arXiv subjects

Gohil S. Thakur

Publications and source records attributed to Gohil S. Thakur.

At least 19 recordsLinked to original sources

arXiv2026

Discovery of Superconductivity in a Bulk Moire Superlattice Material

Moire materials provide a versatile platform realizing emergent electronic states arising from enhanced correlation due to flat bands. A variety of phenomena including superconductivity, low dimensional ferromagnetism, Mott insulating phase, topological phenomena have been reported in such systems. To date, moire phenomena have been predominantly explored in artificially assembled low-dimensional van der Waals heterostructures, where relative twist and lattice alignment are controlled during device fabrication. Recently, intrinsically grown bulk moire crystals have emerged as a complementary materials platform, in which lattice mismatch between constituent layers generates a coherent moire superlattice throughout the bulk crystal. Here we report the evidence of bulk superconductivity in single crystals of a recently reported bulk Moire materials (Sr6TaS8)1+x(TaS2)8 under ambient pressure conditions. The material exhibits a superconducting transition at Tc = 2.5 K, evidenced consistently by electrical transport, magnetic susceptibility, and heat-capacity measurements on single-crystal and polycrystalline samples. Transport measurements reveal a pronounced anomaly near 270 K, suggestive of a charge-density-wave transition in this moire system. The observation of bulk superconductivity establishes superconductivity as an emergent phase in this intrinsically synthesized moire material and highlights bulk moire crystals as a promising platform for investigating correlated quantum phenomena beyond artificially assembled two-dimensional heterostructures.

cond-mat.supr-con↗

arXiv2026

Near-Room-Temperature Antiferromagnetic Ordering in the Quadruple Perovskite Sr4NaRu3O12

We report the synthesis, structure and magnetic properties of two 1:3 ordered quadruple perovskites Sr4MRu3O12 (M = Li and Na). Sr4NaRu3O12 crystallizes in the centrosymmetric space group R-3 and Sr4LiRu3O12 appears to be isostructural to the Na compound based on the PXRD data. In Sr4NaRu3O12, both Na and Ru are predominantly ordered at the B sites (here Na/Li and Ru) and the structure contains only corner-connected RuO6 and NaO6 octahedra. This atomic ordering also leads to a rather large unit cell with a = 11.25 Å and c = 27.6 Å compared to the basic 12R structure (a = 5.5 Å and c ~ 27 Å). Magnetic measurements reveal that Sr4NaRu3O12 undergoes a magnetic transition to an antiferromagnetic state below TN ~ 265 K which is confirmed by DSC and neutron diffraction. The Ru moments show a collinear antiferromagnetic spin alignment along the hexagonal c axis with a propagation vector k = (0, 0, 1.5). Interestingly, those Ru moments lying on the three-fold roto-inversion do not significantly contribute to the magnetic order, since they are located between antiferromagnetically coupled Ru atoms and are therefore probably highly frustrated. Band structure calculations on Sr4NaRu3O12 complement the observed magnetic ground state and a semiconducting behavior in the compound. Sr4LiRu3O12 shows a magnetic anomaly below 110 K, possibly associated with competing ferromagnetic and antiferromagnetic interactions.

cond-mat.str-el↗

arXiv2025

Crystal Growth, Band Structure, Magnetism and Electrochemical Properties of Hexavalent Strontium Ruthenium Oxyhydroxide

Ruthenates comprise an interesting class of materials with a wide range of extremely exciting properties, and thus the discovery of new stable ruthenates remains an active area of investigation. We report the crystal growth and comprehensive studies including crystal and electronic structure, magnetic and electrochemical properties of a hexavalent ruthenium oxyhydroxide Sr3Ru2O9H2 prepared through a low-temperature hydrothermal method. Single crystals and powder samples of this phase are isolated by optimising the Sr(OH)2 to KRuO4 ratio while maintaining a high base concentration. The new structure consists of a rare five-coordinated RuVI featuring isolated trigonal prisms and crystallising in a non-centrosymmetric tetragonal system. Isolated Ru polyhedra leading to a large spatial distance ~ 50 pm between the Ru metal centres render the compound paramagnetic despite strong antiferromagnetic correlation. Band structure calculation suggests a metal-like electronic ground state with mostly Ru d and O p orbitals contributing to the Fermi surface. The electrochemical performance of Sr3Ru2O9H2, though not as impressive as RuO2, remains relevant and is on par with other reported OER catalysts.

