We measured the electrical resistivity and ac magnetic susceptibility of BaFe2As2 and SrFe2As2 single crystals under pressure using a cubic anvil apparatus. For BaFe2As2, the antiferromagnetic (AF) and structural transitions are suppressed with increasing pressure. Unexpectedly, these transitions persist up to 8 GPa, and no signature of a superconducting transition was observed in the pressure range investigated here. On the other hand, the AF and structural transitions of SrFe2As2 collapse at around the critical pressure Pc ~ 5 GPa, resulting in the appearance of bulk superconductivity. The superconducting volume fraction abruptly increases above Pc, and shows a dome centered at approximately 6 GPa. Our results suggest that the bulk superconducting phase competes with the AF/orthorhombic phase and only appears in the narrow pressure region of the tetragonal phase.
We studied the evolution of superconductivity (sc) and antiferromagnetism (afm) in the heavy fermion compound CePt_3Si with hydrostatic pressure. We present a pressure-temperature phase diagram established by electrical transport measurements. Pressure shifts the superconducting transition temperature, T_c, to lower temperatures. Antiferromagnetism is suppressed at a critical pressure P_c=0.5 GPa.
We present direct evidence of a superconducting state existing in the title compound below 300 mK under quasi-hydrostatic pressure. The superconducing transition is observed in the whole pressure range studied, 0 < P < 4 kbar. However, the character of the transition drastically changes with suppressing the charge-density wave state.
In the present work, we measure the temperature dependent electrical resistivity from 300K down to 2K under applied hydrostatic pressure of upto 2.5GPa for SrFBiS2, which is the parent compound for the BiS2 based superconductors. Though the normal state resistivity of the compound decreases with pressure, the same is not superconducting down to 2K under applied pressure of up to 2.5Gpa.
Uniaxial stress, as well as hydrostatic pressure are often used to tune material properties in condensed matter physics. Here, we present a setup which allows for the study of the combined effects of quasi-uniaxial stress and hydrostatic pressure. Following earlier designs for measurements under finite stress at ambient pressure (e.g., Chu et al., Science 337, 710 (2012)), the present setup utilizes a piezoelectric actuator to change stress in situ inside the piston-cylinder pressure cell. We show that the actuator can be operated over the full temperature (from 30K up to 260 K) and pressure r…
Recent high-pressure studies found that superconductivity can be achieved under very low pressure in the parent iron arsenide compound CaFe2As2, although details of the sharpness and temperature of transitions vary between liquid medium and gas medium measurements. To better understand this issue, we performed high-pressure susceptibility and transport studies on CaFe2As2, using helium as the pressure medium. The signatures of the transitions to the low-temperature orthorhombic and collapsed tetragonal phase remained exceptionally sharp and no signature of bulk superconductivity was found unde…
We study the electronic properties of a LaEu0.20Sr0.15CuO4 single crystal under hydrostatic pressure up to 2.9 GPa. Both the freezing of the Cu 3d moments and the structural transition from the orthorhombic (LTO) to the tetragonal (LTT) phase are observed via the relaxation of the nuclear magnetization of La nuclei. Resistivity and magnetic susceptibility measurements have been carried out under pressure on the same sample. The combination of all data reveals the connection between glassy dynamics, charge localization and the disappearance of superconductivity in the LTT phase.
