arXiv subjects

Sajilesh K. P.

Publications and source records attributed to Sajilesh K. P..

17 recordsLinked to original sources

arXiv2026

Unconventional Superconductivity in the Chiral Topological Semimetal Ag2Pd3S

Chiral crystals provide a unique setting where broken inversion symmetry, strong spin-orbit coupling, and electronic topology intertwine, yet superconductivity in intrinsically chiral materials remains rare. Here, we report unconventional superconductivity in the chiral topological semimetal Ag$_2$Pd$_3$S, an enantiomorphic analog of natural mineral coldwellite, crystallizing in the right-handed space group $P4_132$. Bulk superconductivity with a transition temperature $T_C = 1.1(2)$ K is confirmed by electrical resistivity, magnetization, and specific-heat measurements. Muon spin rotation and relaxation ($μ$SR) experiments reveal a fully gapped superconducting state that spontaneously time-reversal symmetry (TRS) breaking establishing Ag$_2$Pd$_3$S as the first chiral topological semimetal superconductor exhibiting intrinsic TRS breaking. First-principles calculations uncover multiple multifold band crossings near the Fermi level, hosting Kramers-Weyl, double spin-1, and spin-3/2 quasiparticles with large topological charges. These unconventional fermions generate symmetry-protected topological surface states and underscore the nontrivial topology of the normal state. Symmetry analysis based on the Ginzburg-Landau theory suggests a loop-supercurrent-ordered superconducting state, yielding a full gap alongside spontaneous TRS breaking. The coexistence of TRS-breaking superconductivity and chiral multifold fermions identifies Ag$_2$Pd$_3$S as a platform for realizing intrinsic superconducting diode effects and chirality-induced spin selectivity, offering a transformative pathway toward dissipationless topological quantum technologies.

cond-mat.supr-con↗

arXiv2026

Conventional superconductivity in single-crystalline BiPt

Binary Bi-Pd/Pt systems have attracted a lot of interest because of their topologically non-trivial nature along with superconductivity. We report the structural and superconducting properties of high-quality single-crystalline BiPt using a comprehensive range of experimental techniques, including X-ray diffraction, electron microscopy, muon spin rotation/relaxation (μSR), magnetization, resistivity, and heat capacity. Our findings establish that BiPt is a weak type-II superconductor with a transition temperature (Tc) of 1.2 K which exhibits pronounced anisotropic superconducting characteristics attributed to its hexagonal crystal structure. Magnetization and electronic transport studies reveal that BiPt lies within the dirty limit, while μSR and heat capacity data indicate conventional s-wave superconductivity that maintains time-reversal symmetry. This work provides valuable insights into the pairing symmetry and superconducting mechanism of topologically trivial BiPt, a sound comparison system for other Bi-based topologically nontrivial superconductors.

cond-mat.supr-con↗

arXiv2026

Machine Learning-Guided Discovery of Kagome Superconductors YRu3B2 and LuRu3B2

We report the experimental discovery of bulk superconductivity in two kagome lattice compounds, YRu$_3$B$_2$ and LuRu$_3$B$_2$, which were predicted through machine learning-accelerated high-throughput screening combined with first principles calculations. These materials crystallize in the hexagonal CeCo$_3$B$_2$-type structure with planar kagome networks formed by Ru atoms. We observe superconducting critical temperatures of $T_{c} = 0.81$~K for YRu$_3$B$_2$ and $T_{c} = 0.95$~K for LuRu$_3$B$_2$, confirmed through magnetization and specific heat measurements. Both compounds exhibit nearly 100\% superconducting volume fractions, demonstrating bulk superconductivity. Compared with LaRu$_3$Si$_2$, YRu$_3$B$_2$ and LuRu$_3$B$_2$ show a more dispersive Ru local $d_{x^2-y^2}$ quasi-flat band (and thus a reduced DOS at $E_F$) together with an overall hardening of the phonon spectrum, both of which lower the electron-phonon coupling (EPC) constant $λ$. Meanwhile, the dominant real-space EPC between Ru local $d_{x^2-y^2}$ states and the low-frequency Ru in-plane local $x$ branch remains nearly unchanged, indicating that the reduction of $λ$ originates from the $d_{x^2-y^2}$ DOS reduction and the overall phonon hardening. Superfluid weight calculations show that conventional contributions dominate over quantum geometric effects due to the dispersive nature of bands near the Fermi level. This work demonstrates the effectiveness of integrating machine learning screening, first principles theory, and experimental synthesis for accelerating the discovery of new superconducting materials.

