arXiv subjects

P. Mandal

Publications and source records attributed to P. Mandal.

At least 19 recordsLinked to original sources

arXiv2025

Observation of Superconducting Solitons by Terahertz-Light-Driven Persistent Pseudo-Spin Coherence

Overcoming the decoherence bottleneck remains a central challenge for advancing coherent superconducting quantum device and information technologies. Solitons -- non-dispersive wave packets stabilized by the collective synchronization of quantum excitations -- offer a robust pathway to mitigating dephasing, yet their realization in superconductors has remained experimentally elusive. Here, we report the observation of a driven soliton state in epitaxial thin films of an iron-based superconductor (Co-doped BaFe$_2$As$_2$), induced by intense, multi-cycle terahertz (THz) periodic driving. The dynamical transition to this soliton state is marked by the emergence of Floquet-like spectral sidebands that exhibit a strongly nonlinear dependence on THz laser field strength and a resonant enhancement with temperature. Quantum kinetic simulations corroborate these observations, allowing us to underpin the emergence of synchronized Anderson pseudo-spin oscillations -- analogous to Dicke superradiance -- mediated by persistent order parameter oscillations. In this coherently driven state, the observed sidebands result from difference-frequency mixing between the THz drive and persistent soliton dynamics. These findings establish a robust framework for coherently driving and controlling superconducting soliton time-crystal-like phases using low dissipation, time-periodic THz fields, enabling prospects for THz-speed quantum gate operations, long-lived quantum memory, and robust quantum sensing based on enhanced macroscopic pseudo-spin coherence.

cond-mat.supr-con↗

arXiv2023

Electronic Transport and Fermi Surface Topology of Zintl Phase Compound SrZn2Ge2

We report a comprehensive study on the electronic transport properties of SrZn2Ge2 single crystals. The electrical resistivity of the compound exhibits metallic behavior, following a T^2 dependence below 35 K, consistent with the Fermi liquid behavior. However, a notable deviation is observed from this behavior at lower temperatures as a pronounced resistivity plateau emerges below 10 K. This plateau is remarkably robust, and persists under the magnetic fields of up to 10 T. Both the transverse and longitudinal magnetoresistance exhibit a crossover at critical field B* from weak-field quadratic-like to high-field unsaturated linear field dependence at low temperatures (T \leq 50 K). Possible sources of linear magnetoresistance are discussed based on the Fermi surface topology, classical and quantum transport models. The Hall resistivity data establish SrZn2Ge2 as a multiband system with contributions from both the electrons and holes. The Hall coefficient is observed to decrease with increasing temperature and magnetic field, changing its sign from positive to negative. The negative Hall coefficient observed at low temperatures in high fields and at high temperatures over the entire field range suggests that the highly mobile electron charge carriers dominate the electronic transport. Our first-principles calculations show that nontrivial topological surface states exist in SrZn2Ge2 within the bulk gap along the Gamma-M path. Notably, these surface states extend from the valence to conduction band with their number varying based on the Sr and Ge termination plane. The Fermi surface of the compound exhibits a distinct tetragonal petal-like structure, with one open and several closed surfaces. Overall, these findings offer crucial insights into the mechanisms underlying the electronic transport of the compound.

cond-mat.str-el↗

arXiv2021

Electric-field-driven resistive transition in multiferroic SrCo$_2$Fe$_{16}$O$_{27}$/Sr$_3$Co$_2$Fe$_{24}$O$_{41}$composite

