Saroj Prasad Dash

Professor at the Department of Microtechnology and Nanoscience, Quantum Device Physics Laboratory

Prof. Saroj Dash is leading a research group on Quantum device Physics, Nanoelectronics and Spintronics research at Chalmers. He holds a PhD degree in Physics from Max Planck Institute (2007, Stuttgart, Germany). His previous positions include postdocs at Uni. of Twente and Uni. of Groningen in Netherlands for three years. He was appointed at Chalmers in November 2010, where his group focus is on electronic charge and spin transport in graphene, semiconductor nanostructures, other two-dimensional materials and topological insulators. His group develops novel approaches for nanofabrication and design new measurement techniques that lead to fundamental physics experiments. The goal is to exploit the quantum and spin degrees of freedom of electrons for the integration of memory and logic functionalities in nanoelectronic devices and integrated circuits.

Research interests
1. Topological Quantum Materials and Devices
2. Graphene nanoelectronics and spintronics
3. van der Waals heterostructures of 2D materials
4. 2D semiconductor nanoelectronics
5. Spin-orbit and Magnetic effects 2D materials heterostructures

Read about the different master thesis projects (30 or 60 credits) available in the Saroj Dash Group at the Teaching tab.

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Group members (present and previous)

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Multifunctional Spin Logic Gates In Graphene Spin Circuits​
SpinLogic.pngAll-spin-based computing combining logic and nonvolatile magnetic memory is promising for emerging information technologies. However, the realization of a universal spin logic operation representing a reconfigurable building block with all-electrical spin current communication has so far remained challenging. Here, we experimentally demonstrate a reprogrammable all-electrical multifunctional spin logic gate in a nanoelectronic device architecture utilizing graphene buses for spin communication and multiplexing and nanomagnets for writing and reading information at room temperature. This gate realizes a multistate majority spin logic operation (sMAJ), which is reconfigured to achieve XNOR, NAND, NOR, AND and OR Boolean operations depending on the magnetization of inputs. These demonstrations provide a platform for scalable all-electric spin logic and neuromorphic computing in the all-spin domain logic-in-memory architecture.​
D. Khokhriakov, S. Sayed, A. Md. Hoque, B. Karpiak, B. Zhao, S. Datta, S.P. DasharXiv:2108.12259 (2021)

Topological Quantum Material Devices​

Weyl Semimetals

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Weyl semimetals are a new class of topological quantum materials​ with novel spin texture and predicted to efficiently convert the charge current to a spin current. Here, we report the direct experimental observation of large charge-spin conversion effects in a layered semimetal WTe2 at room temperature. These experimental findings can pave the way for the utilization of spin-orbit induced phenomena in Weyl semimetals for spin-orbit torque-based device architectures. ​

Unconventional Charge–Spin Conversion in Weyl‐Semimetal   WTe2, B. Zhao, et al., S.P. Dash, Advanced Materials, 2000818 (2020). News

Observation of charge to spin conversion in Weyl semimetal WTe2 at room temperature, B. Zhao, et al., S.P. Dash, Physical Review Research 2 (1), 013286 (2020). News

Charge-spin conversion signal in WTe2 van der Waals hybrid devices with a geometrical design, B. Zhao, et al., S.P. Dash, Applied Physics Letters 117 (24), 242401 (2020)​.


Topological Insulators 

Gr_TI_1.pngTopological insulators (TIs) exhibit a current-induced spin polarization due to spin-momentum locking of massless Dirac Fermions in their surface states. Here we report the room temperature electrical detection of the spin polarization on the surface of BiSe and BiSbTeSe by employing spin sensitive potentiometric measurements. 

Room Temperature Electrical Detection of Spin-Polarized Currents in Topological Insulators, A. Dankert et al., S.P. Dash, Nano Letters, 15, 12, 7976 (2015). News article

Origin and evolution of surface spin current in topological insulators, A Dankert, et al., SP Dash, Phys. Rev. B 97, 125414 (2018).


