arXiv subjects

R. C. Budhani

Publications and source records attributed to R. C. Budhani.

58 records · Page 4Linked to original sources

arXiv2005

Appearance of an inhomogeneous superconducting state in La{0.67}Sr{0.33}MnO{3}-YBa{2}Cu{3}O{7}-La{0.67}Sr{0.33}MnO{3} trilayers

An experimental study of proximity effect in La{0.67}Sr{0.33}MnO3 - YBa2Cu3O7 - La{0.67}Sr{0.33}MnO3 trilayers is reported. Transport measurements on these samples show clear oscillations in critical current (I_c) as the thickness of La{0.67}Sr{0.33}MnO3 layers (d_F) is scanned from ~ 50 A to ~ 1100 A. In the light of existing theories of ferromagnet-superconductor (FM-SC) heterostructures, this observation suggests a long range proximity effect in the manganite, modulated by it's weak exchange energy (~ 2 meV). The observed modulation of the magnetic coupling between the ferromagnetic LSMO layers as a function of d_F, also suggests an oscillatory behavior of the SC order parameter near the FM-SC interface.

cond-mat.supr-con↗

arXiv2005

Superconducting and normal-state interlayer-exchange-coupling in La$_{0.67}$Sr$_{0.33}$MnO${3}$-YBa$_{2}$Cu$_{3}$O$_{7}-La$_{0.67}$Sr$_{0.33}$ MnO${3}$ epitaxial trilayers

The issue of interlayer exchange coupling in magnetic multilayers with superconducting (SC) spacer is addressed in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) - YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) - La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) epitaxial trilayers through resistivity, ac-susceptibility and magnetization measurements. The ferromagnetic (FM) LSMO layers possessing in-plane magnetization suppress the critical temperature (T$_{c})$ of the c-axis oriented YBCO thin film spacer. The superconducting order, however, survives even in very thin layers (thickness d$_{Y} \sim $ 50 Å, $\sim $ 4 unit cells) at T $<$ 25 K. A predominantly antiferromagnetic (AF) exchange coupling between the moments of the LSMO layers at fields $<$ 200 Oe is seen in the normal as well as the superconducting states of the YBCO spacer. The exchange energy J$_{1}$ ($\sim $ 0.08 erg/cm$^{2}$ at 150 K for d$_{Y}$ = 75 Å) grows on cooling down to T$_{c}$, followed by truncation of this growth on entering the superconducting state. The coupling energy J$_{1}$ at a fixed temperature drops exponentially with the thickness of the YBCO layer. The temperature and d$_{Y}$ dependencies of this primarily non-oscillatory J$_{1}$ are consistent with the coupling theories for systems in which transport is controlled by tunneling. The truncation of the monotonic T dependence of J$_{1}$ below T$_{c}$ suggests inhibition of single electron tunneling across the CuO$_{2}$ planes as the in-plane gap parameter acquires a non-zero value.

cond-mat.supr-con↗

arXiv2004

Current-induced metallic behavior in Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ thin films: competition between Joule heating and nonlinear conduction mechanism

Thin films of Pr0.5Ca0.5MnO3 manganites exhibiting charge/orbital-ordered properties with colossal magnetoresistance have been synthesized by the pulsed laser deposition technique on both (100)-SrTiO3 and (100)-LaAlO3 substrates. The effects of current-induced metallic-behavior of the films are investigated as a function of the temperature and the magnetic field. Calculations based on a heat transfer model across the substrate, and our resistivity measurements reveal effects of Joule heating on charge transport over certain ranges of temperatures and magnetic fields. Our results also indicate that a nonlinear conduction, which cannot be explained by homogeneous Joule heating of the film, is observed when the material is less resistive (10-2 W.cm). The origin of this behavior is explained with a model based on local thermal instabilities associated with phase-separation mechanism and a change in the long range charge-ordered state.

cond-mat.str-el↗

arXiv2001

Gapped tunneling spectra in the normal state of Pr$_{2-x}$Ce$_x$CuO$_4$

We present tunneling data in the normal state of the electron doped cuprate superconductor Pr$_{2-x}$Ce$_x$CuO$_4$ for three different values of the doping $x$. The normal state is obtained by applying a magnetic field greater than the upper critical field, $H_{c2}$ for $T < T_c$. We observe an anomalous normal state gap near the Fermi level. From our analysis of the tunneling data we conclude that this is a feature of the normal state density of states. We discuss possible reasons for the formation of this gap and its implications for the nature of the charge carriers in the normal and the superconducting states of cuprate superconductors.

cond-mat.supr-con↗