cond-mat.mtrl-sci↗

arXiv2024

Sr4Os3O12- A Layered Osmate (V,VI) that is Magnetic close to Room Temperature

Black crystals of the mixed-valence osmate(V,VI) Sr4Os3O12 were grown via a gas phase reaction in an evacuated silica tube. The material is attracted to a permanent magnet at room temperature (295 K) but loses this property when heated or cooled. In this temperature interval, soft magnetic behavior with vanishing coercivity is observed, but the saturation magnetization is only 0.05 MuB per formula unit. Resistivity measurements show that Sr4Os3O12 is a semiconductor with a small band gap of about 0.26 eV at room temperature. X-ray diffraction on a single-crystal revealed a rhombohedral structure with the space group R-3m and lattice parameters ar = 554.64(2) pm and cr = 2700.1(1) pm at 300(1) K. The compound crystallizes in the La4Ti3O12 structure type and is isostructural to Sr4CoRe2O12. The structure is a rhombohedral stack of layered blocks, each of which can be considered as a section of three layers of the cubic perovskite structure cut perpendicular to one of its threefold axes. The Os-O-Os bond angle of about 175{/deg} favors superexchange that leads to antiferromagnetic coupling between the osmium atoms with 5d3 and 5d2 configurations. Sr4Os3O12 exhibits strong lattice dynamics. One aspect is the antiferro-rotative lattice modes of the corner-sharing [OsO6] octahedra, which freeze upon cooling. At 100 K, an ordered, yet twinned triclinic superstructure is formed. Strong spin-orbit coupling and other effects cause deformations of the [OsO6] octahedra that differ significantly at 300 K and 100 K, suggesting a change in the electronic configuration. Competing ground states could also explain the temperature dependent band gap and the magnetic fluctuations manifested in the magnetization peak at room temperature.

cond-mat.mtrl-sci↗

arXiv2023

On the synthesis methodologies to prepare Pb$_9$Cu(PO$_4$)$_6$O -- phase, composition, magnetic analysis and absence of superconductivity

We present the results of our various attempts to prepare the presumably room-temperature and ambient-pressure superconducting compound Pb$_9$Cu(PO$_4$)$_6$O (LK-99). We experimented with various starting materials, and used several synthesis techniques like, sealed quartz tubes and air-sintering pathways to prepare the reported phase. Repetition of the exact synthesis process followed by Lee et al failed to reproduce the superconducting phase yielding only a multiphase sample. None of our prepared samples exhibits Meissner effect or Levitation. Very importantly, no copper (or only a trace amount) could be detected in any of the designated LK-99 phase with PXRD pattern identical to the reported one. Additionally, some dark greyish flakes in some samples responded towards the magnet in a way imitating half-levitation. The magnetic measurement on those sample suggest it is diamagnetic in the measured temperature range of 2-325 K but show a weak soft ferromagnetic behavior at 2 K, the origin of which is still unknown to us.

cond-mat.supr-con↗

arXiv2022

New Buckled Honeycomb Lattice Compound Sr3CaOs2O9 Exhibiting Antiferromagnetism above Room Temperature

Synthesis, crystal structure and magnetic properties of a new 2:1 ordered triple perovskite Sr3CaOs2O9 are reported. The compound crystallizes in P21/c space group and features a unique buckled honeycomb lattice of osmium. It exhibits long-range antiferromagnetic ordering with a high Neel temperature of 385 K as confirmed by susceptibility, heat capacity and neutron diffraction measurements and is electrically insulating. This compound is also the first example of a 2:1 ordered osmate perovskite. Theoretical investigations indicate that Sr3CaOs2O9 features a sizeable antiferromagnetic exchange between the puckered planes resulting in a high TN. The magnetic properties of the known compound Sr3CaRu2O9 are elucidated in comparison. It shows antiferromagnetic order below TN = 200 K.

