arXiv subjects

Sourav Marik

Publications and source records attributed to Sourav Marik.

At least 19 recordsLinked to original sources

arXiv2026

Pressure-Driven Structural Transitions without a Displacive Charge-Density Wave in La$_2$SmNi$_2$O$_7$

We investigated the structural properties of bilayer nickelate La$_2$SmNi$_2$O$_7$ as a function of pressure and temperature. At ambient conditions, we show that the material crystallizes as a monoclinic superstructure distinct from the one previously reported and close to the pseudo-orthorhombic structure of pristine La$_3$Ni$_2$O$_7$. No signatures of satellite reflections associated with charge density wave (CDW) ordering are detected at low temperature. Upon compression, a sequence of pressure-induced structural transitions from monoclinic to orthorhombic 15 GPa and then tetragonal 21 GPa symmetry is observed. Within the superconducting dome, the quality of the X-ray diffraction data enables structural refinements enabling theoretical models to understand the emergence of superconductivity.

cond-mat.str-el↗

arXiv2026

Ultra-Soft Ferrimagnetism in a High-Entropy Spinel Oxide Driven by Site-Selective Cation Disorder

High-entropy materials are complex, multifunctional materials that have reshaped the design of advanced functional materials. Their chemically diverse compositions enable access to a broader compositional space than conventional solid solutions, while simultaneously posing significant challenges for fundamental structure property understanding. In this study, we introduce a new highentropy spinel oxide with an exceptionally low coercivity of 1.8 Oe at room temperature, among the lowest reported for bulk spinel oxides, and a high electrical resistivity (1560 ohm-cm). Neutron powder diffraction (NPD) and magnetic measurements reveal long-range collinear ferrimagnetic ordering (k = 0,0,0) with a transition temperature at 420 K. This rare combination of ultra-soft magnetic behavior, robust ferrimagnetic ordering well above room temperature, and high resistivity highlights its strong potential as an advanced soft-magnetic oxide for low-loss, high-frequency applications. Furthermore, X-ray absorption spectroscopy (XAS), Mossbauer spectroscopy, and NPD analyses were combined to determine the cation distribution and site selectivity across the tetrahedral and octahedral sites of the complex structure.

cond-mat.mtrl-sci↗

arXiv2026

Cocktail effect and robust Berry curvature driven anomalous Hall conductivity in the entropy-stabilized Heusler alloy Co$_2$(Ti$_{0.25}$V$_{0.25}$Cr$_{0.25}$Fe$_{0.25}$)Al

The interplay between chemical disorder and persistence of Berry curvature driven transport phenomena remains an important open question in entropy-stabilized systems. Here, we synthesize an entropy-stabilized Heusler alloy Co$_2$(Ti$_{0.25}$V$_{0.25}$Cr$_{0.25}$Fe$_{0.25}$)Al and systematically investigate its structural, magnetic, and magnetotransport properties using a combination of experimental measurements and density functional theory (DFT) calculations. The system crystallizes in cubic space group $Fm\Bar{3}m$ and exhibits ferromagnetism with saturation magnetization in close agreement with the Slater--Pauling prediction. Transport and magnetotransport measurements reveal metallic behavior and a pronounced anomalous Hall effect with an anomalous Hall conductivity of approximately $134.4~ \Omega^{-1}$.cm$^{-1}$. Combined experimental observations and first-principles calculations establish that the anomalous Hall effect is predominantly intrinsic in origin and originates from the Berry curvature of the electronic bands. Remarkably, despite the substantial configurational disorder and the dilution of the constituent parent compounds, the anomalous Hall conductivity remains comparable to the largest values reported in the corresponding parent Heusler systems. This behavior reflects the manifestation of the cocktail effect, one of the core characteristics of entropy-stabilized systems. Our results also demonstrate that Berry curvature mediated transport persists in this chemically disordered system and indicates that entropy engineering can be a promising route for tuning intrinsic anomalous Hall responses.

cond-mat.mtrl-sci↗

arXiv2026

Long-range magnetic ordering and structural phase transition in disordered high-entropy spinel chromites

