R. C. Budhani

Council of Scientific and Industrial Research (CSIR), New Delhi, New Dilli, NCT, India

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Publications (195)492.16 Total impact

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    ABSTRACT: We report a gradual suppression of the two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface on substitution of chromium at the Al sites. The sheet carrier density at the interface (ns) drops monotonically from 2.2x10(14) cm-2 to 2.5x10(13) cm-2 on replacing nearly 60 percent of Al sites by Cr and the sheet resistance (Rs) exceeds the quantum limit for localization (h/2e2) in the concentrating range 40 to 60 percent of Cr.
    10/2014;
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    ABSTRACT: Measurements of magneto-thermopower (S(H, T)) of interfacial delta doped LaTiO$_3$/SrTiO$_3$ (LTO/STO) heterostructure by an iso-structural antiferromagnetic perovskite LaCrO$_3$ are reported. The thermoelectric power of the pure LTO/STO interface at 300 K is $\approx$ 118 $\mu$V/K, but increases dramatically on $\delta$-doping. The observed linear temperature dependence of S(T) over the temperature range 100 K to 300 K is in agreement with the theory of diffusion thermopower of a two-dimensional electron gas. The S(T) displays a distinct enhancement in the temperature range (T $<$ 100 K) where the sheet resistance shows a Kondo-type minimum. We attributed this maximum in S(T) to Kondo scattering of conduction electron by localized impurity spins at the interface. The suppression of S by a magnetic field, and the isotropic nature of the suppression in out-of-plane and in-plane field geometries further strengthen the Kondo model based interpretation of S(H, T).
    08/2014;
  • P. K. Rout, R. K. Rakshit, R. C. Budhani
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    ABSTRACT: We report the Josephson coupling between optimally doped superconducting La1.85Sr0.15CuO4 through the normal metal barrier of La1.85Sr0.15Cu0.97Co0.03O4 (LSCCO). The critical current (Ic) across the junction exists even up to a barrier thickness of 50 nm. The barrier thickness dependence study of Ic yields a large coherence length in LSCCO of (15.2±1.4) nm at 5 K, which indicates the presence of giant proximity effect in such systems.
    03/2014; 1591(1).
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    ABSTRACT: The dynamics of magnetization (M) reversal and relaxation as a function of temperature (T) are reported in three non-interacting NiFe ring arrays having fixed ring outer diameter and varying widths. Additionally, the dependence of M(H) loop on the angle (θ) between magnetic field (H) and the plane of the rings is addressed. The M(H) loops show a double step transition from onion state (OS) to vortex state (VS) at all temperatures (T = 3 to 300 K) and angles (θ = 0 to 90°). The critical reversal fields HC1 (OS to VS) and HC2 (VS to OS) show a pronounced dependence on T, ring width, and θ. Estimation of the transverse and vortex domain wall energies reveals that the latter is favored in the OS. The OS is also the remanent state in the smallest rings and decays with the effective energy scale (U0/T) of 50 and 32 meV/K at 10 and 300 K, respectively. The robust in-plane anisotropy of magnetization of ring assemblies is established by scaling the M(H) with θ.
    03/2014; 115(16).
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    ABSTRACT: We report the effect of δ doping at the LaAlO3/SrTiO3 interface with LaMnO3 monolayers on the photoconducting (PC) state. The PC is realized by exposing the samples to broadband optical radiation of a quartz lamp and 325 and 441 nm lines of a He-Cd laser. Along with the significant modification in electrical transport which drives the pure LaAlO3/SrTiO3 interface from metal-to-insulator with increasing LaMnO3 sub-monolayer thickness, we also observe an enhancement in the photoresponse and relaxation time constant. A possible scenario for the PC based on defect clusters, random potential fluctuations, and large lattice relaxation models, along with the role of structural phase transition in SrTiO3, is discussed. For pure LaAlO3/SrTiO3, the photoconductivity appears to originate from interband transitions between Ti-derived 3d bands which are eg in character and O 2p–Ti t2g hybridized bands. The band structure changes significantly when fractional layers of LaMnO3 are introduced. Here the Mn eg bands (≈1.5 eV above the Fermi energy) within the photoconducting gap lead to a reduction in the photoexcitation energy and a gain in overall photoconductivity.
