arXiv subjects

Gil Drachuck

Publications and source records attributed to Gil Drachuck.

14 recordsLinked to original sources

arXiv2020

Evolution of nematic fluctuations in CaK(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$ with spin-vortex crystal magnetic order

The CaK(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$ superconductors resemble the archetypal 122-type iron-based materials but have a crystal structure with distinctly lower symmetry. This family hosts one of the few examples of the so-called spin-vortex crystal magnetic order, a non-collinear magnetic configuration that preserves tetragonal symmetry, in contrast to the orthorhombic collinear stripe-type magnetic configuration common to the 122-type systems. Thus, nematic order is completely absent from its phase diagram. To investigate the evolution of nematic fluctuations in such a case, we present elastoresistance and elastic modulus measurements in CaK(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$ ($x = 0-0.05$) combined with phenomenological modeling and density functional theory. We find clear experimental signatures of considerable nematic fluctuations, including softening of the Young's modulus $Y_{[110]}$ and a Curie-Weiss type divergence of the B2g elastoresistance coefficient in CaK(Fe$_{0.951}$Ni$_{0.049}$)$_4$As$_4$. Overall, nematic fluctuations within this series bear strong similarities to the hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ series, including a substitution-induced sign change. Our theoretical analysis addresses the effect of the specific crystal symmetry of the 1144-type structure in determining its magnetic ground state and on the nematic fluctuations.

cond-mat.supr-con↗

arXiv2019

Use of Cernox thermometers in AC specific heat measurements under pressure

We report on the resistance behavior of bare-chip Cernox thermometers under pressures up to 2 GPa, generated in a piston-cylinder pressure cell. Our results clearly show that Cernox thermometers, frequently used in low-temperature experiments due to their high sensitivity, remain highly sensitive even under applied pressure. We show that these thermometers are therefore ideally suited for measurements of heat capacity under pressure utilizing an ac oscillation technique up to at least 150 K. Our Cernox-based system is very accurate in determining changes of the specific heat as a function of pressure as demonstrated by measurements of the heat capacity on three different test cases: (i) the superconducting transition in elemental Pb (T_{c} = 7.2 K), (ii) the antiferromagnetic transition in the rare-earth compound GdNiGe3 (T_{N} = 26 K) and (iii) the structural/magnetic transition in the iron-pnictide BaFe2As2 (T_{s,N} = 130 K). The chosen examples demonstrate the versatility of our technique for measuring the specific heat under pressure of various condensed matter systems with very different transition temperatures as well as amounts of removed entropy.

cond-mat.mtrl-sci↗

arXiv2018

The Effect of Nickel Substitution on Magnetism in the Layered van der Waals Ferromagnet Fe$_3$GeTe$_2$

We have grown a series of nickel substituted single crystals of the layered ferromagnet (FM) Fe$_3$GeTe$_2$. The large single crystalline samples of (Fe$_{1-x}$Ni$_x$)$_3$GeTe$_2$ with $x = 0-0.84$ were characterized with single crystal X-ray diffraction, magnetic susceptibility, electrical resistance and muon spin spectroscopy. We find Fe can be continuously substituted with Ni with only minor structural variation. In addition, FM order is suppressed from $T_\mathrm{C}=212$~K for $x=0$ down to $T_\mathrm{C}=50$~K for $x=0.3$, which is accompanied with a strong suppression of saturated and effective moment, and Curie-Weiss temperature. Beyond $x=0.3$, the FM order is continuously smeared into a FM cluster glass phase, with a nearly full magnetic volume fraction. We attribute the observed change in the nature of magnetic order to the intrinsically disordered structure of Fe$_3$GeTe$_2$ and subsequent dilution effects from the Ni substitution.