The effects of hydrostatic pressure on the static magnetism in Eu(Fe$_{0.925}$Co$_{0.075}$)$_{2}$As$_{2}$ are investigated by complementary electrical resistivity, ac magnetic susceptibility and single-crystal neutron diffraction measurements. A specific pressure-temperature phase diagram of Eu(Fe$_{0.925}$Co$_{0.075}$)$_{2}$As$_{2}$ is established. The structural phase transition, as well as the spin-density-wave order of Fe sublattice, is suppressed gradually with increasing pressure and disappears completely above 2.0 GPa. In contrast, the magnetic order of Eu sublattice persists over the w…
The effect of hydrostatic pressure on the superconducting transition temperature of Na{0.35}CoO{2}.yH{2}O was investigated by ac susceptibility measurements up to 1.6 GPa. The pressure coefficient of T{c} is negative and the dependence T{c}(p) is nonlinear over the pressure range investigated. The magnitude of the average dlnT{c}/dp=-0.07 GPa^{-1} is comparable to the pressure coefficient of electron-doped high-T{c} copper oxide superconductors with a similar value of T{c}. Our results provide support to the assumption of two-dimensional superconductivity in Na{0.35}CoO{2}.yH{2}O, which is sim…
We report comprehensive resistivity measurements of single crystalline samples of the Ba(Fe(1-x)Co(x))2As2 high Tc superconductor under hydrostatic pressure up to 2.75 GPa and over a broad concentration range, 0 < x < 0.099. We show that application of pressure progressively suppresses the SDW transition temperature, T_SDW, in the underdoped regime. There is no sign of pressure-induced superconductivity in the undoped BaFe2As2 down to 1.8 K, but applied pressure dramatically enhances Tc in the underdoped regime. The effect of pressure on Tc is very small in the optimally and overdoped regimes.…
We report high pressure magnetic susceptibility and electrical resistivity measurements on Ca_{3}Ir_{4}Sn_{13} single crystals up to 60 kbar. These measurements allow us to follow the evolution of the superconducting critical temperature T_c, the resistivity anomaly temperature T*, the superconducting coherence length and the Fermi velocity under pressure. The pressure-temperature phase diagram constructed for Ca_{3}Ir_{4}Sn_{13} shows a dome-shaped pressure dependence of T_c. The initial rise in T_c, which is accompanied by a decrease in T*, is consistent with a reduction in the partial gappi…
We carried out a combined P-substitution and hydrostatic pressure study on CeFeAs_1-xP_xO single crystals in order to investigate the peculiar relationship of the local moment magnetism of Ce, the ordering of itinerant Fe moments, and their connection with the occurrence of superconductivity. Our results evidence a close relationship between the weakening of Fe magnetism and the change from antiferromagnetic to ferromagnetic ordering of Ce moments at p*=1.95 GPa in CeFeAs_0.78P_0.22O. The absence of superconductivity in CeFeAs_0.78P_0.22O and the presence of a narrow and strongly pressure sens…
The effect of hydrostatic pressure (P) on charge density waves (CDW) in YBa2Cu3Oy has recently been controversial. Using NMR, we find that both the short-range CDW in the normal state and the long-range CDW in high fields are, at most, slightly weakened at P=1.9 GPa. This result is in contradiction with x-ray scattering results finding complete suppression of the CDW at ~1 GPa and we discuss possible explanations of this discrepancy. Quantitative analysis, however, shows that the NMR data is not inconsistent with a disappearance of the CDW on a larger pressure scale, typically ~10-20 GPa. We a…
The majority of the iron-based superconductors (FeSCs) exhibit a two-dimensional square lattice structure. Recent reports of pressure-induced superconductivity in the spin-ladder system, BaFe$_2$X$_3$ (X =S,Se), introduce a quasi-one-dimensional prototype and an insulating parent compound to the FeSCs. Here we report X-ray, neutron diffraction and muon spin relaxation experiments on BaFe$_2$Se$_3$ under hydrostatic pressure to investigate its magnetic and structural properties across the pressure-temperature phase diagram. A structural phase transition was identified at a pressure of 3.7(3) GP…
We present a detailed investigation of the electronic properties of CeFeAsO under chemical (As by P substitution) and hydrostatic pressure by means of in-house and synchrotron Mössbauer spectroscopy. The Fe magnetism is suppressed due to both pressures and no magnetic order was observed above a P-substitution level of 40% or 5.2 GPa hydrostatic pressure. We compared both pressures and found that the isovalent As by P substitution change the crystallographic and electronic properties differently than hydrostatic pressure.