High-entropy spinel oxides provide an excellent platform for investigating entropy-stabilized correlated systems with strong configurational disorder. In this work, we systematically study the temperature evolution of the structural and magnetic properties of Cr-based high-entropy spinels with compositions $(Mn_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})Cr_2O_4$ and $(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})Cr_2O_4$. Our results reveal that both systems crystallize in cubic structure with space group \textit{$Fd\overline{3}m$} at room temperature. Each system undergoes antiferromagnetic ordering below the N\'eel temperatures $ T_N$ = 49 K and 35 K, respectively. Neutron diffraction measurements confirm the emergence of long-range magnetic order with spiral spin arrangement. Both systems exhibit a structural phase transition from cubic \textit{$Fd\overline{3}m$} to orthorhombic \textit{Fddd} symmetry at approximately 55 K and 85 K, respectively. Notably, despite the significant chemical disorder at the A site, both systems undergo transitions analogous to those observed in low entropy spinel systems. This behavior suggests that high configurational entropy may promote global structural stabilization despite local chemical disorder, thereby preserving long-range orderings and the characteristic symmetry-breaking transitions of the pristine spinel systems.

cond-mat.mtrl-sci↗

arXiv2025

Multiband Superconductivity and High Critical Current Density in Entropy Stabilized Nb0.25Ta0.25Ti0.25Zr0.25

High and medium-entropy superconductors with significant intrinsic disorder are a fascinating class of superconductors. Their combination of robust structural integrity, superior mechanical properties, and exceptional irradiation tolerance makes them promising candidates for use in advanced superconducting technologies. Herein, we present a comprehensive theoretical and experimental investigation on the superconductivity of equiatomic entropy-stabilized Nb0.25Ta0.25Ti0.25Zr0.25. The material shows bulk superconductivity (transition temperature = 8K) with a high upper critical field of 11.94T. Interestingly, both the electronic band structure and specific heat data point toward unconventional multiband superconductivity. Our ab initio calculations reveal Dirac-like band crossings close to the Fermi level, with certain degeneracies persisting even in the presence of spin-orbit coupling, suggesting a possible interplay between topological electronic states and the observed unconventional superconductivity. Remarkably, the critical current density exceeds the benchmark of 10^5 A/cm2, surpassing all previously reported as-cast entropy-stabilized superconductors. This high critical current density is likely attributed to strong flux pinning at the grain boundaries, facilitated by extreme intrinsic lattice distortion. Taken together, the demonstrated dynamical stability, excellent metallicity, potential to host unconventional superconductivity, and exceptionally high critical current density highlight the potential of entropy-stabilized alloys as a platform for exploring the confluence of disorder, topology, and unconventional superconductivity.

cond-mat.supr-con↗

arXiv2025

Normal state and superconducting state properties of high entropy Ta0.2Nb0.2V0.2Ti0.2X0.2 (X = Zr and Hf )

High entropy alloy superconductors represent a unique blend of advanced material systems and quantum physics, offering significant potential for advancing superconducting technologies. In this study, we report a detailed theoretical and experimental investigation of high entropy alloy superconductors Ta0.2Nb0.2V0.2Ti0.2X0.2 (X = Zr and Hf). Our study unveils that both the materials crystallize in a body-centered cubic structure (space group: I m -3 m) and exhibit bulk superconductivity with a superconducting onset temperature of (Tonset C ) of 5 K for X = Hf and 6.19 K for X = Zr sample. Our detailed analysis, including magnetization, resistivity, heat capacity measurements, and density functional theory (DFT) calculations indicates moderately coupled isotropic s-wave superconductivity in these materials. Our DFT results find significant spectral weight at the Fermi energy and phonon spectra is free of imaginary modes, confirming the dynamical stability and metallic nature of these alloys. Remarkably, we have observed a high upper critical field (HC2(0)) surpassing the Pauli paramagnetic limit for the X = Hf sample and explained it on the basis of the increased spin-orbit coupling in the structure. Ta0.2Nb0.2V0.2Ti0.2Zr0.2, on the other hand, shows a conventional HC2 behaviour. With the dynamical stability of these alloys, excellent normal state metallic nature, high micro-hardness, and high upper critical field, these samples emerge as potential candidates for future applications in superconducting devices.

cond-mat.supr-con↗

arXiv2024

Validating Mean Field Theory in a New Complex, Disordered High-Entropy Spinel Oxide

