arXiv subjects

J. Jaroszynski

Publications and source records attributed to J. Jaroszynski.

At least 19 recordsLinked to original sources

arXiv2025

Single-gap two-band superconductivity well above the Pauli limit in non-centrosymmetric TaIr$_2$B$_2$

Non-centrosymmetric superconducting materials represent an exciting class of novel superconductors featuring a variety of unconventional properties, including mixed-parity pairing and very high upper critical fields. Here, we present a comprehensive study of TaIr$_2$B$_2$ (with $T_c$ = 5.1 K), using a set of complementary experimental methods, including bulk- and surface-sensitive techniques. We provide evidence that this system is a two-band, yet it behaves as a single-gap superconductor with a strong coupling. The upper critical field of TaIr$_2$B$_2$ significantly exceeds the Pauli limit and exhibits a nearly linear temperature dependence down to the lowest temperatures. This behavior, rarely seen in superconductors, is discussed in terms of anti-symmetric spin-orbit interaction, two-band-, and strong-coupling effects, as well as disorder.

cond-mat.supr-con↗

arXiv2025

Critical Current, Lengthwise Fluctuations, and Flux Jumps in REBCO CC: A Torque Magnetometry Study up to 45 T

Rare Earth Barium Copper Oxide (REBCO) coated conductors (CCs) have emerged for future high field magnets in fields and temperatures inaccessible for Nb based superconductors. However, their exceptionally high current densities pose challenges for low temperature characterization. This paper presents the design and implementation of a simple torque magnetometer that is particularly suitable for characterizing REBCO CC. It details the construction and underlying physics, with a particular emphasis on its capability to assess the angular critical currents Ic in high magnetic fields and low temperatures. The study includes characterizations of multiple REBCO samples from different manufacturers, performed under magnetic fields up to 45 T, demonstrating the exceptional capabilities of REBCO CCs in extreme fields. The results revealed significant lengthwise Ic variations, especially in tapes cut from the edges of 12 mm-wide production tapes compared to those cut from the center. These variations are most pronounced when the field is near the ab plane. Importantly, flux jumps are observed in samples with thick REBCO layers and thin stabilizers, underscoring the potential thermal instabilities. These findings provide valuable insights into the performance of REBCO tapes under extreme magnetic fields, highlighting their relevance for high-field magnet and nuclear fusion applications.

cond-mat.supr-con↗

arXiv2021

Charge order dynamics in underdoped La$\mathbf{_{1.6-\textit{x}}}$Nd$\mathbf{_{0.4}}$Sr$\mathbf{_\textit{x}}$CuO$\mathbf{_{4}}$ revealed by electric pulses

The dynamics of the charge-order domains has been investigated in La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$, a prototypical stripe-ordered cuprate, using pulsed current injection. We first identify the regime in which nonthermal effects dominate over simple Joule heating, and then demonstrate that, for small enough perturbation, pulsed current injection allows access to nonthermally-induced resistive metastable states. The results are consistent with pinning of the fluctuating charge order, with fluctuations being most pronounced at the charge-order onset temperature. The nonequilibrium effects are revealed only when the transition is approached from the charge-ordered phase. Our experiment establishes pulsed current injection as a viable and effective method for probing the charge-order dynamics in various other materials.

cond-mat.str-el↗

arXiv2018

Hole-pocket-driven superconductivity and its universal features in the electron-doped cuprates

After three decades of enormous scientific inquiry, the emergence of superconductivity in the cuprates remains an unsolved puzzle. One major challenge has been to arrive at a satisfactory understanding of the unusual metallic normal state from which the superconducting state emerges upon cooling. A second challenge has been to achieve a unified understanding of hole- and electron-doped compounds. Here we report detailed magnetoresistivity measurements for the archetypal electron-doped cuprate Nd$_{2-x}$Ce$_x$CuO$_{4+δ}$ that, in combination with prior data, provide crucial links between the normal and superconducting states and between the electron- and hole-doped parts of the phase diagram. The characteristics of the normal state (magnetoresistivity, quantum oscillations, and Hall coefficient) and those of the superconducting state (superfluid density and upper critical field) consistently indicate two-band (electron and hole) features and clearly point to hole-pocket-driven superconductivity in these nominally electron-doped materials. We show that the approximate Uemura scaling between the superconducting transition temperature and the superfluid density found for hole-doped cuprates also holds for the small hole component of the superfluid density in the electron-doped cuprates.

cond-mat.str-el↗

arXiv2017

Doping evolution of the anisotropic upper critical fields in iron-based superconductor Ba$_{1-x}$K$_x$Fe$_2$As$_2$

