arXiv subjects

M. S. Torikachvili

Publications and source records attributed to M. S. Torikachvili.

At least 19 recordsLinked to original sources

arXiv2026

Multiband Superconductivity and Charge Density Wave in HfxZr1-xTe3 single crystals

We report on the bulk multiband superconductivity and charge density wave (CDW) in HfxZr1-xTe3 single crystals. The parent compound ZrTe3 is a layered van der Waals material that undergoes a CDW transition near 63 K and exhibits only filamentary superconductivity below 2.0 K. Upon the introduction of a small amount of Hf (x = 0.02), the CDW transition temperature is reduced to TCDW ~ 53 K, while a robust bulk superconducting state emerges at Tc ~ 3.3 K, underscoring a subtle competition between CDW order and superconductivity in this quasi-one-dimensional system. Electrical resistivity, magnetic susceptibility, Hall effect, Seebeck coefficient, and specific heat measurements consistently confirm the bulk nature of the superconducting phase. The temperature dependence of the upper critical field Hc2(T) deviates markedly from single-band behavior, and it is well described by a two-band model, consistent with multiband superconductivity. Analysis of the Hall effect, and thermoelectric behavior reveal pronounced electronic anisotropy, with enhanced effective carrier masses, indicating that the subtle structural modification introduced by Hf substitutions affects the Fermi surface topology, as well as electronic correlations. Measurements of electrical resistivity in hydrostatic pressures up to ~ 2 GPa reveal that pressure drives TCDW to higher temperatures while suppressing Tc. These findings show that Hf doping can be used to fine-tune the balance between the CDW instability and superconductivity, possibly by means of chemical pressure effects, stabilizing a multiband superconducting state in Hf-doped ZrTe3.

cond-mat.supr-con↗

arXiv2023

Superconductivity in Te-deficient ZrTe$_2$

We present structural, electrical, and thermoelectric potential measurements on high-quality single crystals of ZrTe$_{1.8}$ grown from isothermal chemical vapor transport. These measurements show that the Te-deficient ZrTe$_{1.8}$, which forms the same structure as the non-superconducting ZrTe$_2$, is superconducting below 3.2\,K. The temperature dependence of the upper critical field (H$_{c2}$) deviates from the behavior expected in conventional single-band superconductors, being best described by an electron-phonon two-gap superconducting model with strong intraband coupling. For the ZrTe$_{1.8}$ single crystals, the Seebeck potential measurements suggest that the charge carriers are predominantly negative, in agreement with the ab initio calculations. Through first-principles calculations within DFT, we show that the slight reduction of Te occupancy in ZrTe$_2$ unexpectedly gives origin to density of states peaks at the Fermi level due to the formation of localized Zr-$d$ bands, possibly promoting electronic instabilities at the Fermi level and an increase at the critical temperature according to the standard BCS theory. These findings highlight that the Te deficiency promotes the electronic conditions for the stability of the superconducting ground state, suggesting that defects can fine-tune the electronic structure to support superconductivity.

cond-mat.supr-con↗

arXiv2018

Properties and superconductivity in Ti-doped NiTe2 single crystals

Transition metal dichalcogenides (TMDs) usually show simple structures, however, with interesting properties. Recently some TMDs have been pointed out as type-II Dirac semimetals. In the present work, we investigate the physical properties of a new candidate for type-II Dirac semimetal and investigate the effect of titanium doping on physical properties of Ti-doped single crystalline samples of NiTe2. It was found that this compound shows a superconducting properties with a critical temperature close to 4.0 K. Interestingly, applied pressures up to 1.3 GPa have no effect upon the superconducting state. Density Functional Theory (DFT) calculations demonstrate the presence of a Dirac cone in the band structure of NiTe2 literature when Spin-Orbit Coupling (SOC) is included, which is in agreement with a recent report for this compound. Also, our calculations demonstrate that Ti suppresses the formation of these non-trivial states.