Details of the Fermi-surface topology of deuterated $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$ ~have been measured as a function of pressure, and compared with equivalent measurements of the undeuterated salt. We find that the superconducting transition temperature is much more dramatically suppressed by increasing pressure in the deuterated salt. It is suggested that this is linked to pressure-induced changes in the Fermi-surface topology, which occur more rapidly in the deuterated salt than in the undeuterated salt as the pressure is raised. Our data suggest that the negative isotope effect observed on d…
We report on the effects of hydrostatic pressure (HP) on the charge density wave observed in underdoped cuprates. We studied YBa$_2$Cu$_3$O$_{6.6}$ ($T_c$=61 K) using high-resolution inelastic x-ray scattering (IXS), and reveal an extreme sensitivity of the phonon anomalies related to the charge density wave (CDW) order to HP. The amplitudes of the normal state broadening and superconductivity induced phonon softening at Q$_{CDW}$ rapidly decrease as HP is applied, resulting in the complete suppression of signatures of the CDW below $\sim$1 GPa. Additional IXS measurements on YBa$_2$Cu$_3$O$_{…
The magnetic phase diagram of EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ was investigated by means of magnetization and muon-spin rotation studies as a function of chemical (isovalent substitution of As by P) and hydrostatic pressure. The magnetic phase diagrams of the magnetic ordering of the Eu and Fe spins with respect to P content and hydrostatic pressure are determined and discussed. The present investigations reveal that the magnetic coupling between the Eu and the Fe sublattices strongly depends on chemical and hydrostatic pressure. It is found that chemical and hydrostatic pressure have a sim…
In this communication, we report the temperature dependence (3 to 300K) of the electrical resistivity of BiS2 based layered PrO0.5F0.5BiS2 superconductor at ambient and hydrostatic pressure of up to 3GPa. It is observed that Tc increases with pressure at the rate of dTc/dP=0.45/GPa for PrO0.5F0.5BiS2 compound. It is envisaged that one may increase the Superconducting transition temperature (Tc) of recently discovered PrO0.5F0.5BiS2 superconductor by applying hydrostatic external or internal chemical pressure via suitable on site substitutions.
In the iron-pnictide material CeFeAsO not only the Fe moments, but also the local 4f moments of the Ce order antiferromagnetically at low temperatures. We elucidate on the peculiar role of the Ce on the emergence of superconductivity. While application of pressure suppresses the iron SDW ordering temperature monotonously up to 4 GPa, the Ce-4f magnetism is stabilized, until both types of magnetic orders disappear abruptly and a narrow SC dome develops. With further increasing pressure characteristics of a Kondo-lattice system become more and more apparent in the electrical resistivity. This su…
We have performed electrical resistivity measurements on single crystal BaFe2As2 under high pressure P up to 16 GPa with a cubic anvil apparatus, and up to 3 GPa with a modified Bridgman anvil cell. The samples were obtained from the same batch, which was grown with a self-flux method. A cubic anvil apparatus provides highly hydrostatic pressure, and a modified Bridgman anvil cell, which contains liquid pressure transmitting medium, provides quasi hydrostatic pressure. For highly hydrostatic pressure, the crystal phase and magnetic transition temperature decreases robustly with P and disappear…
The pressure effect on the superconducting transition temperature of MgB2 has been determined using gas pressure up to 1 GPa. The transition temperature Tc was found to decrease linearly at a constant rate over the whole pressure range. The recently observed dramatic decrease of dTc/dp at the 40 K freezing pressure (0.5 GPa) cannot be confirmed. The pressure coefficient was also found to be independent of the hydrostatic or nonhydrostatic He environment. The differences in recently reported values of dTc/dp may be attributed to variations in the sample conditions, e.g. stoichiometry.