In-plane resistivity measurements as a function of temperature and magnetic field up to 35~T with precise orientation within the crystallographic $ac-$plane were used to study the upper critical field, $H_{c2}$, of the hole-doped iron-based superconductor Ba$_{1-x}$K$_x$Fe$_2$As$_2$. Compositions of the samples studied were spanning from underdoped $x=$0.17 ($T_c$=12~K) and $x$=0.22 ($T_c$=20~K), both in the coexistence range of stripe magnetism and superconductivity, though optimal doping $x$=0.39 ($T_c$=38.4~K), $x$=0.47 ($T_c$=37.2~K), to overdoped $x$=0.65 ($T_c$=22~K), $x$=0.83 ($T_c$=10~K). We find notable doping asymmetry of the shapes of the anisotropic $H_{c2}(T)$ suggesting important role of paramagnetic limiting effects in $H \parallel a$ configuration in overdoped compositions and multi-band effects in underdoped compositions.

cond-mat.supr-con↗

arXiv2017

Selective mass enhancement close to the quantum critical point in BaFe$_2$(As$_{1-x}$P$_x$)$_2$

A quantum critical point (QCP) is currently being conjectured for the BaFe$_2$(As$_{1-x}$P$_x$)$_2$ system at the critical value $x_{\rm c} \approx$ 0.3. In the proximity of a QCP, all thermodynamic and transport properties are expected to scale with a single characteristic energy, given by the quantum fluctuations. Such an universal behavior has not, however, been found in the superconducting upper critical field $H_{\rm c2}$. Here we report $H_{\rm c2}$-data for epitaxial thin films extracted from the electrical resistance measured in very high magnetic fields up to 67 Tesla. Using a multi-band analysis we find that $H_{\rm c2}$ is sensitive to the QCP, implying a significant charge carrier effective mass enhancement at the doping-induced QCP that is essentially band-dependent. Our results point to two qualitatively different groups of electrons in BaFe$_2$(As$_{1-x}$P$_x$)$_2$. The first one (possibly associated to hot spots or whole Fermi sheets) has a strong mass enhancement at the QCP, and the second one is insensitive to the QCP. The observed duality could also be present in many other quantum critical systems.

cond-mat.supr-con↗

arXiv2016

Intrinsic and extrinsic pinning in NdFeAs(O,F): vortex trapping and lock-in by the layered structure

The Fe-based superconductors (FBS) present a large variety of compounds whose properties are affected to different extents by their crystal structures. Amongst them, the $\it{RE}$FeAs(O,F) ($\it{RE}$1111, where $\it{RE}$ is a rare earth element) is the family with the highest critical temperature $T_c$ but also with a large anisotropy and Josephson vortices as demonstrated in the flux-flow regime in Sm1111 ($T_c$ $\sim$ 55 K). Here we focus our attention on the pinning properties of the lower-$T_c$ Nd1111 in the flux-creep regime. We demonstrate that for H//c critical current density $J_c$ at high temperatures is dominated by point-defect pinning centres, whereas at low temperatures surface pinning by planar defects parallel to the $\it{c}$-axis and vortex shearing prevail. When the field approaches the $\it{ab}$-planes, two different regimes are observed at low temperatures as a consequence of the transition between 3D-Abrikosov and 2D-Josephson vortices: one is determined by the formation of a vortex staircase structure and one by lock-in of the vortices parallel to the layers. This is the first study on FBS showing this behaviour in a full temperature, field, and angular range and it demonstrates that, despite the lower $T_c$ and anisotropy of Nd1111 with respect to Sm1111, this compound is substantially affected by intrinsic pinning generating a strong $\it{ab}$-peak in $J_c$.

cond-mat.supr-con↗

arXiv2015

Unusually high critical current of clean P-doped BaFe2As2 single crystalline thin film

Microstructura lly clean, isov alently P-doped BaFe2As2 (Ba-122) single crystalline thin films have been prepared on MgO (001) substrates by molecular beam epitaxy. These films show a superconducting transition temperature (Tc) of over 30 K although P content is around 0.22, which is lower than the optimal one for single crystals (i.e., 0.33). The enhanced Tc at this doping level is attributed to the in-plane tensile strain. The strained film shows high transport self-field critical current densities (Jc) of over 6 MA/cm2 at 4.2 K, which are among the highest for Fe based superconductors (FeSCs). In-field Jc exceeds 0.1 MA/cm2 at m0H = 35 T for H||ab and m0H = 18 T for H||c at 4.2 K, respectively, in spite of moderate upper critical fields compared to other FeSCs with similar Tc. Structural investigations reveal no defects or misoriented grains pointing to strong pinning centers. We relate this unexpected high Jc to a strong enhancement of the vortex core energy at optimal Tc, driven by in-plane strain and doping. These unusually high Jc make P-doped Ba-122 very favorable for high-field magnet applications.

