arXiv subjects

Rourav Basak

Publications and source records attributed to Rourav Basak.

13 recordsLinked to original sources

arXiv2026

Magnetoresistive Memory in the Paramagnetic Phase of Eu$_5$In$_2$As$_6$

Magnetoresistive materials that respond sensitively to applied fields are central to modern data storage technologies. Here we unveil a novel Magnetoresistive Memory (MRM) in Eu$_5$In$_2$As$_6$, where the electrical resistivity depends not only on the magnitude but also on the history of the applied magnetic field. Such an effect has been reported in only two classes of strongly correlated electron systems: perovskite manganites and pyrochlore iridates. In both cases, the effect has been observed in the magnetically ordered phase. It has been attributed to metastable magnetic states in manganites and conducting domain walls in iridates. Remarkably, the MRM in Eu$_5$In$_2$As$_6$ onsets at twice the antiferromagnetic transition temperature, well within the paramagnetic phase. The temperature, field, and time dependence of resistivity suggest that either a hidden order or a fluctuating phase with short-range correlations underlies this effect. Our results offer MRM as a new platform for quantum sensing and memory technologies, and encourage searching for MRM in related materials.

cond-mat.str-el↗

arXiv2026

Low-Temperature Suppression of Intertwined Orders in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ Thin Films

The strong coupling between spin, charge, and lattice degrees of freedom in perovskite oxides leads to an array of exotic phenomena, giving these materials rich phase diagrams that can include coupled orders. This is exemplified by the A-site doped ferrite La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ (LSFO), which exhibits a coupled paramagnetic-antiferromagnetic and charge ordering phase transition at $\sim$190 K that has been well studied in thin films, bulk, and polycrystalline samples. However, the low temperature behavior of LSFO thin films below $\sim$100 K has not been thoroughly explored. This work uses several X-ray scattering and spectroscopy techniques to directly probe LSFO's magnetic and charge order down to low temperature. Using resonant X-ray scattering, we observe a complete suppression of LSFO's known antiferromagnetic and charge order below $\sim$25 K. Further spectroscopy and coherent scattering measurements provide insight into LSFO's electronic structure and domain dynamics in this new low temperature phase, and we propose possible explanations for the observed order suppression based on reduced dimensionality of domains in our thin films. Our findings provide insight into the effects of competing interactions in strongly correlated materials, particularly those with coupled orders.

cond-mat.str-el↗

arXiv2025

Spectroscopic Determination of Site-Selective Ligand Binding on Single Anisotropic Nanocrystals

Organic surface ligands are integral components of nanocrystals and nanoparticles that have a strong influence on their physicochemical properties, their interaction with the environment, and their ability to self-assemble and order into higher-order structures. These hybrid nanomaterials are tunable with applications in catalysis, directed self-assembly, next-generation optoelectronics, and chemical and quantum sensing. Critically, future advances depend on our ability to rationally engineer their surface chemistry. However, fundamental knowledge of ligand-nanoparticle behavior is limited by uncertainty in where and how these ligands bind to surfaces. For nanoparticles, in particular, few characterization techniques offer both the high spatial resolution and the precise chemical mapping needed to identify specific ligand binding sites. In this study, we utilized synchrotron infrared nanospectroscopy (SINS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM) together with first-principles computer simulations to validate the site-selective adsorption of organic ligands on a shaped nanocrystal surface. Specifically, we demonstrate that the sterically encumbered isocyanide ligands (CNAr^{Mes2}) preferentially bind to the high curvature features of Ag nanocubes (NCs), where low-coordinate Ag atoms are present. In contrast, isocyanide ligands that do not exhibit these steric properties show no surface selectivity. SINS serves as an effective tool to validate these surface binding interactions at the near-single molecule level. These results indicate that steric effects can be successfully harnessed to design bespoke organic ligands for fine-tuning nanocrystal surface chemistry and the properties of the nanocrystal ligand shell.

