Condensed Matter Experiments

1. Nature of studies of various types Magnetism, Superconductivity, Transport (elctrical), Phase transitions, Imaging Condensed Matter Experiments Kind of Systems Studied Correlated Electron Systems (superconductors, GMR systems, …) Semiconductors (amorphous, organic, …) Electronic Materials Soft Matter 2D and 1D systems (thin films, heterostructures, nanoparticles, graphene, …) Techniques used Low temperature, High Pressure, High Temperature Microscopy, Spectroscopy, Magneto-optics

2. Amorphous semiconductors Lab Electronic Structure of disordered semiconductors in thin film form is studied, with a view to understand their behaviour upon exposure to external stimuli, causing metastabilities. Special attention has been paid to the degradation of hydrogenated amorphous silicon (a-Si:H) caused by exposure to light (Steabler-Wronski effect, SWE). Measurements of conductivity, thermopower, sub-gap absorption, Surface photovoltage, ESR, SSPG, etc. have given valuable information about SWE. Some of the important results are: i) SWE affects the surface as well as the bulk of a-Si:H [1], ii) the inhomogeneous samples, having larger potential fluctuations degrade more [2]. SCA 1

3. Nanocrystalline silicon made by the electrochemical method (Porous Silicon) shows Photoluminescence (PL), but degrades when exposed to ordinary visible light. This is similar to SWE in a-Si:H, but unlike a-Si:H, seems to be mostly a surface effect. We have been able to arrest the PL degradation by coating nc-PSi with a thin layer of a polymer [3] • Another study involves the understanding of the switching behaviour of chalcogenide glasses and find out why some compositions can produce a more durable switch than the others [4]. Some significant publications • Shailendra Kumar and S.C. Agarwal, Appl. Phys. Lett. 45, 575-577 (1984). • S.C. Agarwal, J. Mater. Sci. – Mater. Electronics, 14, 703-706 (2003). • N .P. Mandal, A. Sharma, and S.C. Agarwal, Solid State Comm. 129, 183-186 (2004). • D.A. Baker, M.A. Paesler, G. Lucovsky, S.C. Agarwal and P.C. Taylor, Phys. Rev. Lett. 96, 255501 (2006).

4. PECVD setupPlasma Enhanced Chemical Vapour Deposition SCA 2

5. Condensed Matter-Low Dimensional Systems Laboratory Research Facilities • Pulsed Laser Deposition facility • X'Pert Pro MPD X-Ray Diffractometer • 14 Tesla, 0.3K, Quantum Design Physical Property Measurement System • Resistivity, Hall, magnetoresistance, tunneling measurements down to 4.2 K • Contact-less measuremnts of the dynamical behavior of vortices in high Tc superconductors in the frequency range of 2 Hz~6 MHz; Penetration depth measurement using a tunnel diode oscillator based resonant circuit  • 1.6 K Close Cycle Refrigerator with extreme temperature stability of 0.001 K • Quantum Design SQUID magnetometer. • Time and frequency domain measurements of photo-induced non-equilibrium effects in solids. He-Cd and He-Ne continuous-wave lasers and frequency tripled pulsed (~ 6 nsec) Nd-YAG laser, Low temperature cryostat with fast electronics. • Liquid phase pulsed laser ablation using a frequency doubled Nd-YAG laser for preparation of metal nano particle solution • RHK Technology Scanning Probe Microscope with UHV and low temperature facility.

6. Recent Results • NbN-Fe-NbN Josephson Junction array • Vortex-Antivortex Pair Unbinding Driven by the Spin Texture of a Ferromagnet-Superconductor Bilayer • Spin Reorientation in La0.67Ca0.33MnO3 thin film observed by Magnetic Force Microscopy • Field Effect in LTO-STO Heterostructure • Interface Superconductivity • Spintronics : Magnetic Tunnel Junctions

7. n B θ I NbN ~ 50 nm Fe #1 NbN NbN i i NbN #2 NbN-Fe-NbN Josephson Junction array (c) (a) [110] [100] (b) 200 nm c) The angular dependence of magnetoresistance of Fe-NbN composite shows maximum super- current dissipation when field (3.5kG) is in the plane of the film (B | n). This is in stark contrast to pure NbN case (max. R when B || n). Upper inset shows the measurement geometry. a) SEM micrograph of 40 nm thick Fe nano-plaquettes covered with 30 nm SC NbN. b) Schematic showing two distinct parallel conduction path for supercurrent. Bose et al, APL 2009 Student working : Saurabh K Bose

