Scientia Iranica F (2017) 24(6), 3448{3451 Sharif University of Technology Scientia Iranica Transactions F: Nanotechnology www.scientiairanica.com Spintronics in nano scales: An approach from DNA spin polarization S. Behnia and S. Fathizadeh Department of Physics, Faculty of Science, Urmia University of Technology, Urmia, Iran. Received 8 August 2016; received in revised form 28 September 2016; accepted 5 December 2016 KEYWORDS Abstract. DNA nanotechnology is a purist approach to biomolecular engineering. The eld is aimed to create molecular structures and devices through the exclusive use of DNA DNA nanowire; as an engineering material. On the other hand, DNA Spintronics, as a DNA nanotechnology Spintronics; eld, uses the electron spin to store and process information. In this work, we have Pure spin current; used the Peyrard-Bishop-Holstein model combined with spin-orbit interaction for studying Spin polarization; the spin transfer mechanism in DNA nanowires. In this work, the electrical currents Spin-orbit coupling. corresponding to the spin-up and spin-down electrons are obtained directly using the Hamiltonian equations of system. We can obtain the best functional ranges for external agents, such as magnetic and electrical elds, and surroundings temperature to use in spintronics applications. By considering the simultaneous e ects of parameters, we have determined the islands with pure spin current. However, the considerable result is where we have applied the time periodic magnetic eld and observed the characteristic peaks in polarization diagram. These peaks can be used for information coding as zero-one codes. Therefore, one could construct DNA nanowires that lter the spin current, create the nearly pure spin currents, and act as a spintronics device for processing and transferring information. © 2017 Sharif University of Technology. All rights reserved. 1. Introduction motors or circuits that can autonomously move or process information. In the last 30 years, the DNA DNA as a molecule that carries the genetic informa- nanotechnology community has gone from an initial tion of a living organism is diverse in structure and wave of making static structures of di erent shapes function. In nature, this complementary base pairing and sizes to a second wave of creating increasingly contributes to DNA's helical structure and the way sophisticated and dynamic structures capable of car- genetic information is stored and retrieved. Because rying drugs, interacting with cell surface proteins, and of its programmability, DNA has also earned itself a performing certain functions inside cells [1,2]. In the reputation as a versatile engineering material. The case of dynamic structures, such as those that can move well-characterized nature of DNA base pairing provides or perform computational tasks, strand displacement is an easy means to control DNA interactions; this used, whereby the nanodevice is programed to respond `sequence programmability' has allowed the rational to an incoming DNA strand that displaces an existing design of precisely de ned structures, and molecular one on the nanodevice [3]. The ability to program these structures to fold a certain way to carry information *. Corresponding author. Fax: +98 4433554184 and recon gure themselves means that DNA nanode- E-mail address: [email protected] (S. Behnia) vices can be designed to do many things. They can, for example, carry drugs and deliver them to targets doi: 10.24200/sci.2017.4421 in clever ways [4], or can be designed to have movable S. Behnia and S. Fathizadeh/Scientia Iranica, Transactions F: Nanotechnology 24 (2017) 3448{3451 3449 parts that can sense and/or amplify signals, or even where: perform logic functions like a computer. On the other hand, the ability of DNA for charge transfer makes it Dn;n+1 =itso sin fsin[n] + sin[(n + 1)] a suitable candidate for any design of nanoelectronical devices, nanosensors, nanocercuits, and nanowires [5]. + i cos[n] + i cos[(n + 1)]g; Moreover, the spin transport properties of the DNA, as an organic molecule, make it applicable as a spintronic and tso is the spin-orbit coupling constant, is the device [6]. Spintronic systems exploit the fact that the twisting angle of DNA, and ' = n is the cylindrical electron current is composed of spin-up and spin-down coordinate angle. carriers, which carry information encoded in their spin HLead is the Hamiltonian corresponding to the left state and interact di erently with magnetic materials. and right leads