cond-mat.mtrl-sci↗

arXiv2025

Electronic origin of delicate antiferromagnetism in Fe$_{x}$NbS$_2$

Among the family of intercalated transition-metal dichalcogenides (TMDs), Fe$_{x}$NbS$_2$ is found to possess unique current-induced resistive switching behaviors, tunable antiferromagnetic states, and a commensurate charge order, all of which are tied to a critical Fe doping of $x_c$ = 1/3. However, the electronic origin of such extreme stoichiometry sensitivities remains unclear. Combining angle-resolved photoemission spectroscopy (ARPES) with density functional theory (DFT) calculations, we identify and characterize a dramatic eV-scale electronic restructuring that occurs across the $x_c$. Moment-carrying Fe 3$d_{z^2}$ electrons manifest as narrow bands within 200 meV of the Fermi level, distinct from other transition metal intercalated TMD magnets. These states strongly hybridize with itinerant electrons in TMD layer, rapidly lose coherence above $x_c$ due to correlation-driven effects. This sudden quasiparticle decoherence collapses the Fe-Nb hybridization, which explicitly suppresses the out-of-plane effective Fe-Fe exchange interaction, driving the transformation of the magnetic ground state from an antiferromagnetic stripe phase to a zigzag phase. These observations resemble the exceptional electronic and magnetic sensitivity of strongly correlated systems, and demonstrate that quantifying orbital-specific hybridization via ARPES offers an alternative pathway to evaluate effective magnetic exchange in metallic magnets, complementing inelastic neutron and resonant x-ray scattering probes.

cond-mat.str-el↗

arXiv2024

Antiferromagnetic order in a layered magnetic topological insulator MnBi$_2$Se$_4$ probed by resonant soft x-ray scattering

The quasi-two-dimensional magnetic topological insulator MnBi$_2$Se$_4$, stabilized via non-equilibrium molecular beam epitaxy, is investigated by resonant soft x-ray scattering. Kiessig fringes are observed, confirming a high sample quality and a thin film thickness of 10 septuple layers ($\sim$13 nm). An antiferromagnetic Bragg peak is observed at the structurally forbidden reflection, whose magnetic nature is validated by studying its temperature, energy, and polarization dependence. Through a detailed analysis, an A-type antiferromagetic order with in-plane moments is implied. This alternative spin structure in MnBi$_2$Se$_4$, in contrast to the Ising antiferromagnetic states in other magnetic topological insulators, might be relevant for hosting new topological states.

cond-mat.str-el↗

arXiv2023

Disentangling transport mechanisms in a correlated oxide by photoinduced charge injection

We present a novel heterostructured approach to disentangle the mechanism of electrical transport of the strongly correlated PrNiO3, by placing the nickelate under the photoconductor CdS. This enables the injection of carriers into PrNiO3 in a controlled way, which can be used to interrogate its intrinsic transport mechanism. We find a non-volatile resistance decrease when illuminating the system at temperatures below the PrNiO3 metal-insulator transition. The photoinduced change becomes more volatile as the temperature increases. These data help understand the intrinsic transport properties of the nickelate-CdS bilayer. Together with data from a bare PrNiO3 film, we find that the transport mechanism includes a combination of mechanisms including both thermal activation and variable range hopping. At low temperatures without photoinduced carriers the transport is governed by hopping, while at higher temperatures and intense illumination the activation mechanism becomes relevant. This work shows a new way to optically control the low-temperature resistance of PrNiO3.

cond-mat.str-el↗

arXiv2023

Discovery of Charge Order in the Transition Metal Dichalcogenide Fe$_{x}$NbS$_2$

The Fe intercalated transition metal dichalcogenide (TMD), Fe$_{1/3}$NbS$_2$, exhibits remarkable resistance switching properties and highly tunable spin ordering phases due to magnetic defects. We conduct synchrotron X-ray scattering measurements on both under-intercalated ($x$ = 0.32) and over-intercalated ($x$ = 0.35) samples. We discover a new charge order phase in the over-intercalated sample, where the excess Fe atoms lead to a zigzag antiferromagnetic order. The agreement between the charge and magnetic ordering temperatures, as well as their intensity relationship, suggests a strong magnetoelastic coupling as the mechanism for the charge ordering. Our results reveal the first example of a charge order phase among the intercalated TMD family and demonstrate the ability to stabilize charge modulation by introducing electronic correlations, where the charge order is absent in bulk 2H-NbS$_2$ compared to other pristine TMDs.