cond-mat.supr-con↗

arXiv2025

Chiral charge density wave in 4Hb- and 1T-TaS$_2$: The Role of interlayer coupling

We use micro-angle-resolved photoemission spectroscopy (micro-ARPES) to investigate chiral charge density waves (CDWs) in 4Hb-TaS$_2$ with micron-scale spatial resolution. In the 1T layers of 4Hb-TaS$_2$, we uncover coexisting left- and right-handed CDW domains and resolve four distinct spectral patterns arising from the interplay of chirality and rotational stacking. In contrast, bulk 1T-TaS$_2$ exhibits a uniform chirality. In addition, 4Hb-TaS$_2$ shows negligible out-of-plane dispersion of the 1T-derived bands, in contrast to the pronounced interlayer coupling observed in bulk 1T-TaS$_2$. Density functional theory (DFT) calculations corroborate this picture, revealing that the interlayer interaction of the chiral order in 4Hb-TaS$_2$ is nearly two orders of magnitude weaker than in the 1T polytype. Our findings establish 4Hb-TaS$_2$ as a quasi-two-dimensional platform for exploring tunable chiral CDW phenomena.

cond-mat.str-el↗

arXiv2025

Ground-states of the Shastry-Sutherland Lattice Materials Gd$_2$Be$_2$GeO$_7$ and Dy$_2$Be$_2$GeO$_7$

The recent realization that the rare-earth melilites RE$_2$Be$_2$GeO$_7$ host the Shastry-Sutherland lattice within planes of RE$^{3+}$ ions has sparked a number of studies. This family of materials lacks appreciable site mixing and conductivity, making them promising candidates for the Shastry-Sutherland model. Herein, we present the magnetic ground states of two of these rare-earth melilites: RE = Gd and Dy. We find, through measurements of magnetic susceptibility, magnetization, and specific heat capacity (RE = Dy only), that these two melilites are antiferromagnets (T$_N$ $\sim$~1~K). Gd$_2$Be$_2$GeO$_7$, in accordance with its electronic configuration, has isotropic single-ion anisotropy but shows a quadratic contribution to its magnetization. Dy$_2$Be$_2$GeO$_7$ has Ising-like single-ion ansiotropy and is likely an effective spin-$1/2$ system. Both materials exhibit metamagnetic transitions. We identify this transition in Dy$_2$Be$_2$GeO$_7$, occurring at 86(1)~mT for T=500~mK, to likely be a spin-flip transition.

cond-mat.str-el↗

arXiv2025

Emergence of a Fermi-surface in the current-driven Hidden state of 1T-TaS$_2$

The origin of the insulating state in 1T-TaS$_2$ has long been a subject of debate. A short current pulse transforms this insulating state into a metastable metallic phase. Using micro-ARPES, we investigate the electronic structure of this phase and uncover spatially dependent modifications caused by the current pulse. In some regions of the sample, a Fermi surface emerges, while others remain gapped. Detailed band structure analysis reveals that the metallic regions exhibit an electronic structure similar to that observed in the high-temperature phase of 1T-TaS$_2$, characterized by suppressed energy gaps and bands crossing the Fermi level. Furthermore, the metallic and insulating regions display distinct dispersions along the out-of-plane direction. These observations suggest a scenario in which the current pulse breaks the star-of-David dimers characteristic of the insulating phase, implicating these dimers as the likely origin of the insulating behavior in 1T-TaS$_2$.