We report observation of electric-field-driven resistive transition at a characteristic threshold field $E_{th}(T)$ across a temperature range 10-200 K in an off-stoichiometric composite of (~80 vol%) W- and (~20 vol%) Z-type hexaferrites. The dielectric constant $\epsilon$ and the relaxation time constant $\tau$ too exhibit anomalous jump at $E_{th}(T)$. The $E_{th}(T)$, the extent of jump in resistivity ($\Delta\rho$), and the hysteresis associated with the jump [$\Delta E_{th}(T)$] are found to decrease systematically with the increase in temperature ($T$). Several temperature-driven phase transitions have also been noticed in low and high resistive states (LRS and HRS). The temperature-driven conduction turns out to be governed by activated hopping of small polarons at all the phases with electric ($E$) and magnetic ($H$) field dependent activation energy $U(E,H)$. Interestingly, as the temperature is raised, the $E$-driven conduction at a fixed temperature evolves from $\textit{Ohmic}$ to $\textit{non-Ohmic}$ across 10-200 K and within 110-200 K, $\rho$ follows three-dimensional variable range hopping (3D-VRH) with stretched exponential $\sim$ $exp[(E_0/E)^4]$ or power law $\sim$ $(E_0/E)^m$ ($m$ varies within $\sim$0.6-0.7 and $\sim$0.6-0.8 at LRS and HRS, respectively) dependence depending on the localization length ($\zeta_E$) to diffusion length ($d_E$) ratio associated with $E$-driven conduction. The $\rho(E,T)$ follows universal scaling only at LRS within 10-110 K but not at higher temperature or at HRS. The entire set of observations has been discussed within the framework of structural evolution of the point-defect (cation vacancies or oxygen excess) network. This comprehensive map of esoteric $\rho-E-T-H$ and $\epsilon-E-T-H$ patterns provides insights on defect driven effects in a composite useful for tuning both the resistive transition and multiferroicity.

cond-mat.str-el↗

arXiv2021

Any Axion Insulator Must be a Bulk Three-Dimensional Topological Insulator

In recent attempts to observe axion electrodynamics, much effort has focused on trilayer heterostructures of magnetic topological insulators, and in particular on the examination of a so-called zero Hall plateau, which has misguidedly been overstated as direct evidence of an axion insulator state. We investigate the general notion of axion insulators, which by definition must contain a nontrivial volume to host the axion term. We conduct a detailed magneto-transport analysis of Chern insulators comprised of a single magnetic topological insulator layer of varying thickness as well as trilayer structures, for samples optimized to yield a perfectly quantized anomalous Hall effect. Our analysis gives evidence for a topological magneto-electric effect quantized in units of e$^2$/2h, allowing us to identify signatures of axion electrodynamics. Our observations may provide direct experimental access to electrodynamic properties of the universe beyond the traditional Maxwell equations, and challenge the hitherto proclaimed exclusive link between the observation of a zero Hall plateau and an axion insulator.

cond-mat.mes-hall↗

arXiv2018

Giant magnetocaloric effect in exchange-frustrated GdCrTiO5 antiferromagnet

We report the effect of exchange frustration on the magnetocaloric properties of GdCrTiO$_5$ compound. Due to the highly exchange-frustrated nature of magnetic interaction, in GdCrTiO$_5$, the long-range antiferromagnetic ordering occurs at much lower temperature $T_N$=0.9 K and the magnetic cooling power enhances dramatically relative to that observed in several geometrically frustrated systems. Below 5 K, isothermal magnetic entropy change (-$ΔS_{\rm m}$) is found to be 36 J kg$^{-1}$ K$^{-1}$, for a field change ($ΔH$) of 7 T. Further, -$ΔS_{\rm m}$ does not decrease from its maximum value with decreasing in $T$ down to very low temperatures and is reversible in nature. The adiabatic temperature change, $ΔT_{\rm ad}$, is 15 K for $ΔH$=7 T. These magnetocaloric parameters are significantly larger than that reported for several potential magnetic refrigerants, even for small and moderate field changes. The present study not only suggests that GdCrTiO$_5$ could be considered as a potential magnetic refrigerant at cryogenic temperatures but also promotes further studies on the role of exchange frustration on magnetocaloric effect. In contrast, only the role of geometrical frustration on magnetocaloric effect has been previously reported theoretically and experimentally investigated on very few systems.

