arXiv subjects

M. Biswas

Publications and source records attributed to M. Biswas.

7 recordsLinked to original sources

arXiv2026

Disorder-driven coexistence of distinct dynamical states in frustrated Sr$_3$CuNb$_2$O$_9$: a microscopic $\mu$SR and $^{93}$Nb NMR study

Despite recent progress in identifying the exotic random singlet (RS) state in disordered frustrated magnets as a distinct correlated phase, three-dimensional (3D) realizations remain scarce. Sr$_3$CuNb$_2$O$_9$ was proposed to be one of such 3D frustrated systems with magnetic site disorder hosting an RS ground state. Here, we report a detailed microscopic investigation of Sr$_3$CuNb$_2$O$_9$ employing muon spin relaxation ($\mu$SR) and $^{93}$Nb nuclear magnetic resonance (NMR) techniques. The $\mu$SR zero-field relaxation rate reveals a power-law divergence of the relaxation rate as a function of temperature. Also, a power-law divergence is present in the relaxation rate as a function of applied longitudinal field, consistent with the formation of an RS phase. The $^{93}$Nb NMR spectra unambiguously resolve two components with distinct local magnetic environments, whose nature is further elucidated through spin-lattice relaxation measurements analyzed via an inverse Laplace transform (ILT) of the nuclear magnetization recovery. The relaxation-rate distribution obtained from ILT reveals two well-separated channels: a fast component, $(1/T_1)_{\mathrm{fast}}$, and a slow component, $(1/T_1)_{\mathrm{slow}}$. Both components follow distinct power-law temperature dependences ($T^{\alpha}$), with $\alpha = 0.6$ and $1.1$ for the fast and slow channels, respectively. The combined spectral and relaxation data demonstrate that the fast channel qualitatively represents an RS-like state, whereas the slow channel exhibits quantum spin liquid (QSL) like behavior, thereby establishing the microscopic coexistence of RS and QSL-like phases in Sr$_3$CuNb$_2$O$_9$.

cond-mat.str-el↗

arXiv2023

DFT insights into MAX phase borides Hf2AB [A = S, Se, Te] in comparison with MAX phase carbides Hf2AC [A = S, Se, Te]

In this work, density functional theory (DFT) based calculations were performed to compute the physical properties (structural stability, mechanical behavior, electronic, thermodynamic, and optical properties) of synthesized MAX phases Hf2SB, Hf2SC, Hf2SeB, Hf2SeC, Hf2TeB, and the as-yet-undiscovered MAX carbide phase Hf2TeC. Calculations of formation energy, phonon dispersion curves, and elastic constants confirmed the stability of the aforementioned compounds. The obtained values of lattice parameters, elastic constants, and elastic moduli of Hf2SB, Hf2SC, Hf2SeB, Hf2SeC, and Hf2TeB showed fair agreement with earlier studies, whereas the values of the mentioned parameters for the predicted Hf2TeC exhibit a good consequence of B replacement by C. The anisotropic mechanical properties are exhibited by the considered MAX phases. The metallic nature and its anisotropic behavior were revealed by the electronic band structure and density of states. The analysis of the thermal properties Debye temperature, melting temperature, minimum thermal conductivity, and Gruneisen parameter confirmed that the carbide phases were more suited than the boride phases considered herein. The MAX phase response to incoming photons further demonstrated that they were metallic. Their suitability for use as coating materials to prevent solar heating was demonstrated by the reflectivity spectra. Additionally, this study demonstrated the impact of B replacing C in the MAX phases.

