arXiv subjects

C. Petrovic

Publications and source records attributed to C. Petrovic.

At least 181 records · Page 10Linked to original sources

arXiv2010

Pauli-limited upper critical field in Fe1+yTe1-xSex

In this work we investigated the temperature dependence of the upper critical field u0Hc2(T) of Fe1.02(3)Te0.61(4)Se0.39(4) and Fe1.05(3)Te0.89(2)Se0.11(2) single crystals by measuring the magnetotransport properties in stable dc magnetic fields up to 35 T. Both crystals show that u0Hc2(T) in the ab-plane and along the c-axis exhibit saturation at low temperatures. The anisotropy of u0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic when the temperature T->0. Furthermore, u0Hc2(0) deviates from the conventional Werthamer-Helfand-Hohenberg (WHH) theoretical prediction values for both field directions. Our analysis indicates that the spin-paramagnetic pair-breaking effect is responsible for the temperature-dependent behavior of u0Hc2(T) in both field directions.

cond-mat.supr-con↗

arXiv2010

Effects of excess Fe on upper critical field and magnetotransport in Fe1+y(Te1-xSx)z

We have investigated the upper critical field anisotropy and magnetotransport properties of Fe1.14(1)Te0.91(2)S0.09(2) single crystals in stable magnetic fields up to 35 T. The results show that u0Hc2(T) along the c axis and in the ab-plane exhibit saturation at low temperatures. The anisotropy of u0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic for T->0. Our analysis indicates that the spin-paramagnetic pair-breaking with spin-orbital scattering is responsible for the behavior of u0Hc2(T). Furthermore, from analysis of the normal state properties, we show evidence that the excess Fe acting as Kondo-type impurities is a key factor determining the normal and superconducting state physical properties.

cond-mat.supr-con↗

arXiv2010

Normal state charge dynamics of Fe1.06Te0.88S0.14 superconductor probed with infrared spectroscopy

We have used optical spectroscopy to probe the normal state electrodynamic response of Fe$_{1.06}$Te$_{0.88}$S$_{0.14}$, a member of the 11 family of iron-based superconductors with T$_c$= 8 K. Measurements have been conducted over a wide frequency range (50 - 50000 cm$^{-1}$) at selected temperatures between 10 and 300 K. At low temperatures the material behaves as an "incoherent metal": a Drude-like peak is absent from the optical conductivity, and all optical functions reveal that quasiparticles are not well defined down to the lowest measured temperature. We introduce "generalized spectral weight" analysis and use it to track temperature induced redistribution of spectral weight. Our results, combined with previous reports, indicate that the 11 family of iron-based superconductors might be different from other families.

cond-mat.supr-con↗

arXiv2010

Observations of Pauli Paramagnetic Effects on the Flux Line Lattice in CeCoIn5

From small-angle neutron scattering studies of the flux line lattice (FLL) in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field- and temperature-dependence of the FLL form factor, which is a measure of the spatial variation of the field in the mixed state. We extend our earlier work [A.D. Bianchi et al. 2008 Science 319, 177] to temperatures up to 1250 mK. Over the entire temperature range, paramagnetism in the flux line cores results in an increase of the form factor with field. Near H_c2 the form factor decreases again, and our results indicate that this fall-off extends outside the proposed FFLO region. Instead, we attribute the decrease to a paramagnetic suppression of Cooper pairing. At higher temperatures, a gradual crossover towards more conventional mixed state behavior is observed.

cond-mat.supr-con↗

arXiv2010

London penetration depth and superfluid density in single crystals of Fe(Te,Se) and Fe(Te,S) superconductors

The in-plane London penetration depth, $λ(T)$, was measured in single crystals of the iron-chalcogenide superconductors Fe$_{1.03}$(Te$_{0.63}$Se$_{0.37}$) and Fe$_{1.06}$(Te$_{0.88}$S$_{0.14}$) by using a radio-frequency tunnel diode resonator. As is also the case for the iron-pnictides, these iron-chalcogenides exhibit a nearly quadratic temperature variation of $λ(T)$ at low temperatures. The absolute value of the penetration depth in the $T \to 0$ limit was determined for Fe$_{1.03}$(Te$_{0.63}$Se$_{0.37})$ by using an Al coating technique, giving $λ(0)\approx560 \pm 20$ nm. The superfluid density $ρ_s(T)=λ^2(0)/λ^2(T)$ was fitted with a self-consistent two-gap $γ-$model. While two different gaps are needed to describe the full-range temperature variation of $ρ_s(T)$, a non-exponential behavior at low temperatures requires additional factors, such as scattering and/or significant gap anisotropy.