cond-mat.supr-con↗

arXiv2017

Absence of superconductivity in NbB

A systematic study of the superconducting properties in a series of arc-melted Nb-B samples close to the 1:1 composition was carried out. Powder X-ray diffraction (XRD) shows that all samples are both non-stoichiometric, and comprising of two crystal phases: a majority orthorhombic NbB-type phase, and traces of a minor body-centered cubic Nb-rich phase Nb$_{ss}$ with stoichiometry close to Nb$_{0.98}$B$_{0.02}$. The emergence of superconductivity near T$_c \sim$ 9.0 K was inferred from magnetization data in chunk and powder samples. However, the very small superconducting volume fractions are inconsistent with superconductivity arising from the major NbB phase. On the other hand, micrographs of selected samples clearly show that the minority Nb$_{ss}$ forms a three-dimensional network of filaments that meander around the grains of the majority phase, forming a percolation path. Here we report the superconductivity of the Nb$_{ss}$ phase, and argue that the low superconducting volume fraction of non-stoichiometric NbB and zero resistance are due to the filaments of the minority phase. The electronic contribution to the entropy of the superconducting state, yielded from an analysis using the alpha model for single-band systems, indicates that the Sommerfeld constant of the arc-melted samples is close to the values found in non-superconducting NbB. Micrograph, XRD, and bulk measurements of magnetization, electrical resistivity, and specific heat suggest that the superconducting state in the NbB samples bearing some Nb$_{ss}$ minority phase is due to the latter.

cond-mat.supr-con↗

arXiv2016

Tuning the electronic and the crystalline structure of LaBi by pressure

Extreme magnetoresistance (XMR) in topological semimetals is a recent discovery which attracts attention due to its robust appearance in a growing number of materials. To search for a relation between XMR and superconductivity, we study the effect of pressure on LaBi taking advantage of its simple structure and simple composition. By increasing pressure we observe the disappearance of XMR followed by the appearance of superconductivity at P=3.5 GPa.The suppression of XMR is correlated with increasing zero-field resistance instead of decreasing in-field resistance. At higher pressures, P=11 GPa, we find a structural transition from the face center cubic lattice to a primitive tetragonal lattice in agreement with theoretical predictions. We discuss the relationship between extreme magnetoresistance, superconductivity, and structural transition in LaBi.

cond-mat.supr-con↗

arXiv2016

Combined effects of Sr substitution and pressure on the ground states in CaFe$_2$As$_2$

We present a detailed study of the combined effects of Sr substitution and hydrostatic pressure on the ground-state properties of CaFe$_2$As$_2$. Measurements of the electrical resistance and magnetic susceptibility, both at ambient and finite pressure $P$ $\leq$ 2$\,$GPa, were performed on Ca$_{1-x}$Sr$_x$Fe$_2$As$_2$ single crystals grown out of Sn flux. We find that upon Sr substitution the ranges of stability of both the structural-magnetic transition and the transition into the non-magnetic collapsed tetragonal phase are shifted to higher pressure levels with the latter moving at a higher rate. This suggests the possibility of separating the two phase lines, which intersect already at elevated temperatures for $x$ = 0 and low Sr concentration levels. For $x$ = 0.177 we find strong evidence that both phases remain separated down to lowest temperature and that a zero-resistance state emerges in this intermediate pressure window. This observation indicates that Sr-substitution combined with hydrostatic pressure provides another route for stabilizing superconductivity in CaFe$_2$As$_2$. Our results are consistent with the notion that (i) preserving the fluctuations associated with the structural-magnetic transition to low temperatures is vital for superconductivity to form in this material and that (ii) the non-magnetic collapsed tetragonal phase is detrimental for superconductivity.

cond-mat.supr-con↗

arXiv2015

Solidification and loss of hydrostaticity in liquid media used for pressure measurements