8. (a) (b) • NbN TC = 16 K • HoNi5 TCurie = 5.5 K T Curie < TC • Temperature dependent R Vs. H Measurements of NbN (10 nm)/ HoNi5 (50 nm) bilayer on (100) MgO substrate. • Comparison of R vs. H and M vs. H at temperature 1.7 K. Singh et al. Manuscript submitted Student working : Gyanendra Singh

9. Spin Reorientation in La0.67Ca0.33MnO3 thin film observed by Magnetic Force Microscopy 200 G 0 G 300 G Out of Plane Magnetization 420 G 1000 G Interface In Plane Magnetization • T = 110 K • In Plane Magnetic Field Singh et al. Manuscript under preparation Student working : Gyanendra Singh

10. Field Effect in LTO-STO Heterostructure • LTO Mott Insulator • STO Band Insulator Vsd STO Effect of electric field on LaTiO3 thin film deposited on 0.5mm thick SrTiO3 (100) substrate. Upper inset shows the schematic of the device and lower inset shows the variation in conductance of drain to source channel with gate field. Gate Vg Rastogi et al. Manuscript submitted Student working : Ankur Rastogi

11. La1.84Sr0.16CuO4 (50 nm) La1.48Nd0.4Sr0.12CuO4 (100 nm) Substrate SLAO (001) Interface Superconductivity Temperature dependence of the real and imaginary parts of the pick-up coil voltage of two-coil mutual inductance setup And resistivity measured by four probe method Student working : Prasanna Kumar Rout

12. 20 μm Spintronics Magnetic Tunnel Junctions (MTJs) Photograph of junctions SEM image of the junction with one junction zoomed in. Junction area 25 μm x 25 μm Student working : Prasanta Kumar Muduli

13. Non-equilibrium features in phase separated state of NdNiO3 • Exhibit time dependent effects in phase • separated state • These time dependent effects are attributed • to stochastic switching of supercooled • metallic regions to stable insulating state. • If we decrease the sample size such that it • contains few SC regions, then we can observe • the effect of switching of individual SC region. Journal of Physics: Condensed Matter 21 185402 (2009) Journal of Physics: Condensed Matter 21 485402 (2009). KPR 1

14. Magnetization Dynamics in Antiferromagnetic Nanoparticles Aging of ZFC magnetization in NiO nanoparticles at 25 K. Inset shows FC aging. Memory experiments in ZFC protocol. Difference in magnetization without and with a stop of one hour at 100 K. Vijay Bisht and K P Rajeev, J. Phys. : Condens. Matter 22, 016003 (2010). Vijay Bisht, K.P. Rajeev,and Sangam Banerjee. Solid State communications (in press) Earlier related work from the group: S D Tiwari and K P Rajeev , Phys. Rev. B 72 104433 (2005). S D Tiwari and K P Rajeev, Thin Solid Films 505 113 (2006). S D Tiwari and K P Rajeev, Phys. Rev. B 77, 224430 (2008) KPR 2

15. Physics of Novel Magnetic and Superconducting Materials • Zakir Hossain- Department of Physics, IIT Kanpur • Research Interest: • Correlated Electron Systems- • Quantum Phase Transition and Unconventional Superconductivity • (ii) Search for Novel Superconductors • Interplay of superconductivity and magnetism • (iii) Phase transitions: Magnetic order, Quadrupolar order, • valence transition • (iv) Properties of Materials under extreme condition of • ultra low temperature, high pressure and high magnetic field. ZH 1

16. Magnetism and Superconductivity in Eu0.5K0.5Fe2As2 Eu0.5K0.5Fe2As2 • Featutes in the magnetic susceptibility are similar to that found in HoNi2B2C which show double reentrance behavior. • Coexistence of short range ordering of the Eu moments with the superconducting state below 15 K is confirmed by 151Eu Mössbauer and magnetic susceptibility. • Parent compound EuFe2As2 exhibits two magnetic transitions at T1 (Eu-moments order) ~ 19K and T2 (Fe-moment order)~ 190 K • Suppression of Fe-moment ordering by potassium doping leads to superconductivity below 32 K. H. S. Jeevan et.al. PRB 78, 092406 2008 Anupam et.al. J. Phys. Cond. Mat (2009) ZH 2

