arXiv subjects

Prathum Saraf

Publications and source records attributed to Prathum Saraf.

10 recordsLinked to original sources

arXiv2026

Resilient $j$=3/2 superconductivity in topological semimetal YPtBi

Cooper pairing in most of the known fermionic superfluids occurs via spin-1/2 quasiparticle interactions that lead to spin-singlet or spin-triplet pairing. In the topological semimetal YPtBi, strong spin-orbit coupling results in a band inversion between highly symmetric $s$- and $p$-like electronic bands and a degeneracy at the $Γ$ point that ensures the manifold of $j$=3/2 quasiparticle states thrive near the Fermi level, where superconducting pairing occurs. Here we study the effects of magnetic and nonmagnetic disorder and carrier density on this exotic superconducting pairing state. By varying levels of disorder and carrier densities by nearly two and three orders of magnitude, respectively, we show that the superconducting critical temperature of YPtBi has a remarkable robustness, with little variation across this span. Our results suggest that superconductivity in YPtBi may reside in a regime where phase stiffness, rather than pair formation, governs the transition temperature. The insensitivity of Cooper pairing to dramatic changes in quasiparticle environment in a $j$=3/2 superconductor highlights a new form of protection realized in topological high-spin superconductors.

cond-mat.supr-con↗

arXiv2026

Quantum oscillations and Dirac dispersion in tunable kagome lattice Lu$_{1-y}$Y$_y$(Nb$_{1-x}$Ta$_x$)$_6$Sn$_6$

Kagome lattice crystal systems present interesting symmetry-protected band structure features such as flat bands, van Hove singularities, and linearly dispersing Dirac/Weyl points that provide a rich playground for strongly correlated electron physics. Motivated by the rich properties and charge density wave evolution through the 1-6-6 series of compounds, we present our results in single crystal growth and characterization of the of Lu$_{1-y}$Y$_y$(Nb$_{1-x}$Ta$_x$)$_6$Sn$_6$ double-alloy system, including evolution of the charge density wave transition, electrical transport behavior and resultant phase diagrams. Using a novel growth technique, the synthesis of high quality crystals with extended length along the crystallographic $c$-axis allows us to follow the gradual suppression of charge density wave (CDW) order with Y substitution, and observe quantum oscillations in both magnetoresistance and magnetization throughout the series. We review the evolution of Fermi surfaces, effective masses and quasiparticle dispersion through the alloy series, revealing a decrease in size of Fermi surfaces that trends with both substitutions, and a scaling between effective mass and Fermi wavevector that suggests a regime with Dirac-like dispersion. The ability to fine-tune crystallographic, ground state and electronic dispersion properties of the \lit\ system with minimal impact of disorder opens a path torward further understanding the nature of the kagome lattice and its novel states and interactions.

cond-mat.str-el↗

arXiv2026

Quantum Oscillations and Superconductivity in YPtBi Under Pressure

The topological semimetal YPtBi has attracted considerable attention, owing to its novel superconducting and normal state properties. A strong band inversion from spin-orbit coupling allows the existence of $j=3/2$ quasiparticles near the Fermi level, which form Cooper pairs with angular momentum potentially higher than single or triplet states. In this report, we present high-pressure magnetotransport and Shubnikov-de Haas effect measurements on high-quality YPtBi up to $P = 2.08$ GPa. As a function of pressure, we observe a trend toward more insulating resistivity at low temperatures concomitant with a suppression of quantum oscillation amplitude. Together with a decrease of the upper critical field and significant increase in the Dingle temperature, the pressure-induced changes point to a weakening of the band inversion and potential tuning of the topological nature of YPtBi, suggesting pressure as a useful tool for understanding the nature of topology in other related half-Heusler compounds.

cond-mat.supr-con↗

arXiv2025

Thermoelectric quantum oscillations and Zeeman splitting in topological Dirac semimetal BaAl$_{4}$