We carried out a study of the pressure dependence of the solidification temperature in nine pressure transmitting media that are liquid at ambient temperature, under pressures up to 2.3 GPa. These fluids are: 1:1 isopentane/n-pentane, 4:6 light mineral oil/n-pentane, 1:1 isoamyl alcohol/n-pentane, 4:1 methanol/ethanol, 1:1 FC72/FC84 (Fluorinert), Daphne 7373, isopentane, and Dow Corning PMX silicone oils 200 and 60,000 cst. We relied on the sensitivity of the electrical resistivity of Ba(Fe1-xRux)2As2 single crystals to the freezing of the pressure media, and cross-checked with corresponding anomalies observed in the resistance of the manganin coil that served as the ambient temperature resistive manometer. In addition to establishing the Temperature-Pressure line separating the liquid (hydrostatic) and frozen (non-hydrostatic) phases, these data permit rough estimates of the freezing pressure of these media at ambient temperature. This pressure establishes the extreme limit for the medium to be considered hydrostatic. For higher applied pressures the medium has to be treated as non-hydrostatic.

cond-mat.mtrl-sci↗

arXiv2013

Search for Pressure Induced Quantum Criticality in YbFe2Zn20

Electrical transport measurements of the heavy fermion compound YbFe2Zn20 were carried out under pressures up to 8.23 GPa and down to temperatures of nearly 0.3 K. The pressure dependence of the low temperature Fermi-liquid state was assessed by fitting rho(T) = rho_0 + AT^n with n = 2 for T < T_FL. Power law analysis of the low temperature resistivities indicates n = 2 over a broad temperature range for P < 5 GPa. However, at higher pressures, the quadratic temperature dependence is only seen at the very lowest temperatures, and instead shows a wider range of n < 2 power law behavior in the low temperature resistivities. As pressure was increased, T_FL diminished from ~11 K at ambient pressure to ~0.6 K at 8.23 GPa. Over the same pressure range, the A parameter increased dramatically with a functional form of A proportional to (P-Pc)^-2 with Pc~9.8GPa being the critical pressure for a possible quantum critical point.

cond-mat.str-el↗

arXiv2012

Two-Dimensional Magnetic Correlations and Partial Long-Range Order in Geometrically Frustrated Sr2YRuO6

Neutron diffraction on the double perovskite Sr2YRuO6 with a quasi-face-centered cubic (FCC) lattice of Ru moments reveals planar magnetic correlations that condense into a partial long-range ordered state with coupled alternate antiferromagnetic (AFM) YRuO4 square layers coexisting with short-range correlations below T{N1}=32 K. A second transition to a fully ordered AFM state below T{N2}=24 K is observed. These observations are ascribed to the cancellation of the magnetic coupling between consecutive AFM square layers in FCC antiferromagnets, notably the simplest three-dimensional frustrated magnet model system. Inhomogeneous superconductivity in Sr2YRu_{1-x}Cu_{x}O6, reported in earlier works, may be nucleated in magnetically disordered YRu_{1-x}Cu_{x}O4 layers with strong spin fluctuations.

cond-mat.str-el↗

arXiv2011

Structural, electronic, magnetic, and thermal properties of single-crystalline UNi0.5Sb2

We studied the properties of the antiferromagnetic (AFM) UNi0.5Sb2 (TN \approx 161 K) compound in Sb-flux grown single crystals by means of measurements of neutron diffraction, magnetic susceptibility (χ), specific heat (Cp), thermopower (S), thermal conductivity (κ), linear thermal expansion (ΔL/L), and electrical resistivity (ρ) under hydrostatic pressures (P) up to 22 kbar. The neutron diffraction measurements revealed that the compound crystallizes in the tetragonal P42/nmc structure, and the value of the U-moments yielded by the histograms at 25 K is \approx 1.85 \pm 0.12 μB/U-ion. In addition to the features in the bulk properties observed at TN, two other hysteretic features centered near 40 and 85 K were observed in the measurements of χ, S, ρ, and ΔL/L. Hydrostatic pressure was found to raise TN at the rate of \approx 0.76 K/kbar, while suppressing the two low temperature features. These features are discussed in the context of Fermi surface and hybridization effects.