    Physical Review B 03/2014; 89:125127. · 3.66 Impact Factor
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    Pramod Kumar, Anjana Dogra, R. C. Budhani
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    ABSTRACT: We report the growth of ultrathin film of Mn doped LaTiO3 on TiO2 terminated SrTiO3 (001) substrate by pulsed laser deposition (PLD) and their electrical transport characteristics including magnetoresistance (MR). Though the replacement of Mn in LaTiO3 at the Ti site in dilute limit does not affect the metallic behaviour of films but variation in resistance is observed. Normalised resistance behaviour is explained on the basis of variation in charge carriers and increased interaction between Mn atoms in the system under investigation.
    03/2014; 1591(1).
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    ABSTRACT: The breaking of inversion symmetry combined with polar discontinuity and the presence of strong electronic correlations due to partially filled 3d electronic shell of Ti ions at the LaAlO$_3$/SrTiO$_3$ (LAO/STO) and LaTiO$_3$/SrTiO$_3$ (LTO/STO) interfaces conspire to produce exotic electronic phases. These include macroscopic superconducting and ferromagnetic orders and electronic transport renormalized by strong spin-orbit (S-O) interaction originating to the built-in electrostatic fields at the interface and scattering by localized moments. An important ingredient in this exotic soup of causes and effects is also the quantum paraelectric nature of STO. In order to separate out the contributions of these phenomena from electronic behavior of oxide interfaces, new approaches need to be developed. Here, we present a study of delta doping at LTO/STO interface with iso-structural perovskite of LaCrO$_3$ (LCO) that dramatically alters the properties of the two dimensional electron gas (2DEG) at the interface. The effects include a reduction in sheet-carrier density, prominence of the low temperature resistivity minimum in LAO/STO and LTO/STO 2DEG, enhancement of weak antilocalization below 10 K and observation of a strong anisotropic magnetoresistance (MR). The positive and negative MR for out-of-plane and in-plane field respectively and the field and temperature dependencies of MR suggest Kondo scattering by localized Ti$^{3+}$ moments renormalized by S-O at T < 10 K, with the increase of Cr$^{3+}$ concentration at the interface.
    02/2014;
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    ABSTRACT: The influence of epitaxial strain on uniaxial magnetic anisotropy of Co$_{2}$FeSi (CFS) and Co$_{2}$MnSi (CMS) Heusler alloy thin films grown on (001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is susceptible to tune by varying the thickness of the films on STO, while on MgO the films show in-plane easy axis for magnetization (\overrightarrow{M}) irrespective of their thickness. A variational analysis of magnetic free energy functional within the Stoner-Wohlfarth coherent rotation model with out-of-plane uniaxial anisotropy for the films on STO showed the presence of magnetoelastic anisotropy with magnetostriction constant $\approx$ (12.22$\pm$0.07)$\times 10^{-6}$ and (2.02$\pm$0.06)$\times 10^{-6}$, in addition to intrinsic magnetocrystalline anisotropy $\approx$ -1.72$\times 10^{6}$ erg/cm$^{3}$ and -3.94$\times 10^{6}$ erg/cm$^{3}$ for CFS and CMS, respectively. The single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane orientation of magnetization with the decreasing film thickness. A maximum canting angle of 41.5$^{\circ}$ with respect to film plane is predicted for the magnetization of the thinnest (12 nm) CFS film on STO. The distinct behaviour of \overrightarrow{M} in the films with lower thickness on STO is attributed to strain-induced tetragonal distortion.
    Applied Physics Letters 01/2014; 104(2):022402. · 3.79 Impact Factor