cond-mat.str-el↗

arXiv2024

Fractionalized Magnetization Plateaus in the Shastry-Sutherland Lattice Material Er$_2$Be$_2$GeO$_7$

The experimental study of magnetism on the Shastry-Sutherland lattice has been ongoing for more than two decades, following the discovery of the first Shastry-Sutherland lattice materials SrCu$_2$(BO$_3$)$_2$. However, the study of Shastry-Sutherland systems is often complicated by the requirements of high magnetic fields ($>$~20~T SrCu$_2$(BO$_3$)$_2$) or the presence of itinerate electrons (e.g. REB$_4$). In this paper, we present the magnetic properties of the Shastry-Sutherland lattice material Er$_2$Be$_2$GeO$_7$. Like SrCu$_2$(BO$_3$)$_2$, Er$_2$Be$_2$GeO$_7$ exhibits fractionalized magnetization plateaus. Unlike SrCu$_2$(BO$_3$)$_2$, Er$_2$Be$_2$GeO$_7$ exhibits long-range order below $\sim1~$K, and the plateaus are accessible using commercial laboratory equipment, occurring for fields <~1~T. The fractions of magnetization present are closest to $\frac{1}{4}$ and $\frac{1}{2}$ of the full powder moment; we show that the $\frac{1}{4}$ magnetization plateau in Er$_2$Be$_2$GeO$_7$ has a classical analog, well represented by the magnetic structure (canted antiferromagnetic) observed in powder neutron diffraction. The lack of itinerate electrons, chemical disorder, and the low fields required to access the fractionalized magnetization plateaus promises Er$_2$Be$_2$GeO$_7$ to be a prime candidate for the study of frustrated magnetism on the Shastry-Sutherland lattice.

cond-mat.str-el↗

arXiv2024

Ising superconductivity in the bulk incommensurate layered material (PbS)$_{1.13}$(TaS$_2$)

Exploiting the spin-valley degree of freedom of electrons in materials is a promising avenue for energy-efficient information storage and quantum computing. A key challenge in utilizing spin-valley polarization is the realization of spin-valley locking in bulk systems. Here, we report a comprehensive study of the noncentrosymmetric bulk misfit compound (PbS)$_{1.13}$(TaS$_2$), showing a strong spin-valley locking. Our investigation reveals Ising superconductivity with a transition temperature of 3.14 K, closely matching that of a monolayer of TaS$_2$. Notably, the absence of charge density wave (CDW) signatures in transport measurements suggests that the PbS layers primarily act as spacers between the dichalcogenide monolayers. This is further supported by angle-resolved photoemission spectroscopy (ARPES), which shows negligible interlayer coupling, a lack of dispersion along the $k_{\perp}$ direction and significant charge transfer from the PbS to the TaS$_2$ layers. Spin resolved ARPES shows strong spin-valley locking of the electronic bands. Muon spin rotation experiments conducted in the vortex phase reveal an isotropic superconducting gap. However, the temperature dependence of the upper critical field and low-temperature specific heat measurements suggest the possibility of multigap superconductivity. These findings underscore the potential of misfit compounds as robust platforms for both realizing and utilizing spin-valley locking in bulk materials, as well as exploring proximity effects in two-dimensional structures.

cond-mat.supr-con↗

arXiv2024

A Candidate for the Quantum Spin Liquid Ground-State in the Shastry-Sutherland Lattice Material Yb$_2$Be$_2$GeO$_7$