Three-dimensional topological semimetals hosting Dirac or Weyl fermions are a new kind of materials class in which conduction and valence bands cross each other. Such materials harbor a nontrivial Berry phase, which is an additional geometrical phase factor arising along the path of an adiabatic surface and can give rise to experimentally measurable quantities such as an anomalous Hall component. Here we report a systematic study of quantum oscillations of thermoelectric power in single crystals of the topological Dirac nodal-line semimetal BaAl$_{4}$. We show that the thermoelectric power (TEP) is a sensitive probe of the multiple oscillation frequencies in this material, with two of these frequencies shown to originate from the three-dimensional Dirac band. The detected Berry phase provides evidence of the angular dependence and non-trivial state under high magnetic fields. We also have probed the signatures of Zeeman splitting, from which we have extracted the Landé $g$-factor for this system, providing further insight into the non-trivial topology of this family of materials.

cond-mat.str-el↗

arXiv2025

Tuning Incommensurate Charge Order in Ba$_{1-x}$Sr$_x$Al$_4$ and Ba$_{1-y}$Eu$_y$Al$_4$

The BaAl$_4$-type structure family is home to a vast landscape of interesting and exotic properties, with descendant crystal structures hosting a variety of electronic ground states including magnetic, superconducting and strongly correlated electron phenomena. BaAl$_4$ itself hosts a non-trivial topological band structure, but is otherwise a paramagnetic metal. However, the other members of the $A$Al$_4$ family ($A$= alkali earth), including SrAl$_4$ and EuAl$_4$, exhibit symmetry-breaking ground states including charge density wave (CDW) and magnetic orders. Here we investigate the properties of the solid solution series Ba$_{1-x}$Sr$_x$Al$_4$ and Ba$_{1-y}$Eu$_y$Al$_4$ using transport, thermodynamic and scattering experiments to study the evolution of the charge-ordered state as it is suppressed with Ba substitution to zero near 50% substitution in both systems. Neutron and x-ray diffraction measurements reveal an incommensurate CDW state in SrAl$_4$ with $c$-axis-oriented ordering vector (0, 0, 0.097) that evolves with Ba substitution toward a shorter wavelength. A similar progression is observed in the Ba$_{1-y}$Eu$_y$Al$_4$ series that also scales with the ordering temperature, revealing a universal correlation between charge-order transition temperature and ordering vector that points to a critical wavevector that stabilizes CDW order in both systems. We study the evolution of the phonon band structure in the Ba$_{1-x}$Sr$_x$Al$_4$ system, revealing the suppression of the CDW phase matches the suppression of a phonon instability at precisely the same momentum as observed in experiments, confirming the electron-phonon origin of charge order in this system.

cond-mat.str-el↗

arXiv2025

Complex single-site magnetism and magnetotransport in single-crystalline Gd$_{2}$AlSi$_{3}$

We present a detailed investigation of single-crystal samples of the magnetic compound Gd$_{2}$AlSi$_{3}$, which crystallizes in the $α$-ThSi$_2$ type tetragonal structure. We report the temperature and magnetic field dependence of the magnetic susceptibility, magnetization, heat capacity, electrical resistivity, and magnetoresistance for magnetic fields applied along both the tetragonal $c$-axis and in the basal $ab$-plane. X-ray diffraction measurements confirm a centrosymmetric, $I4_{1}/amd$ space group of the crystal structure. Despite single-site occupancy of the Gd position in this tetragonal structure, we identify two successive antiferromagnetic phase transitions at Neél temperatures 32~K and 23~K via magnetic susceptibility, heat capacity and transport measurements, as well as a complex magnetic interaction with a magnetic anisotropy that plays an important role in the direction-dependent transport response. Our identification of multiple magnetic phases in Gd$_{2}$AlSi$_{3}$, where Gd is the only magnetic species, helps to elucidate the field-induced skyrmionic behavior in the Gd-based intermetallic compounds.

cond-mat.str-el↗

arXiv2023

Potential Lifshitz transition at optimal substitution in nematic pnictide Ba$_{1-x}$Sr$_x$Ni$_2$As$_2$

