1 Di raction sur des composés multiferroïques 2 Chaine

•
•
•
RMn2O5R
a= 2b a = 3c
R = Pr Z= 59
(x, y, 0) (−x, −y, 0) (1/2−x, 1/2 + y, 0)
(1/2 + x, 1/2−y, 0)
(a, b)
Pr
S h k l S(0kl)S(h0l)
Pr
a a
φ2n
φ2n+1

hφ2n|H|φ2n±1i=hφ2n±1|H|φ2ni=−t
hφ2n|H|φ2n±2i=hφ2n±2|H|φ2ni=−t0
hφ2n+1 |H|φ2n+1±2i=hφ2n+1±2|H|φ2n+1i=−t00
hφ2n|H|φ2ni=hφ2n+1 |H|φ2n+1i= 0.
t t0t00
ψkk E(k)
|ψki=X
n
cn|φ2ni+dn|φ2n+1i
cndnc0d0
E(k)
E(k)2+ 2 E(k) (t0+t00) cos ka −2t2(1 + cos ka)+4t0t00 cos2ka = 0
t00 << t0< t E(k)
t t0
t0= 0 E(k)
t6= 0, t0=t00 = 0
kFEF
t06= 0 t0< t E(k)
k= 0 k=±π/a k =±π/2a
k=±π/a
E(k)

EF
kF
EFkF
R
Tc(B)
B
Ba
Ψ = √nsexp (iθ(−→ r)) .
−→
v=1
m−i~−→
∇+ 2e−→ A−→ A
−→
js.
−→
js−→ vs

vs=~
mR p+Φ Φ0pΦ0=h 2e
ΦB
vs=k−→ vsk
vsΦ
T=Tcns
|Ψ|2=α1−0.55
1−T
Tc(B=0) mvsξ0
~2α
ξ0Tc(B)−Tc(B=0)
Tc(B=0)
∆Tc=Tc(B)−Tc(B=0)
Tc(B=0)
Φ
Tc