cond-mat.str-el↗

arXiv2011

Physical and magnetic properties of Ba(Fe_(1-x)Mn_x)_2As_2 single crystals

Single crystals of Ba(Fe_(1-x)Mn_x)_2As_2, 0 0.1-0.2. Our measurements show that whereas the structural/magnetic phase transition found in pure BaFe_2As_2 at 134 K is initially suppressed by Mn substitution, superconductivity is not observed at any substitution level. Although the effect of hydrostatic pressure up to 20 kbar in the parent BaFe_2As_2 compound is to suppress the structural/magnetic transition at the approximate rate of 0.9 K/kbar, the effects of pressure and Mn substitution in the x=0.102 compound are not cumulative. Phase diagrams of transition temperature versus substitution concentration, x, based on electrical transport, magnetization and thermopower measurements have been constructed and compared to those of the Ba(Fe_(1-x)TM_x)_2As_2 (TM=Co and Cr) series.

cond-mat.supr-con↗

arXiv2011

Anelastic spectroscopy study of the metal-insulator transition of Nd(1-x)EuxNiO3

Measurements are presented of the complex dynamic Young's modulus of NdNiO3 and Nd0.65Eu0.35NiO3 through the Metal-Insulator Transition (MIT). On cooling, the modulus presents a narrow dip at the MIT followed by an abrupt stiffening of ~6%. The anomaly is reproducible between cooling and heating in Nd0:65Eu0:35NiO3 but only appears as a slow stiffening during cooling in undoped NdNiO3, conformingly with the fact that the MIT in RNiO3 changes from strongly first order to second order when the mean R size is decreased. The elastic anomaly seems not to be associated with the antiferromagnetic transition, which is distinct from the MIT in Nd0.65Eu0.35NiO3. It is concluded that the steplike stiffening is due to the disappearance or freezing of dynamic Jahn- Teller (JT) distortions through the MIT, where the JT active Ni3+ is disproportionated into alternating Ni3+d and Ni3-d. The fluctuating octahedral JT distortion necessary to justify the observed jump in the elastic modulus is estimated as ~3%, but does not have a role in determining the MIT, since the otherwise expected precursor softening is not observed.

cond-mat.str-el↗

arXiv2011

Combined effects of pressure and Ru substitution on BaFe2As2

The ab-plane resistivity of Ba(Fe1-xRux)2As2 (x = 0.00, 0.09, 0.16, 0.21, and 0.28) was studied under nearly hydrostatic pressures, up to 7.4 GPa, in order to explore the T-P phase diagram and to compare the combined effects of iso-electronic Ru substitution and pressure. The parent compound BaFe2As2 exhibits a structural/magnetic phase transition near 134 K. At ambient pressure, progressively increasing Ru concentration suppresses this phase transition to lower temperatures at the approximate rate of ~5 K/% Ru and is correlated with the emergence of superconductivity. By applying pressure to this system, a similar behavior is seen for each concentration: the structural/magnetic phase transition is further suppressed and superconductivity induced and ultimately, for larger x Ru and P, suppressed. A detailed comparison of the T-P phase diagrams for all Ru concentrations shows that 3 GPa of pressure is roughly equivalent to 10% Ru substitution. Furthermore, due to the sensitivity of Ba(Fe1-xRux)2As2 to pressure conditions, the melting of the liquid media, 4 : 6 light mineral oil : n-pentane and 1 : 1 iso-pentane : n-pentane, used in this study could be readily seen in the resistivity measurements. This feature was used to determine the freezing curves for these media and infer their room temperature, hydrostatic limits: 3.5 and 6.5 GPa, respectively.

cond-mat.supr-con↗

arXiv2010

Metal-insulator transition in Nd1-xEuxNiO3 probed by specific heat and anelastic measurements

Oxides RNiO3 (R = rare-earth, R # La) exhibit a metal-insulator (MI) transition at a temperature TMI and an antiferromagnetic (AF) transition at TN. Specific heat (CP) and anelastic spectroscopy measurements were performed in samples of Nd1-xEuxNiO3, 0 <= x <= 0.35. For x = 0, a peak in CP is observed upon cooling and warming at essentially the same temperature TMI = TN ~ 195 K, although the cooling peak is much smaller. For x >= 0.25, differences between cooling and warming curves are negligible, and two well defined peaks are clearly observed: one at lower temperatures, that define TN, and the other one at TMI. An external magnetic field of 9 T had no significant effect on these results. The elastic compliance (s) and the reciprocal of the mechanical quality factor (Q^-1) of NdNiO3, measured upon warming, showed a very sharp peak at essentially the same temperature obtained from CP, and no peak is observed upon cooling. The elastic modulus hardens below TMI much more sharply upon warming, while the cooling and warming curves are reproducible above TMI. On the other hand, for the sample with x = 0.35, s and Q^-1 curves are very similar upon warming and cooling. The results presented here give credence to the proposition that the MI phase transition changes from first to second order with increasing Eu doping.