We report Cu nuclear-quadrupole-resonance results under pressure on a homogeneous CeCu2Si2 (Tc = 0.65 K) that revealed critical magnetic fluctuations at the border to an antiferromagnetic phase. This exotic superconducting phase evolves into the typical heavy-fermion superconducting phase at minute pressures exceeding Pc ~ 0.2 GPa. The nuclear spin-lattice relaxation data in a pressure range 0.85 - 2.58 GPa are shown to be accountable by the SCR theory based on the nearly antiferromagnetic Fermi-liquid model. In 0 < P < Pc ~ 0.2 GPa, by contrast, we conclude that the exotic superconducting pha…
The discoveries of iron-based superconductors with relatively high transition temperature are under intense experimental and theoretical investigation. Here we present magnetotransport measurements on FeSe superconductor under hydrostatic pressure. We show that in Fe-deficient tetragonal FeSe binary compound, the onset of superconducting transition is almost doubled under 1.98GPa pressure and the estimated upper critical field of 26.7Tesla is increased to 47.5Tesla.
We report on measurements of the magnetic susceptibility and electrical resistance under He-gas pressure on single crystals of Ca(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$. We find that for properly heat-treated crystals with modest Co-concentration, $x$ = 0.028, the salient ground states associated with iron-arsenide superconductors, i.e., orthorhombic/antiferromagnetic (o/afm), superconducting, and nonmagnetic collapsed-tetragonal (cT) states can be accessed all in one sample with reasonably small and truly hydrostatic pressure. This is possible owing to the extreme sensitivity of the o/afm (for $T …
We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe2As2, BaFe2As2, and (Ba0.55K0.45)Fe2As2, by means of measurements of electrical resistivity (rho) in the 1.8 - 300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe2As2 and BaFe2As2 (lightly doped with Sn) display structural phase transitions near 170 K and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba0.55K0.45)Fe2As2 is superconducting for T < 30 K. …
The impact of hydrostatic pressure up to 1.2 GPa on the critical current density (Jc) and the nature of the pinning mechanism in MgB2 have been investigated within the framework of the collective theory. We found that the hydrostatic pressure can induce a transition from the regime where pinning is controlled by spatial variation in the critical transition temperature (δT_c) to the regime controlled by spatial variation in the mean free path (δl). Furthermore, Tc and low field Jc are slightly reduced, although the Jc drops more quickly at high fields than at ambient pressure. We found that the…
The origin of uniaxial and hydrostatic pressure effects on $T_c$ in the single-layered cuprate superconductors is theoretically explored. A two-orbital model, derived from first principles and analyzed with the fluctuation exchange approximation gives axial-dependent pressure coefficients, $\partial T_c/\partial P_a>0$, $\partial T_c/\partial P_c<0$, with a hydrostatic response $\partial T_c/\partial P>0$ for both La214 and Hg1201 cuprates, in qualitative agreement with experiments. Physically, this is shown to come from a unified picture in which higher $T_c$ is achieved with an "orbital dist…
We report impact of hydrostatic pressure on the newly discovered BiS2 based superconductors. In last couple of years the new BiS2 based superconductor attracted great attention of the condensed matter physics community. These new layered BiS2-based compounds are very sensitive to the concentration of carriers doping and pressure that cause profound changes in their physical properties with appearance of superconductivity in the vicinity of their insulating/semiconducting state. The BiS2-based new compounds are expected to provide us with the next stage of exploring new superconductors and to d…
We report the impact of hydrostatic pressure (0-1.97GPa) on superconductivity of recently discovered 2K superconductor Sr0.5La0.5FBiS2. Resistivity under pressure measurements are performed by using HPC-33 Piston type pressure cell with Quantum design DC resistivity Option. The superconducting transition temperature (Tc) is increased by 5 fold to around 10K with just above 1GPa pressure, which remains nearly unaltered for studied higher pressures of up to 1.97GPa. The fivefold increase in Tc of Sr0.5La0.5FBiS2 with just above 1GPa pressure suggests very strong electron correlations in these sy…
We report an unexpected positive hydrostatic pressure derivative of the superconducting transition temperature in the doped topological insulator \NBS via $dc$ SQUID magnetometry in pressures up to 0.6 GPa. This result is contrary to reports on the homologues \CBS and \SBS where smooth suppression of $T_c$ is observed. Our results are consistent with recent Ginzburg-Landau theory predictions of a pressure-induced enhancement of $T_c$ in the nematic multicomponent $E_u$ state proposed to explain observations of rotational symmetry breaking in doped Bi$_2$Se$_3$ superconductors.
