature-dependent coupling strengths between phonons and the electronic continuum, with pronounced angular anisotropy in F3GT but isotropic behavior in F5GT--- a consequence of its multiple Fe sites and enhanced interlayer hybridization in the latter. Our results demonstrate the role of crystal structure and magnetic anisotropy in shaping the anisotropically coupled electron-phonon-spin dynamics in these layered metallic ferromagnets, and highlight Fe$_x$GeTe$_2$ as a versatile platform for microscopic insight into chiral light-matter interactions in layered metallic ferromagnets.

cond-mat.str-el↗
arXiv2026

Anisotropic electron-phonon coupling and chiral phonons in van der Waals room temperature ferromagnet Fe$_{5}$GeTe$_{2}$

The layered van der Waals Fe$_5$GeTe$_2$ (F5GT) compound exhibits room-temperature ferromagnetism, making it a promising candidate for technological applications. In our study, combined temperature, wavelength, and polarization-dependent Raman measurements, along with {\it ab initio} calculations reveal important aspects of lattice dynamics and electron-phonon interactions. The angle-resolved Raman intensity under linear polarization configurations exhibits a strong tilt in the laboratory coordinate system, indicating the existence of anisotropic electron-phonon coupling. The temperature evolution of this anisotropy is discussed by extracting the phase factor of the Raman tensor elements from the angle-resolved intensity measured at different temperatures, also uncovering a spin-orbit coupling-mediated electron-phonon response in F5GT. The thermal evolution of electron-phonon coupling is also examined by measuring the temperature dependence of the Fano parameter of the asymmetric peak in the Raman spectra, while wavelength-dependent measurements establish the role of optical resonance in enhancing the anisotropic interaction. Finally, the threefold rotational symmetry guarantees the existence of chiral phonons. We present direct spectroscopic evidence for these chiral vibrational modes through cross-circularly polarized Raman measurements, complemented by theoretical calculations of phonon circular polarization. Together, these results identify F5GT as an ideal platform for investigating emergent couplings among lattice, electronic, and magnetic degrees of freedom and for advancing the understanding of chiral phonons in magnetic van der Waals materials.

cond-mat.mtrl-sci↗
arXiv2024

Single MoS2-flake as a high TCR non-cryogenic bolometer

Temperature coefficient of resistance (TCR) of a bolometer can be tuned by modifying the thermal conductance of an absorbing materials since they sense radiations via the temperature change in the absorber. However, the thermal conductance of the absorber can be reduced by engineering the appropriate thermal isolation, which can be an ultimate solution towards making a highly sensitive thermal detector. Here, we have developed an atomically thin 2D bolometer detector made up of a mechanically transferred suspended multilayer-MoS2 flake, eliminating the use of challenging thin-film fabrication process. The strength of our detector lies on the two factors: its large surface-to-volume window to absorb the radiations; the suspended configuration which prevents the heat dissipation through the substrate and therefore reduces the thermal conductance. The bolometric response of the detector is tested in both modes, via the photoresponse and the thermal response. The prototype is found to exhibit a very high TCR ~ -9.5%/K with the least achievable thermal noise-equivalent power (NEP) ~ 0.61 pWHz-1/2, in ambient conditions at 328 K.

physics.app-ph↗
arXiv2023

Origin of magnetic anisotropy in $La_{(1\-x)}Sr_{x}MnO_{3}$

Here, we report the origin of magnetic anisotropy in Sr-doped infinite layer manganites $La_{(1\-x)}Sr_{x}MnO_{3}$ (0.125 \leq x \leq 0.400). Magnetic anisotropy is responsible for the large difference in the temperature dependence of field-cooled and zero-field-cooled magnetization. Translational symmetry breaking in the context of spins around the boundary between the ferromagnetic (FM) antiferromagnetic (AFM) region leads to FM-AFM interaction and results in magnetic anisotropy (exchange anisotropy). Here, we propose that FM-AFM interaction around the boundary between FM clusters or domains in the AFM background or between AFM clusters or domains in the ferromagnetic background is responsible for doping-dependent nonmonotonic behavior and the origin of magnetic anisotropy.

cond-mat.str-el↗
arXiv2021

New physics in $b\rightarrow se^+e^-$: A model independent analysis

The lepton universality violating flavor ratios $R_K/R_{K^*}$ indicate new physics either in $b \to s μ^+ μ^-$ or in $b \to s e^+ e^-$ or in both. If the new physics is only $b \to s e^+ e^-$ transition, the corresponding new physics operators, in principle, can have any Lorentz structure. In this work, we perform a model independent analysis of new physics only in $b \to se^+e^-$ decay by considering effective operators either one at a time or two similar operators at a time. We include all the measurements in $b\rightarrow se^+e^-$ sector along with $R_K/R_{K^*}$ in our analysis. We show that various new physics scenarios with vector/axial-vector operators can account for $R_K/R_{K^*}$ data but those with scalar/pseudoscalar operators and with tensor operators can not. We also show that the azimuthal angular observable $P_1$ in $B \to K^* e^+ e^-$ decay is most suited to discriminate between the different allowed solutions.