cond-mat.mtrl-sci↗

arXiv2022

Signatures of Weyl fermion annihilation in a correlated kagome magnet

The manipulation of topological states in quantum matter is an essential pursuit of fundamental physics and next-generation quantum technology. Here we report the magnetic manipulation of Weyl fermions in the kagome spin-orbit semimetal Co$_3$Sn$_2$S$_2$, observed by high-resolution photoemission spectroscopy. We demonstrate the exchange collapse of spin-orbit-gapped ferromagnetic Weyl loops into paramagnetic Dirac loops under suppression of the magnetic order. We further observe that topological Fermi arcs disappear in the paramagnetic phase, suggesting the annihilation of exchange-split Weyl points. Our findings indicate that magnetic exchange collapse naturally drives Weyl fermion annihilation, opening new opportunities for engineering topology under correlated order parameters.

cond-mat.str-el↗

arXiv2021

Crystal Growth of a New 8H Perovskite Sr8Os6.3O24 Exhibiting High TC Ferromagnetism

Single crystals of a new twinned hexagonal perovskite compound Sr8Os6.3O24 have been synthesized, and structural and magnetic properties have been determined. The compound crystallizes in a hexagonal cell with lattice parameters a = 9.6988(3) Å and c = 18.1657(5) Å. The structure is an eight-layered hexagonal B-site deficient perovskite with the layer sequence (ccch)2 and represents the first example of a hexagonal structure among 5d oxides adopting a twin option. The sample shows spontaneous ferromagnetic magnetization below 430 K with a small saturation moment of 0.11 μB/Os ion. This is the highest Curie temperature (TC) reported for any bulk perovskite containing only 5d ions at the B site.

cond-mat.mtrl-sci↗

arXiv2021

Na9Bi5Os3O24: A Unique Diamagnetic Oxide Featuring a Pronouncedly Jahn-Teller Compressed Octahedral Coordination of Osmium(VI)

The Jahn-Teller theorem constitutes one of the most popular and stringent concepts, applicable to all fields of chemistry. In open shell transition elements chemistry and physics, 3d4, 3d9, and 3d7(low-spin) configurations in octahedral complexes serve as particular illustrative and firm examples, where a striking change (distortion) in local geometry is associated to a substantial reduction of electronic energy. However, there has been a lasting debate, about the fact that the octahedra are found to exclusively elongate, (at least for eg electrons). Against this background, the title compound displays two marked features, (1) the octahedron of oxygen atoms around Os6+ (d2) is drastically compressed, in contrast to the standard JT expectations, and (2) the splitting of the t2g set induced by this compression is extreme, such that a diamagnetic ground state results. What we see is obviously a Jahn-Teller distortion resulting in a compression of the respective octahedron and acting on the t2g set of orbitals. Both these issues are unprecedented. Noteworthy, the splitting into a lower dxy (hosting two d electrons with opposite spin) and two higher dxz and dyz orbitals is so large that for the first time ever the Hund's coupling for t2g electrons is overcome. We show that these effects are not forced by structural frustration, the structure offers sufficient space for Os to shift the apical oxygen atoms to a standard distance. Local electronic effects appear to be responsible, instead. The relevance of these findings is far reaching, since they provide insights in the hierarchy of perturbations defining ground states of open shell electronic systems. The system studied here, offers substantially more structural and compositional degrees of freedom, such that a configuration could form that enables Os6+ to adopt its apparently genuine diamagnetic ground state.

cond-mat.mtrl-sci↗

arXiv2020

Crystal Growth of Spin-Frustrated Ba4Nb0.8Ir3.2O12: A Possible Spin Liquid Material

Polycrystalline Ba4NbIr3O12 has recently been shown to be a promising spin liquid candidate. We report an easy and reliable method to grow millimeter-sized single crystals of this trimer based spin liquid candidate material with the actual stoichiometry of Ba4Nb0.8Ir3.2O12. The growth of large crystals is achieved using BaCl2 as flux. The crystals show hexagonal plate-like habit with edges up to 3 mm in length. The structure is confirmed by single crystal X-ray diffraction and is found to be the same as of previously reported phase Ba12Nb2.4Ir9.6O36 [Ba4Nb0.8Ir3.2O12], indeed with a mixed occupancy of Nb/Ir at 3a site. The magnetic and calorimetric study on the individual single crystals confirms the possibility of a spin liquid state consistent with a recent report on a polycrystalline sample

cond-mat.mtrl-sci↗

arXiv2020

Intrinsic anomalous Hall effect in Ni-substituted magnetic Weyl semimetal Co3Sn2S2