We investigate the evolution of the electrical resistivity of BaFe2As2 single crystals with pressure. The samples used were from the same batch grown from self flux and showed properties that were highly reproducible. Samples were pressurised using three different pressure media: pentane-isopentane (in a piston cylinder cell), Daphne oil (in an alumina anvil cell) and steatite (in a Bridgman cell). Each pressure medium has its own intrinsic level of hydrostaticity, which dramatically affects the phase diagram. An increasing uniaxial pressure component in this system quickly reduces spin densit…
We report the effect of hydrostatic pressure (0-1.97GPa) on the superconductivity of BiS2 based CeO0.5F0.5BiS2 compound. The CeO0.5F0.5BiS2 superconductor was synthesized by the solid state reaction route and the compound is crystallized in tetragonal P4/nmm space group. The studied compound shows superconductivity with transition temperature of 2.5K (Tconset) at ambient pressure, which has been enhanced to 8 K at applied pressure of 1.97 GPa. The observed normal resistivity exhibited semiconducting behavior. The data of normal state resistivity R(T) has been fitted by activation type equation…
Strong pinning depends on the pinning force strength and number density of effective defects. Using hydrostatic pressure method, we demonstrate that hydrostatic pressure up to 1.2 GPa can significantly enhance flux pinning or Jc by a factor of up to 5 especially in both low and high fields in optimally doped Ba0.6K0.4Fe2As2 crystals. Our analysis on the flux pining mechanism indicate that both pinning centre number density (Np) and pinning force (Fp) are greatly increased by the pressure and contribute to strong pinning.
We present heat capacity, c-axis thermal expansion and pressure dependent, low field, temperature dependent magnetization for pressures up to ~ 12 kbar, data for KFe2As2 single crystals. Tc decreases under pressure with dTc/dP ~ -0.10 K/kbar. The inferred uniaxial, c-axis, pressure derivative is positive, dTc/dpc ~ 0.11 K/kbar. The data are analyzed in comparison with those for overdoped Fe-based superconductors. Arguments are presented that superconductivity in KFe2As2 may be different from the other overdoped, Fe-based materials in the 122 family.
We report the appearance of superconductivity under hydrostatic pressure (0.35 to 2.5GPa) in Sr0.5RE0.5FBiS2 with RE = Ce, Nd, Pr and Sm. The studied compounds, synthesized by solid state reaction route, are crystallized in tetragonal P4/nmm space group. At ambient pressure though the RE = Ce exhibit the onset of superconductivity below 2.5K, the Nd, Pr and Sm samples are not superconducting down to 2K. With application of hydrostatic pressure (up to 2.5GPa), superconducting transition temperature is increased to around 10K for all the studied samples. The magneto-transport measurements are ca…
The dependence of the superconducting transition temperature T_{c} on nearly hydrostatic pressure has been determined to 67 GPa in an ac susceptibility measurement for a Li sample embedded in helium pressure medium. With increasing pressure, superconductivity appears at 5.47 K for 20.3 GPa, T_{c} rising rapidly to ~ 14 K at 30 GPa. The T_{c}(P)-dependence to 67 GPa differs significantly from that observed in previous studies where no pressure medium was used. Evidence is given that superconductivity in Li competes with symmetry breaking structural phase transitions which occur near 20, 30, and…
The dependence of Tc for MgB2 on purely hydrostatic or nearly hydrostatic pressure has been determined to 23 GPa for single-crystalline and to 32 GPa for polycrystalline samples, and found to be in good agreement. Tc decreases from 39 K at ambient pressure to 15 K at 32 GPa with an initial slope dTc/dP = -1.11(2) K/GPa. Evidence is presented that the differing values of dTc/dP reported in the literature result primarily from shear-stress effects in nonhydrostatic pressure media and not differences in the samples. Although comparison of these results with theory supports phonon-mediated superco…
