High-pressure Transport Studies Research Articles

Destabilization of the Charge Density Wave and the Absence of Superconductivity in ScV6Sn6 under High Pressures up to 11 GPa.

RV6Sn6 (R = Sc, Y, or rare earth) is a new family of kagome metals that have a similar vanadium structural motif as AV3Sb5 (A = K, Rb, Cs) compounds. Unlike AV3Sb5, ScV6Sn6 is the only compound among the series of RV6Sn6 that displays a charge density wave (CDW) order at ambient pressure, yet it shows no superconductivity (SC) at low temperatures. Here, we perform a high-pressure transport study on the ScV6Sn6 single crystal to track the evolutions of the CDW transition and to explore possible SC. In contrast to AV3Sb5 compounds, the CDW order of ScV6Sn6 can be suppressed completely by a pressure of about 2.4 GPa, but no SC is detected down to 40 mK at 2.35 GPa and 1.5 K up to 11 GPa. Moreover, we observed that the resistivity anomaly around the CDW transition undergoes an obvious change at ~2.04 GPa before it vanishes completely. The present work highlights a distinct relationship between CDW and SC in ScV6Sn6 in comparison with the well-studied AV3Sb5.

Pressure-Induced Superconductivity in Flat-Band Kagome Compounds Pd3P2(S1 – x Se x )8

We performed high-pressure transport studies on the flat-band Kagome compounds, Pd3P2(S1 – x Se x )8 (x = 0, 0.25), with a diamond anvil cell. For both compounds, the resistivity exhibits an insulating behavior with pressure up to 17 GPa. With pressure above 20 GPa, a metallic behavior is observed at high temperatures in Pd3P2S8, and superconductivity emerges at low temperatures. The onset temperature of superconducting transition T C rises monotonically from 2 K to 4.8 K and does not saturate with pressure up to 43 GPa. For the Se-doped compound Pd3P2(S0.75Se0.25)8, the T C is about 1.5 K higher than that of the undoped one over the whole pressure range, and reaches 6.4 K at 43 GPa. The upper critical field with field applied along the c axis at typical pressures is about 50% of the Pauli limit, suggesting a 3D superconductivity. The Hall coefficient in the metallic phase is low and exhibits a peaked behavior at about 30 K, which suggests either a multi-band electronic structure or an electron correlation effect in the system.

Pressure-induced topological insulator-to-metal transition and superconductivity in Sn-doped Bi1.1Sb0.9Te2S

Tetradymite-type topological insulator Sn-doped $\mathrm{B}{\mathrm{i}}_{1.1}\mathrm{S}{\mathrm{b}}_{0.9}\mathrm{T}{\mathrm{e}}_{2}\mathrm{S}$ (Sn-BSTS), with a surface state Dirac point energy well isolated from the bulk valence and conduction bands, is an ideal platform for studying the topological transport phenomena. Here, we present high-pressure transport studies on single-crystal Sn-BSTS, combined with Raman scattering and synchrotron x-ray diffraction measurements. Over the studied pressure range of 0.7--37.2 GPa, three critical pressure points can be observed: (i) At $\ensuremath{\sim}9$ GPa, a pressure-induced topological insulator-to-metal transition is revealed due to closure of the bulk band gap, which is accompanied by changes in slope of the Raman frequencies and a minimum in $c$/$a$ within the pristine rhombohedral structure ($R\text{\ensuremath{-}}3m$); (ii) at $\ensuremath{\sim}13$ GPa, superconductivity is observed to emerge, along with the $R\text{\ensuremath{-}}3m$ to a $C2$/$c$ (monoclinic) structural transition; (iii) at $\ensuremath{\sim}24$ GPa, the superconducting transition onset temperature ${T}_{\mathrm{C}}$ reaches a maximum of $\ensuremath{\sim}12\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, accompanied by a second structural transition from the $C2$/$c$ to a body-centered cubic $Im\text{\ensuremath{-}}3m$ phase.

Pressure-tuned superconductivity and normal-state behavior in Ba(Fe0.943Co0.057)2As2 near the antiferromagnetic boundary

Superconductivity in iron pnictides is unconventional and pairing may be mediated by magnetic fluctuations in the Fe-sublattice. Pressure is a clean method to explore superconductivity in iron based superconductors by tuning the ground state continuously without introducing disorder. Here we present a systematic high pressure transport study in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ single crystals with $x=$ 0.057, which is near the antiferromagnetic instability. Resistivity $\rho=\rho_0+AT^{n}$ was studied under applied pressure up to 7.90 GPa. The parameter $n$ approaches a minimum value of $n\approx 1$ at a critical pressure $P_c =$ 3.65 GPa. Near $P_c$, the superconducting transition temperature $T_c$ reaches a maximum value of 25.8 K. In addition, the superconducting diamagnetism at 2 K shows a sudden change around the same critical pressure. These results may be associated with a possible quantum critical point hidden inside the superconducting dome, near optimum $T_c$.