hep-ph↗
arXiv2020

Flavor signatures of complex anomalous $tcZ$ couplings

In this work we study the effects of anomalous $tcZ$ couplings. Such couplings would potentially affect several neutral current decays of $K$ and $B$ mesons via $Z$-penguin diagrams. Using constraints from relevant observables in $K$ and $B$ sectors, we find that the 2$σ$ upper bound on the branching ratio of ${\cal B}(t \to c Z)$ is $1.47 \times 10^{-5}$ for real coupling and $1.91 \times 10^{-4}$ for complex coupling. The current experimental upper bound from ATLAS and CMS collaborations on the branching ratio of $t \to c Z$ are $2.4 \times 10^{-4}$ and $4.9\times 10^{-4}$ at $95\%$ C.L., respectively. Hence the possibility of observation of $t \to c Z$ decay at the level of $10^{-4}$ would imply the anomalous couplings to be complex. Such complex couplings should also show up its presence in other related decays. We find that an order of magnitude enhancement is possible in the branching ratio of $K_L \to π^0 ν\barν$. Further, the complex $tcZ$ coupling can also provide large enhancements in many $CP$ violating angular observables in $B \to K^* μ^+ μ^-$ decay.

hep-ph↗
arXiv2019

$B^*_s\rightarrow l^+l^-$ decays in light of recent $B$ anomalies

Some of the recent measurements in the neutral current sector $b\rightarrow s l^+l^-$ ($l=e$ or $μ$) as well as in the charged current sector $b \rightarrow c τ\barν$ show significant deviations from their Standard Model predictions. It has been shown that two different new physics solutions, in the form of vector and/or axial vector, can explain all the anomalies in $b\rightarrow s l^+l^-$ sector. We show that the muon longitudinal polarization asymmetry in $B^*_s\rightarrow μ^+\,μ^-$ decay is a good discriminant between the two solutions if it can be measured to a precision of $\sim 10\%$, provided the new physics Wilson coefficients are real. We also investigate the potential impact of $b \rightarrow c τ\barν$ anomalies on $B_s^* \rightarrow τ^+ τ^-$ decay. We consider a model where the new physics contributions to these two transitions are strongly correlated. We find that two orders of magnitude enhancement in the branching ratio of $B^*_s\rightarrow τ^+\,τ^-$ is allowed by the present $b \rightarrow c τ\barν$ data.

hep-ph↗
arXiv2019

New physics effects in purely leptonic $B^*_s$ decays

Recently several measurements in the neutral current sector $b\rightarrow s l^+l^-$ ($l=e$ or $μ$) as well as in the charged current sector $b \rightarrow c τ\barν$ show significant deviations from their Standard Model predictions. It has been shown that two different new physics solutions can explain all the anomalies in $b\rightarrow s l^+l^-$ sector. Both these solutions are in the form of linear combinations of the two operators $(\bar{s}γ^αP_Lb)(\barμγ_αμ)$ and $(\bar{s}γ^αP_Lb)(\barμγ_αγ_5μ)$. We show that the longitudinal polarization asymmetry of the muons in $B^*_s\rightarrow μ^+\,μ^-$ decay is a good discriminant between the two solutions if it can be measured to a precision of $10\%$, provided the new physics Wilson coefficients are real. If they are complex, the theoretical uncertainties in this asymmetry are too large to provide effective discrimination. We also investigate the potential impact of $b \rightarrow c τ\barν$ anomalies on $b \rightarrow s τ^+ τ^-$ transitions. We consider a model where the new phyics contributions to these two transitions are strongly correlated. We find that the branching ratio of $B^*_s\rightarrow τ^+\,τ^-$ can be enhanced by three orders of magnitude.

hep-ph↗
arXiv2017

Probing new physics through $B^*_s \rightarrow μ^+ μ^-$ decay

We perform a model independent analysis of new physics in $B^*_s \rightarrow μ^+ μ^-$ decay. We intend to identify new physics operator(s) which can provide large enhancement in the branching ratio of $B^*_s \rightarrow μ^+ μ^-$ above its standard model prediction. For this, we consider new physics in the form of vector, axial-vector, scalar and pseudoscalar operators. We find that scalar and pseudoscalar operators do not contribute to the branching ratio of $B^*_s \rightarrow μ^+ μ^-$. We perform a global fit to all relevant $b \to s μ^+ μ^-$ data for different new physics scenarios. For each of these scenarios, we predict $Br(B^*_s \rightarrow μ^+ μ^-)$. We find that a significant enhancement in $Br(B^*_s \rightarrow μ^+ μ^-)$ is not allowed by any of these new physics operators. In fact, for all new physics scenarios providing a good fit to the data, the branching ratio of $B^*_s \rightarrow μ^+ μ^-$ is suppressed as compared to the SM value. Hence the present $b \to s μ^+ μ^-$ data indicates that the future measurements of $Br(B^*_s \rightarrow μ^+ μ^-)$ is expected to be suppressed in comparison to the standard model prediction.

hep-ph↗