Graphene - Topological Insulator Heterostructures

Dirac materials such as graphene and topological insulators (TIs) are known to have unique electronic and spintronic properties. We combine graphene with BiSe and BiSbTeSe in van der Waals heterostructures to demonstrate the emergence of a strong proximity-induced spin-orbit coupling in graphene. 
D Khokhriakov, et al., SP Dash, Science Advances 4 (9), eaat9349 (2018)News article 
We further utilized the proximity-induced spin-orbit coupling in graphene in proximity with topological insulators (TIs), to demonstrate a gate-tunable spin-galvanic effect (SGE) at room temperature, allowing for efficient conversion of a non-equilibrium spin polarization into a transverse charge current. Importantly, using a gate voltage, we reveal a strong electric field tunability of both amplitude and sign of the spin-galvanic signal. These findings provide an efficient route for realizing all-electrical and gate-tunable spin-orbit technology using TIs and graphene in heterostructures, which can enhance the performance and reduce power dissipation in spintronic circuits.
Gate-tunable spin-galvanic effect in graphene-topological insulator van der Waals heterostructures at room temperature, D Khokhriakov, et al., SP Dash, Nature Communications 11 (1), 1-7 (2020)News article 

2D Magnets

Room Temperature spin-valve with van der Waals magnet
FGT_Gr.pngThe discovery of van der Waals (vdW) magnets opened up a new paradigm for condensed matter physics and spintronic technologies. However, the operations of active spintronic devices with vdW magnets are so far limited to cryogenic temperatures, inhibiting its broader practical applications. Here, for the first time, we demonstrate room temperature spin-valve devices using vdW itinerant ferromagnet FeGeTe in heterostructures with graphene. The tunnel spin polarization of the FeGeTe/graphene vdW interface is detected to be significantly large ~ 45 % and negative at room temperature. Lateral spin-valve device design enables electrical control of spin signal and realization of basic building blocks for device application such as efficient spin injection, transport, precession, and detection functionalities. Furthermore, measurements with different magnetic orientations provide unique insights into the magnetic anisotropy of FeGeTe and its relation with spin polarization and dynamics in the heterostructure. These findings open opportunities for the applications of vdW magnet-based all-2D spintronic devices and integrated spin circuits at ambient temperatures.

Van der Waals Magnet based Spin-Valve Devices at Room Temperature, B. Zhao, et al., S.P. Dash, (2021) preprint @ arXiv:2107.00310


Magnetic proximity effect in graphene in van der Waals heterostructure with CrGeTe

Gr-CGT.pngEngineering 2D material heterostructures by combining the best of different materials in one ultimate unit can offer a plethora of opportunities in condensed matter physics. Here, in the van der Waals heterostructures of the ferromagnetic insulator CrGe Te and graphene, our observations indicate an out-of-plane proximity-induced ferromagnetic exchange interaction in graphene. The perpendicular magnetic anisotropy of CrGeTe results in significant modification of the spin transport and precession in graphene, which can be ascribed to the proximity-induced exchange interaction.
Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene, B. Karpiak et al, SP Dash, 2D Materials 7 (1), 015026 (2019)News article


Graphene spin interconnect

Graphene is an ideal medium for long-distance spin communication due to its low spin-orbit coupling and high electron mobility. Here we demonstrate high spintronic performance in CVD graphene on SiO2/Si substrate at room temperature and its applications in spintronic circuits. Our findings in wafer-scale graphene and opens up new prospects for the development of lateral spin-based memory and logic applications.

Robust spin interconnect with isotropic spin dynamics in chemical vapor deposited graphene layers and boundaries, D Khokhriakov et al, SP Dash, ACS nano 14 (11), 15864-15873 (2020).

Two-dimensional spintronic circuit architectures on large scale graphene, D Khokhriakov, B Karpiak, AM Hoque, SP Dash, Carbon 161, 892-899​ (2020)News

Long distance spin communication in chemical vapour deposited graphene, M.V. Kamalakar, et al., S.P. DashNature Communications, 6, 6766 (2015). News

 

2D materials heterostructures

Graphene/MoS2 

Two-dimensional (2D) crystals offer a unique platform due to their remarkable and contrastingGr_MoS2.png
spintronic properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in molybdenum disulfide (MoS2). Here we combine graphene and MoS2 in a van der Waals heterostructure (vdW
h) to demonstrate the electric gate control of the spin current and spin lifetime at room temperature. Our findings demonstrate an all-electrical spintronic device at room temperature with the creation, transport and control of the spin in 2D materials heterostructures. 

