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Nonreciprocal charge transport up to room temperature in bulk...
Nonreciprocal charge transport up to room temperature in bulk...
논문 Nonreciprocal charge transport up to room temperature in bulk Rashba semiconductor 'Alpha'-GeTe
문단별로
1. Nonreciprocal charge transport
Nonreciprocal charge transport. Inequivalent of rightward and leftward currents. Netflow of charge?
Nonreciprocal charge transport can be expressed as
여기서 R_0는 resistance at B=0
베타는 the coefficient of the normal magnetoresistance.
감마는 nonreciprocal cofficient
* Nonreciprocal charge transport in non-centrosymmetric materials without FM layers.
-> New paradigm of uni-directional magnetoresistance for second-order response to the electric field.
* Low Rashba spin splitting energy
-> Nonreciprocal transport can only be observed at very low temperature
Gamma values decrease dramatically with increasing temperature due to the thermal fluctuation.
2. What is 'Alpha'-GeTe?
애초에 Rashba effect는 low dimensional system, heterostructure에만 적용된다.
Rashba splitting in bulk material : 'Alpha'-GeTe?
3. Result& Discussion
The rhombohedral crystal structure <= 'Alpha'-GeTe
-> Noncentrosymmetric 이면
-> Ferroelectric order p
-> The Rashba-type spin splitting band
Alpha-GeTe
-> Low resistivity rho~0.12옴cm at 300K
-> metallic behavior down to 3K .......... temperature dependence
Hall resistance -> as usual semiconductor
Positive slope -> the dominant carriers are holes (ARPES 통해 Fermi surface가 valence band에 있음을 확인)
Carrier concentration -> Anomalous temperature dependence. But absolute change in the magnitude remains weak.
-> Negligible shift of Fermi level with temperature.
4. Nonreciprocal transport response
Via angular dependent AC harmonic measurement;
-> Sinusoidal AC current I_w
-> Rotation of the applied magnetic field in three geometries.
R_2w
-> xy/yz : sinusoidal angular dependence (almost same amplitude and a period of 360 degree)
-> xz : vanishingly small
5. R_2w at 300K
changes sign when resistivity the magnetic field ( => characteristic of UMR)
Similar UMR characteristics were also observed in other nonmagnetic noncentrosymmetric system with spin-momentum locking
(FM/TI, FM/HM originates from the spin accumulation at the interfaces involved by the spin Hall effect or the Rashba-Edelstein effect and complies with the chiral rul (\hat{j}x\hat{z})\dot\vec{M}
6. The The nonreciprocal coefficient 'Gamma'
Gamma = 2* DeltaR_2w/R_0 B I -> anomalous temperature dependence
Shift of Fermi level driven by temperature which was used to interpret the temperature dependent non-linear magnetotransport observed in semimetal WTe2.
7. Theory
Nonreciprocal response when
1. the systems without the inversion symmetry (이거 자체로 Rashba-type spin splitting of energy bands with spin-momentum locking 발현)
2. The time reversal symmetry is broken.
6.
from http://spin-current.tistory.com/15 by ccl(A) rewrite - 2021-05-13 15:00:36