Possibility for conventional superconductivity in Sr0.1Bi2Se3 from high-pressure transport studies

SrxBi2Se3 is recently reported to be a superconductor derived from topological insulator Bi2Se3. It shows a maximum resistive Tc of 3.25 K at ambient pressure. We report magnetic (up to 1 GPa) and transport properties (up to 8 Gpa) under pressure for single crystalline Sr0.1Bi2Se3 superconductor. Magnetic measurements show that Tc decreases from ∼2.6 K (0 GPa) to ∼1.9 K (0.81 GPa). Similar behavior is observed in transport properties as well without much change in the metallic characteristics in normal-state resistivity. No reentrant superconducting phase (Zhou Y. et al., Phys. Rev. B, 93 (2016) 144514) is observed at high pressure. Normal-state resistivity near Tc is explained by Fermi liquid model. Band structure calculations indicate decreasing density of states at Fermi level with pressure. In consonance with transition temperature suppression in conventional BCS low-Tc superconductors, the pressure effect in SrxBi2Se3 is well accounted by pressure-induced band broadening.

High-pressure study of the basal-plane anisotropy of the upper critical field of the topological superconductor SrxBi2Se3

We report a high-pressure transport study of the upper-critical field, $B_{c2}(T)$, of the topological superconductor Sr$_{0.15}$Bi$_2$Se$_3$ ($T_c = 3.0$ K). $B_{c2}(T)$ was measured for magnetic fields directed along two orthogonal directions, $a$ and $a^*$, in the trigonal basal plane. While superconductivity is rapidly suppressed at the critical pressure $p_c \sim 3.5$ GPa, the pronounced two-fold basal-plane anisotropy $B_{c2}^a/B_{c2}^{a^*} = 3.2$ at $T=0.3$ K, recently reported at ambient pressure (Pan et al., 2016), is reinforced and attains a value of $\sim 5$ at the highest pressure (2.2 GPa). The data reveal that the unconventional superconducting state with broken rotational symmetry is robust under pressure.

High pressure transport studies of the LiFeAs analogs CuFeTe2 and Fe2As

We have synthesized two iron-pnictide/chalcogenide materials, CuFeTe2 and Fe2As, which share crystallographic features with known iron-based superconductors, and carried out high pressure electrical resistivity measurements on these materials to pressures in excess of 30 GPa. Both compounds crystallize in the Cu2Sb-type crystal structure that is characteristic of LiFeAs (with CuFeTe2 exhibiting a disordered variant). At ambient pressure, CuFeTe2 is a semiconductor and has been suggested to exhibit a spin-density-wave transition, while Fe2As is a metallic antiferromagnet. The electrical resistivity of CuFeTe2, measured at 4 K, decreases by almost two orders of magnitude between ambient pressure and 2.4 GPa. At 34 GPa, the electrical resistivity decreases upon cooling the sample below 150 K, suggesting the proximity of the compound to a metal–insulator transition. Neither CuFeTe2 nor Fe2As superconduct above 1.1 K throughout the measured pressure range.

High-pressure transport study of a charge-transfer salt based on cytosine and TCNQ using a diamond anvil cell

Transport properties of a strongly correlated organic conductor (CHC+)TCNQ− were examined under high pressures up to about 7 GPa using a diamond anvil cell, where CHC+ denotes hemiprotonated cytosine pair and TCNQ represents 7,7,8,8-tetracyanoquinodimethane. This salt is a highly conductive semiconductor as a fully ionic TCNQ salt with the activation energy Ea of 0.14 eV at ambient pressure. Application of high pressure gradually increased the conductivity. The Ea decreased monotonically by a rate of 0.013 eV/GPa.

C6Yband graphite: A comparative high-pressure transport study

Reference LNNME-ARTICLE-2007-006View record in Web of Science URL: http://link.aip.org/link?prb/76/045426 Record created on 2007-08-15, modified on 2016-08-08

Magnetic transitions and electrical transport in lanthanum strontium manganite: Effects of substitutions and high pressure

The observation of a substitution-induced ferromagnetic order (Tc=200 K) is reported in antiferromagnetic La0.9Sr0.1MnO3 (TN=130 K) when 0.05 of La is replaced by yttrium. Important results of ferromagnetic resonance (FMR) and high-pressure transport studies are as follows. (i) Data on FMR linewidth and resistivity provide evidence for the presence of microscopic magnetic inhomogeneities, possibly La0.9Sr0.1MnO3. (ii) For zero external pressure, a resistivity peak at 130 K due to intergrain tunneling, a secondary peak close to Tc, and magnetoresistance (MR) on the order of 30% are observed. (iii) At high pressures, the resistivity peaks shift to higher temperatures at the rate of 24–26 K/GPa and MR values decrease. (iv) An internal pressure of 3 GPa due to Y substitution is inferred from high-pressure transport studies.