The dependence of Tc on hydrostatic (He-gas) pressure has been determined to 0.7 GPa. We find that Tc decreases linearly and reversibly under pressure at the rate dTc/dP = -1.11 +- 0.02 K/GPa. These studies were carried out on the same sample used in earlier structural studies under He-gas pressure which yielded the bulk modulus B = 147.2 +- 0.7 GPa. The value of the logarithmic volume derivative of Tc is thus accurately determined, dlnTc/dlnV = +4.16 +- 0.08, allowing quantitative comparison with theory. The present results support the emerging picture that MgB2 is a BCS superconductor with e…
The dependence of the critical current density Jc on hydrostatic pressure to 0.6 GPa is determined for a single 25-degree [001]-tilt grain boundary in a bicrystalline ring of nearly optimally doped melt-textured YBa2Cu3Ox. Jc is found to increase rapidly under pressure at +20 %/GPa. A new diagnostic method is introduced (pressure-induced Jc relaxation) which reveals a sizeable concentration of vacant oxygen sites in the grain boundary region. Completely filling such sites with oxygen anions should lead to significant enhancements in Jc.
We investigate the pressure phase diagram of FeTe, predicting structural and magnetic properties in the normal state at zero temperature within density functional theory (DFT). We carefully examined several possible different crystal structures over a pressure range up to $\approx 30 $ GPa: simple tetragonal (PbO type), simple monoclinic, orthorhombic (MnP type), hexagonal (NiAs and wurzite type) and cubic (CsCl and NaCl type). We predict pressure to drive the system through different magnetic ordering (notably also some ferromagnetic phases) eventually suppressing magnetism at around 17GPa. W…
The interplay between magnetism and superconductivity in LaFeAsO_0.945F_0.055 was studied as a function of hydrostatic pressure up to p~2.4GPa by means of muon-spin rotation (\muSR) and magnetization measurements. The application of pressure leads to a substantial decrease of the magnetic ordering temperature T_N and a reduction of the magnetic phase volume and, at the same time, to a strong increase of the superconducting transition temperature T_c and the diamagnetic susceptibility. From the volume sensitive \muSR measurements it can be concluded that the superconducting and the magnetic are…
We study the impact of hydrostatic pressure on superconductivity of new BiS2 based layered REO0.5F0.5BiS2 (RE-La, Pr, and Nd) compounds through the measurements of dc electrical resistivity. The REO0.5F0.5BiS2 (RE-La, Pr and Nd) compounds synthesized by solid state reaction route via vacuum encapsulation are crystallized in the tetragonal P4/nmm space group. At ambient pressure the superconducting transition onset temperatures are 2.7K, 3.5K and 4.5K which are enhanced substantially under external hydrostatic pressure to 10.5K, 7.8K and 7.5K for LaO0.5F0.5BiS2, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS…
We investigate the external hydrostatic pressure effect on the superconducting transition temperature (Tc) of new layered superconductors Bi4O4S3 and NdO0.5F0.5BiS2. Though the Tc is found to have moderate decrease from 4.8 K to 4.3 K (dTconset/dP = -0.28 K/GPa) for Bi4O4S3 superconductor, the same increases from 4.6 K to 5 K (dTconset/dP = 0.44 K/GPa) upto 1.31 GPa followed by a sudden decrease from 5 K to 4.7 K upto 1.75 GPa for NdO0.5F0.5BiS2 superconductor. The variation of Tc in these systems may be correlated to increase or decrease of the charge carriers in the density of states under e…
Superconductivity under pressure in FeSe ($T_{\rm c}$$\sim$7.5 K) has been investigated using single-crystal specimens through the measurements of DC magnetization and electrical resistivity. A characteristic three-step increase in $T_{\rm c}$ has been found under hydrostatic pressure up to $\sim$34 K above 7 GPa. The structural transition from a tetragonal phase to an orthorhombic phase ($T_{\rm s}$$\sim$87 K) is found to disappear at $P$$\sim$2.3 GPa, above which $T_{\rm c}$ increases rapidly, suggesting that the superconductivity is enhanced by the tetragonal environment. Under non-hydrosta…