cond-mat.str-el↗

arXiv2018

Electronic structure of topological superconductor candidate Au${}_{2}$Pb

We use magnetization measurements, high-resolution angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations to study the electronic properties of Au${}_{2}$Pb, a topological superconductor candidate. The magnetization measurements reveal three discontinuities at 40, 51, and 99~K that agree well with reported structural phase transitions. ARPES measurements of the Au${}_{2}$Pb (111) surface at 110~K shows a shallow hole pocket at the center and flower-petal-like surface states at the corners of the Brillouin zone. These observations match the results of DFT calculations relatively well. The flower-petal-like surface states appear to originate from a Dirac like dispersion close to the zone corner. For the Au${}_{2}$Pb (001) surface at 150~K, ARPES reveals at least one electron pocket between the $Γ$ and $M$ points, consistent with the DFT calculations. Our results provide evidence for the possible existence of Dirac state in this material.

cond-mat.str-el↗

arXiv2017

Collapsed Tetragonal Phase Transition in LaRu$_2$P$_2$

The structural properties of LaRu$_2$P$_2$ under external pressure have been studied up to 14 GPa, employing high-energy x-ray diffraction in a diamond-anvil pressure cell. At ambient conditions, LaRu$_2$P$_2$ (I4/mmm) has a tetragonal structure with a bulk modulus of $B=105(2)$ GPa and exhibits superconductivity at $T_c= 4.1$ K. With the application of pressure, LaRu$_2$P$_2$ undergoes a phase transition to a collapsed tetragonal (cT) state with a bulk modulus of $B=175(5)$ GPa. At the transition, the c-lattice parameter exhibits a sharp decrease with a concurrent increase of the a-lattice parameter. The cT phase transition in LaRu$_2$P$_2$ is consistent with a second order transition, and was found to be temperature dependent, increasing from $P=3.9(3)$ GPa at 160 K to $P=4.6(3)$ GPa at 300 K. In total, our data are consistent with the cT transition being near, but slightly above 2 GPa at 5 K. Finally, we compare the effect of physical and chemical pressure in the RRu$_2$P$_2$ (R = Y, La-Er, Yb) isostructural series of compounds and find them to be analogous.

cond-mat.supr-con↗

arXiv2017

Dynamic Elastoresistivity Evidence for Slow Nematic Fluctuations in BaFe$_2$As$_2$

An instrumentation problem with the signal acquisition at high frequencies was discovered and we no longer believe that the experimental data presented in the manuscript, showing a frequency enhancement of the elastoresistivity, are correct. After correcting the problem, the elastoresistivity data is frequency independent in the range investigated. Therefore, the authors have withdrawn this submission. We would like to thank Alex Hristov, Johanna Palmstrom, Josh Straquadine and Ian Fisher (Stanford) for the kind discussions and assistance we received which helped us identify these problems.

cond-mat.str-el↗

arXiv2016

Opening a nodal gap by fluctuating spin-density-wave in lightly doped La$_{2-x}$Sr$_x$CuO$_4$

We investigate whether the spin or charge degrees of freedom are responsible for the nodal gap in underdoped cuprates by performing inelastic neutron scattering and x-ray diffraction measurements on La$_{2-x}$Sr$_x$CuO$_4$, which is on the edge of the antiferromagnetic phase. We found that fluctuating incommensurate spin-density-wave (SDW) with a the bottom part of an hourglass dispersion exists even in this magnetic sample. The strongest component of these fluctuations diminishes at the same temperature where the nodal gap opens. X-ray scattering measurements on the same crystal show no signature of charge-density-wave (CDW). Therefore, we suggest that the nodal gap in the electronic band of this cuprate opens due to fluctuating SDW with no contribution from CDW.

cond-mat.supr-con↗

arXiv2016

Magnetization and transport properties of single crystalline RPd${_2}$P${_2}$ (R=Y, La-Nd, Sm-Ho, Yb)