cond-mat.mtrl-sci↗

arXiv2018

Collapse of ferromagnetism with Ti doping in Sm$_{0.55}$Sr$_{0.45}$MnO$_3$: A combined experimental and theoretical study

We have investigated the effect of Ti doping on the transport properties coupled with the magnetic ones in Sm$_{0.55}$Sr$_{0.45}$Mn$_{1-η}$Ti$_η$O$_3$ ($0 \leq η\leq 0.04$). The parent compound, Sm$_{0.55}$Sr$_{0.45}$MnO$_3$, exhibits a first-order paramagnetic-insulator to ferromagnetic-metal transition just below $T_{\rm c}$ = 128 K. With substitution of Ti at Mn sites ($B$-site), $T_{\rm c}$ decreases approximately linearly at the rate of 22 K$\%^{-1}$ while the width of thermal hysteresis in magnetization and resistivity increases almost in an exponential fashion. The most spectacular effect has been observed for the composition $η$=0.03, where a magnetic field of only 1 T yields a huge magnetoresistance, $1.2 \times 10^7$ $\%$ at $T_c\approx$ 63 K. With increasing magnetic field, the transition shifts towards higher temperature, and the first-order nature of the transition gets weakened and eventually becomes crossover above a critical field ($H_{cr}$) which increases with Ti doping. For Ti doping above 0.03, the system remains insulting without any ferromagnetic ordering down to 2 K. The Monte-Carlo calculations based on a two-band double exchange model show that the decrease of $T_{\rm c}$ with Ti doping is associated with the increase of the lattice distortions around the doped Ti ions.

cond-mat.mtrl-sci↗

arXiv2017

Unconventional transport properties of an itinerant ferromagnet: EuTi$_{1-x}$Nb$_{x}$O$_3$ ($x$=0.10$-$0.20)

We report the temperature and magnetic field dependence of resistivity ($ρ$) for single-crystalline EuTi$_{1-x}$Nb$_{x}$O$_3$ ($x$=0.10$-$0.20), an itinerant ferromagnetic system with very low Curie temperature ($T_C$). The detailed analysis reveals that the charge conduction in EuTi$_{1-x}$Nb$_{x}$O$_3$ is extremely sensitive to Nb concentration and dominated by several scattering mechanisms. Well below the $T_C$, where the spontaneous magnetization follows the Bloch's $T^{3/2}$ law, $ρ$ exhibits $T^2$ dependence with a large coefficient $\sim$10$^{-8}$ $Ω$ cm K$^{-2}$ due to the electron-magnon scattering. Remarkably, all the studied samples exhibit a unique resistivity minimum at $T$$=$$T_{\rm min}$ below which $ρ$ shows logarithmic increment with $T$ (for $T_{\rm C}$$<$$T$$<$$T_{\rm min}$) due to the Kondo scattering of Nb 4$d^1$ itinerant electrons by the localized 4$f$ moments of Eu$^{2+}$ ions which suppresses strongly with applied magnetic field. In the paramagnetic state, $T^{2}$ and $T^{3/2}$ dependence of the resistivity have been observed, suggesting an unusual crossover from a Fermi-liquid to a non-Fermi-liquid behavior with increasing $T$. The observed temperature and magnetic field dependence of resistivity has been analysed using different theoretical models.

cond-mat.str-el↗

arXiv2017

Large nonsaturating magnetoresistance and signature of non-degenerate Dirac nodes in ZrSiS