17. Motivation: Promising candidate for spintronic application To prepare a good quality film with high crystal and interface perfectionand low disorder. Successful in preparing high quality thin film on SrTiO3(STO) using PLD. Residual resistivity, ρ10K = 0.65 μΩ cm Residual resistivity ratio (RRR) = 438 Such a high value of RRR and low value of residual resistivity has not been observed so far for any Heusler alloy thin films. Higher deposition temperature leads to better crystalline quality as compared to lower deposition temperatures which is in contrast to thin film grown on GaAs semiconductor. Co2FeSi Heusler alloy thin films Anupam et al. to be published ZH 3

18. Laboratory for Optical Spectroscopy at Extreme Conditions of high P and low T Rajeev Gupta Research Interests: • Multifunctional Materials: Bulk and thin films. • Theoretical and experimental measurements on strongly correlated electron systems e.g Vanadates, ruthenates and manganites. • Li ion battery materials. Alternate cathode materials. Theory and experiments. • Biomaterials: Structure property correlation in doped Hydroxy-apatite. • Nano-materials such as nc-silicon, nanowires etc. • Diamond like carbon films and other nanostructures such as carbon nanotubes. RG 1

19. Research Facility • MicroRaman system with CCD. • Low T (~ 9 K) cryostat. • High T (~900 K) microscope hot stage. • Miniature high pressure cell. • Simultaneously measurement of transport and optical properties. • Thermal measurements (DSC) upto 900 K. • Sample, pressure calibrant and pressure medium to be loaded in a 200 microns hole! • Location: 107 ACMS Building • Please do visit us sometime! RG 2

20. Research Area: Multifunctional Oxides Background: Phase stability of BiFeO3 and improved properties • New Findings: • Zirconium doping stabilizes the phase of BiFeO3. Single phase films prepared by sol-gel process obtained. • Significant enhancement in electrical and magnetic properties. • Dielectric measurements show that Zr-doping of BiFeO3 films significantly reduces the dielectric loss and leakage currents. • Detailed structural characterization and analysis reveals that the films have a monoclinic structure. • Improvement in properties due to “quenching” of defects in doped films. RG 3

21. Research Area: Li ion Battery materials Critical issue: Cheaper and environmental friendly substitutes for traditional cathode material in Li ion batteries (LiCoO2) • New Findings: • Effect of doping spinel LiMn2O4 with chromium and magnesium has been studied using the first-principles spin density functional theory and compared with experiments. • Suppression of Jahn-Teller distortion on doping supported by experiments and theory. • Theory predicts Insulator-Metal-Insulator transition as a function of doping in case of Cr and in case of Mg the ground state is found to move from insulating to the half metallic state as a function of doping. RG 4

22. Research Area: Strongly Correlated Oxides Motivation: • Interplay between spin, orbital and charge degrees of freedom leads • to different sequential phase transitions in transition metal oxides MnV2O4 ZnV2O4 Sharp transitions at temperatures T1 ~ 57 K and T2 ~ 55 K. Transitions at temperatures T1 ~ 57K and T2 ~ 41K. Closeby magnetic and structural transitions suggesting strong evidence of magneto – elastic coupling. RG 5

23. Research Area: Biocompatible Materials- Hydroxyapatite Critical issues: • To study the structure-property correlation with Ag doping and do antimicrobial studies with S. Epidermidis and E. Coli bacteria. New Findings: • Silver doped samples shows presence of TCP. • Ag doped samples show comparable hardness with Parent HAp. • Raman studies show that mode intensity decreases with Ag doping in HAp. • Ag doped samples shows antimicrobial properties. • Ionic conductivity on doped samples shows a cross-over at 450 C. RG 6

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29. Homemade STM Manganite CDW in 2H-NbSe2 at 8K HOPG CDW gap Moire on HOPG, 139nm Bi2Te3 at 77K AKG 1 Ref: Gupta et.al. Rev. Sci. Instr., 79, 063701 (2008)