written as follows: Rich physics behind the organic materials and speci c X X + + functions, such as switchability with light and electrical HLead = "kak ak +t fak (c1 +cN )+H:c:g; (4) or magnetic elds, are two important motivations for k k; using the organic materials such as DNA. where " is the on-site energy of leads, and t is the In the current study, we have tried to investigate k hopping constant between leads and DNA. the electron transfer in DNA nanowires by consider- It is clear that the Hamiltonian terms are complex ing the electron spin. We have taken into account and dealing with them is hard. Then, considering the the electron-lattice interaction through the Peyrard- nonlinear dynamics tools could open a new horizon Bishop-Holstein (PBH) model by considering the spin in understanding the spin transfer mechanism and its degree of freedom. On the other hand, spin-orbit e ects on DNA. In this way, we have obtained the interaction is combined with the PBH model. evolution equations of the system as follows: 2. Materials and methods 2aD y = eayn eayn 1 n m We have considered DNA spin-charge lattice with the h following Hamiltonian: kb 2 + eb(yn+yn1) (y y ) 2m n n1 H = HPBH + Hso + HLead; (1) i b(yn+1+yn) 2 where HPBH is the Hamiltonian of PBH model for +e (yn+1 yn) the description of DNA lattice and charge carriers dynamics by considering the spin degree of freedom. " 2 # 2 cn + cn ; (5) HPBH is written as follows [7]: m X 1 n 2 " i " " " HPBH = my_ + V (yn) + W (yn; yn+1) c_ = (" + y )c V c + c 2 n n n n n n;n+1 n1 n+1 n ~ o X X " # " + + + +Dn:n+1c Dn1;nc + t a ; (6) + f"ncn cn Vn;n+1(cn cn+1 +cn+1cn) n+1 n1 k n; k;n=1 n + i # # + yncn cng; (2) c_# = (" + y )c# V c + c n ~ n n n n;n+1 n1 n+1 ay 2 where V (yn) = D(e n 1) as Morse poten- o X tial describes the hydrogen binding between the D c" + D c" + t a#; (7) k n;n+1 n+1 n1;n n1 k complementary base pairs, W (yn; yn+1) = 2 (1 + k b(y +y ) 2 e n+1 n )(yn+1 yn) is the stacking interaction h i + i in a DNA chain, cn (cn) is the creation (annihilation) " " " " a_ k = "kak + t c1 + cN ; (8) operator for a spinor with spin , Vn;n+1 is the hopping ~ constant, and is the charge-lattice coupling. i h i H is the spin-orbit coupling Hamiltonian ex- # # # # so a_ k = "kak + t c1 + cN : (9) pressed by the second quantization method as follows: ~ X h "+ # #+ " 3. Results and discussion Hso = Dn;n+1cn cn+1 Dn;n+1cn cn+1 n For analyzing the spin transfer mechanism in DNA and i investigating the a ected parameters, we have tried to +D c#+c" D c"+c# ; (3) n1;n n n1 n1;n n n1 obtain the electrical current for spin-up and spin-down 3450 S. Behnia and S. Fathizadeh/Scientia Iranica, Transactions F: Nanotechnology 24 (2017) 3448{3451 electrons, directly from eld equations. These currents where B is the Bohr magneton, and B is the magnetic are written as follows: eld in the direction of DNA helix axes. This Hamil- " # i " i # ( tonian term modi esc _n(_cn) by BBcn( BBcn). ie X h ~ ~ I" = V c"+c" + c"+c" Figure 1 shows the regions in magnetic eld values ~ n;n+1 n n1 n n+1 in which the minimum charge current exists; as a result, n the maximum spin current ows through DNA. These i +D c"+c# D c"+c# regions are the best values for spintronics applications. n;n+1 n n+1 n1;n n n1 For examining the e ect of external magnetic eld ) over the time, we have considered the time series of Xh i +t c"+ +c"+ a"+ a"+ c"+ +c"+ ; one of the spin currents (spin-up current) versus the 1 N k k 1 N variation of external magnetic intensity (see Figure 2). k (10) It is clear in a 3D scheme that in low eld values, ( the spin-up current is almost zero, but after about B = ie X h I# = V c#+c# + c#+c# 0:2 mT, the current increases in time. ~ n;n+1 n n1 n n+1 n On the other hand, by applying a time variable i eld with frequency !, one could obtain the best in- #+ # #+ " terval in frequency domain with maximal spin ltering. Dn;n+1cn cn+1 + Dn1;ncn cn1 To this end, we have considered external magnetic eld ) Xh i B = B0 cos !t, where B0 and ! are the eld intensity #+ #+ #+ #+ #+ #+ and frequency, respectively. +t c1 +cN ak ak c1 +cN : k (11) It is clear in Figure 3 that spin polarization shows the characteristic peaks in certain frequencies. The Using the above relations, we could de ne the net maximal peak appears in ! = 0:7 THz. By considering charge (Ic) and the net spin currents; as a result, the this result, one could design an information coder based spin polarization relation is as follows: on zero-one codes for information transfer aims.