The quasi-2D Shastry-Sutherland model has remained topical in the field of condensed matter physics for the last two decades, following the experimental realization of the model in the material SrCu$_2$(BO$_3$)$_2$. Since then, research into the Shastry-Sutherland system has revealed more nuanced physics than initially predicted; recent theoretical works have even predicted a quantum spin liquid phase may exist. Herein, we report on a new Shastry-Sutherland lattice material, Yb$_2$Be$_2$GeO$_7$, of the rare-earth melilite family RE$_2$Be$_2$GeO$_7$. We find, through SQUID magnetometry, powder neutron diffraction, specific heat capacity, and muon spin relaxation, that Yb$_2$Be$_2$GeO$_7$ lacks magnetic order and exhibits persistent spin dynamics to at least 17 mK. We propose the Shastry-Sutherland lattice material Yb$_2$Be$_2$GeO$_7$ as a candidate to host a quantum spin liquid ground-state.

cond-mat.str-el↗

arXiv2024

The transition-metal-dichalcogenide family as a superconductor tuned by charge density wave strength

Metallic transition metal dichalcogenides (TMDs), consisting of H-NbSe$_2$, H-NbS$_2$, H-TaSe$_2$ and H-TaS$_2$, remain superconducting down to a thickness of a single layer. In these materials, thickness affects a variety of properties, including Ising protection, two-band superconductivity, and the critical temperature $T_C$, which decreases for the Nb-based, and increases for the Ta-based materials. This contradicting trend is puzzling, and has precluded the development of a unified theory. We approach the question of thickness-evolution of $T_C$ and the superconducting gap $Δ$ by measuring high-resolution tunneling spectra in TaS$_2$-based stacked devices. Our measurements allow for simultaneous evaluation of $Δ$, $T_C$, and the upper critical field $H_{C2}$. The latter, we find, is strongly enhanced towards the single-layer limit, following a $H_{C2} \propto Δ^2$ proportionality ratio. Our main finding is that the same ratio holds for the entire family of metallic TMDs: TaS$_2$ and NbSe$_2$ of all thicknesses, bulk TaSe$_2$ and bulk NbS$_2$, extending over 4 orders of magnitude in $H_{C2}$ and covering both clean and dirty limits. We propose that this tunability across the TMD family is controlled by the competing charge density wave (CDW) phase. Using Gor'kov's theory, we calculate how a CDW order affects the quasiparticle density of states and the resulting $T_C$ and $H_{C2}$. Our results suggest that CDW is the key determinant factor limiting $T_C$ in the TMD family. They also show that $H_{C2}$ is universally enhanced by a factor of two orders of magnitude above the expected value, an effect that remains an open question.

cond-mat.supr-con↗

arXiv2024

Evidence for conventional superconductivity in Bi$_2$PdPt and prediction of topological superconductivity in disorder-free $γ$-BiPd

We present comprehensive investigations into the structural, superconducting, and topological properties of Bi$_2$PdPt. Magnetization and heat capacity measurements performed on polycrystalline Bi$_2$PdPt demonstrate a superconducting transition at $\approx$ 0.8 K. Moreover, muon spin relaxation/rotation ($μ$SR) measurements present evidence for a time reversal symmetry preserving, isotropically gapped superconducting state in Bi$_2$PdPt. We have also performed density-functional theory (DFT) calculations on Bi$_2$PdPt alongside the more general isostructural systems, BiPd$_{x}$Pt$_{1-x}$, of which Bi$_2$PdPt and $γ$-BiPd are special cases for $x=0.5$ and $x=1$ respectively. We have calculated the $Z_2$ topological index from our DFT calculations for a range of substitution fractions, $x$, between $x=0$ and $x=1$ characterizing the topology of the band structure. We find a non-trivial topological state when $x>0.75$ and a trivial topological state when $x<0.75$. Therefore our results indicate that BiPd$_{x}$Pt$_{1-x}$ could be a topological superconductor for $x>0.75$.

cond-mat.supr-con↗

arXiv2023

Evidence for non-unitary triplet-pairing superconductivity in noncentrosymmetric TaRuSi and comparison with isostructural TaReSi