30. Spectroscopy : ~ Nsam (eV) (T ~ 0) Quantum Tunneling and STM Topography : k ~ 1 Å-1 AKG 2

31. Our STM Systems AKG 3

32. LSMO LCMO ZBC Hwang et. al., PRL 75, p914 (1995) LPCMO PCMO LPCMO Manganites: effect of bandwidth Epitaxial, PLD filmsOn NGO or LSAT Singh, et. al., PRB 77, 014404 (08); APL 93, 212503(08); JPCM 21, 355001 (09) AKG 4

33. A Vb SiO2 Doped Si Vg Raman Transport Slope: 1.21 x 10-3e STM/S on Graphene FET Ref.: RMP 81, 109 (2009 ); AKG 5

34. Weak Link μ-SQUIDs AKG 6

35. Soft Matter Physics: Inspirational Bio-Organisms for Advanced Materials Applications 1 m Lotus Leaf (superhydrophobicity) Microfluidics (nano/pico-liter liquid control and manipulation) Gecko Foot (dry/wet adhesion, self-cleaning) Hierarchical structures with multi-faceted functions KC 1

36. Wetting: coating something...... close-up view liquid beads off substrate Applications: protection,self-cleaning, foul-releasing, anti-fogging, anti-static, non-stick, anti-friction, drag reduction, anti-graffiti, optical Coating failure (due to dewetting) KC 2

37. Wetting Wetting of planar surfaces Wetting of rough surfaces Wenzel state Cassie state cosq = (ssg – ssl)/slg Tunable wettability Electrowetting KC 3

38. Wetting Thermowetting Poly(N-isopropylacrylamide) (PNIPAAm) • Conventional approach: • Vary wettability either by changing the surface chemistry or the physical roughness. • My approach: • Use to the combination of surface topography and chemistry and control the overall roughness thus the wettability. • Also use responsive polymers to tune the wettability by changing e.g. temperature, electrical signal, light or pH. Smooth surface q ~ 40o q ~ 88o Topographic surface q ~ 158o q ~ 80o KC 4

39. Microfluidics: liquid transport in microchannels Patterns of hydrphobic / hydrophilic stripes Patterns of surface grooves KC 5

40. Molecular Semiconductors : Strategies to understand & Optimize Materials for Devices Yashowanta N. MohapatraSatyendra Kumar Physics, SCDT, MSP Physics, SCDT IIT Kanpur

41. Al Ca Polymer ITO Glass Single Layer Polymer Light Emitting Diode Schematic: Device Structure PEDOT:PSS

42. Diode :A Critical Component

43. Goal : Basket of Applications & Products Source: w4.siemens.de/.../archiv/ pof/heft2_03/artikel18/

46. Nano-engineering for Macro-electronics PACK & Align • BLEND • EMBEDD Reese et al. Mat. Today 2004 F8:F38 : E.Moons J Phy C’05 For better: Luminescence, Mobility, Stability, Excitonics

47. EL Enhancement: Blend Dilution • Single layer devices • Low output Effect of blend compositions: dramatic and unmistakable

48. Photoelectronic Process in Polymeric Semiconductor Schematic showing typical probes and response functions used in characterization of conjugated polymers The processes to understand – formation and dissociation of excitons & charges and their conversion to one another

49. Phenomenological Model: Density of States - 2.2 eV LUMO - 2.9 eV 2.2 eV 2.6 eV 1.5 eV 1.9 eV 3.6 eV - 4.4 eV* - 4.8 eV HOMO HOMO - - 2.2eV 2.2eV - - 2.2eV 2.2eV Hot Excitons - - 2.9eV 2.9eV HOMO - 5.8 eV - - 4.8eV 4.8eV LUMO LUMO - - 5.7eV 5.7eV - - 5.7eV 5.7eV AVPV AVPV PVK PVK PVK PVK Polymer Polymer Polymer PVK Relaxed Carriers PL EL

50. Molecules Films (Condensed Phase) Interfaces Device Structures  Systems Inject Carriers Transport charge carriers (across interfaces) Carriers form excitons (photophysical species) Manage excitonic & polaronic processes Key : Disorder,Delocalization & DOS