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Tribhuvan P. Pareek
Research Summary:
My main research has been focused on spin and charge transport in
mesoscopic systems. Though the charge transport has been well studied
using Landauer- Büttiker formalism but for spin transport there is
no consistent theory yet. The main question has been the
what is the spin current for mesoscopic devices. The
standard way to define spin currents is to subtract up spin current
from down spin current for a given quantization axis. However this only gives
a part of spin current. To resolve these issues I generalized
Landauer Buttiker theory for multi-terminal spin transport as well [1].
This study led to the following important results namely
a) One can have equilibrium spin currents consistent with charge conservation and time reversal symmetry.
b) The spin currents can be generated intrinsically
using spin orbit interaction, hence one can avoid the spin injection problem altogether
c) further in multi-terminal transport , pure spin currents
(no accompanying charge current) can be generated and measured.
Further I am looking at equilibrium spin currents in mesoscopic systems
and the work is under progress. The published work[1] just argues
that it can exist without violating any basic physics. However to
have a better understanding a detailed study is required which is
under progress.
I have also proposed a new absolute spin valve device[2].
In the standard spin valve devices a two ferromagnetic contact are attached to
a non-magnetic spacer layer. The conductance of such device
depends on the relative orientation of magnetization direction.
However in presence of spin orbit interaction, one does not need two ferromagnetic contacts rather one ferromagnetic contact is enough to show
spin valve effect. Now it depends on the absolute direction of magnetization
since the presence of spin orbit interaction breaks the rotational invariance in spin space.
Further I am at present in the processes of completing a manuscript on
three terminal analog spin transistor. This again exploits the analog freedom
available for magnetization to point in any arbitrary direction which is
rather different from digital.
The manuscript is under preparation
and would be soon submitted for publication.
Publications:
- Pure spin currents and associated electrical voltage, T. P. Pareek,
Phys. Rev. Lett. 92, 076601 (2004).
- Absolute spin valve effect: Charge transport in two dimensional
hybrid system, T. P. Pareek, accepted for publication in PRB.
Preprints:
- Quantum Beating of Ballistic conductance, T. P. Pareek
submitted for publication.
Invited Lectures/Seminars:
A seminar on "decoherence and dephasing in four terminal mesoscopic rings"
was given in the Literature Chat prog. at HRI.
Other Activities:
Four students spent four weeks each here during summer and winter and did reading projects on the following topics :
a) Negative refractive index and Left handed materials
b) Quantum computation and no cloning theorem and its relation with Heisenberg uncertainty relation
c)Spintronics, and
d) Berry phase due to spin orbit interaction.
These are the topics where I would like to diversify in future.
The students were Moitri Maiti (Jadavpur University),
Manhoar Shivum (Dhanbad) T. V. Chandrasekhar (Madaras),
K. Malathi (Hyderabad) and a student from Indian Institute of Information Technology Gawalior.
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