We have studied the superconducting properties of the isostructural ternary noncentrosymmetric superconductors TaXSi (X = Re, Ru) with the help of muon spin rotation/relaxation ($μ$SR) and density functional theory calculations. Our transverse-field $μ$SR measurements indicate isotropic s-wave superconductivity in TaReSi and multi-gap superconductivity in TaRuSi. Zero-field $μ$SR measurements, highly sensitive to very small magnetic fields, and no evidence for spontaneous fields in the superconducting state of TaReSi, whereas we observe small spontaneous fields that onset with superconductivity indicating broken time-reversal symmetry (TRS) superconductivity in TaRuSi. Using density functional theory calculations, we find that spin-orbit coupling is relatively weak in TaRuSi and strong in TaReSi. Using symmetry analysis, we attribute the broken time-reversal symmetry (TRS) in TaRuSi to a non-unitary triplet pairing state. Such a state is not allowed in the presence of strong spin-orbit coupling: our finding of no evidence for broken TRS in TaReSi is consistent with this expectation.

cond-mat.supr-con↗

arXiv2021

Superconductivity in noncentrosymmetric NbReSi investigated by muon spin rotation and relaxation

Noncentrosymmetric materials are promising paradigm to explore unconventional superconductivity. In particular, several Re containing noncentrosymmetric materials have attracted considerable attention due to a superconducting state with a broken time reversal symmetry. A comprehensive study on the superconducting ground state of NbReSi was investigated using magnetization, resistivity, and muon spin rotation/relaxation measurements. Zero field muon spectroscopy results showed the absence of any spontaneous magnetic field below the superconducting transition temperature, T$ _{c} $ = 6.29 K, indicating the preserved time-reversal symmetry. Transverse field muon spin rotation measurements confirms a s-wave nature of the sample with $Δ(0)/k_{B}T_{c} $ = 1.726. This study urges further investigation on more noncentrosymmetric materials to elucidate the selective appearance of unconventional nature and unveil its dependence on antisymmetric spin-orbit coupling strength.

cond-mat.supr-con↗

arXiv2020

Superconducting properties of the non-centrosymmetric Superconductors TaXSi (X= Re, Ru)

We have investigated the ternary noncentrosymmetric superconductors TaXSi (X=Re, Ru) by magnetization, resistivity, and specific heat measurements. The samples crystallize in orthorhombic TiFeSi structure having superconducting transition Tc = 5.32 K and 3.91 K, for TaReSi and TaRuSi respectively. Specific heat measurements indicated an s-wave nature of both materials with a moderately coupled nature. However, a low value of specific heat jump and the concave nature of the upper critical field suggests a nontrivial superconducting gap.

cond-mat.supr-con↗

arXiv2020

Study of the superconducting ground state of topological superconducting candidates Ti$_{3}$X (X = Ir, Sb)

The topologically non-trivial band structure of A15 compounds has drawn attention owing to the possible realization of topological superconductivity. Here, we report a microscopic investigation of the superconducting ground state in A15 compound Ti$_{3}$X (X = Ir, Sb) by muon spectroscopy measurements. Zero field muon measurements have shown that time-reversal symmetry is preserved in these materials. Furthermore, specific heat and a transverse field muon spectroscopy measurement rule out any possibility to have a nodal or anisotropic superconducting gap, revealing a conventional s-wave nature in the superconducting ground state. This work classifies A15 compound Ti$_{3}$X (X = Ir, Sb) as a time-reversal preserved topological superconductor.

cond-mat.supr-con↗

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↗

arXiv2017

Superconducting properties of the noncentrosymmetric superconductor TaOs

The noncentrosymmetric superconductor TaOs has been characterized using x-ray diffraction, resistivity, magnetization, and specific heat measurements. Magnetization and specific heat measurements show a bulk superconducting transition at 2.07 K. These measurements suggest that TaOs is a weakly coupled type-II superconductor. The electronic specific heat in the superconducting state can be explained by the single-gap BCS model, suggesting s-wave superconductivity in TaOs.

cond-mat.supr-con↗