The advent of novel high-entropy oxides has sparked substantial research interest due to their exceptional functional properties, which often surpass the mere sum of their constituent elements' characteristics. This study introduces a complex high-entropy spinel oxide with composition (Ni$_{0.2}$Mg$_{0.2}$Co$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)(Mn$_{0.66}$Fe$_{0.66}$Cr$_{0.66}$)O$_{4}$. We performed comprehensive structural (X-ray and Neutron diffraction), microstructural, magnetic, and local electronic structure investigations on this material. Despite the material's high degree of disorder, detailed magnetization measurements and low temperature neutron powder diffraction studies reveal long-range ferrimagnetic ordering beginning at 293 K. The sample exhibits a high saturation magnetization of 766 emu-cm${^3}$ (at 50 K), a low coercivity (H$_C$) of 100 Oe (50 K), a high transition temperature (T$_C$) around room temperature, and high resistivity value of 4000 Ohm-cm at room temperature, indicating its potential for high density memory devices. The magnetic structure is determined using a collinear-type ferrimagnetic model with a propagation vector k = 0,0,0. Various analytical techniques, including modified Arrott plots, Kouvel-Fischer analysis, and critical isotherm analysis, are employed to investigate the phase transitions and magnetic properties of this complex system. Our results indicate a second-order phase transition. Remarkably, despite the complex structure and significant disorder, the critical exponents obtained are consistent with the mean field model. The high entropy leads to a remarkably homogeneous distribution of multiple cations, validating the approximation of average local magnetic environments and supporting the mean field theory.

cond-mat.str-el↗

arXiv2024

Structural, magnetic and x-ray absorption spectroscopy studies of new Cr-based low, medium and high-entropy spinel oxides

The emergence of high-entropy oxides has spurred significant research interest in recent times. These compounds exhibit exotic functional properties that often transcend simple linear combinations of their constituent elements. Herein, we present a new series of Cr-based low, medium, and high entropy spinel oxides with composition NiCr2O4, [Ni0.5Mn0.5]Cr2O4, [Ni0.33Mn0.33Co0.33]Cr2O4, [Ni0.25Mn0.25Co0.25Cu0.25]Cr2O4, [Ni0.2Mn0.2Co0.2Cu0.2Zn0.2]Cr2O4, and [Ni0.2Mg0.2Co0.2Cu0.2Zn0.2]Cr2O4. We conducted detailed structural (X-ray and Neutron diffraction), microstructural, Raman spectroscopy, magnetic, and X-ray absorption spectroscopy measurements on these materials. Our study reveals that the incorporation of multiple cations at the A-site of the structure (AB2O4) significantly modulates the magnetic properties. These compounds exhibit transitions from complex ferrimagnetic ([Ni0.2Mn0.2Co0.2Cu0.2Zn0.2]Cr2O4) to antiferromagnetic ([Ni0.2Mg0.2Co0.2Cu0.2Zn0.2]Cr2O4) states, with remarkable coercivity variations, demonstrating the ability to tailor magnetic responses through compositional design.

cond-mat.mtrl-sci↗

arXiv2023

Tuning the magnetic properties in MPS3 (M = Mn, Fe, and Ni) by proximity-induced Dzyaloshinskii Moriya interactions

Tailoring the quantum many-body interactions in layered materials through appropriate heterostructure engineering can result in emergent properties that are absent in the constituent materials thus promising potential future applications. In this article, we have demonstrated controlling the otherwise robust magnetic properties of transition metal phosphorus trisulphides (Mn/Fe/NiPS3) in their heterostructures with Weyl semimetallic MoTe2 which can be attributed to the Dzyaloshinskii Moriya (DM) interactions at the interface of the two different layered materials. While the DM interaction is known to scale with the strength of the spin-orbit coupling (SOC), we also demonstrate here that the effect of DM interaction strongly varies with the spin orientation/dimensionality of the magnetic layer and the low-energy electronic density of state of the spin-orbit coupled layer. The observations are further supported by a series of experiments on heterostructures with a variety of substrates/underlayers hosting variable SOC and electronic density of states.

cond-mat.mes-hall↗

arXiv2023

Magnetism and exchange bias properties in Ba$_{2}$ScRuO$_{6}$

This paper presents structural, detailed magnetic, and exchange bias studies in polycrystalline Ba$_{2}$ScRuO$_{6}$ synthesized at ambient pressure. In contrast to its strontium analogue, this material crystallizes in a 6L hexagonal structure with the space group P$\overline{3}$m1. The Rietveld refinement using the room-temperature powder X-ray diffraction pattern suggests a Ru-Sc disorder in the structure. The temperature variation of the dc-electrical resistivity highlights a semiconducting behaviour with the electron conduction corresponding to the Mott 3D-VRH model. Detailed magnetization measurements show that Ba$_{2}$ScRuO$_{6}$ develops antiferromagnetic ordering at T$_{N}$ $\approx$ 9 K. Interestingly, below 9 K (T$_{N}$), the field cooled (FC) magnetic field variation of the magnetization curves highlights exchange bias effect in the sample. The exchange bias field reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the magnetic ordering temperature can be attributed to inhomogeneous magnetic correlations owing to the disorder in the structure.