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    ABSTRACT: We report remarkably low residual resistivity, giant residual resistivity ratio, free-electron-like Hall resistivity, and high mobility (≈10^4 cm^2V^−1s^−1) charge transport in epitaxial films of Co2MnSi and Co2FeSi grown on (001) SrTiO3. This unusual behavior is not observed in films deposited on other cubic oxide substrates of comparable lattice parameters. The scaling of the resistivity with thickness of the films allows the extraction of interface conductance, which can be attributed to a layer of oxygen vacancies confined within 1.9 nm of the interface as revealed by atomically resolved electron microscopy and spectroscopy. The high mobility transport observed here at the interface of a fully spin polarized metal is potentially important for spintronics applications.
    Physical Review B 01/2014; 89(2):020401(R). · 3.66 Impact Factor
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    ABSTRACT: We report significant enhancement of the thermoelectric figure-of-merit of Mg2Si by double-doping with a combination of Bi, Pb, and Sb as doping elements. Addition of any two of these three elements to Mg2Si increases the electrical conductivity by more than three orders of magnitude at 323 K, irrespective of the doping elements used. However, a corresponding decrease in the Seebeck coefficient is observed in comparison with undoped Mg2Si. Irrespective of the combination of the three elements used for double doping, a figure-of-merit of approximately 0.7 at 873 K is obtained for Mg2Si; this is primarily because of enhancement of the electrical conductivity.
    Journal of Electronic Materials 12/2013; · 1.64 Impact Factor
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    ABSTRACT: The multilayers of [Fe(5Å)/Pt(25 Å)]×15 were prepared by dc magnetron sputtering on 50 Å Pt-buffered MgO substrates. The structural characterization of the multilayers was carried out using X-ray diffraction, X-ray reflectivity. The Secondary ion mass spectroscopy measurement reveals the depth profile and compositional modulations of the multilayer films as per our design specifications. Room temperature magnetic measurements were carried out by using SQUID both in-plane and out-of-plane sample geometry. Magnetization measurements show similar M-H loops for both in-plane and out-of-plane directions of external magnetic field with a coercivity of 190 Oe. These measurements indicate that our samples are magnetically soft and have multifunctional character which is important for making magnetic tunnel junctions.
    58th DAE Solid State Physics Symposium (DAE-SSPS-2013), Thapar University, Patiala, Punjab, India; 12/2013
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    ABSTRACT: Proximity coupling and magnetic switching dynamics are shown to be correlated in bilayers (B) of fully spin polarized ferromagnet (F) Co2FeSi and superconductor (S) NbN. The upper critical field derived from resistivity measurements shows a dimensional crossover with a reduced effective thickness of the S layer. At temperatures (T) << superconducting Tc, the measured M-H loops show two step switching; one at T-independent value ~ 7 Oe and other at strongly T-dependent value becoming very large ~ 1 kOe at 2 K. These results reveal induced ferromagnetism in S-layer at the S/F interface with vortex pinning influenced dynamics.
    Applied Physics Letters 10/2013; 103(18). · 3.79 Impact Factor
  • Applied Physics Letters 10/2013; 103(18):9902-. · 3.79 Impact Factor
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    ABSTRACT: Superconductivity (S) and ferromagnetism (F) are probed through transport and magnetization measurements in nanometer scale HoNi5-NbN (F-S) bilayers and HoNi5-NbN-HoNi5 (F-S-F) trilayers. The choice of materials has been made on the basis of their comparable ordering temperatures and strong magnetic anisotropy in HoNi5. We observe the normal state reentrant behavior in resistance vs. temperature plots of the F-S-F structures just below the superconducting transition in the limited range of HoNi5 layer thickness dHN () when is fixed at. The reentrance is quenched by increasing the out-of-plane () magnetic field and transport current where as in-plane () field of has no effect on the reentrance. The origin of the reentrant behavior seen here in the range is attributed to a delicate balance between the magnetic exchange energy and the condensation energy in the interfacial regions of the trilayer.