Iron-based superconductors are well-known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition. In particular, the widely-observed tetragonal-to-orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to as nematic transition. Nematicity is therefo…
In an experiment in a diamond anvil cell utilizing helium pressure medium, yttrium metal displays a superconducting transition temperature which increases monotonically from Tc ? 3.5 K at 30 GPa to 17 K at 89.3 GPa, one of the highest transition temperatures for any elemental superconductor. The pressure dependence of Tc differs substantially from that observed in previous studies under quasihydrostatic pressure to 30 GPa. Remarkably, the dependence of Tc on relative volume V/Vo is linear over the entire pressure range above 33 GPa, implying that higher values of Tc are likely at higher pressu…
We investigate the hydrostatic pressure dependence of interfacial superconductivity occurring at the atomically sharp interface between two non-superconducting materials: the topological insulator (TI) Bi2Te3 and the parent compound Fe1+yTe of the chalcogenide iron based superconductors. Under pressure, a significant increase in the superconducting transition temperature Tc is observed. We trace the pressure dependence of a superconducting twin gap structure by Andreev reflection point contact spectroscopy (PCARS), which shows that a large superconducting gap associated with the interfacial su…
We report the impact of hydrostatic pressure on the superconductivity and normal state resistivity of FeTe0.5Se0.5 superconductor. At the ambient pressure the FeTe0.5Se0.5 compound shows the superconducting transition temperature Tconset at above 13K and TcR=0 at 11.5K. We measure pressure dependent resistivity from 250K to 5K, which shows that the normal state resistivity increases initially for the applied pressures of up to 0.55GPa and then the same is decreased monotonically with increasing pressure of up to 1.97GPa. On the other hand the superconducting transition temperatures (Tconset an…
The superfluid density and superconducting gaps of superconducting RbFe_{2}As_{2} have been determined as a function of temperature, magnetic field and hydrostatic pressure by susceptibility and muon-spin spectroscopy measurements. From the data, fundamental microscopic parameters of the superconducting state like the London penetration depth λ, the gap values Δ, the upper critical field B_{c2}, and the Ginzburg-Landau parameter κhave been obtained. In accordance with earlier measurements the ratio of the superfluid density n_{s} \propto λ^{-2} to the superconducting transition temperature T_{…
Hydrostatic pressure Raman measurements have been carried out on the SmFeAsO series of oxypnictides with varying amount of doping (F substitution for O and Co for Fe) and transition temperature (T_{c}), in order to investigate lattice modifications and their connection to doping and superconductivity. Synchrotron XRD data on some of these compounds indicated that at low doping the lattice constants vary smoothly with pressure, but with increasing F concentration there is a deviation from the normal equation of state and these effects are related with modifications in the superconducting FeAs4 …
Magnetization and muon spin rotation experiments were performed in La_(2-x)Ba_xCuO_4 (x = 1/8) as a function of hydrostatic pressure up to p = 2.2 GPa. It was found that the magnetic volume fraction of the static stripe phase strongly decreases linearly with pressure, while the superconducting volume fraction increases by the same amount. This demonstrates competition between bulk superconductivity and static magnetic order in the stripe phase of La_1.875Ba_0.125CuO_4 and that these phenomena occur in mutually exclusive spatial regions. The present results also reveal that the static spin-stri…