Topological materials have recently attracted considerable attention among materials scientists as their properties are predicted to be protected against perturbations such as lattice distortion and chemical substitution. However, any experimental proof of such robustness is still lacking. In this study, we experimentally demonstrate that the topological properties of the ferromagnetic kagome compound Co3Sn2S2 are preserved upon Ni substitution. We systematically vary the Ni content in Co3Sn2S2 single crystals and study their magnetic and anomalous transport properties. For the intermediate Ni substitution, we observe a remarkable increase in the coercive field while still maintaining significant anomalous Hall conductivity. The large anomalous Hall conductivity of these compounds is intrinsic, consistent with first-principle calculations, which proves its topological origin. Our results can guide further studies on the chemical tuning of topological materials for better understanding.

cond-mat.mtrl-sci↗

arXiv2017

Magnetic structures of rare earth intermetallic compounds RCuAs$_2$ (R = Pr, Nd, Tb, Dy, Ho, and Yb)

Neutron scattering studies have been carried out on polycrystalline samples of a series of rare earth intermetallic compounds RCuAs$_2$ (R = Pr, Nd, Dy, Tb, Ho and Yb) as a function of temperature to determine the magnetic structures and the order parameters. These compounds crystallize in the ZrCuSi$_2$ type structure, which is similar to that of the RFeAsO (space group P4/nmm) class of iron-based superconductors. PrCuAs$_2$ develops commensurate magnetic order with K = (0, 0, 0.5) below T$_N$ = 6.4 (2) K, with the ordered moments pointing along the c-axis. The irreducible representation analysis shows either a $Γ$$^1_2$ or $Γ$$^1_3$ representation. NdCuAs$_2$ and DyCuAs$_2$ order below T$_N$ = 3.54(5) K and T$_N$ = 10.1(2) K, respectively, with the same ordering wave vector but the moments lying in the a-b plane (with a $Γ$$^2_9$ or $Γ$$^2_{10}$ representation). TbCuAs$_2$ and HoCuAs$_2$ exhibit incommensurate magnetic structures below T$_N$ = 9.44(7) and 4.41(2) K, respectively. For TbCuAs$_2$, two separate magnetic ordering wave vectors are established as K$_{1(Tb)}$ = (0.240,0.155,0.48) and K$_{2(Tb)}$ = (0.205, 0.115, 0.28), whereas HoCuAs$_2$ forms a single K$_{(Ho)}$ = (0.121, 0.041, 0.376) magnetic structure with 3$^{rd}$ order harmonic magnetic peaks. YbCuAs$_2$ does not exhibit any magnetic Bragg peaks at 1.5 K, while susceptibility measurements indicate an antiferromagnetic-like transition at 4 K, suggesting that either the ordering is not long range in nature or the ordered moment is below the sensitivity limit of $\approx$ 0.2 $μ_B$.

cond-mat.mtrl-sci↗

arXiv2016

Enhanced zero-bias conductance peak and splitting at mesoscopic interfaces between an $s$-wave superconductor and a 3D Dirac semimetal

Mesoscopic point contacts between elemental metals and the topological 3D Dirac semimetal Cd$_3$As$_2$ have been recently shown to be superconducting with unconventional pairing while Cd$_3$As$_2$ itself does not superconduct. Here we show that the same superconducting phase at mesoscopic interfaces on Cd$_3$As$_2$ can be induced with a known conventional superconductor Nb where a pronounced zero-bias conductance peak is observed which undergoes splitting in energy under certain conditions. The observations are consistent with the theory of the emergence of Andreev bound states (ABS) due to the presence of a pair potential with broken time reversal symmetry. The data also indicate the possibility of Majorana bound states as expected at the interfaces between $s$-wave superconductors and topologically non-trivial materials with high degree of spin-orbit coupling.