While the discovery of Dirac and Weyl type excitations in electronic systems is a major breakthrough in recent condensed matter physics, finding appropriate materials for fundamental physics and technological applications, is an experimental challenge. In all the reported materials, linear dispersion survives only up to a few hundred meV from the Dirac or Weyl nodes. On the other hand, real materials are subject to uncontrolled doping during preparation and thermal effect near room temperature can hinder the rich physics. In ZrSiS, ARPES measurements have shown an unusually robust linear dispersion (up to $\sim$2 eV) with multiple non-degenerate Dirac nodes. In this context, we present the magnetotransport study on ZrSiS crystal, which represents a large family of materials (\textit{WHM} with \textit{W} = Zr, Hf; \textit{H} = Si, Ge, Sn; \textit{M} = O, S, Se, Te) with identical band topology. Along with extremely large and non-saturating magnetoresistance (MR), $\sim$ 1.4 $\times$ 10$^{5}$ \% at 2 K and 9 T, it shows strong anisotropy depending on the direction of the magnetic field. Quantum oscillation and Hall effect measurements have revealed large hole and small electron Fermi pockets. Non-trivial $π$ Berry phase confirms the Dirac fermionic nature for both types of charge carriers. The long-sought relativistic phenomenon of massless Dirac fermions, known as Adler-Bell-Jackiw chiral anomaly, has also been observed.

cond-mat.mtrl-sci↗

arXiv2016

Continuously Varying Critical Exponents Beyond Weak Universality

Renormalization group theory does not restrict the from of continuous variation of critical exponents which occurs in presence of a marginal operator. However, the continuous variation of critical exponents, observed in different contexts, usually follows a weak universality scenario where some of the exponents (e.g., $β, γ, ν$) vary keeping others (e.g., $δ, η$) fixed. Here we report a ferromagnetic phase transition in (Sm$_{1-y}$Nd$_{y}$)$_{0.52}$Sr$_{0.48}$MnO$_3$ $(0.5\le y\le1)$ single crystal where all critical exponents vary with $y.$ Such variation clearly violates both universality and weak universality hypothesis. We propose a new scaling theory that explains the present experimental results, reduces to the weak universality as a special case, and provides a generic route leading to continuous variation of critical exponents and multicriticality.

cond-mat.stat-mech↗

arXiv2016

Tuning the scattering mechanism in three-dimensional Dirac semimetal Cd$_{3}$As$_{2}$

To probe the charge scattering mechanism in Cd$_{3}$As$_{2}$ single crystal, we have analyzed the temperature and magnetic field dependence of the Seebeck coefficient ($S$). The large saturation value of $S$ at high field clearly demonstrates the linear energy dispersion of three-dimensional Dirac fermion. A wide tunability of the charge scattering mechanism has been realized by varying the strength of the magnetic field and carrier density via In doping. With the increase in magnetic field, the scattering time crosses over from being nearly energy independent to a regime of linear dependence. On the other hand, the scattering time enters into the inverse energy-dependent regime and the Fermi surface strongly modifies with 2\% In doping at Cd site. With further increase in In content from 2 to 4\%, we did not observe any Shubnikov-de Haas oscillation up to 9 T field, but the magnetoresistance is found to be quite large as in the case of undoped sample.

cond-mat.str-el↗

arXiv2016

Magnetodielectric and spin-lattice coupling in quasi 1D Ising spin chain CoNb$_{2}$O$_{6}$

We have studied magnetodielectric and spin-lattice coupling in CoNb$_{2}$O$_{6}$ single crystals. Magnetostriction and magnetodielectric experiments are performed at temperatures in and above antifferomagnetic phase of quasi 1D Ising spin chain CoNb$_{2}$O$_{6}$. Field induced magnetic transitions are clearly reflected in magnetodielectric measurement as well as magnetostriction measurement also. Two sharp anomalies are found around the critical fields of antiferromagnetic to ferrimagnetic transition and ferrimagnetic to saturated paramagnetic transition in both magnetodielectric and magnetostriction experiments. High field anomaly is more pronounced for magnetodielectric response and magnetostriction also. So, in CoNb$_{2}$O$_{6}$, spins are strongly coupled with lattice as well as charges also.

cond-mat.str-el↗

arXiv2016

Determination of intrinsic ferroelectric polarization in lossy improper ferroelectric systems