Polycrystalline samples of Sr1-xRExFBiS2 (RE: La, Ce, Pr, Nd, and Sm) were synthesized via the solid-state reaction and characterized using synchrotron X-ray diffraction. Although all the Sr0.5RE0.5FBiS2 samples exhibited superconductivity at transition temperatures (Tc) within the range of 2.1-2.7 K under ambient pressure, the estimated superconducting volume fraction was small. This indicated the non-bulk nature of superconductivity in these samples under ambient pressure. A dramatic evolution of the bulk superconducting phases was achieved on applying an external hydrostatic pressure. Near …
The influence of hydrostatic pressure up to P=1.05 GPa on resistivity R, excess conductivity $σ'(T)$ and pseudogap $Δ*(T)$ is studied in slightly doped single crystals of YBa2Cu3O7-$δ (Tc=49.2 K, δ~ 0.5)$. The critical temperature Tc is found to increase with increasing pressure at a rate dTc/dP = 5.1 K/GPa, while R(300)K decreases at a rate d(ln R)/dP = 0.19% 1/GPa. Near Tc, independently on pressure, the $σ'(T)$ is well described by the Aslamasov-Larkin and Hikami-Larkin fluctuation theories, demonstrating a 3D-2D crossover with increase of temperature. The crossover temperature To determine…
A notable characteristic of PbTaSe$_2$, a prototypical noncentrosymmetric (NCS) superconductor, is that its superconductivity can be modulated through a structural transition under hydrostatic pressure [Phys. Rev. B 95, 224508 (2017)]. Here we report on simultaneous pressure-sensitive point-contact Andreev reflection (PCAR) spectroscopy and bulk resistance measurements on PbTaSe$_2$, to elucidate the nature of the surface and bulk superconductivity and their evolution with hydrostatic pressure. It is found that in high pressure region the superconducting gap opening temperature $T_c^A$ is sign…
We report on the crystal growth and characterization of ABi3 (A=Ba,Sr) superconductors. Single crystals of both compounds were grown by the self-flux technique. BaBi3 crystallized in a tetragonal structure with space group P4/mmm and SrBi3 in a cubic structure with space group Pm-3m. Superconductivity at Tc = 6.0 K for BaBi3 and Tc = 5.6 K for SrBi3 have been confirmed through dc magnetic susceptibility and electrical transport measurements. The dc magnetic susceptibility under hydrostatic pressure shows a positive pressure coefficient of dTc/dP = 1.22 K/GPa for BaBi3 and a negative pressure c…
Using projector augmented wave approach within the generalized gradient approximation, we have studied the structural property and electronic structure of ZrB12. The calculated lattice constants and bulk modulus are in good agreement with the available experimental values. A detailed study of the electronic structure and the charge-density redistribution reveals the features of strong covalent B-B and weak covalent Zr-B bondings in ZrB12. The states at the Fermi level mainly come from the $σ$-$p_{y}$ and $π$-$p_{z}$ orbitals of boron atoms, which are slightly hybridized with the $t_{2g}$-$d_{x…
In this paper we report parallel in situ neutron powder diffraction and Tc(P) measurements versus pressure on the same MgB2 sample in a He-gas apparatus to 0.6 GPa; in addition, we present Tc(P) measurements in a helium-loaded diamond-anvil-cell to 20 GPa on the same sample. Our results are compared with those of other groups. The high precision achieved in these measurements allows a quantitative evaluation of the change in Tc as a function of the changes in structure. Our results are consistent with electron-phonon pairing in MgB2.
We have investigated the pressure effect on the newly discovered samarium doped La1-xSmxO0.5F0.5BiS2 superconductors. More than threefold increase in Tc (10.3 K) is observed with external pressure (at ~1.74 GPa at a rate of 4.08 K/GPa)) for x = 0.2 composition. There is a concomitant large improvement in the quality of the superconducting transition. Beyond this pressure Tc decreases monotonously at the rate of -2.09 K/GPa. In the x = 0.8 sample, we do not observe any enhancement in Tc with application of pressure (up to 1.76 GPa). The semiconducting behavior observed in the normal state resis…
