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, Techniques used Low temperature, High Pressure, High Temperature Microscopy, Spectroscopy, Magneto- optics Nature of studies of various types Magnetism, Superconductivity, Transport (elctrical), Phase transitions, Imaging
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Condensed Matter Experiments Kind of Systems Studied Correlated Electron Systems (superconductors, GMR systems, …) Semiconductors (amorphous, organic,
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Condensed Matter ExperimentsKind of Systems StudiedCorrelated Electron Systems(superconductors, GMR systems, …)
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
• 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 publications1. Shailendra Kumar and S.C. Agarwal, Appl. Phys. Lett. 45,
(2003).3. N .P. Mandal, A. Sharma, and S.C. Agarwal, Solid State
Comm. 129, 183-186 (2004).4. D.A. Baker, M.A. Paesler, G. Lucovsky, S.C. Agarwal and P.C.
Taylor, Phys. Rev. Lett. 96, 255501 (2006).
PECVD setupPlasma Enhanced Chemical Vapour Deposition
SCA 2
Research FacilitiesPulsed Laser Deposition facilityX'Pert Pro MPD X-Ray Diffractometer14 Tesla, 0.3K, Quantum Design Physical Property Measurement SystemResistivity, Hall, magnetoresistance, tunneling measurements down to 4.2 KContact-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 KQuantum 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 solutionRHK Technology Scanning Probe Microscope with UHV and low temperature facility.
Condensed Matter-Low Dimensional Systems Laboratory
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
(a)[110]
[100]
200 nm
NbN-Fe-NbN Josephson Junction array
Bose et al, APL 2009
0 90 180 270 360
4
5
6
7
8
9
6 K
NbN (30 nm)
R (
a.u.
)
R ()
(Deg)
Fe-NbN (30 nm)
0 90 180 270 360
0
25
50
(Rav, 3.5 kOe)
(RI+, 3.5 kOe)
(RI- , 3.5 kOe)
BθnI
(c)
Fe
NbN~ 50 nm
#2
#1i i
NbN NbN
NbN
(b)
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.
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.
Student working : Saurabh K Bose
-300 -150 0 150 3000.00.40.8 0.0
0.40.8
0.00.40.8
0.00.40.8
1.16 mA
1.12 mA
.95 mA
1.1 mA
.81 mA
1.14 mA
1.17 mA
H (Oe)
1.7 K
1.9 K
0.0
0.5
2.1 K
2.4 K
0.00.40.8
R ()
2.7 K
3 K
0.0
0.5
3.5 K
R
()
-2
-1
0
1
2
0.0
0.5
1.0
1.5
M (
emu)
*10-4
-1000 -500 0 500 1000
H (Oe)
R ()
N
O
L
M
(a)
(b)
(a) Temperature dependent R Vs. H Measurements of NbN (10 nm)/ HoNi5 (50 nm) bilayer on (100) MgO substrate.
(b) Comparison of R vs. H and M vs. H at temperature 1.7 K.
NbN TC = 16 K
HoNi5 TCurie = 5.5 K
T Curie < TC
Singh et al. Manuscript submittedStudent working : Gyanendra Singh
0 G 200 G 300 G
420 G 1000 G
Spin Reorientation in La0.67Ca0.33MnO3 thin film observed by Magnetic Force Microscopy
In Plane Magnetization
Out of Plane Magnetization
Interface
T = 110 KIn Plane Magnetic Field
Singh et al. Manuscript under preparation Student working : Gyanendra Singh
-20 -10 0 10 200
2
4
-100 -50 0 50 100
-60
-40
-20
0
20
40
60
-20 kV/cm
Cur
rent
(A
)
Vds
(mV)
+20 kV/cm
20K
20 K
Gv(
0) m
S
Eg (kV/cm)
Gv(
0) m
S
0.18
0.20
0.22
0.24 300 K
Vsd
Vg
STOGate 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.
Rastogi et al. Manuscript submitted
Field Effect in LTO-STO Heterostructure
LTO Mott InsulatorSTO Band Insulator
Student working : Ankur Rastogi
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
Interface Superconductivity
La1.48Nd0.4Sr0.12CuO4 (100 nm)
La1.84Sr0.16CuO4 (50 nm)
Substrate SLAO (001)
5 10 15 20 25
0
5
10
15
20
25
30
V (V
)
T (K)
0.0
0.1
0.2
0.3
0.4Im V
(m.
cm)
Re V X 2
Student working : Prasanna Kumar Rout
Spintronics
Magnetic Tunnel Junctions (MTJs)
-1.0
-0.5
0.0
0.5
1.0
-500 -400 -300 -200 -100 0 100 200 300 400 500
6.4
6.5
6.6
6.7
6.8
6.9(b)
HCo
C
HLSMO
C
(a)
R(k)
Field (Oe)
M(H
)/M
(100
0 O
e)
CoLSMO
20 μm
Junction area 25 μm x 25 μm
Photograph of junctions
SEM image of the junction with one junction zoomed in.
Student working : Prasanta Kumar Muduli
0.004 0.006 0.008 0.010 0.012
1E-3
0.01
0.1
1
10
300 200 100
0.0068 0.00700.01
0.1 (
cm)
1/T (K-1)
(
cm)
1/T (K-1)
T (K)
a
b
c
100 150 200
100
1000
10000
R (O
hm)
T (K)
Non-equilibrium features in phase separated state of NdNiO3
Exhibit time dependent effects in phase separated stateThese 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
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.
0 100 200 300-3
-2
-1
0
M (
10-4
em
u/g)
T (K)
Stop of 1 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
Physics of Novel Magnetic and Superconducting Materials
Zakir Hossain- Department of Physics, IIT Kanpur
Research Interest:(i) 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
Magnetism and Superconductivity in Eu0.5K0.5Fe2As2
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.
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.H. S. Jeevan et.al. PRB 78, 092406 2008 Anupam et.al. J. Phys. Cond. Mat (2009)
To prepare a good quality film with high crystal and interface perfection and 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.
20 30 40 50 60 70 80
10
1000
100000STO (300)
STO (200)
STO (100)
Td = 200oC
2 (Degree)
10
1000
100000STO (300)
STO (200)
STO (100)
Co2FeSi (400)
Td = 400oC
Inte
nsi
ty (
a.
u.)
10
1000
100000STO (300)
STO (200)
STO (100)
Td = 600oC
Co2FeSi (400)
0 80 160 240
0
80
160
240
Td = 600oC
25 50 75 1000
15
30
45
(c
m)
T(K)
cm
T (K) Anupam et al. to be publishedZH 3
Laboratory for Optical Spectroscopy at Extreme Conditions of high P and low T
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.
Rajeev Gupta
RG 1
Research Facility
• Sample, pressure calibrant and pressure medium to be loaded in a 200 microns hole!
•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.
Location: 107 ACMS Building•Please do visit us sometime! RG 2
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
Research Area: Li ion Battery materials
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.
Critical issue: Cheaper and environmental friendly substitutes for traditional cathode material in Li ion batteries (LiCoO2)
RG 4
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
10 20 30 40 50 60 70 80 90 100-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
45 50 55 60 65
T2 T1
T2
M (
X10
3 emu
/mo
l)
100G
Temperature (K)
ZF FCC FCH
T1
dM
/dT
(a.
u.)
Temperature(K)
10 20 30 40 50 60 70 80 90 100
3
4
5
6
7
30 40 50 60 70
T2 T1
T2
M
x10-1
(em
u/m
ol)
Temperature (K)
ZF FCC FCH
T1
100G
dM
/dT
(a.
u.)
Temperature (K)
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
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.
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.