cond-mat.str-el↗

arXiv2009

Effect of pressure on transport and magnetotransport properties in CaFe2As2 single crystals

The effects of pressure generated in a liquid medium, clamp, pressure cell on the in-plane and c-axis resistance, temperature-dependent Hall coefficient and low temperature, magnetoresistance in CaFe2As2 are presented. The T - P phase diagram, including the observation of a complete superconducting transition in resistivity, delineated in earlier studies is found to be highly reproducible. The Hall resistivity and low temperature magnetoresistance are sensitive to different states/phases observed in CaFe2As2. Auxiliary measurements under uniaxial, c-axis, pressure are in general agreement with the liquid medium clamp cell results with some difference in critical pressure values and pressure derivatives. The data may be viewed as supporting the potential importance of non-hydrostatic components of pressure in inducing superconductivity in CaFe2As2.

cond-mat.supr-con↗

arXiv2009

Structural, magnetic and superconducting phase transitions in CaFe2As2 under ambient and applied pressure

At ambient pressure CaFe2As2 has been found to undergo a first order phase transition from a high temperature, tetragonal phase to a low temperature orthorhombic / antiferromagnetic phase upon cooling through T ~ 170 K. With the application of pressure this phase transition is rapidly suppressed and by ~ 0.35 GPa it is replaced by a first order phase transition to a low temperature collapsed tetragonal, non-magnetic phase. Further application of pressure leads to an increase of the tetragonal to collapsed tetragonal phase transition temperature, with it crossing room temperature by ~ 1.7 GPa. Given the exceptionally large and anisotropic change in unit cell dimensions associated with the collapsed tetragonal phase, the state of the pressure medium (liquid or solid) at the transition temperature has profound effects on the low temperature state of the sample. For He-gas cells the pressure is as close to hydrostatic as possible and the transitions are sharp and the sample appears to be single phase at low temperatures. For liquid media cells at temperatures below media freezing, the CaFe2As2 transforms when it is encased by a frozen media and enters into a low temperature multi-crystallographic-phase state, leading to what appears to be a strain stabilized superconducting state at low temperatures.

cond-mat.supr-con↗

arXiv2008

Direct determination of the crystal field parameters of Dy, Er and Yb impurities in the skutterudite compound CeFe$_{4}$P$_{12}$ by Electron Spin Resonance

Despite extensive research on the skutterudites for the last decade, their electric crystalline field ground state is still a matter of controversy. We show that Electron Spin Resonance (ESR) measurements can determine the full set of crystal field parameters (CFPs) for the Th cubic symmetry (Im3) of the Ce$_{1-x}$R$_{x}$Fe$_{4}$P$_{12}$ (R = Dy, Er, Yb, $x\lesssim 0.003$) skutterudite compounds. From the analysis of the ESR data the three CFPs, B4c, B6c and B6t were determined for each of these rare-earths at the Ce$^{3+}$ site. The field and temperature dependence of the measured magnetization for the doped crystals are in excellent agreement with the one predicted by the CFPs Bnm derived from ESR.

cond-mat.str-el↗

arXiv2008

Pressure-induced volume-collapsed tetragonal phase of CaFe2As2 as seen via neutron scattering

Recent investigations of the superconducting iron-arsenide families have highlighted the role of pressure, be it chemical or mechanical, in fostering superconductivity. Here we report that CaFe2As2 undergoes a pressure-induced transition to a non-magnetic, volume "collapsed" tetragonal phase, which becomes superconducting at lower temperature. Spin-polarized total-energy calculations on the collapsed structure reveal that the magnetic Fe moment itself collapses, consistent with the absence of magnetic order in neutron diffraction.

cond-mat.supr-con↗