Electrical gate control of spin current in van der Waals heterostructures at room temperature.
A. Dankert, S.P. Dash;
Nature Communications 8, 16093 (2017).
News - https://graphene-flagship.eu/field-effect-transistor-using-graphenes-electron-spin

Graphene/h-BN
Two dimensional atomically thin crystals of graphene and its insulating isomorph hexagonal boron nitride (h-BN) are promising materials for spintronic applications. While graphene is an ideal medium for long-distance spin transport, h-BN is an insulating tunnel barrier that has potential for efficient spin polarized tunneling from ferromagnets. Here, we demonstrate the spin filtering effect in cobalt|few layer h-BN|graphene junctions leading to a large negative spin polarization in graphene at room temperature. These spintronic effects in two-dimensional van der Waals heterostructures hold promise for future spin based logic and memory applications.

Inversion of spin signal and spin filtering in ferromagnet| hexagonal boron nitride-graphene van der Waals heterostructures; MV Kamalakar et al, SP DashScientific reports 6, 21168 (2016)
Enhanced Tunnel Spin Injection into Graphene using CVD Hexagonal Boron Nitride;
MV Kamalakar et al, SP DashScientific Reports, 4: 61446 (2014)

2D Semiconductor Transistor

Molybdenum disulfide has recently emerged as a promising two-dimensional semiconducting material for nanoelectronic, optoelectronic, and spintronic applications. Here, we investigate the field-effect transistor behavior of MoS2 and elucidate that the presence of a large Schottky barrier at the MoS2/ferromagnet interface is a major obstacle for electronic devices. We circumvent this problem by a reduction in the Schottky barrier height with the introduction of a thin TiO2 tunnel barrier between the ferromagnet and MoS2. This results in an enhancement of the transistor on-state current and an increment in the field-effect mobility.

High Performance Molybdenum Disulfide Field Effect Transistors with Spin Tunnel Contacts

A. Dankert, et al, S.P. DashACS Nano 8 (1), 476 (2014).
Nature Communications 8, 16093 (2017).

Black phosphorus (BP) has been recently unveiled as a promising 2D direct bandgap semiconducting material. Here, ambipolar field-effect transistor behavior of nanolayers of BP with ferromagnetic tunnel contacts is reported. Using TiO2/Co contacts, a reduced Schottky barrier <50 meV, which can be tuned further by the gate voltage, is obtained. 

V.K. Mutta, et al., SP Dash, Small 11 (18), 2209-2216 (2015).


Silicon Spintronics

The control and manipulation of the electron spin in semiconductors is central to spintronics, which aims to represent digital information using spin orientation rather than electron charge. Here we demonstrate room-temperature electrical injection of spin polarization into n-type and p-type silicon from a ferromagnetic tunnel contact, spin manipulation using the Hanle effect and the electrical detection of the induced spin accumulation. These results open the way to the implementation of spin functionality in complementary silicon devices and electronic circuits operating at ambient temperature.Silicon Spin.png

Electrical creation of spin polarization in silicon at room temperature, S.P. Dash, et al., Nature 462, 491 (2009).

Most significant breakthroughs in 2009 (3rd on the list) by Physics world. News​


Spin-dependent electronic transport is widely used to probe and manipulate magnetic materials and develop spin-based devices. Here we demonstrate electrostatic modification of the magnitude of spin polarization in a silicon quantum well, and detection thereof by means of tunnelling to a ferromagnet, producing prominent oscillations of tunnel magnetoresistance of up to 8%. The electric modification of the spin polarization relies on discrete states in the Si with a Zeeman spin splitting, an approach that is also applicable to organic, carbon-based and other materials with weak spin–orbit interaction.

Oscillatory spin-polarized tunneling from silicon quantum wells controlled by electric field, R. Jansen, B.C. Min, S.P. Dash; Nature Materials 9, 133 (2010).


2D Magnetic Tunnel Junctions

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The two-dimensional (2D) atomically thin insulator h-BN and semiconducting MoS2 constitute a new paradigm in tunnel-based devices. A large band gap, along with its atomically flat nature without dangling bonds or interface trap states, makes it an ideal candidate for tunnel spin transport in magnetic tunnel junctions. Here, we demonstrate the tunneling of spin-polarized electrons through monolayer h-BN and multi-layer MoS2 prepared by chemical vapor deposition, in magnetic tunnel junctions. These results open the way for the integration of 2D spin tunnel barriers in active spintronic devices and circuits.

A. Dankert, et. al., S.P. Dash, ACS Nano, 11(6), 6389–6395 (2017)

A. Dankert, et al., S. P. Dash, Nano Research, 8(4), 1357–1364 (2015)


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Read more about the Saroj Dash Group


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Full list of Publications, see Google Scholar here

Link to Chalmers Research,  here​

Page manager Published: Fri 10 Sep 2021.