Single crystals of RPd${_2}$P${_2}$ (R=Y, La-Nd, Sm-Ho, Yb) were grown out of a high temperature solution rich in Pd and P and characterized by room-temperature powder X-ray diffraction, anisotropic temperature- and field-dependent magnetization and temperature-dependent in-plane resistivity measurements. In this series, YPd${_2}$P${_2}$ and LaPd${_2}$P${_2}$ and YbPd${_2}$P${_2}$ (with Yb$^{+2}$) are non local-moment bearing, whereas CePd${_2}$P${_2}$ and PrPd${_2}$P${_2}$ order at low temperature with a ferromagnetic component along the crystallographic c-axis. The rest of the series manifest low temperature antiferromagnetic ordering. EuPd${_2}$P${_2}$ has Eu$^{+2}$ ions and both EuPd${_2}$P${_2}$ and GdPd${_2}$P${_2}$ have isotropic paramagnetic susceptibilities consistent with $L = 0$ and $J=S=\frac{7}{2}$ and exhibit multiple magnetic transitions. For R=Eu-Dy, there are multiple, $T>1.8$ K transitions in zero applied magnetic field and for R=Nd, Eu, Gd, Tb, and Dy there are clear metamagnetic transitions at T=2.0 K for $H<55$ kOe. Strong anisotropies arising mostly from crystal electric field (CEF) effects were observed for most magnetic rare earths with $L\neq 0$. The experimentally estimated CEF parameters B$^2_0$ were calculated from the anisotropic paramagnetic $θ_{ab}$ and $ θ_{c}$ values and compared to theoretical trends across the rare earth series. The ordering temperatures as well as the polycrystalline averaged paramagnetic Curie-Weiss temperature, $θ_{ave}$, were extracted from magnetization and resistivity measurements, and compared to the de-Gennes factor.

cond-mat.str-el↗

arXiv2015

Correlation of the Superconducting Critical Temperature with Spin and Orbital Excitation Energies In (Ca{x}La{1-x})(Ba{1.75-x}La{0.25+x})Cu{3}O{y} as Measured by Resonant Inelastic X-ray Scattering

Electronic spin and orbital (dd) excitation spectra of (Ca{x}La{1-x})(Ba{1.75-x}La{0.25+x})Cu{3}O{y} samples are measured by resonant inelastic x-ray scattering (RIXS). In this compound, Tc of samples with identical hole dopings is strongly affected by the Ca/Ba substitution x due to subtle variations in the lattice constants, while crystal symmetry and disorder as measured by line-widths are x independent. We examine two extreme values of x and two extreme values of hole-doping content y corresponding to antiferromagnetic and superconducting states. The x dependence of the spin mode energies is approximately the same for both the antiferromagnetic and superconducting samples. This clearly demonstrates that RIXS is sensitive to J even in doped samples. A positive correlation between the superexchange J and the maximum of Tc at optimal doping Tc^{max} is observed. We also measured the x dependence of the d_{xy} -> d_{x^2-y^2} and d_{xz/yz} -> d_{x^2-y^2} orbital splittings. We infer that the effect of the unresolved d_{3z^2-r^2} -> d_{x^2-y^2} excitation on Tc^{max} is much smaller than the effect of J. There appears to be dispersion in the d_{xy} -> d_{x^2-y^2} peak of up to 0.05 eV. Our fitting of the peaks furthermore indicates an asymmetric dispersion for the d_{xz/yz} -> d_{x^2-y^2} excitation. A peak at ~0.8 eV is also observed, and attributed to a dd excitation in the chain layer.

cond-mat.supr-con↗

arXiv2014

Relation between cuprate superconductivity and magnetism: A Raman study of (CaLa)(BaLa)$_{2}$Cu$_{3}$O$_{y}$

We present an investigation of charge-compensated antiferromagnetic (Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_{3}$O$_{y}$ single crystals using Raman scattering as well as muon spin rotation. In this system the parameter $x$ controls the Cu-O-Cu superexchange interaction via bond distances and buckling angles. The oxygen content $y$ controls the charge doping. In the absence of doping the two-magnon peak position is directly proportional to the superexchange strength $J$. We find that both $x$ and $y$ affect the peak position considerably. The Néel temperature determined from muon spin rotation on the same samples independently confirms the strong dependence of the magnetic interaction on $x$ and $y$. We find a considerable increase in the maximum superconducting transition temperature $T_{c}^{max}$ with $J$. This is strong evidence of the importance of orbital overlap to superconductivity in this family of cuprates.

cond-mat.supr-con↗

arXiv2014

Spin-charge interplay in antiferromagnetic La$_{2-x}$Sr$_{x}$CuO$_{4}$ studied by the muons, neutrons, and ARPES techniques