cond-mat.supr-con↗

arXiv2009

Magnetism, Superconductivity and Stoichiometry in Single Crystals of Fe1+y(Te1-xSx)z

We report synthesis of high quality Fe1+y(Te1-xSx)z single crystals and a comprehensive study of structural, magnetic and transport properties. There is high sensitivity to material stoichiometry which includes vacancies on the Te(S) site. Our results reveal competition and coexistence of magnetic order and percolative superconductivity for x >= 0.03, while zero resistivity is acheived for x >= 0.1.

cond-mat.supr-con↗

arXiv2009

Isotropic superconducting state and high critical currents in Fe1+yTe1-xSx single crystals

We report single crystal growth and a study of superconducting properties in Fe_{1+y}Te_{1-x}S_{x}. We demonstrate the smallest upper critical field anisotropy, gamma=H_{c2}^{//c}/H_{c2}^{//a}, among all iron based superconductors, the value of gamma reaches 1.05 at T=0.65T_{C} for Fe_{1.09}Te_{0.89}S_{0.11}, while still maintaining large values of upper critical field.

cond-mat.supr-con↗

arXiv2009

Signatures of electron-boson coupling in half-metallic ferromagnet Mn$_5$Ge$_3$: study of electron self-energy $Σ(ω)$ obtained from infrared spectroscopy

We report results of our infrared and optical spectroscopy study of a half-metallic ferromagnet Mn$_5$Ge$_3$. This compound is currently being investigated as a potential injector of spin polarized currents into germanium. Infrared measurements have been performed over a broad frequency (50 - 50000 cm$^{-1}$) and temperature (10 - 300 K) range. From the complex optical conductivity $σ(ω)$ we extract the electron self-energy $Σ(ω)$. The calculation of $Σ(ω)$ is based on novel numerical algorithms for solution of systems of non-linear equations. The obtained self-energy provides a new insight into electron correlations in Mn$_5$Ge$_3$. In particular, it reveals that charge carriers may be coupled to bosonic modes, possibly of magnetic origin.

cond-mat.str-el↗

arXiv2009

Pressure Evolution of a Field Induced Fermi Surface Reconstruction and of the Neel Critical Field in CeIn3

We report high-pressure skin depth measurements on the heavy fermion material CeIn3 in magnetic fields up to 64 T using a self-resonant tank circuit based on a tunnel diode oscillator. At ambient pressure, an anomaly in the skin depth is seen at 45 T. The field where this anomaly occurs decreases with applied pressure until approximately 1.0 GPa, where it begins to increase before merging with the antiferromagnetic phase boundary. Possible origins for this transport anomaly are explored in terms of a Fermi surface reconstruction. The critical magnetic field at which the Neel ordered phase is suppressed is also mapped as a function of pressure and extrapolates to the previous ambient pressure measurements at high magnetic fields and high pressure measurements at zero magnetic field.

cond-mat.str-el↗

arXiv2009

Universal heat transport in a heavy-fermion superconductor

The symmetry of the order parameter is the defining property of a superconductor and a strong clue to its pairing mechanism. While d-wave symmetry is firmly established in high-Tc superconductors, in no heavy-fermion superconductor is the symmetry known definitively. One way to elucidate the order parameter is to locate the symmetry-imposed nodes in the energy gap by measuring the heat carried by the zero-energy quasiparticles associated with those nodes as a function of direction. As verified in high-Tc superconductors a line of nodes yields universal heat transport independent of impurity scattering. Here we show that heat conduction in the heavy-fermion superconductor CeIrIn5 is also universal, but only for a current perpendicular to the tetragonal axis of its crystal structure, not parallel to it. This uniaxial anisotropy is strong evidence for a line of nodes in the basal plane, which is inconsistent with the d-wave symmetry proposed for the isostructural superconductor CeCoIn5. Different symmetries in the two materials would explain why the phase diagram of these heavy-fermion compounds consists of two separate superconducting domes.

cond-mat.str-el↗

arXiv2008

Generalized Elliott-Yafet theory of electron spin relaxation in metals: the origin of the anomalous electron spin life-time in MgB2