cond-mat.supr-con↗

arXiv2016

Superconductivity in Se-doped new materials EuSr2Bi2S4F4 and Eu2SrBi2S4F4

From our powder x ray diffraction pattern, electrical transport and magnetic studies we report the effect of isovalent Se substitution at S sites in the newly discovered systems EuSr2Bi2S4F4 and Eu2SrBi2S4F4. We have synthesized two new variants of 3244 type superconductor with Eu replaced by Sr which is reported elsewhere [Z. Haque et. al.]. We observe superconductivity at Tc 2.9 K (resistivity) and 2.3 K (susceptibility) in EuSr2Bi2S4-xSexF4 series for x = 2. In the other series Eu2SrBi2S4-xSexF4, two materials (x= 1.5; Tc = 2.6 K and x = 2; Tc = 2.75 K) exhibit superconductivity.

cond-mat.supr-con↗

arXiv2016

High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high ($\sim$ 47\%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47\% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane is strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.

cond-mat.supr-con↗

arXiv2016

Evidence of a pseudogap driven by competing orders of multi-band origin in the ferromagnetic superconductor Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$

From temperature and magnetic field dependent point-contact spectroscopy on the ferromagnetic superconductor Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$ (bulk superconducting $T_c$ = 2.5 K) we observe (a) a pseudogap in the normal state that sustains to a remarkably high temperature of 40 K and (b) two-fold enhancement of $T_c$ upto 5 K in the point-contact geometry. In addition, Andreev reflection spectroscopy reveals a superconducting gap of 6 meV for certain point-contacts suggesting that the mean field $T_c$ of this system could be approximately 40 K, the onset temperature of pseudo-gap. Our results suggest that quantum fluctuations originating from other competing orders in Sr$_{0.5}$Ce$_{0.5}$FBiS$_2$ forbid a global phase coherence at high temperatures thereby suppressing $T_c$. Apart from the known ordering to a ferromagnetic state, our first-principles calculations reveal nesting of a multi-band Fermi surface and a significant electron-phonon coupling that could result in charge density wave-like instabilities.

cond-mat.supr-con↗

arXiv2015

Coexistence of superconductivity and itinerant ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), the first non-U material with Tc < TFM

We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (x = 0.5, 1) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se-doping produces several effects: it suppresses semiconducting like behavior observed in the undoped Sr0.5Ce0.5FBiS2, ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and superconducting transition temperature, Tc, gets enhanced slightly to 2.9 - 3.3 K. Thus in these Se-doped materials, TFM is just marginally higher than Tc. Magnetization studies provide an evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex. Quite remarkably, as compared with the effective paramagnetic Ce-moment (~ 2.2 muB), the ferromagnetically ordered Ce-moment in the superconducting state is rather small (~ 0.1 muB). To the best of our knowledge, the title compounds are the first Ce-based superconducting itinerant ferromagnetic materials (Tc < TFM). We stress that Ce-4f electrons are responsible for both superconductivity and ferromagnetism just as U-5f electrons are in UCoGe. Furthermore, a novel feature of these materials is a dual hysteresis loop corresponding to both the ferromagnetism and the coexisting superconductivity. Such features of Sr0.5Ce0.5FBiS2-xSex put these materials apart from the well known U-containing superconducting ferromagnets reported so far.

cond-mat.supr-con↗

arXiv2015

Structural and magnetic properties of a new and ordered quaternary alloy MnNiCuSb (SG: F-43m)

We have synthesized a new crystallographically ordered quaternary Heusler alloy, MnNiCuSb. The crystal structure of the alloy has been determined by Rietveld refinement of the powder x-ray diffraction data. This alloy crystallizes in the LiMgPdSb type structure with F-43m space group. MnNiCuSb is a ferromagnet with a high TC ~ 690K and magnetic moment of 3.85MuB/f.u. Besides this we have also studied two other off-stoichiometric compositions; one Cu rich and the other Ni rich (MnNi0.9Cu1.1Sb and MnNi1.1Cu0.9Sb) which are also ferromagnets. It must be stressed that MnNiCuSb is one of the very few known, non-Fe containing quaternary Heusler alloys with 1: 1: 1: 1 composition.

cond-mat.mtrl-sci↗