cond-mat.mtrl-sci↗

arXiv2012

Direct observation of the decay of first excited Hoyle state in $^{12}$C

An excited state of $^{12}$C having excitation energy E$_x \sim$ 9.65 $\pm$ 0.02 MeV and width (FWHM) $\sim607\pm$ 55 keV, which decays to three $ α$-particles via Hoyle state ($E_x \sim$ 7.65 MeV), has been directly identified for the first time in the exclusive inelastic scattering of 60 MeV $^{4}$He on $^{12}$C, measured in coincidence with the recoiling $^{12}$C$ ^* $ Hoyle state (decaying mostly as $^{12}$C$ ^* $ $\rightarrow \ ^{8} $Be + $ α$ $\rightarrow \ α+ α+ α$) by event-by-event kinematic reconstruction of the completely detected (4$ α$) events. This state is likely to be a candidate for 2$_2^+$ first excited Hoyle state, the existence of which has recently been indirectly evidenced from the recent inclusive inelastic scattering studies.

nucl-ex↗

arXiv2011

Study of transfer reaction channel in $^{12}$C + $^{27}$Al system

The 1p transfer channel in the $^{27}$Al($^{12}$C, $^{11}$B)$^{28}$Si reaction has been studied at E$_{lab}$ = 73, 81 and 85 MeV. The finite range distorted wave Born approximation calculations have been performed using phenomenological optical model potential to analyze the angular distributions for 3 transitions populating the 0.0, 1.78 and 4.62 MeV states of $^{28}$Si and 2 transitions populating the 2.12 and 4.44 MeV states of $^{11}$B via the $^{27}$Al($^{12}$C, $^{11}$B)$^{28}$Si reaction. The spectroscopic strengths as well as spectroscopic factors have been extracted for all the five states. The extracted strength values are compared with shell model calculations.

nucl-ex↗

arXiv2010

Sub- and above barrier fusion of loosely bound $^6$Li with $^{28}$Si

Fusion excitation functions are measured for the system $^6$Li+$^{28}$Si using the characteristic $γ$-ray method, encompassing both the sub-barrier and above barrier regions, viz., $E_{lab}$= 7-24 MeV. Two separate experiments were performed, one for the above barrier region ($E_{lab}$= 11-24 MeV) and another for the below barrier region ($E_{lab}$= 7-10 MeV). The results were compared with our previously measured fusion cross section for the $^7$Li+$^{28}$Si system. We observed enhancement of fusion cross section at sub-barrier regions for both $^6$Li and $^7$Li, but yield was substantially larger for $^6$Li. However, for well above barrier regions, similar type of suppression was identified for both the systems.

nucl-ex↗

arXiv2008

Sub-barrier fusion excitation for the system $^7$Li+$^{28}$Si

The sub-barrier fusion excitation functions are measured for the first time for the system $^7$Li +$^{28}$Si by the characteristic $γ$-ray method in the energy range $E_{lab}$= 7-11.5 MeV. The results show an enhancement, below the barrier, by about a factor of two when compared with the one-dimensional barrier penetration (1D BPM) model. Introduction of coupling with the rotational 2$^{+}$ state (1.779MeV) of the target improves the fit somewhat, but still an enhancement of about 25-40% remains.

nucl-ex↗

arXiv2008

The study of threshold behaviour of effective potential for $^{6}$Li+$^{58,64}$Ni systems

The elastic scattering for $^6$Li+$^{64}$Ni system was measured in the bombarding energy range of 13 MeV $\leq$ $E_{lab}$ $\leq$ 26 MeV. A phenomenological optical model analysis was performed and the behaviour of the surface strengths of the potential components with decreasing energy was extracted. A further analysis of the measured angular distributions, along with the existing data for $^6$Li+$^{58}$Ni, was performed with two different model potentials - one with the folded potential normalized with a complex factor (OMP1) and the other with a {\it hybrid} potential composed of a renormalized folded real and a phenomenological imaginary (OMP2) potential components - were used in the calculation. All the model potentials predict similar energy dependent behaviour for the interaction potential around the barrier. The observed energy dependence of the strengths of the real and imaginary potentials corroborate with the dispersion relation prediction for both the $^6$Li+$^{64}$Ni and $^6$Li+$^{58}$Ni systems. Though the evidence of breakup is distinct in the energy variation of the potential strengths, close to the barrier the variation is more in the line of conventional threshold anomaly. Also the threshold behaviour of the interaction potential does not indicate any distinct isotopic dependence.

nucl-ex↗