cond-mat.mtrl-sci↗

arXiv2021

Tailoring the Phase Transition and Electron-Phonon Coupling in 1T'-MoTe2 by Charge Doping: A Raman Study

Transition metal dichalcogenides (TMDs) are a class of widely studied 2D layered materials which exist in various polymorphs. The 1T' phase of MoTe2 is of prime importance as it has been reported to show quantum spin hall (QSH) behavior with a fairly large band-gap of ~ 60 meV, in contrast to most QSH materials known. It is noteworthy that though the monolayer 1T'-MoTe2 was initially predicted to show the QSH behavior, recent theoretical studies claim that the few-layered counterparts also exhibit higher order topological behavior. Besides, 1T'-MoTe2 also undergoes a hysteretic phase transition to the Td phase (which is a type-II Weyl semimetal) by breaking the inversion symmetry of the crystal. While the phase transition between these two topological phases is of utmost importance, its study has been mostly restricted to bulk single crystal flakes, thereby not sufficiently exploring the effect of dimensionality. We have studied the phase transition in 1T'-MoTe2 as a function of flake-thickness. Though our Raman studies show a suppression of the phase transition in the thin (thickness <10 nm) flakes [similar to the report Phys. Rev. B 97, 041410 (2018)], we have experimentally demonstrated the possibility of stabilizing the desired phase (1T' or Td) at room temperature by charge doping. Further, we have observed clear signatures of electron-phonon coupling in MoTe2, which evolves as a function of flake-thickness and charge doping.

cond-mat.str-el↗

arXiv2021

Field induced hysteretic structural phase switching and possible CDW in Re-doped MoTe$_2$

Novel electronic systems displaying exotic physical properties can be derived from complex topological materials through chemical doping. MoTe$_2$, the candidate type-II Weyl semimetal shows dramatically enhanced superconductivity up to 4.1 K upon Re doping in Mo sites. Based on bulk transport and local scanning tunneling microscopy (STM) here we show that Re doping also leads to the emergence of a possible charge density wave (CDW) phase in Re$_{0.2}$Mo$_{0.8}$Te$_2$. In addition, the tunneling $I-V$ characteristics display non-linearity and hysteresis which is commensurate with a hysteresis observed in the change in tip-height ($z$) as a function of applied voltage $V$. The observations indicate an electric field induced hysteretic switching consistent with piezoelectricity and possible ferroelectricity.

cond-mat.str-el↗

arXiv2019

Magnetization reversal, giant exchange bias effect and magnetoresistance in oxygen vacancy ordered Sr$_{4}$Fe$_{3}$CoO$_{11}$

We report the structural, magnetic, exchange bias and magnetotransport effect in Sr$_{4}$Fe$_{3}$CoO$_{11}$. The material crystallizes in the orthorhombic $\textit{Cmmm}$ space group. It shows antiferromagnetic (G-type) transition (T$_{N}$ = 255 K) along with interesting temperature induced magnetization reversal (T$_{Comp.}$= 47 K measured at 100 Oe). The magnetic reversal can be elucidated considering the increased magnetocrystalline anisotropy with Co substitution. Magnetoresistance measurements shows an interesting crossover from negative to positive side at $\sim$ 100 K. The negative magnetoresistance reaches 80 $\%$ at 25 K in 7 T magnetic field. Giant exchange bias effect is observed below T$_{N}$ under field cooling condition. The origin of the negative magnetoresistance and giant exchange bias in this sample can be attributed to the magnetic frustration.

cond-mat.str-el↗

arXiv2019

Nodeless s-wave superconductivity in the α-Mn structure type noncentrosymmetric superconductor TaOs: A μSR study

Noncentrosymmetric superconductors can lead to a variety of exotic properties in the superconducting state such as line nodes, multigap behavior, and time-reversal symmetry breaking. In this paper, we report the properties of the new noncentrosymmetric superconductor TaOs, using muon spin relaxation and rotation measurements. It is shown using the zero-field muon experiment that TaOs preserve the time-reversal symmetry in the superconducting state. From the transverse field muon measurements, we extract the temperature dependence of $λ(T)$ which is proportional to the superfluid density. This data can be fit with a fully gapped s-wave model for $α$ = $Δ(0)/k_{B}T_{c}$ = 2.01 $\pm$ 0.02. Furthermore, the value of magnetic penetration depth is found to be 5919 $\pm$ 45 \textÅ, which is consistent with the value obtained from the bulk measurements.