    EPL (Europhysics Letters) 09/2013; 103(4):47013. · 2.26 Impact Factor
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    ABSTRACT: The thermoelectric properties of Pb doped Mg2Si, synthesized using reactive sintering employing spark plasma sintering, are investigated and are compared with other dopants reported in literature. While a moderate decrease in Seebeck coefficient and thermal conductivity is observed for 2 at. % of Pb doping in Mg2Si, a substantial enhancement in the material's thermoelectric figure-of-merit is observed, which is due to an enormous increase in its electrical conductivity. A brick-layer model is proposed to explain these results, wherein the inter-granular electronic conductivity is facilitated by Pb (or Mg2Pb) phases at grain boundaries, which is supported by microstructural evidences.
    Applied Physics Letters 07/2013; 103(5). · 3.79 Impact Factor
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    ABSTRACT: Superconductivity at the LaTiO3/SrTiO3 interface is studied by low temperature and high magnetic field measurements as a function of a back-gate voltage. We show that it is intimately related to the appearance of a low density (a few 1012 cm-2) of high mobility carriers, in addition to low mobility ones always present in the system. These carriers form superconducting puddles coupled by a metallic two-dimensional electron gas, as revealed by the analysis of the phase transition driven by a perpendicular magnetic field. Two critical fields are evidenced, and a quantitative comparison with a recent theoretical model is made.
    Journal of Physics Conference Series 07/2013; 449(1):2035-.
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    ABSTRACT: Driving a two-dimensional superconductor normal by applying a high magnetic field may lead to Cooper pair localization. In this case, there should be a quantum critical point associated with specific scaling laws. Such a transition has been evidenced in a number of low critical temperature superconducting thin films and has been suggested to occur also in high temperature cuprate superconductors. Here we show experimental evidence for two distinct quantum critical regimes when applying perpendicular magnetic fields to underdoped La2-xSrxCuO4 thin films. At intermediate values of the magnetic field (18T-20T), a "ghost" QCP is observed, for which the values of the related critical exponents point towards a fermionic -as opposed to bosonic- scenario. At higher (about 37 T) magnetic field, another QCP is observed, which suggests the existence of either a 2D/3D or a clean/dirty temperature crossover.
    06/2013;
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    ABSTRACT: Here we investigate LaAlO_3-SrTiO_3 heterostructure with\delta-doping of the interface by LaMnO_3 at less than one monolayer. This doping strongly inhibits the formation of mobile electron layer at the interface. This results in giant increase of the resistance and the thermopower of the heterostructure. Several aspects of this phenomena are investigated. A model to calculate the carrier concentration is presented and effect of doping and detailed temperature dependence is analyzed in terms of model parameters and the weak-scattering theory. The large enhancement of thermopower is attributed to the increased spin and orbital entropy originating from the LaMnO_3 mono-layer.
    EPL (Europhysics Letters) 06/2013; · 2.26 Impact Factor

Publication Stats

1k Citations
492.16 Total Impact Points

Institutions

  • 2012–2014
    • Council of Scientific and Industrial Research (CSIR), New Delhi
      New Dilli, NCT, India
  • 1994–2014
    • Indian Institute of Technology Kanpur
      • Department of Physics
      Cawnpore, Uttar Pradesh, India
  • 1989–2014
    • Brookhaven National Laboratory
      • • Condensed Matter Physics & Materials Science Department
      • • Physics Department
      New York City, New York, United States
  • 2011–2013
    • National Physical Laboratory - India
      • Division of Materials Physics and Engineering (NPL)
      Old Delhi, NCT, India
  • 2001–2002
    • University of Maryland, College Park
      • • Department of Chemistry and Biochemistry
      • • Department of Physics
      College Park, MD, United States