Exploring whether a spin density wave (SDW) is responsible for the charge excitations gap in the high-temperature superconducting cuprates is difficult, since the region of the phase diagram where the magnetic properties are clearly exposed is different from the region where the band dispersion is visible. On the one hand, long range magnetic order disappears as doping approaches 2% from below, hindering our ability to perform elastic neutron scattering (ENS). On the other hand, cuprates become insulating at low temperature when the doping approaches 2% from above, thus restricting angle-resolved photoemission spectroscopy (ARPES). In fact, ARPES data for samples with doping lower than 3% are rare and missing the quasiparticle peaks in the energy distribution curves (EDCs). The main problem is the high resistivity of extremely underdoped samples, which is detrimental to ARPES due to charging effects. Nevertheless, the resistivity of La$_{2-x}$Sr$_{x}$CuO$_{4}$ as a function of temperature, at 2% doping, has a broad minimum around 100K. This minimum opens a window for both experiments. By preparing a series of LSCO single crystals with $\sim $0.2-0.3% doping steps around 2%, we managed to find one to which both techniques apply. This allows us to explore the cross talk between the magnetic and electronic properties of the material.

cond-mat.supr-con↗

arXiv2014

Linking Dynamic and Thermodynamic Properties of Cuprates; an ARPES study of (CaLa)(BaLa)$_{2}$Cu$_{3}$O$_{y}$

We report angle-resolved photoemission spectroscopy (ARPES) on two families of high temperature superconductors (Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$ La $% _{0.25+x}$)Cu$_{3}$O$_{y}$ with $x=0.1$ ($T_{c}^{max}=56$ K) and $x=0.4$ ($% T_{c}^{max}=82$ K). The Fermi surface (FS) is found to be independent of $x$ or $y$, and its size indicates extreme sample-surface overdoping. This universal FS allowes the comparison of dynamical properties between superconductors of similar structure and identical doping, but different $% T_{c}^{max}$. We find that the high-energy ($\left\vert E\right\vert >50$% meV) nodal velocity in the $x=0.4$ family is higher than in the $x=0.1$ family. The implied correlation between $T_{c}^{max}$ and the hopping rate $% t $ supports the notion of kinetic energy driven superconductivity in the cuprates. We also find that the antinodal gap is higher for the $x=0.4$ family.

cond-mat.supr-con↗

arXiv2012

Parallel and Perpendicular Susceptibility Above $T_{c}$ in La$_{2-x}$Sr$_{x}$CuO$_{4}$ Single Crystals

We report direction-dependent susceptibility and resistivity measurements on La$_{2-x}$Sr$_{x}$CuO$_{4}$ single crystals. These crystals have rectangular needle-like shapes with the crystallographic "c" direction parallel or perpendicular to the needle axis,which, in turn, is in the applied field direction. At optimal doping we find finite diamagnetic susceptibility above $T_{c}$, namely fluctuating superconductivity (FSC), only when the field is perpendicular to the planes. In underdoped samples we could find FSC in both field directions. We provide a phase diagram showing the FSC region, although it is sample dependent in the underdoped cases. The variations in the susceptibility data suggest a different origin for the FSC between underdoping (below 10%) and optimal doping. Finally, our data indicates that the spontaneous vortex diffusion constant above $T_c$ is anomalously high.

cond-mat.supr-con↗

arXiv2012

New Perspectives for Cuprate Research: CLBLCO Single Crystals

We report the successful growth of a large (Ca$_{x}$La$_{1-x}$)(Ba$_{1.75-x}$La$_{0.25+x}$)Cu$_{3}$O$_{y}$ (CLBLCO) single crystal. In this material, $x$ controls the maximum of Tc ($T_{c}^{\max}$), with minimal structural changes. Therefore, it allows a search for correlations between material properties and $T_{c}^{\max}$. We demonstrate that the crystals are good enough for neutron scattering and cleave well enough for Raman scattering. These results open new possibilities for cuprate research.

cond-mat.supr-con↗