BaNi$_2$As$_2$ is a structural analog of the pnictide superconductor BaFe$_2$As$_2$, which, like the iron-based superconductors, hosts a variety of ordered phases including charge density waves (CDWs), electronic nematicity, and superconductivity. Upon isovalent Sr substitution on the Ba site, the charge and nematic orders are suppressed, followed by a sixfold enhancement of the superconducting transition temperature ($T_c$). To understand the mechanisms responsible for enhancement of $T_c$, we present high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements of the Ba$_{1-x}$Sr$_{x}$Ni$_2$As$_2$ series, which agree well with our density functional theory (DFT) calculations throughout the substitution range. Analysis of our ARPES-validated DFT results indicates a Lifshitz transition and reasonably nested electron and hole Fermi pockets near optimal substitution where $T_c$ is maximum. These nested pockets host Ni $d_{xz}$/$d_{yz}$ orbital compositions, which we associate with the enhancement of nematic fluctuations, revealing unexpected connections to the iron-pnictide superconductors. This gives credence to a scenario in which nematic fluctuations drive an enhanced $T_c$.

cond-mat.supr-con↗

arXiv2023

Charge Order Evolution of Superconducting BaNi2As2 Under High Pressure

BaNi$_2$As$_2$, a non-magnetic superconductor counterpart to BaFe$_2$As$_2$, has been shown to develop nematic order, multiple charge orders, and a dramatic six-fold enhancement of superconductivity via isovalent chemical substitution of Sr for Ba. Here we present high pressure single-crystal and powder x-ray diffraction measurements of BaNi$_2$As$_2$ to study the effects of tuning lattice density on the evolution of charge order in this system. Single-crystal X-ray experiments track the evolution of the incommensurate (Q=0.28) and commensurate (Q=0.33 and Q=0.5) charge orders, and the tetragonal-triclinic distortion as a function of temperature up to pressures of 10.4 GPa, and powder diffraction experiments at 300 K provide lattice parameters up to 17 GPa. We find that applying pressure to BaNi$_2$As$_2$ produces a similar evolution of structural and charge-ordered phases as found as a function of chemical pressure in Ba$_{1-x}$Sr$_{x}$Ni$_2$As$_2$ , with coexisting commensurate charge orders appearing on increasing pressure. These phases also exhibit a similar abrupt cutoff at a critical pressure of (9 $\pm$ 0.5) GPa, where powder diffraction experiments indicate a collapse of the tetragonal structure at higher temperatures. We discuss the relationship between this collapsed tetragonal phase and the discontinuous phase boundary observed at the optimal substitution value for superconductivity in Ba$_{1-x}$Sr$_{x}$Ni$_2$As$_2$

cond-mat.str-el↗

arXiv2022

Quasi-2D Fermi surface of superconducting line-nodal metal CaSb$_2$

We report on the Fermi surfaces and superconducting parameters of CaSb$_2$ single crystals (superconducting below $T_{\text{c}}\sim 1.8~\text{K}$) grown by the self-flux method. The frequency of de-Haas-van-Alphen and Shubnikov-de-Haas oscillations evidences a quasi-two-dimensional (quasi-2D) Fermi surface, consistent with one of the Fermi surfaces forming Dirac lines predicted by first-principles calculations. Measurements in the superconducting state reveal that CaSb$_2$ is close to a type-I superconductor with the Ginzburg-Landau (GL) parameter of around unity. The temperature dependence of the upper critical field $H_{\text{c2}}$ is well described by a model considering two superconducting bands, and the enhancement of the effective mass estimated from $H_{\text{c2}}(0~\text{K})$ is consistent with the quasi-2D band observed by the quantum oscillations. Our results indicate that a quasi-2D band forming Dirac lines contributes to the superconductivity in CaSb$_2$.

cond-mat.supr-con↗

arXiv2019

Pressure-Driven Valence Increase and Metallization in Kondo Insulator Ce$_3$Bi$_4$Pt$_3$

We report the results of high pressure x-ray diffraction, x-ray absorption, and electrical transport measurements of Kondo insulator Ce$_3$Bi$_4$Pt$_3$ up to 42 GPa, the highest pressure reached in the study of any Ce-based KI. We observe a smooth decrease in volume and movement toward intermediate Ce valence with pressure, both of which point to increased electron correlations. Despite this, temperature-dependent resistance data show the suppression of the interaction-driven ambient pressure insulating ground state. We also discuss potential ramifications of these results for the predicted topological KI state.

cond-mat.str-el↗