The temperature dependence of the electron spin relaxation time in MgB2 is anomalous as it does not follow the temperature dependence of the resistivity above 150 K, it has a maximum around 400 K, and it decreases for higher temperatures. This violates the well established Elliot-Yafet theory of electron spin relaxation in metals. We show that the anomaly occurs when the quasi-particle scattering rate (in energy units) becomes comparable to the energy difference between the conduction- and a neighboring band. We find that the anomalous behavior is related to the unique band structure of MgB$_2$ and the large electron-phonon coupling. The saturating spin-lattice relaxation can be regarded as the spin transport analogue of the Ioffe-Regel criterion of electron transport.

cond-mat.str-el↗

arXiv2008

Evidence for the band broadening across the ferromagnetic transition in Cr$_{1/3}$NbSe$_2$

The electronic structure of Cr$_{1/3}$NbSe$_2$ is studied via optical spectroscopy. We observe two low-energy interband transitions in the paramagnetic phase, which split into four peaks as the compound enters the ferromagnetic state. The band structure calculation indicates the four peaks are interband transitions to the spin up Cr e$_g$ states. We show that the peak splitting below the Curie temperature is \emph{not} due to the exchange splitting of spin up and down bands, but directly reflects a band broadening effect in Cr-derived states upon the spontaneous ferromagnetic ordering.

cond-mat.str-el↗

arXiv2008

Giant Carrier Mobility in Single Crystals of FeSb2

We report the giant carrier mobility in single crystals of FeSb2. Nonlinear field dependence of Hall resistivity is well described with the two-carrier model. Maximum mobility values in high mobility band reach ~10^5 cm^2/Vs at 8 K, and are ~10^2 cm^2/Vs at the room temperature. Our results point to a class of materials with promising potential for applications in solid state electronics.

cond-mat.str-el↗

arXiv2008

Composition and field tuned magnetism and superconductivity in Nd1-xCexCoIn5

The Nd1-xCexCoIn5 alloys evolve from local moment magnetism (x = 0) to heavy fermion superconductivity (x =1). Magnetic order is observed over a broad range of x. For a substantial range of x (0.83 <= x <= 0.95) in the temperature - composition phase diagram we find that superconductivity may coexist with spin - density wave magnetic order at the Fermi surface. We show that a delicate balance betwen superconducting and magnetic instabilities can be reversibly tuned by both the Ce/Nd ratio and magnetic field, offering a new and unique model electronic system.

cond-mat.str-el↗

arXiv2008

Anisotropy in magnetic and transport properties of Fe1-xCoxSb2

Anisotropic magnetic and electronic transport measurements were carried out on large single crystals of Fe1-xCoxSb2 (0<= x <=1). The semiconducting state of FeSb2 evolves into metallic and weakly ferromagnetic by substitution of Fe with Co for x<0.5. Further doping induces structural transformation from orthorhombic Pnnm structure of FeSb2 to monoclinic P21/c structure of CoSb2 where semiconducting and diamagnetic ground state is restored again. Large magnetoresistance and anisotropy in electronic transport were observed.

cond-mat.str-el↗

arXiv2008

Anisotropy of Electrical Transport and Superconductivity in Metal Chains of Nb2Se3

In this work we have shown bulk superconductivity and studied the anisotropy in both the normal and superconducting states in quasi-1D conductor Nb2Se3. Electron - electron Umklapp scattering dominates electronic transport along the direction of Nb metal chains as well as perpendicular to it. The superconducting state is rather anisotropic with possible multi - band features.

cond-mat.supr-con↗

arXiv2008

Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2

We have investigated anisotropy in magnetic and electrical transport properties of Fe1-xCrxSb2 (0<= x <=1) single crystals. The magnetic ground state of the system evolves from paramagnetic to antiferromagnetic with gradual substitution of Fe with Cr. Anisotropy in electrical transport diminishes with increased Cr substitution and fades away by x=0.5. We find that the variable range hopping (VRH) conduction mechanism dominates at low temperatures for 0.4<= x <=0.75.

cond-mat.str-el↗

arXiv2008

Weak Ferromagnetism in Fe1-xCoxSb2

Weak ferromagnetism in Fe1-xCoxSb2 is studied by magnetization and Mossbauer measurements. A small spontaneous magnetic moment of the order of 10^-3 uB appears along the b-axis for 0.2<= x <= 0.4. Based on the structural analysis, we argue against extrinsic sources of weak ferromagnetism. We discuss our results in the framework of the nearly magnetic electronic structure of the parent compound FeSb2.

cond-mat.str-el↗