cond-mat.supr-con↗

arXiv2014

Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, Tc, of the material. In this paper we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density Fp by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m^3 at 22.5T and 4.2 K, the highest value ever reported in any 122 phase.

cond-mat.supr-con↗

arXiv2013

Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:O$_{x}$

We report an unusual persistence of superconductivity against high magnetic fields in the iron chalcogenide film FeTe:O$_{x}$ below ~ 2.5 K. Instead of saturating like a mean-field behavior with a single order parameter, the measured low-temperature upper critical field increases progressively, suggesting a large supply of superconducting states accessible via magnetic field or low-energy thermal fluctuations. We demonstrate that superconducting states of finite momenta can be realized within the conventional theory, despite its questionable applicability. Our findings reveal a fundamental characteristic of superconductivity and electronic structure in the strongly-correlated iron-based superconductors.

cond-mat.supr-con↗

arXiv2012

Artificial and self-assembled pinning centers in Ba(Fe1-xCox)2As2 thin films as a route to very high current density

We report on the superior vortex pinning of single and multilayer Ba(Fe1-xCox)2As2 thin films with self-assembled c-axis and artificially introduced ab-plane pins. Ba(Fe1-xCox)2As2 can accept a very high density of pins (15-20 vol%) without Tc suppression. The matching field is greater than 12 T, producing a significant enhancement of the critical current density Jc, an almost isotropic Jc (Theta,20T) > 10^5 A/cm2, and global pinning force density Fp of about 50 GN/m^3. This scenario strongly differs from the high temperature cuprates where the addition of pins without Tc suppression is limited to 2-4 vol%, leading to small HIrr enhancements and improved Jc only below 3-5 Tesla.

cond-mat.supr-con↗

arXiv2012

Conductance noise in an out-of-equilibrium two-dimensional electron system

A study of the conductance noise in a two-dimensional electron system (2DES) in Si at low temperatures (T) reveals the onset of large, non-Gaussian noise after cooling from an equilibrium state at a high T with a fixed carrier density n_s. This behavior, which signifies the falling out of equilibrium of the 2DES as T->0, is observed for n_s<n_g (n_g - glass transition density). A protocol where density is changed by a small value Δn_s at low T produces the same results for the noise power spectra. However, a detailed analysis of the non-Gaussian probability density functions (PDFs) of the fluctuations reveals that Δn_s has a qualitatively different and more dramatic effect than ΔT, suggesting that Δn_s induces strong changes in the free energy landscape of the system as a result of Coulomb interactions. The results from a third, waiting-time (t_w) protocol, where n_s is changed temporarily during t_w by a large amount, demonstrate that non-Gaussian PDFs exhibit history dependence and an evolution towards a Gaussian distribution as the system ages and slowly approaches equilibrium. By calculating the power spectra and higher-order statistics for the noise measured over a wide range of the applied voltage bias, it is established that the non-Gaussian noise is observed in the regime of Ohmic or linear response, i.e. that it is not caused by the applied bias.

cond-mat.str-el↗

arXiv2012

Anisotropy of the irreversibility field for Zr-doped $(Y,Gd)Ba_2Cu_3O_{7-x}$ thin films up to 45T

The anisotropic irreversibility field B$_{Irr}$ of two $YBa_2Cu_3O_{7-x}$ thin films doped with additional rare earth (RE)=(Gd,Y) and Zr and containing strong correlated pins (splayed BaZrO$_{3}$ nanorods, and $RE_2O_3$ nanoprecipitates), has been measured over a very broad range up to 45T at temperatures 56 K<T<$T_c$. We found that the experimental angular dependence of $B_{Irr}(θ)$ does not follow the mass anisotropy scaling $B_{Irr}(θ)=B_{Irr}(0)(cos^2θ+γ^{-2}sin^2θ)^{-1/2}$, where $γ=(m_c/m_{ab})^{1/2}=5-6$ for the RE-doped $YBa_2Cu_3O_{7-x}$ (REBCO) crystals, m$_{ab}$ and m$_{c}$ are the effective masses along the ab plane and the c-axis, respectively, and $θ$ is the angle between B and the c-axis. For B parallel to the ab-planes and to the c-axis correlated pinning strongly enhances B$_{Irr}$, while at intermediate angles, $B_{Irr}(θ)$ follows the scaling behavior $B_{Irr}(θ)\propto(cos^2θ+γ_{RP}^2sin^2θ)^{1/2}$ with the effective anisotropy factor $γ_{RP}\approx3$ significantly smaller than the mass anisotropy would suggest. In spite of the strong effects of c-axis BaZrO$_{3}$ nanorods, we found even greater enhancements of B$_{Irr}$ for fields along the ab-planes than for fields parallel to the c-axis, as well as different temperature dependences of the correlated pinning contributions to B$_{Irr}$ for B//ab and B//c. Our results show that the dense and strong pins, which can now be incorporated into REBCO thin films in a controlled way, exert major and diverse effects on the measured vortex pinning anisotropy and the irreversibility field over wide ranges of B and T. In particular, we show that the relative contribution of correlated pinning to B$_{Irr}$ for B//c increases as the temperature increases due to the suppression of thermal fluctuations of vortices by splayed distribution of BaZrO$_{3}$ nanorods.