We measured the intrinsic hysteretic polarization in lossy improper and nanoferroelectric systems where the nonhysteretic polarization and leakage are large and the relaxation takes place over a broader time scale. We used different measurement protocols such as standard single triangular voltage pulse, a pulse train of PUND (Positive Up Negative Down), and an even more complicated pulse train of fourteen voltage pulses and compared the results obtained. We show that a protocol which sends a train of fourteen pulses is more appropriate for extracting relaxed (i.e., time scale independent) and intrinsic remanent polarization for these samples. We also point out that it is possible to select and design an appropriate measurement protocol depending on the magnitude of polarization and leakage of the system.

cond-mat.str-el↗

arXiv2016

Geometrically frustrated GdInO$_3$: An exotic system to study negative thermal expansion and spin-lattice coupling

In this article, we report negative thermal expansion and spin frustration in hexagonal GdInO$_{3}$. Rietveld refinement of the XRD patterns reveal that the negative thermal expansion in the temperature range of 50-100K stems from the triangular lattice of Gd$^{3+}$ ions. At low temperature, the downward deviation of the inverse susceptibility ($χ^{-1}$) vs. $T$ plot from the Curie-Weiss law indicates spin frustration which inhibits long-range magnetic ordering down to 2K. Magnetostriction measurements clearly demonstrate a strong spin-lattice coupling. Low temperature anomalous phonon softening, as obtained from temperature dependent Raman measurements, also reveals the same. Our experimental observations are supported by first principles density functional theory calculations of the electronic and phonon dispersion of GdInO$_3$. The calculations suggest that the GdInO$_3$ lattice is highly frustrated at low temperature. Further, the calculated normal mode frequencies of the Gd related $Γ$ point phonons are found to depend on the magnetic structure of the lattice, suggesting significant magneto-elastic coupling.

cond-mat.mtrl-sci↗

arXiv2016

Magnetic and magnetocaloric properties of quasi-one-dimensional Ising spin chain CoV$_{2}$O$_{6}$

We have investigated the magnetic and magnetocaloric properties of antiferromagnetic Ising spin chain CoV$_{2}$O$_{6}$ by magnetization and heat capacity measurements. Both monoclinic $α$-CoV$_{2}$O$_{6}$ and triclinic $γ$-CoV$_{2}$O$_{6}$ exhibit field-induced metamagnetic transition from antiferromagnetic to ferromagnetic state via an intermediate ferrimagnetic state with 1/3 magnetization plateau. Due to this field-induced metamagnetic transition, these systems show large conventional as well as inverse magnetocaloric effects. In $α$-CoV$_{2}$O$_{6}$, we observe field-induced complex magnetic phases and multiple magnetization plateaux at low temperature when the field is applied along $c$ axis. Several critical temperatures and fields have been identified from the temperature and field dependence of magnetization, magnetic entropy change and heat capacity to construct the $H$-$T$ phase diagram. As compared to $α$-CoV$_{2}$O$_{6}$, $γ$-CoV$_{2}$O$_{6}$ displays a relatively simple magnetic phase diagram. Due to the large magnetic entropy change and adiabatic temperature change at low or moderate applied magnetic field, $γ$-CoV$_{2}$O$_{6}$ may be considered as a magnetic refrigerant in the low-temperature region.

cond-mat.str-el↗

arXiv2015

Perpendicular standing spin wave and magnetic anisotropic study on amorphous FeTaC films