cond-mat.str-el↗

arXiv2022

Full-Field Nanoscale X-ray Diffraction-Contrast Imaging using Direct Detection

Recent developments in x-ray science provide methods to probe deeply embedded mesoscale grain structures and spatially resolve them using dark field x-ray microscopy (DFXM). Extending this technique to investigate weak diffraction signals such as magnetic systems, quantum materials and thin films proves challenging due to available detection methods and incident x-ray flux at the sample. We present a direct detection method focusing on DFXM studies in the hard x-ray range of 10s of keV and above capable of approaching nanoscale resolution. Additionally, we compare this direct detection scheme with routinely used scintillator based optical detection and achieve an order of magnitude improvement in exposure times allowing for imaging of weakly diffracting ordered systems.

physics.ins-det↗

arXiv2022

Spin-carrier coupling induced ferromagnetism and giant resistivity peak in EuCd$_2$P$_2$

EuCd$_2$P$_2$ is notable for its unconventional transport: upon cooling the metallic resistivity changes slope and begins to increase, ultimately 100-fold, before returning to its metallic value. Surprisingly, this giant peak occurs at 18K, well above the N\'{e}el temperature ($T_N$) of 11.5K. Using a suite of sensitive probes of magnetism, including resonant x-ray scattering and magneto-optical polarimetry, we have discovered that ferromagnetic order onsets above $T_N$ in the temperature range of the resistivity peak. The observation of inverted hysteresis in this regime shows that ferromagnetism is promoted by coupling of localized spins and itinerant carriers. The resulting carrier localization is confirmed by optical conductivity measurements.

cond-mat.str-el↗

arXiv2022

Stabilization of three-dimensional charge order through interplanar orbital hybridization in Pr$_x$Y$_{1-x}$Ba$_2$Cu$_3$O$_{6+\delta}$

The shape of 3$d$-orbitals often governs the electronic and magnetic properties of correlated transition metal oxides. In the superconducting cuprates, the planar confinement of the $d_{x^2-y^2}$ orbital dictates the two-dimensional nature of the unconventional superconductivity and a competing charge order. Achieving orbital-specific control of the electronic structure to allow coupling pathways across adjacent planes would enable direct assessment of the role of dimensionality in the intertwined orders. Using Cu-$L_3$ and Pr-$M_5$ resonant x-ray scattering and first-principles calculations, we report a highly correlated three-dimensional charge order in Pr-substituted YBa$_2$Cu$_3$O$_{7}$, where the Pr $f$-electrons create a direct orbital bridge between CuO$_2$ planes. With this, we demonstrate that interplanar orbital engineering can be used to surgically control electronic phases in correlated oxides and other layered materials.

cond-mat.str-el↗

arXiv2021

Robust surface states and coherence phenomena in magnetically alloyed SmB6

Samarium hexaboride is a candidate for the topological Kondo insulator state, in which Kondo coherence is predicted to give rise to an insulating gap spanned by topological surface states. Here we investigate the surface and bulk electronic properties of magnetically alloyed Sm1-xMxB6 (M=Ce, Eu), using angle-resolved photoemission spectroscopy (ARPES) and complementary characterization techniques. Remarkably, topologically nontrivial bulk and surface band structures are found to persist in highly modified samples with up to 30% Sm substitution, and to coexist with antiferromagnetism in the case of Eu doping. The results are interpreted in terms of a hierarchy of energy scales, in which surface state emergence is linked to the formation of a direct Kondo gap, while low temperature transport trends depend on the indirect gap.

cond-mat.str-el↗

arXiv2019

High temperature singlet-based magnetism from Hund's rule correlations

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. The antiferromagnetic dipnictide USb2 has been of recent interest due to the discovery of rich proximate phase diagrams and unusual quantum coherence phenomena. Here, linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb2 and isostructural UBi2. Of these two materials, only USb2 is found to enable strong Hund's rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. Theoretical analysis reveals that these and other anomalous properties of the material may be understood by attributing it as the first known high temperature realization of a singlet ground state magnet, in which magnetism occurs through a process that resembles exciton condensation.

cond-mat.str-el↗

arXiv2018

Electron Capture Beta Decay of Partially Polarized Nuclei

We compute the spin excess for the neutrinos radiated in the process of electron capture beta decay of partially polarized nuclei. The results of computation are presented for the $^{119}$Sb nuclei polarized by the strong hyperfine field in a ferromagnetic substance. This system was suggested as a possible source of directed neutrino radiation. We directly compute the spin excess of radiated neutrinos and show that it is greater than that estimated previously under simplifying assumptions.

nucl-th↗