cond-mat.supr-con↗

arXiv2019

Superconductivity in a new hexagonal high entropy alloy

High entropy alloys (HEAs) are the new class of materials with an attractive combination of tunable mechanical and physicochemical properties. They crystallize mainly in cubic structures, however, for practical applications, HEAs with hexagonal close-packed (hcp) structure are highly desirable in connection to their in general high hardness. Herein, we report the synthesis, structure and detailed superconducting properties of Re$_{0.56}$Nb$_{0.11}$Ti$_{0.11}$Zr$_{0.11}$Hf$_{0.11}$-the first hexagonal superconducting high entropy alloy (HEA) composed of five randomly distributed transition-metals. Combination of room temperature precession electron diffraction, precession electron diffraction tomography and powder X-ray diffraction is utilized to determine the room temperature crystal structure. Transport, magnetic and heat capacity measurements show that the material is a type-II superconductor with the bulk superconducting transition at $T_{c}$ = 4.4 K, lower critical field $H_{c1}$(0) = 2.3 mT and upper critical field $H_{c2}$(0) = 3.6 T. Low-temperature specific heat measurement indicates that Re$_{0.56}$Nb$_{0.11}$Ti$_{0.11}$Zr$_{0.11}$Hf$_{0.11}$ is a phonon-mediated superconductor in the weak electron-phonon coupling limit with a normalized specific heat jump $\frac{ΔC_{el}}{γ_{n}T_{c}}$ = 1.32. Further, hexagonal to cubic structural transition is observed by lowering the valence electron counts and $T_{c}$ follows crystalline-like behaviour.

cond-mat.supr-con↗

arXiv2019

Generation of strain-induced pseudo-magnetic field in a doped type-II Weyl semimetal

In Weyl semimetals, there is an intriguing possibility of realizing a pseudo-magnetic field in presence of small strain due to certain special cases of static deformations. This pseudo-magnetic field can be large enough to form quantized Landau levels and thus become observable in Weyl semimetals. In this paper, we experimentally show the emergence of a pseudo-magnetic field (~ 3 Tesla) by Scanning Tunneling Spectroscopy (STS) on the doped Weyl semimetal Re-MoTe2, where distinct Landau level oscillations in the tunneling conductance are clearly resolved. The crystal lattice is intrinsically strained where large area STM imaging of the surface reveals differently strained domains where atomic scale deformations exist forming topographic ripples with varying periodicity in the real space. The effect of pseudo-magnetic field is clearly resolved in areas under maximum strain.

cond-mat.mes-hall↗

arXiv2019

Superconducting and normal state properties of noncentrosymmetric superconductor NbOs$_{2}$ investigated by muon spin relaxation and rotation

Noncentrosymmetric superconductors with $α$-manganese structure has attracted much attention recently, after the discovery of time-reversal symmetry breaking in all the members of Re$_{6}$X (X = Ti, Hf, Zr) family. Similar to Re$_{6}$X, NbOs$_{2}$ also adopts $α$-$Mn$ structure and found to be superconducting with critical temperature $T_{c}$ $\approx$ 2.7 K. The results of the resistivity, magnetization, specific heat and muon-spin relaxation/rotation measurements show that NbOs$_{2}$ is a weakly coupled type-II superconductor. Interestingly, the zero-field muon experiments indicate that the time-reversal symmetry is preserved in the superconducting state. The low-temperature transverse-field muon measurements and the specific heat data evidence a conventional isotropic fully gapped superconductivity. However, the calculated electronic properties in this material show that the NbOs$_{2}$ is positioned close to the band of unconventionality of the Uemura plot, indicating that NbOs$_{2}$ potentially borders an unconventional superconducting ground state.

cond-mat.supr-con↗

arXiv2018

Enhancement of the superconducting transition temperature by Re doping in Weyl semimetal MoTe$_{2}$

This work presents the emergence of superconductivity in Re substituted topological Weyl semimetal MoTe$_{2}$. Re substitution for Mo sites lead to a sizable enhancement in the superconducting transition temperature (T$_{c}$). A record high T$_{c}$ at ambient pressure in a 1T$'$-MoTe$_{2}$ (room temperature structure) related sample is observed for the Mo$_{0.7}$Re$_{0.3}$Te$_{2}$ composition (T$_{c}$ = 4.1 K, in comparison MoTe$_{2}$, shows a T$_{c}$ of 0.1 K). The experimental and theoretical studies indicate that Re substitution is doping electrons and facilitates the emergence of superconductivity by enhancing the electron-phonon coupling and density of states at the Fermi level. Our findings, therefore, open a new way to further manipulate and enhance the superconducting state together with the topological states in 2D van der Waals materials.

cond-mat.supr-con↗