Magnetic anisotropy, spin wave (SW) excitation and exchange stiffness constant of amorphous FeTaC ($d$ = 20-200 nm) films were studied as a function of thickness using micro-strip ferromagnetic resonance (MS-FMR) technique. The MS-FMR spectra for in-plane applied magnetic field show the presence of uniform precessional mode ($n$ = 0) along with first perpendicular standing spin wave (PSSW) mode ($n$ = 1) especially for $d$ = 50, 100 and 200 nm films. The angular ($φ_{H}$) dependence of resonance field ($H_{r}$) and magnetic field dependence of resonance frequencies ($f_{r}$) in planar configuration for the uniform and PSSW modes were modeled successfully by using dispersion relation which arises from a combination of exchange and dipolar interactions. The relevant parameters such as saturation magnetization ($4πM_{S}$), uniaxial anisotropic constant ($K_{u}$), $g$-factor, and exchange stiffness constants ($A_{ex}$) are estimated for different FeTaC film thickness. $A_{ex}$ is found to increase from 1.52(4)$\times$10$^{-7}$ to 5.0(5)$\times$10$^{-6}$ erg/cm as the thickness of film increases from 50 to 200 nm, possibly due to surface pinning effect or significant inhomogeneity especially at higher thickness films.

cond-mat.mes-hall↗

arXiv2015

Weak ferromagnetism and magnetization reversal in YFe$_{1-x}$Cr$_x$O$_3$

We present combined experimental and theoretical studies on the magnetic properties of a solid solution between yttrium orthoferrite and yttrium orthochromite systems, YFe$_{1-x}$Cr$_x$O$_3$ (0 $\leq$ x $\leq$ 1) where Fe$^{3+}$ and Cr$^{3+}$ ions are distributed randomly at the same crystallographic site (4b). We found that all the compositions exhibit weak ferromagnetism below the Néel temperature that decreases non-linearly with increasing $x$, while certain intermediate compositions ($x = 0.4,0.5$) show a compensation point and magnetization reversal. This unusual behavior is explained based on a simple model comprising the isotropic superexchange and the antisymmetric Dzyaloshinskii-Moriya interactions. This model explains the magnetization behavior in the entire range of doping and temperature including the magnetization reversal which results from an interplay of various DM interactions such as, Fe-O-Fe, Cr-O-Cr and Fe-O-Cr.

cond-mat.str-el↗

arXiv2015

Giant magnetothermal conductivity and magnetostriction effect in charge ordered Nd$_{0.8}$Na$_{0.2}$MnO$_{3}$ compound

We present results on resistivity ($ρ$), magnetization ($M$), thermal conductivity ($κ$), magnetostriction ($\frac{ΔL}{L(0)}$) and specific heat ($C_{p}$) of charge-orbital ordered antiferromagnetic Nd$_{0.8}$Na$_{0.2}$MnO$_{3}$ compound. Magnetic field-induced antiferromagnetic/charge-orbital ordered insulating to ferromagnetic metallic transition leads to giant magnetothermal conductivity and magnetostriction effect. The low-temperature irreversibility behavior in $ρ$, $M$, $κ$ and $\frac{ΔL}{L(0)}$ due to field cycling together with striking similarity among the field and temperature dependence of these parameters manifest the presence of strong and complex spin-charge-lattice coupling in this compound. The giant magnetothermal conductivity is attributed mainly to the suppression of phonon scattering due to the destabilization of spin fluctuations and static/dynamic Jahn-Teller distortion by the application of magnetic field.

cond-mat.str-el↗

arXiv2015

Large adiabatic temperature and magnetic entropy changes in EuTiO3

We have investigated the magnetocaloric effect in single and polycrystalline samples of quantum paraelectric EuTiO3 by magnetization and heat capacity measurements. Single crystalline EuTiO3 shows antiferromagnetic ordering due to Eu2+ magnetic moments below TN = 5.6 K. This compound shows a giant magnetocaloric effect around its Neel temperature. The isothermal magnetic entropy change is 49 Jkg-1K-1, the adiabatic temperature change is 21 K and the refrigeration capacity is 500 JKg-1 for a field change of 7 T at TN. The single crystal and polycrystalline samples show similar values of the magnetic entropy change and adiabatic temperature changes. The large magnetocaloric effect is due to suppression of the spin entropy associated with localized 4f moment of Eu2+ ions. The giant magnetocaloric effect together with negligible hysteresis, suggest that EuTiO3 could be a potential material for magnetic refrigeration below 20 K.

cond-mat.mtrl-sci↗