cond-mat.supr-con↗

arXiv2011

On the large role of weak uncorrelated pinning introduced by BZO nanorods at low temperatures in REBCO thin films

REBa$_{2}$Cu$_{3}$O$_{x}$ films can achieve remarkably high critical current density values by the incorporation of insulating nanoparticles. A particular interesting case concerns BaZrO$_{3}$ (BZO) nanorods, whose strongly correlated effect is seen at high temperatures. Here we investigate the field, temperature and angular dependence of the critical current density over a wide temperature range from 4.2 K to 77 K, and magnetic fields up to 31 T. We show that the correlated c-axis pinning of BZO nanorods becomes progressively less obvious at lower temperature. Indeed at 4.2 K and fields up to 31 T, the only correlated pinning is for fields parallel to the film plane. We interpret the change as being due to significant contributions from dense but weak pins that thermal fluctuations render ineffective at high temperatures but which become strong at lower temperatures.

cond-mat.supr-con↗

arXiv2011

Significant enhancement of upper critical fields by doping and strain in Fe-based superconductors

We report measurements of Hc2(T) up to 85 Tesla on Ba1-xKxAs2Fe2 single crystals and FeSe1-xTex films tuned by doping and strain. We observed an Hc2 enhancement by nearly 25 T at 30 K for the optimally-doped Ba1-xKxAs2Fe2 as compared to the previous results and extraordinarily high slopes dHc2/dT = 250-500 T/K near Tc in FeSe1-xTex indicating an almost complete suppression of the orbital pair-breaking. Theoretical analysis of Hc2(T) in FeSe1-xTex and the optimally doped Ba1-xKxAs2Fe2 predicts an inhomogeneous Fulde-Ferrel-Larkin-Ovchinnikov state for H//ab and T < 3-10 K, and shows that Hc2 in multiband Fe based superconductor can be enhanced by doping and strain much more effectively than by the conventional way of increasing disorder.

cond-mat.supr-con↗

arXiv2011

Iron-chalcogenide FeSe$_{0.5}$Te$_{0.5}$ coated superconducting tapes for high field applications

The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe$_{0.5}$Te$_{0.5}$ layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1$\times10^{4}$A/cm$^{2}$) at about 4.2K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.

cond-mat.supr-con↗

arXiv2010

Quantum Hall states under conditions of vanishing Zeeman energy

We report on magneto-transport measurements of a two-dimensional electron gas confined in a Cd$_{0.997}$Mn$_{0.003}$Te quantum well structure under conditions of vanishing Zeeman energy. The electron Zeeman energy has been tuned via the $s-d$ exchange interaction in order to probe different quantum Hall states associated with metallic and insulating phases. We have observed that reducing Zeeman energy to zero does not necessary imply the disappearing of quantum Hall states, i.e. a closing of the spin gap. The spin gap value under vanishing Zeeman energy conditions is shown to be dependent on the filling factor. Numerical simulations support a qualitative description of the experimental data presented in terms of a crossing or an avoided-crossing of spin split Landau levels with same orbital quantum number $N$.

cond-mat.mes-hall↗

arXiv2009

Aging and memory in a two-dimensional electron system in Si

The relaxations of conductivity after a temporary change of carrier density n_s during the waiting time t_w have been studied in a strongly disordered two-dimensional electron system in Si. At low enough n_s < n_g (n_g - the glass transition density), the nonexponential relaxations exhibit aging and memory effects at low temperatures T. The aging properties change abruptly at the critical density for the metal-insulator transition n_c < n_g. The observed complex dynamics of the electronic transport is strikingly similar to that of other systems that are far from equilibrium.

cond-mat.str-el↗